Mark Taylor

Acoustic emission monitoring and 3D visualization of polymerization‐induced damage of acrylic polymer materials

Publisher: Wiley

Date: 15-12-2008

DOI: 10.1002/JBM.B.31276

Abstract: To improve the longevity of total hip replacements, techniques such as vacuum mixing have been developed to reduce the amount of porosity within the cement. However, data from the Swedish hip registry has demonstrated an increased risk of revision for vacuum-mixed cemented devices in the first 5 years postoperatively. Theoretical and experimental evidence suggests that stresses induced by cement shrinkage during polymerization alone are sufficient to induce cracking. However, very little evidence of preload cracking is available due to the limitations of current inspection methods. The present work combines two forms of nondestructive evaluation technique to assess the state of an acrylic-based polymer mantle both in real time during polymerization using the acoustic emission (AE) technique and immediately post polymerization using micro-computed tomography (CT). AE data enabled the location, type, and chronology of events to be obtained. The use of micro-CT in combination with a radiopaque dye-penetrant was shown to be an effective method for highlighting preload polymerization cracking and verified the findings of the AE data. The AE data indicated that the first signs of damage occurred approximately 3-6 min after the peak temperature obtained during exotherm, confirming that thermal contraction rather than pure volumetric shrinkage is the dominant factor in preload damage initiation. The methodology developed in this study enables detailed information on the condition of a cement mantle to be obtained without the need for serial sectioning.

Fatigue characterization of a polymer foam to use as a cancellous bone analog material in the assessment of orthopaedic devices

Publisher: Springer Science and Business Media LLC

Date: 2004

DOI: 10.1023/B:JMSM.0000010098.65572.3B

Abstract: Analog materials are used as a substitute to cancellous bone for in vitro biomechanical tests due to their uniformity, consistency in properties and availability. To date, only the static material properties of these materials have been assessed, although they are often used in fatigue tests. Cancellous bone exhibits complex material behavior when subjected to fatigue loads, including modulus degradation, accumulation of permanent strain and increasing hysteresis. Analog materials should exhibit similar fatigue behavior to cancellous bone if they are to be used in cyclic loading tests. In our study, a polymer foam (commercial name HEREX C70.55) has been studied for its static and fatigue behavior and compared with that of cancellous bone. In compression, the foam exhibited qualitatively similar mechanical behavior, but the degree of modulus degradation and accumulation of permanent strain was lower than expected for cancellous bone. In general, the tensile properties of the foam were greater than found in compression, the opposite to the mechanical behavior of cancellous bone. The methodology employed here could form the basis of selecting suitable analog materials for cancellous bone in the future.

Explicit Finite Element Simulation of Eccentric Loading in Total Knee Replacement

Publisher: Ovid Technologies (Wolters Kluwer Health)

Date: 09-2003

DOI: 10.1097/01.BLO.0000079267.91782.58

Abstract: In vivo kinematic data indicate that unicondylar or edge loading occurs during normal activities in well-aligned and malpositioned knee replacements. Using a validated explicit finite element model of a knee replacement, the effects of eccentric loading of a total knee replacement are simulated. Only minor variations were observed in the kinematics with a medial offset of the vertical load of as much as 15 mm (representing a medial:lateral loading ratio of 86:14), although the polyethylene stresses did increase by approximately 3 MPa throughout the stance phase of gait. There was a significant change in the kinematics and stresses when unicondylar loading occurred (95:5 medial:lateral loading ratio). Even for the unicondylar load case, contact always was maintained within the lateral compartment. This raises the question whether lift-off often observed in fluoroscopy studies really occurs. The model predicted regions of plastic deformation that closely resemble those observed in retrieved specimens of catastrophic wear. The explicit finite element model offers considerable insight into the kinematics and stresses generated by total knee replacement during different and varied loading conditions that occur during normal usage.

Mechanical properties of single bovine trabeculae are unaffected by strain rate

Publisher: Elsevier BV

Date: 03-2011

DOI: 10.1016/J.JBIOMECH.2010.12.008

Finite element modelling?predictor of implant survival?

Publisher: Springer Science and Business Media LLC

Date: 12-1995

DOI: 10.1007/BF00134322

Wear in the Prosthetic Shoulder: Association With Design Parameters

Publisher: ASME International

Date: 04-10-2006

DOI: 10.1115/1.2486060

Abstract: Total replacement of the glenohumeral joint provides an effective means for treating a variety of pathologies of the shoulder. However, several studies indicate that the procedure has not yet been entirely optimized. Loosening of the glenoid component remains the most likely cause of implant failure, and generally this is believed to stem from either mechanical failure of the fixation in response to high tensile stresses, or through osteolysis of the surrounding bone stock in response to particulate wear debris. Many computational studies have considered the potential for the former, although only few have attempted to tackle the latter. Using finite-element analysis an investigation, taking into account contact pressures as well as glenohumeral kinematics, has thus been conducted, to assess the potential for polyethylene wear within the artificial shoulder. The relationships between three different aspects of glenohumeral design and the potential for wear have been considered, these being conformity, polyethylene thickness, and fixation type. The results of the current study indicate that the use of conforming designs are likely to produce slightly elevated amounts of wear debris particles when compared with less conforming joints, but that the latter would be more likely to cause material failure of the polyethylene. The volume of wear debris predicted was highly influenced by the rate of loading, however qualitatively it was found that wear predictions were not influenced by the use of different polyethylene thicknesses nor fixation type while the depth of wearing was. With the thinnest polyethylene designs (2mm) the maximum depth of the wear scar was seen to be upwards of 20% higher with a metal-backed fixation as opposed to a cemented design. In all-polyethylene designs peak polymethyl methacrylate tensile stresses were seen to reduce with increasing polyethylene thickness. Irrespective of the rate of loading of the shoulder joint, the current study indicates that it is possible to optimize glenoid component design against abrasive wear through the use of high conformity designs, possessing a polyethylene thickness of at least 6mm.

Use of a statistical model of the whole femur in a large scale, multi-model study of femoral neck fracture risk

Publisher: Elsevier BV

Date: 09-2009

DOI: 10.1016/J.JBIOMECH.2009.05.038

Abstract: Interpatient variability is often overlooked in orthopaedic computational studies due to the substantial challenges involved in sourcing and generating large numbers of bone models. A statistical model of the whole femur incorporating both geometric and material property variation was developed as a potential solution to this problem. The statistical model was constructed using principal component analysis, applied to 21 in idual computer tomography scans. To test the ability of the statistical model to generate realistic, unique, finite element (FE) femur models it was used as a source of 1000 femurs to drive a study on femoral neck fracture risk. The study simulated the impact of an oblique fall to the side, a scenario known to account for a large proportion of hip fractures in the elderly and have a lower fracture load than alternative loading approaches. FE model generation, application of subject specific loading and boundary conditions, FE processing and post processing of the solutions were completed automatically. The generated models were within the bounds of the training data used to create the statistical model with a high mesh quality, able to be used directly by the FE solver without remeshing. The results indicated that 28 of the 1000 femurs were at highest risk of fracture. Closer analysis revealed the percentage of cortical bone in the proximal femur to be a crucial differentiator between the failed and non-failed groups. The likely fracture location was indicated to be intertrochantic. Comparison to previous computational, clinical and experimental work revealed support for these findings.

Simulation of a knee joint replacement during a gait cycle using explicit finite element analysis

Publisher: Elsevier BV

Date: 03-2005

DOI: 10.1016/J.JBIOMECH.2004.03.026

Efficacy and efficiency of multivariate linear regression for rapid prediction of femoral strain fields during activity

Publisher: Elsevier BV

Date: 2019

DOI: 10.1016/J.MEDENGPHY.2018.12.001

Abstract: Multivariate Linear Regression-based (MLR) surrogate models were explored to reduce the computational cost of predicting femoral strains during normal activity in comparison with finite element analysis. The musculoskeletal model of one in idual, the finite-element model of the right femur, and experimental force and motion data for normal walking, fast walking, stair ascent, stair descent, and rising from a chair were obtained from a previous study. Equivalent Von Mises strain was calculated for 1000 frames uniformly distributed across activities. MLR surrogate models were generated using training sets of 50, 100, 200 and 300 s les. The finite-element and MLR analyses were compared using linear regression. The Root Mean Square Error (RMSE) and the 95th percentile of the strain error distribution were used as indicators of average and peak error. The MLR model trained using 200 s les (RMSE < 108 µε peak error < 228 µε) was used as a reference. The finite-element method required 66 s per frame on a standard desktop computer. The MLR model required 0.1 s per frame plus 1848 s of training time. RMSE ranged from 1.2% to 1.3% while peak error ranged from 2.2% to 3.6% of the maximum micro-strain (5020 µε). Performance within an activity was lower during early and late stance, with RMSE of 4.1% and peak error of 8.6% of the maximum computed micro-strain. These results show that MLR surrogate models may be used to rapidly and accurately estimate strain fields in long bones during daily physical activity.

Experimental–Computational Evaluation of Human Bone Marrow Stromal Cell Spreading on Trabecular Bone Structures

Publisher: Springer Science and Business Media LLC

Date: 19-03-2009

DOI: 10.1007/S10439-009-9676-3

Abstract: The clinical application of macro-porous scaffolds for bone regeneration is significantly affected by the problem of insufficient cell colonization. Given the wide variety of different scaffold structures used for tissue engineering it is essential to derive relationships for cell colonization independent of scaffold architecture. To study cell population spreading on 3D structures decoupled from nutrient limitations, an in vitro culture system was developed consisting of thin slices of human trabecular bone seeded with Human Bone Marrow Stromal Cells, combined with dedicated microCT imaging and computational modeling of cell population spreading. Only the first phase of in vitro scaffold colonization was addressed, in which cells migrate and proliferate up to the stage when the surface of the bone is covered as a monolayer, a critical prerequisite for further tissue formation. The results confirm the model's ability to represent experimentally observed cell population spreading. The key advantage of the computational model was that by incorporating complex 3D structure, cell behavior can be characterized quantitatively in terms of intrinsic migration parameters, which could potentially be used for predictions on different macro-porous scaffolds subject to additional experimental validation. This type of modeling will prove useful in predicting cell colonization and improving strategies for skeletal tissue engineering.

A finite element study on the mechanical response of the head-neck interface of hip implants under realistic forces and moments of daily activities: Part 1, level walking

Publisher: Elsevier BV

Date: 11-2017

DOI: 10.1016/J.JMBBM.2017.08.012

Abstract: This paper investigates the mechanical response of a modular head-neck interface of hip joint implants under realistic loads of level walking. The realistic loads of the walking activity consist of three dimensional gait forces and the associated frictional moments. These forces and moments were extracted for a 32mm metal-on-metal bearing couple. A previously reported geometry of a modular CoCr/CoCr head-neck interface with a proximal contact was used for this investigation. An explicit finite element analysis was performed to investigate the interface mechanical responses. To study the level of contribution and also the effect of superposition of the load components, three different scenarios of loading were studied: gait forces only, frictional moments only, and combined gait forces and frictional moments. Stress field, micro-motions, shear stresses and fretting work at the contacting nodes of the interface were analysed. Gait forces only were found to significantly influence the mechanical environment of the head-neck interface by temporarily extending the contacting area (8.43% of initially non-contacting surface nodes temporarily came into contact), and therefore changing the stress field and resultant micro-motions during the gait cycle. The frictional moments only did not cause considerable changes in the mechanical response of the interface (only 0.27% of the non-contacting surface nodes temporarily came into contact). However, when superposed with the gait forces, the mechanical response of the interface, particularly micro-motions and fretting work, changed compared to the forces only case. The normal contact stresses and micro-motions obtained from this realistic load-controlled study were typically in the range of 0-275MPa and 0-38µm, respectively. These ranges were found comparable to previous experimental displacement-controlled pin/cylinder-on-disk fretting corrosion studies.

Finite element analysis of the initial stability of ankle arthrodesis with internal fixation: flat cut versus intact joint contours

Publisher: Elsevier BV

Date: 03-2003

DOI: 10.1016/S0268-0033(02)00207-3

Abstract: Qualitative comparison of the initial stability provided by two joint preparation techniques and various screw configurations in ankle arthrodesis, using the finite element method.Design. A three-dimensional model of a healthy ankle was developed from computed tomography images. Two groups of models were built, one with the joint contours resected to produce flat surfaces, and the second with the joint contours preserved. In each case, a variety of screw orientations were examined. Despite the improved results of ankle arthrodesis, failure rates due to non-union are still reported. The initial stability of the arthrodesis construct seems important in the final outcome of the fusion. Non-linear contact finite element analyses were performed in the arthrodesis constructs subjected to internal/external torsion and dorsiflexion. Micromotions at the bone-to-bone interface were calculated for frictionless and Coulomb friction contact, and compared for the two joint preparation techniques and screw configurations. Overall lower peak micromotions were predicted when preserving the joint contours both in torsion and dorsiflexion. For both preparation techniques, the lowest micromotions tended to occur with the screws inserted at 30 degrees with respect to the long axis of the tibia, crossing above the fusion site. Inclusion of friction in the models caused a general decrease on the magnitude of the micromotions as compared to the frictionless case, but did not affect the ranking of the models. The finite element method can be used as a qualitative tool to study the initial stability of ankle arthrodesis, overcoming the difficulties of measuring bone-to-bone interface micromotions experimentally. Better initial stability was predicted for ankle arthrodesis when the joint contours were preserved rather than resected. Crossing the screws above the fusion site at a steeper angle also tended to increase the stability at the fusion site. Finite element analyses can help during the pre-operative planning of ankle arthrodesis. When bone density is not compromised, preserving the joint contour and inserting the screws at less than 45 degrees to the long axis of the tibia, crossing over the arthrodesis site, may offer better initial stability.

Computational assessment of the effect of polyethylene wear rate, mantle thickness, and porosity on the mechanical failure of the acetabular cement mantle

Publisher: Wiley

Date: 30-11-2009

DOI: 10.1002/JOR.21040

Abstract: Clinical studies have revealed that aseptic loosening is the dominant cause of failure in total hip arthroplasty, particularly for the acetabular component. For a cemented polyethylene cup, failure is generally accompanied by the formation of fibrous tissue at the cement-bone interface. A variety of reasons for the formation of this tissue have been suggested, including osteolysis and mechanical overload at the cement-bone interface. In this study, a computational cement damage accumulation method was used to investigate the effect of polyethylene cup penetration, cement mantle thickness, and cement porosity on the number of cycles required to achieve mechanical fatigue failure of the cement mantle. Cup penetration was found to increase cement mantle stresses, resulting in a reduction in cement mantle fatigue life of 9% to 11% for a high cup penetration rate. The effect of using a thin (2 mm) over a thick (4 mm) cement mantle also reduced cement mantle fatigue life between 9% and 11%, and greatly raised cancellous bone stresses. Cement porosity was found to have very little effect on cement mantle fatigue life. Failure modes and cement stresses involved suggest that only extreme combinations of a thin cement mantle and high cup penetration may lead to mechanical failure of the cement mantle, thereby allowing wear debris access to the cement-bone interface. A thin cement mantle may also lead to the mechanical overload of the cement-bone interface. In this manner, the authors suggest that the mechanical factors may contribute to the failure mode of cemented polyethylene cups.

Minimal-resection arthroplasty to treat meniscal tears with associated condyle lesions: Finite element analysis

Publisher: SAGE Publications

Date: 18-12-2008

DOI: 10.1243/09544119JEIM510

Abstract: An early intervention prosthesis which minimizes the extent of resected healthy bone would be advantageous to patients for whom a total or unicompartmental replacement would sacrifice extensive healthy tissue. In this study the use of a device to treat osteoarthritis localized upon a single condyle of the femur with an associated irreparable meniscal tear is considered. The effects of implant alignment are considered from the standpoint of kinematics and potential for cartilage damage. The results suggest that alterations in implant position influence joint kinematics during stance. Anteroposterior (AP) adjustment of the medial prosthesis minimizes the capability of the knee to rotate internally, placing higher demands on the cruciate ligaments. AP adjustments of the lateral prosthesis induces greater posterior drawback, reducing internal—external rotation. Natural knee kinematics are best reproduced by the medial condyle rather than the lateral condyle. Stress exposure of the cartilage increased with the introduction of the femoral condyle prosthesis, which may progress eventually to osteoarthritis, although the results indicate that the medial condyle device is less likely to lead to cartilage damage than is lateral condyle replacement. This study demonstrates that a minimal-resection femoral condyle device may provide sufficient knee joint function to serve as an interim treatment prior to total or unicompartmental knee arthroplasty.

On the constitutive modeling of biological soft connective tissues

Publisher: Elsevier BV

Date: 04-2002

DOI: 10.1016/S0020-7683(02)00084-7

An Analytical Calculation of Frictional and Bending Moments at the Head-Neck Interface of Hip Joint Implants during Different Physiological Activities

Publisher: MDPI AG

Date: 05-12-2016

DOI: 10.3390/MA9120982

Damage Rate is a Predictor of Fatigue Life and Creep Strain Rate in Tensile Fatigue of Human Cortical Bone Samples

Publisher: ASME International

Date: 28-09-2004

DOI: 10.1115/1.1865188

Abstract: We present results on the growth of damage in 29 fatigue tests of human femoral cortical bone from four in iduals, aged 53–79. In these tests we examine the interdependency of stress, cycles to failure, rate of creep strain, and rate of modulus loss. The behavior of creep rates has been reported recently for the same donors as an effect of stress and cycles (Cotton, J. R., Zioupos, P., Winwood, K., and Taylor, M., 2003, “Analysis of Creep Strain During Tensile Fatigue of Cortical Bone,” J. Biomech. 36, pp. 943–949). In the present paper we first examine how the evolution of damage (drop in modulus per cycle) is associated with the stress level or the “normalized stress” level (stress ided by specimen modulus), and results show the rate of modulus loss fits better as a function of normalized stress. However, we find here that even better correlations can be established between either the cycles to failure or creep rates versus rates of damage than any of these three measures versus normalized stress. The data indicate that damage rates can be excellent predictors of fatigue life and creep strain rates in tensile fatigue of human cortical bone for use in practical problems and computer simulations.

Sampling strategies for approximating patient variability in population‐based finite element studies of total hip replacement

Publisher: Wiley

Date: 18-11-2019

DOI: 10.1002/CNM.3168

Abstract: Total hip replacements must be robust to patient variability for long-term success in the population. The challenge during the design process is evaluating an implant in a erse population but the computational cost of simulating a population of subject-specific finite element (FE) models is not practical. We examined five strategies to generate representative subsets of subjects from a cohort of 103 implanted hip joint FE models to approximate the variability in output metrics. Comparing with the median and distribution of the 95

A novel analytical approach for determining the frictional moments and torques acting on modular femoral components in total hip replacements

Publisher: Elsevier BV

Date: 04-2015

DOI: 10.1016/J.JBIOMECH.2015.02.010

Abstract: A three dimensional analytical approach was developed to determine the frictional moment vector generated by the relative sliding of the head-cup bearing couple of a total hip replacement. The frictional moment projection onto the femoral neck was also determined over the loading cycle. Predicted frictional moments for nine combinations of bearing materials and diameters were in close agreement with existing in vitro data. The analytical method was then applied to simplified gait (lubrication conditions of dry and serum), ISO standard gait and physiological level gait loading cycles. ISO standard gait had a total contact force of about two fold of physiological level gait and there was a corresponding increase in the maximum frictional torque on neck from 0.66×BW%m to 0.88×BW%m. For the ISO standard gait, the maximum frictional torque occurred at the same instance of maximum frictional moment and the maximum contact force. In contrast, for the physiological level gait, the frictional torque did not occur at the same instance as the peak load. This suggests that the neck frictional torque is a function of other parameters, such as angle between neck axis and frictional moment vector, as well as the magnitude of the contact force and frictional moment. The developed methodology was able to predict the maximum magnitude and change of directions of moments and the variation of torque at the head neck interface. The data will be useful for experimental studies assessing the fretting behaviour of the head neck junction, by providing appropriate loading data.

Statistical shape modelling versus linear scaling: Effects on predictions of hip joint centre location and muscle moment arms in people with hip osteoarthritis

Publisher: Elsevier BV

Date: 03-2019

DOI: 10.1016/J.JBIOMECH.2019.01.031

Abstract: Marker-based dynamic functional or regression methods are used to compute joint centre locations that can be used to improve linear scaling of the pelvis in musculoskeletal models, although large errors have been reported using these methods. This study aimed to investigate if statistical shape models could improve prediction of the hip joint centre (HJC) location. The inclusion of complete pelvis imaging data from computed tomography (CT) was also explored to determine if free-form deformation techniques could further improve HJC estimates. Mean Euclidean distance errors were calculated between HJC from CT and estimates from shape modelling methods, and functional- and regression-based linear scaling approaches. The HJC of a generic musculoskeletal model was also perturbed to compute the root-mean squared error (RMSE) of the hip muscle moment arms between the reference HJC obtained from CT and the different scaling methods. Shape modelling without medical imaging data significantly reduced HJC location error estimates (11.4 ± 3.3 mm) compared to functional (36.9 ± 17.5 mm, p = <0.001) and regression (31.2 ± 15 mm, p = <0.001) methods. The addition of complete pelvis imaging data to the shape modelling workflow further reduced HJC error estimates compared to no imaging (6.6 ± 3.1 mm, p = 0.002). Average RMSE were greatest for the hip flexor and extensor muscle groups using the functional (16.71 mm and 8.87 mm respectively) and regression methods (16.15 mm and 9.97 mm respectively). The effects on moment-arms were less substantial for the shape modelling methods, ranging from 0.05 to 3.2 mm. Shape modelling methods improved HJC location and muscle moment-arm estimates compared to linear scaling of musculoskeletal models in patients with hip osteoarthritis.

Assigning trabecular bone material properties in finite element models simulating the pelvis before and after the development of peri-prosthetic osteolytic lesions

Publisher: Elsevier BV

Date: 09-2022

DOI: 10.1016/J.JMBBM.2022.105311

Abstract: Estimating strain distribution in the acetabulum before and after the development of peri-prosthetic osteolytic lesions secondary to total hip arthroplasty may assist with understanding the pathogenesis of this condition. This could be achieved by performing patient-specific finite element analysis of (1) total hip arthroplasty recipients with developed acetabular osteolytic lesions, and (2) models simulating the patient's pelvis and implant immediately after primary surgery. State of the art patient-specific total hip arthroplasty finite element analysis simulations obtain trabecular bone material properties from Hounsfield units within computed tomography (CT) scans of patients. However, this is not feasible when an implant is already in situ due to metal artefact disruption and, in turn, incorrectly reproduced Hounsfield units. Therefore, alternative methods of assigning trabecular bone material properties within such models were tested and strain results compared. It was found that assigning set material properties throughout the trabecular bone geometry was sufficient for the desired application. Simulating the primary implant and pelvis requires geometric and material based assumptions. Therefore, comparisons were made between strain values obtained from simulated primary models, from state of the art methods using material properties obtained from intact bone within a CT scan, and from models with osteolytic lesions. Strain values found using the finite element models simulating the pelvis before osteolytic lesion developed were considerably closer to those found using state of the art methods than those found for the bone loss models. These models could be used to determine relationships between strain distribution and factors such as bone loss.

Four decades of finite element analysis of orthopaedic devices: Where are we now and what are the opportunities?

Publisher: Elsevier BV

Date: 03-2015

DOI: 10.1016/J.JBIOMECH.2014.12.019

Abstract: Finite element has been used for more than four decades to study and evaluate the mechanical behaviour total joint replacements. In Huiskes seminal paper "Failed innovation in total hip replacement: diagnosis and proposals for a cure", finite element modelling was one of the potential cures to avoid poorly performing designs reaching the market place. The size and sophistication of models has increased significantly since that paper and a range of techniques are available from predicting the initial mechanical environment through to advanced adaptive simulations including bone adaptation, tissue differentiation, damage accumulation and wear. However, are we any closer to FE becoming an effective screening tool for new devices? This review contains a critical analysis of currently available finite element modelling techniques including (i) development of the basic model, the application of appropriate material properties, loading and boundary conditions, (ii) describing the initial mechanical environment of the bone-implant system, (iii) capturing the time dependent behaviour in adaptive simulations, (iv) the design and implementation of computer based experiments and (v) determining suitable performance metrics. The development of the underlying tools and techniques appears to have plateaued and further advances appear to be limited either by a lack of data to populate the models or the need to better understand the fundamentals of the mechanical and biological processes. There has been progress in the design of computer based experiments. Historically, FE has been used in a similar way to in vitro tests, by running only a limited set of analyses, typically of a single bone segment or joint under idealised conditions. The power of finite element is the ability to run multiple simulations and explore the performance of a device under a variety of conditions. There has been increasing usage of design of experiments, probabilistic techniques and more recently population based modelling to account for patient and surgical variability. In order to have effective screening methods, we need to continue to develop these approaches to examine the behaviour and performance of total joint replacements and benchmark them for devices with known clinical performance. Finite element will increasingly be used in the design, development and pre-clinical testing of total joint replacements. However, simulations must include holistic, closely corroborated, multi-domain analyses which account for real world variability.

Three-dimensional finite element modelling of the human ACL: simulation of passive knee flexion with a stressed and stress-free ACL

Publisher: Elsevier BV

Date: 11-2004

DOI: 10.1016/J.JBIOMECH.2004.01.030

Influence of collars on the primary stability of cementless femoral stems: A finite element study using a diverse patient cohort

Publisher: Wiley

Date: 11-2017

DOI: 10.1002/JOR.23744

Abstract: For cementless femoral stems, there is debate as to whether a collar enhances primary stability and load transfer compared to collarless designs. Finite Element (FE) analysis has the potential to compare stem designs within the same cohort, allowing for subtle performance differences to be identified, if present. Subject-specific FE models of intact and implanted femora were run for a erse cohort (21 males, 20 females BMI 16.4-41.2 kg/m

Stress and strain distribution within the intact femur: compression or bending?

Publisher: Elsevier BV

Date: 03-1996

DOI: 10.1016/1350-4533(95)00031-3

Abstract: The aim of this research was to test the hypothesis that the intact femur is loaded predominately in compression. The study was composed of two parts: a finite element analysis of the intact femur to assess if a compressive stress distribution could be achieved in the diaphyseal region of the femur using physiological muscle and joint contact forces a simple radiological study to assess the in vivo deflections of the femur during one legged stance. The results of this investigation strongly support the hypothesis that the femur is loaded primarily in compression, and not bending as previously thought. The finite element analysis demonstrated that a compressive stress distribution in the diaphyseal femur can be achieved, producing a stress distribution which appears to be consistent with the femoral cross-sectional geometry. The finite element analysis also predicted that for a compressive load case there would be negligible deflections of the femoral head. The radiological study confirmed this, with no measurable in vivo deflection of the femur occurring during one legged stance.

Development of a surrogate model based on patient weight, bone mass and geometry to predict femoral neck strains and fracture loads

Publisher: Elsevier BV

Date: 04-2017

DOI: 10.1016/J.JBIOMECH.2017.02.022

Abstract: Osteoporosis and related bone fractures are an increasing global burden in our ageing society. Areal bone mineral density assessed through dual energy X-ray absorptiometry (DEXA), the clinically accepted and most used method, is not sufficient to assess fracture risk in idually. Finite element (FE) modelling has shown improvements in prediction of fracture risk, better than aBMD from DEXA, but is not practical for widespread clinical use. The aim of this study was to develop an adaptive neural network (ANN)-based surrogate model to predict femoral neck strains and fracture loads obtained from a previously developed population-based FE model. The surrogate model performance was assessed in simulating two loading conditions: the stance phase of gait and a fall. The surrogate model successfully predicted strains estimated by FE (r

Do Capsular Pressure and Implant Motion Interact to Cause High Pressure in the Periprosthetic Bone in Total Hip Replacement?

Publisher: ASME International

Date: 12-2011

DOI: 10.1115/1.4005455

Abstract: When there is a debonding at the bone-implant interface, the difference in stiffness between the implant and the bone can result in micromotion, allowing existing gaps to open further or new gaps to be created during physiological loading. It has been suggested that periprosthetic fluid flow and high pressure may play an important role in osteolysis development in the proximity of these gaps. To explain this phenomenon, the concepts of “effective joint space” and “pumping stem” have been cited in many studies. However, there is no clear understanding of the factors causing, or contributing to, these mechanisms. It is likely that capsular pressure, gap dimensions, and micromotion of the gap during cyclic loading of an implant can play a defining role in inducing periprosthetic flow. In order to obtain a better understanding of the main influences on periprosthetic flows and the development of osteolysis, steady state and transient 2D computational fluid dynamic simulations were performed for the joint capsule of the lateral side of a stem-femur system, and a gap in communication with the capsule and the surrounding bone. It was shown that high capsular pressure may be the main driving force for high fluid pressure and flow in the bone surrounding the gap, while micromotion of only very long and narrow gaps can cause significant pressure and flow in the bone. At low capsular pressure, micromotion induced large flows in the gap region however, the flow in the bone tissue was almost unaffected. The results also revealed the existence of high velocity spikes in the bone region at the bottom of the gap. These velocity spikes can exert excessive fluid shear stress on the bone cells and disturb the local biological balance of the surrounding interstitial fluid which can result in osteolysis development. High capsular pressure was observed to be the main cause of these velocity spikes whereas, at low capsular pressure, gap micromotion of only very long and narrow gaps generated significant velocity spikes in the bone at the bottom of the gaps.

Lower functioning patients demonstrate atypical hip joint loading before and following total hip arthroplasty for osteoarthritis

Publisher: Wiley

Date: 29-05-2020

DOI: 10.1002/JOR.24716

Should the cement mantle around the femoral component be thick or thin?

Publisher: British Editorial Society of Bone & Joint Surgery

Date: 2003

DOI: 10.1302/0301-620X.85B1.13055

Abstract: We have compared the survival and radiological outcome at ten years after total hip replacement using two techniques for preparing the femoral canal. The same prosthesis was used throughout and all operations were performed by the same surgical team. In technique 1 the canal was over-reamed by 2 mm and in technique 2 it was reamed to the same size as the prosthesis. Technique 1 was performed on 92 patients and technique 2 on 97 patients. The survival at ten years was 97.2% (90.6 to 99.2) for technique 1 and 98.8% (92.9 to 99.8) for technique 2. Vertical migration was greater in technique 1 (1.8 mm versus 1.0 mm at five years p = 0.36). There were significantly more lytic lesions and radiolucent lines at five years (p = 0.0061) with technique 1. We conclude that technique 2 is not worse and may produce better long- term results than current teaching suggests.

Development of a fretting corrosion model for metallic interfaces using adaptive finite element analysis

Publisher: Elsevier BV

Date: 09-2018

DOI: 10.1016/J.FINEL.2018.05.004

Comparison of long-term numerical and experimental total knee replacement wear during simulated gait loading

Publisher: Elsevier BV

Date: 2007

DOI: 10.1016/J.JBIOMECH.2006.07.027

Abstract: Pre-clinical experimental wear testing of total knee replacement (TKR) components is an invaluable tool for evaluating new implant designs and materials. However, wear testing can be a lengthy and expensive process, and hence parametric studies evaluating the effects of geometric, loading, or alignment perturbations may at times be cost-prohibitive. The objectives of this study were to develop an adaptive FE method capable of simulating wear of a polyethylene tibial insert and to compare predicted kinematics, weight loss due to wear, and wear depth contours to results from a force-controlled experimental knee simulator. Finite element-based computational wear predictions were performed to 5 million gait cycles using both force- and displacement-controlled inputs. The displacement-controlled inputs, by accurately matching the experimental tibiofemoral motion, provided an evaluation of the simple wear theory. The force-controlled inputs provided an evaluation of the overall numerical method by simultaneously predicting both kinematics and wear. Analysis of the predicted wear convergence behavior indicated that 10 iterations, each representing 500,000 gait cycles, were required to achieve numerical accuracy. Using a wear factor estimated from the literature, the predicted kinematics, polyethylene wear contours, and weight loss were in reasonable agreement with the experimental data, particularly for the stance phase of gait. Although further development of the simplified wear theory is important, the initial predictions are encouraging for future use in design phase implant evaluation. In contrast to the experimental testing which occurred over approximately 2 months, computational wear predictions required only 2h.

Cement mantle fatigue failure in total hip replacement: Experimental and computational testing

Publisher: Elsevier BV

Date: 2007

DOI: 10.1016/J.JBIOMECH.2006.07.029

Abstract: One possible loosening mechanism of the femoral component in total hip replacement is fatigue cracking of the cement mantle. A computational method capable of simulating this process may therefore be a useful tool in the preclinical evaluation of prospective implants. In this study, we investigated the ability of a computational method to predict fatigue cracking in experimental models of the implanted femur construct. Experimental specimens were fabricated such that cement mantle visualisation was possible throughout the test. Two different implant surface finishes were considered: grit blasted and polished. Loading was applied to represent level gait for two million cycles. Computational (finite element) models were generated to the same geometry as the experimental specimens, with residual stress and porosity simulated in the cement mantle. Cement fatigue and creep were modelled over a simulated two million cycles. For the polished stem surface finish, the predicted fracture locations in the finite element models closely matched those on the experimental specimens, and the recorded stem displacements were also comparable. For the grit blasted stem surface finish, no cement mantle fractures were predicted by the computational method, which was again in agreement with the experimental results. It was concluded that the computational method was capable of predicting cement mantle fracture and subsequent stem displacement for the structure considered.

Periprosthetic wear particle migration and distribution modelling and the implication for osteolysis in cementless total hip replacement

Publisher: Elsevier BV

Date: 04-2014

DOI: 10.1016/J.JMBBM.2014.01.005

Abstract: In total hip replacement (THR), wear particles play a significant role in osteolysis and have been observed in locations as remote as the tip of femoral stem. However, there is no clear understanding of the factors and mechanisms causing, or contributing to particle migration to the periprosthetic tissue. Interfacial gaps provide a route for particle laden joint fluid to transport wear particles to the periprosthetic tissue and cause osteolysis. It is likely that capsular pressure, gap dimensions and micromotion of the gap during cyclic loading of an implant, play defining roles to facilitate particle migration. In order to obtain a better understanding of the above mechanisms and factors, transient two-dimensional computational fluid dynamic simulations have been performed for the flow in the lateral side of a cementless stem-femur system including the joint capsule, a gap in communication with the capsule and the surrounding bone. A discrete phase model to describe particle motion has been employed. Key findings from these simulations include: (1) Particles were shown to enter the periprosthetic tissue along the entire length of the gap but with higher concentrations at both proximal and distal ends of the gap and a maximum rate of particle accumulation in the distal regions. (2) High capsular pressure, rather than gap micromotion, has been shown to be the main driving force for particle migration to periprosthetic tissue. (3) Implant micromotion was shown to pump out rather than draw in particles to the interfacial gaps. (4) Particle concentrations are consistent with known distributions of (i) focal osteolysis at the distal end of the gap and (ii) linear osteolysis along the entire gap length.

A Computational Efficient Method to Assess the Sensitivity of Finite-Element Models: An Illustration With the Hemipelvis

Publisher: ASME International

Date: 03-11-2016

DOI: 10.1115/1.4034831

Abstract: Assessing the sensitivity of a finite-element (FE) model to uncertainties in geometric parameters and material properties is a fundamental step in understanding the reliability of model predictions. However, the computational cost of in idual simulations and the large number of required models limits comprehensive quantification of model sensitivity. To quickly assess the sensitivity of an FE model, we built linear and Kriging surrogate models of an FE model of the intact hemipelvis. The percentage of the total sum of squares (%TSS) was used to determine the most influential input parameters and their possible interactions on the median, 95th percentile and maximum equivalent strains. We assessed the surrogate models by comparing their predictions to those of a full factorial design of FE simulations. The Kriging surrogate model accurately predicted all output metrics based on a training set of 30 analyses (R2 = 0.99). There was good agreement between the Kriging surrogate model and the full factorial design in determining the most influential input parameters and interactions. For the median, 95th percentile and maximum equivalent strain, the bone geometry (60%, 52%, and 76%, respectively) was the most influential input parameter. The interactions between bone geometry and cancellous bone modulus (13%) and bone geometry and cortical bone thickness (7%) were also influential terms on the output metrics. This study demonstrates a method with a low time and computational cost to quantify the sensitivity of an FE model. It can be applied to FE models in computational orthopaedic biomechanics in order to understand the reliability of predictions.

Corroboration of coupled musculoskeletal model and finite element predictions with in vivo RSA migration of an uncemented acetabular component

Publisher: Wiley

Date: 10-08-2023

DOI: 10.1002/JOR.25671

Abstract: While finite element (FE) models have been used extensively in orthopedic studies, validation of their outcome metrics has been limited to comparison against ex vivo testing. The aim of this study was to validate FE model predictions of the initial cup mechanical environment against patient‐matched in vivo measurements of acetabular cup migration using radiostereometric analysis (RSA). Tailored musculoskeletal and FE models were developed using a combination of three‐dimensional (3D) motion capture data and clinical computerized tomography (CT) scans for a cohort of eight in iduals who underwent primary total hip replacement and were prospectively enrolled in an RSA study. FE models were developed to calculate the mean modulus of cancellous bone, composite peak micromotion (CPM), composite peak strain (CPS) and percentage area of bone ingrowth. The RSA cup migration at 3 months was used to corroborate the FE output metrics. Qualitatively, all FE‐predicted metrics followed a similar rank order as the in vivo RSA 3D migration data. The two cases with the lowest predicted CPM ( µm), lowest CPS ( .0041), and high bone modulus ( MPa) were confirmed to have the lowest in vivo RSA 3D migration ( .14 mm). The two cases with the largest predicted CPM ( µm), larger CPS ( .0119) and lowest bone modulus ( MPa) were confirmed to have the largest in vivo RSA 3D migration ( .78 mm). This study enabled the first corroboration between tailored musculoskeletal and FE model predictions with in vivo RSA cup migration. Investigation of additional patient‐matched CT, gait, and RSA examinations may allow further development and validation of FE models.

A combined RSA and FE study of the implanted proximal tibia: correlation of the post-operative mechanical environment with implant migration

Publisher: Elsevier BV

Date: 08-2004

DOI: 10.1016/J.JBIOMECH.2003.12.004

Finite Element Analysis of the Human ACL Subjected to Passive Anterior Tibial Loads

Publisher: Informa UK Limited

Date: 02-2004

DOI: 10.1080/10255840410001658839

The mechanics of head-neck taper junctions: What do we know from finite element analysis?

Publisher: Elsevier BV

Date: 04-2021

DOI: 10.1016/J.JMBBM.2021.104338

Analysis of creep strain during tensile fatigue of cortical bone

Publisher: Elsevier BV

Date: 07-2003

DOI: 10.1016/S0021-9290(03)00063-0

Abstract: During fatigue tests of cortical bone specimens, at the unload portion of the cycle (zero stress) non-zero strains occur and progressively accumulate as the test progresses. This non-zero strain is hypothesised to be mostly, if not entirely, describable as creep. This work examines the rate of accumulation of this strain and quantifies its stress dependency. A published relationship determined from creep tests of cortical bone (Journal of Biomechanics 21 (1988) 623) is combined with knowledge of the stress history during fatigue testing to derive an expression for the amount of creep strain in fatigue tests. Fatigue tests on 31 bone s les from four in iduals showed strong correlations between creep strain rate and both stress and "normalised stress" (sigma/E) during tensile fatigue testing (0-T). Combined results were good (r(2)=0.78) and differences between the various in iduals, in particular, vanished when effects were examined against normalised stress values. Constants of the regression showed equivalence to constants derived in creep tests. The universality of the results, with respect to four different in iduals of both sexes, shows great promise for use in computational models of fatigue in bone structures.

Cancellous bone stresses surrounding the femoral component of a hip prosthesis: an elastic-plastic finite element analysis

Publisher: Elsevier BV

Date: 10-1995

DOI: 10.1016/1350-4533(95)00018-I

Abstract: The cancellous bone stresses surrounding the femoral component of total hip replacement were investigated using the finite element method. Four versions of a certain femoral hip prosthesis (the Freeman, Corin Medical), cemented, HA coated, press-fit, and press-fit with ridges were analysed. Each model was subjected to two separate load cases with the cancellous bone modelled as an elastic perfectly plastic material. The effect of bone quality was investigated by varying the cancellous bone stiffness. The resulting cancellous bone stress distributions were compared to that of the intact femur. The results were also compared to clinical subsidence data (published elsewhere) for the Freeman femoral prosthesis to determine if the initial cancellous bone stress distribution could be used to predict the migration of the various versions of this prosthesis. The results showed that the press-fit designs of prosthesis generated substantially higher cancellous bone stresses than the cemented and HA coated designs, and that these stresses were up to 6.5 times higher than found in the intact femur. For all forms of fixation the cancellous bone stress distribution was found to be insensitive to changes in the trabecular bone stiffness: thus poor quality cancellous bone is more likely to promote 'plastic' deformation, and therefore subsidence of the prosthesis. Comparison with the clinical migration data showed a good correlation and revealed that it may be possible to use the calculated initial cancellous bone stresses to predict the migration of the implant, and hence the probability of early and mid-term aseptic loosening.(ABSTRACT TRUNCATED AT 250 WORDS)

An Overview of the Stability and Fretting Corrosion of Microgrooved Necks in the Taper Junction of Hip Implants

Publisher: MDPI AG

Date: 25-11-2022

DOI: 10.3390/MA15238396

Abstract: Fretting corrosion at the head–neck interface of modular hip implants, scientifically termed trunnionosis/taperosis, may cause regional inflammation, metallosis, and adverse local tissue reactions. The severity of such a deleterious process depends on various design parameters. In this review, the influence of surface topography (in some cases, called microgrooves/ridges) on the overall performance of the microgrooved head–neck junctions is investigated. The methodologies together with the assumptions and simplifications, as well as the findings from both the experimental observations (retrieval and in vitro) and the numerical approaches used in previous studies, are presented and discussed. The performance of the microgrooved junctions is compared to those with a smooth surface finish in two main categories: stability and integrity wear, corrosion, and material loss. Existing contradictions and disagreements among the reported results are reported and discussed in order to present a comprehensive picture of the microgrooved junctions. The current research needs and possible future research directions on the microgrooved junctions are also identified and presented.

Computationally efficient prediction of bone–implant interface micromotion of a cementless tibial tray during gait

Publisher: Elsevier BV

Date: 05-2014

DOI: 10.1016/J.JBIOMECH.2014.02.018

Abstract: Cementless tibial fixation in total knee replacement (TKR) has potential for improved fixation and ease of revision. Achieving primary stability in cementless TKR is critical to the performance of the components. Excessive micromotion may prevent osseointegration at the bone-implant interface. Computational finite element (FE) studies have been used to predict micromotion at the interface, but analysis of an entire activity cycle is computational expensive, prohibiting large numbers of analyses. Surrogate modeling methods can be used to train a numerical model to predict the response of an FE model. These models are computationally efficient and are suitable for high-volume or iterative analyses requiring probabilistic, statistical or optimization methods. The objective of this work was to train a surrogate model capable of predicting micromotion over the entire bone-implant interface. A proximal tibial bone with mapped material properties was virtually implanted with a tibial tray. A FE model, with six-degree-of-freedom loads s led from telemetric patients during walking, was used to generate training data for the surrogate model. The linear response surrogate model was evaluated for six full gait cycles the average and peak micromotion across the interface, and the percentage of bone-implant interface surface area experiencing micromotions less than 50 and greater than 150µm were calculated both as a function of the activity cycle and as the composite peak micromotion throughout the cycle. Differences in root-mean-square (RMS) micromotion between FE and surrogate models were less than 14µm. FE analysis time for a complete gait cycle was 15h, compared to 30s for the surrogate model. Surrogate models have significant potential to rapidly predict micromotion over the entire bone-implant interface, allowing greater range in loading conditions to be explored than is possible through conventional methods.

Accounting for patient variability in finite element analysis of the intact and implanted hip and knee: A review

Publisher: Wiley

Date: 18-12-2012

DOI: 10.1002/CNM.2530

Abstract: It is becoming increasingly difficult to differentiate the performance of new joint replacement designs using available preclinical test methods. Finite element analysis is commonly used and the majority of published studies are performed on representative anatomy, assuming optimal implant placement, subjected to idealised loading conditions. There are significant differences between patients and accounting for this variability will lead to better assessment of the risk of failure. This review paper provides a comprehensive overview of the techniques available to account for patient variability. There is a brief overview of patient-specific model generation techniques, followed by a review of multisubject patient-specific studies performed on the intact and implanted femur and tibia. In particular, the challenges and limitations of manually generating models for such studies are discussed. To efficiently account for patient variability, the application of statistical shape and intensity models (SSIM) are being developed. Such models have the potential to synthetically generate thousands of representative models generated from a much smaller training set. Combined with the automation of the prosthesis implantation process, SSIM provides a potentially powerful tool for assessing the next generation of implant designs. The potential application of SSIM are discussed along with their limitations.

Bone remodelling inside a cemented resurfaced femoral head

Publisher: Elsevier BV

Date: 07-2006

DOI: 10.1016/J.CLINBIOMECH.2006.01.010

Abstract: Although the short-term performance of modern resurfacing hip arthroplasty is impressive, the long-term performance is still unknown. It is hypothesised that bone remodelling and the resulting changes in stress/strain distribution within the resurfaced femur influence the risk of fixation failure. Three-dimensional finite element models and adaptive bone remodelling algorithms have been used to predict long-term changes in bone density following cemented femoral head resurfacing. Applied loading conditions include normal walking and stair climbing. The remodelling simulation was validated by comparing the results of an analysis of a proximal femur implanted with a Charnley femoral component with known clinical data in terms of bone density adaptations. Resurfacing caused a reduction of strain of 20-70% in the bone underlying the implant as compared to the intact femur, immediately post operative. Elevated strains, ranging between 0.50 and 0.80% strain, were generated post-operatively around the proximal femoral neck regions, indicating a potential risk of neck fracture. However, this strain concentration was considerably reduced after bone remodelling. After remodelling, bone resorption of 60-90% was observed in the bone underlying the implant. Reduction in bone density of 5-47% occurred in the lateral femoral head. Bone apposition was observed in the proximal-medial cortex, around the inferior edge of the implant. Hardly any changes in bone density occurred in the distal neck or the femoral diaphysis. Although resurfacing has produced encouraging clinical results, bone remodelling within the femoral head might be a concern for long-term fixation. Regions of strain concentration at the head-neck junction, which may increase the initial risk of femoral neck fracture, are reduced with bone remodelling. In order to reduce this risk of femoral neck fracture, patients should avoid activities which induce high loading of the hip during the early rehabilitation period after surgery.

Near-surface damage - a persistent problem in crowns obtained by computer-aided design and manufacturing

Publisher: SAGE Publications

Date: 04-2005

DOI: 10.1243/095441105X9363

Abstract: Robust dental systems obtained by computer-aided design and manufacture (CAD/CAM) have been introduced and, in parallel, the strength of the ceramic materials used in fabricating dental crowns has improved. Yet all-ceramic crowns suffer from near-surface damage, limiting their clinical success, especially on posterior teeth. Factors directly associated with CAD/CAM fabrication that contribute to the degree of damage include material selection and machining parameters and strategies. However, a number of additional factors also either create new damage modes or exacerbate subcritical damage, potentially leading to catastrophic failure of the crown. Such factors include post-fabrication manipulations in the laboratory or by the clinician, fatigue associated with natural occlusal function, and stress fields created by compliance or distortion within the supporting tooth structure and/or adhesive material holding the crown to the tooth. Any damage reduces the strength of a crown, increasing the probability of catastrophic failure. The challenge is to understand and manage the combination of competing damage initiation sites and mechanisms, limitations imposed by the demand for aesthetics, and biologically related constraints.

Micro-CT scan optimisation for mechanical loading of tibia with titanium tibial tray: A digital volume correlation zero strain error analysis

Publisher: Elsevier BV

Date: 10-2022

DOI: 10.1016/J.JMBBM.2022.105336

Abstract: Primary stability of press-fit tibial trays is achieved by introducing an interference fit between bone and implant. The internal cancellous bone strains induced during this process and during loading have yet to be quantified experimentally. Advancements in large-gantry micro-CT imaging and digital volume correlation (DVC) allow quantification of such strains. However, before undertaking such a test, experimental requirements and DVC performance need to be examined, particularly considering the presence of a large orthopaedic implant (tibial tray). The aim of this study was to assess the DVC zero-strain accuracy (mean absolute error: MAER) and precision (standard deviation of error: SDER) on a cadaveric human tibia implanted with a titanium press-fit tray across four plausible scanning configurations, using a cabinet micro-CT system (Nikon XT H 225 ST). These varied in rotation step and resulting scanning time (106 min vs. 66 min), presence or absence of a 2 mm-thick aluminium cylinder for mechanical testing, and X-ray tube voltage (150 kVp vs. 215 kVp). One proximal tibia was implanted and micro-CT scanned (42 μm ixel), with repeated scanning and specimen repositioning in between. DVC (DaVis, LaVision, direct correlation) was performed on nine cubic volumes of interest (VOIs: 13.4 mm-side) and across the entire proximal tibia. Strain errors were comparable across the four scanning configurations and sufficiently low for assessing bone within its elastic region in VOIs (MAER=223-540 με SDER=88-261 με) and at organ level (MAER=536 με SDER=473 με). Whilst the investigated experimental conditions, including a large titanium implant, present added complexity for DVC analysis, scans of sufficient quality can be achieved, reaching a compromise between the DVC requirements and the wanted application. The approach used for choosing the X-ray source settings considering the transmitted X-ray signal intensity and source power, is also discussed.

Simulation of a knee joint replacement during a gait cycle using explicit finite element analysis

Publisher: Elsevier BV

Date: 02-2002

DOI: 10.1016/S0021-9290(01)00179-8

Abstract: The stress distribution within the polyethylene insert of a total knee joint replacement is dependent on the kinematics, which in turn are dependent on the design of the articulating surfaces, the relative position of the components and the tension of the surrounding soft tissues. Implicit finite element analysis techniques have been used previously to examine the polyethylene stresses. However, these have essentially been static analyses and hence ignored the influence of the kinematics. The aim of this work was to use an explicit finite element approach to simulate both the kinematics and the internal stresses within a single analysis. A simulation of a total knee joint replacement subjected to a single gait cycle within a knee wear simulator was performed and the results were compared with experimental data.The predicted kinematics were in close agreement with the experimental data. Various solution-dependent parameters were found to have little influence on the predicted kinematics. The predicted stresses were found to be dependent on the mesh density. This study has shown that an explicit finite element approach is capable of predicting the kinematics and the stresses within a single analysis at relatively low computational cost.

Population-Based Bone Strain During Physical Activity: A Novel Method Demonstrated for the Human Femur

Publisher: Springer Science and Business Media LLC

Date: 26-02-2020

DOI: 10.1007/S10439-020-02483-3

Finite element analysis of the implanted proximal tibia

Publisher: Elsevier BV

Date: 04-1998

DOI: 10.1016/S0021-9290(98)00022-0

Abstract: The cancellous bone stresses within the implanted proximal tibia were examined using a three-dimensional anatomical finite element model. Three versions of a proximal tibial prosthesis were examined: an all polyethylene press-fit design a metal backed, stemmed press-fit design and a (horizontally) cemented metal backed, stemmed design. All three designs had published migration and survivorship data. The objectives of the study were (i) to compare the stresses generated by each of the tibial components, (ii) examine the influence of the resected surface morphology and (iii) compare the initial cancellous bone stresses with the published migration and survivorship data. The all polyethylene prosthesis generated the highest cancellous bone stresses. Addition of a metal backing and a stem reduced the stresses, but the cemented device produced the lowest cancellous bone stresses. The surface morphology had a significant effect on the cancellous bone stresses generated by press-fit prostheses. As the bone-prosthesis contact area decreased, the peak cancellous bone stresses increased by as much as 243%. The surface morphology had no effect on the cancellous bone stresses generated by the cemented implant. Good correlation was found between the predicted cancellous bone stresses and the migration and survivorship data, with the implant generating the highest cancellous bone stresses migrating the most and having the poorest survival rates at 5 year. The results support the hypothesis that the progressive failure of cancellous bone is a mechanism of implant migration regardless of the method of fixation and the implantation site.

Assessing changes in subjective and objective function from pre- to post-knee arthroplasty using the Cardiff Dempster–Shafer theory classifier

Publisher: Informa UK Limited

Date: 22-04-2015

DOI: 10.1080/10255842.2015.1034115

Abstract: The purpose of this study is to assess changes in subjective and objective function from pre- to post-knee arthroplasty (KA) using a combined classifier technique. Twenty healthy adults (50-80 years) and 31 KA patients (39-81 years) were studied (4 weeks pre- and 6 months post-KA). Questionnaire measures of subjective pain, joint stability, activity and function were collected. Objective functional assessment included goniometry, ultrasound imaging and 3-D motion analysis/inverse modelling of gait and sit-stand. An optimal set of variables were used to classify function using the Cardiff Dempster-Shafer theory (DST) method. Out of s le accuracy of the classifiers ranged between 90% and 94% for segregating healthy in iduals and pre-KA patients. Post-KA subjective function improved with 74% classified as healthy. However, there was minimal improvement in objective measures (23% classified as healthy). The novel use of Cardiff DST segregated KA patients from healthy in iduals and estimated changes in function from pre- to post-surgery. KA patients had improved pain and function post-operation but objective knee joint measures remained different to healthy in iduals.

Investigation into the effect of varus–valgus orientation on load transfer in the resurfaced femoral head: A multi-femur finite element analysis

Publisher: Elsevier BV

Date: 08-2007

DOI: 10.1016/J.CLINBIOMECH.2007.03.011

Abstract: Femoral head resurfacing is a popular procedure for younger active hip replacement patients. Whilst the current generation of metal-on-metal resurfacing arthroplasties appear to have cured the osteolysis problems that plagued earlier resurfacing implants, fracture of the femoral head and aseptic loosening are still factors of concern in its survivorship. Several studies have shown a tendency towards failure in resurfaced femurs where the implant has been set at a varus angle. This work aims to investigate the influence of varus-valgus orientation on load transfer within the resurfaced proximal femur. This study uses Computer Tomography based finite element analysis to determine the effect of implant orientation on load transfer in the proximal femur with respect to the intact femur. A group of 16 femurs were studied to take into account inter-patient variation four models were produced for each femur, one of the intact femur, one resurfaced with the implant set inline with the femoral neck and one each representing varus and valgus implant alignment. Results showed the valgus aligned resurfaced femur to produce strain patterns more akin to the intact femur. As the implant's angle to the femoral shaft increases from varus to valgus the strains in the superior femoral neck are reduced while those in the inferior neck are increased. The study concluded that valgus alignment of the resurfacing arthroplasty is preferential to varus alignment as it induces a more physiological strain pattern and reduces the risk of femoral neck fracture. These findings are in line with clinical experience, which has shown an increase of failure with varus implanted prostheses.

Determination of suitable sample sizes for multi-patient based finite element studies

Publisher: Elsevier BV

Date: 12-2007

DOI: 10.1016/J.MEDENGPHY.2006.11.007

Abstract: Finite element analysis is used extensively to assess joint replacements, but the majority of these are single s le studies. Recent investigations have suggested that such studies are unable to account for natural inter-patient variation in bone geometry and material property distribution. Recent developments in computer tomography based analyses make multiple s le studies possible the question remains how many femurs are required to perform a study which accounts for such variations. This work investigates the factors that should be considered in answering this question. It explores s le sizing techniques when comparing strain distribution in the intact and implanted femur and when comparing two or more implant designs in a group of femurs. An ex le analysis of the effect of femoral head resurfacing was undertaken. Two s le sizing calculations were utilised, one based on achieving the desired precision in results, the other based on determining if a significant difference exists between two designs. The analysis shows that reasonable statistical precision can be achieved with a group of femurs. The study was also able to determine a suitable s le size for the analysis of a statistically significant difference between two groups of femurs with varying design parameters. The study concluded that while s le sizing is recommended for an accurate analysis, consideration must be made for the practicality of such a task.

Sensitivity analysis of a cemented hip stem to implant position and cement mantle thickness

Publisher: Informa UK Limited

Date: 13-02-2013

DOI: 10.1080/10255842.2012.761693

Abstract: Patient-specific finite element models of the implanted proximal femur can be built from pre-operative computed tomography scans and post-operative X-rays. However, estimating three-dimensional positioning from two-dimensional radiographs introduces uncertainty in the implant position. Further, accurately measuring the thin cement mantle and the degree of cement-bone interdigitation from imaging data is challenging. To quantify the effect of these uncertainties in stem position and cement thickness, a sensitivity study was performed. A design-of-experiment study was implemented, simulating both gait and stair ascent. Cement mantle stresses and bone-implant interface strains were monitored. The results show that small variations in alignment affect the implant biomechanics, especially around the most proximal and most distal ends of the stem. The results suggest that implant position is more influential than cement thickness. Rotation around the medial-lateral axis is the dominant factor in the proximal zones and stem translations are the dominant factors around the distal tip.

A review on the finite element simulation of fretting wear and corrosion in the taper junction of hip replacement implants

Publisher: Elsevier BV

Date: 03-2021

DOI: 10.1016/J.COMPBIOMED.2020.104196

Predicted knee kinematics and kinetics during functional activities using motion capture and musculoskeletal modelling in healthy older people

Publisher: Elsevier BV

Date: 02-2011

DOI: 10.1016/J.GAITPOST.2010.11.018

Abstract: Knowledge of joint forces and moments is essential for comparisons between healthy people and those with pathological conditions, with observed changes at joints providing basis for a particular intervention. Currently the literature analysing both kinematics and kinetics at the knee has been limited to small s les, typically of young subjects or those who have undergone joint arthroplasty. In this study, we examined tibiofemoral joint (TFJ) kinematics and kinetics during gait, sit-stand-sit, and step-descent in 20 healthy older subjects (aged 53-79 years) using motion capture data and inverse dynamic musculoskeletal models. Mean peak distal-proximal force in the TFJ were 3.1, 1.6, and 3.5 times body weight (N/BW) for gait, sit-stand, and step-descent respectively. There were also significant posterior-anterior forces, with sit-stand activity peaking at 1.6 N/BW. Moments about the TFJ peaked at a mean of 0.07 Nm/BW during the sit-stand activity. One of the most important findings of this study was variability found across the subjects, who spanned a wide age range, showing large standard deviations in all of the activities for both kinematics and kinetics. These data have provided an initial prediction for assessing kinematics and kinetics in the older population. Larger studies are needed to refine the database, in particular to reduce the variability in the results by studying sub-populations, to enable more robust comparisons between healthy and pathological TFJ kinematics and kinetics.

Finite Element Analysis of the Resurfaced Femoral Head

Publisher: SAGE Publications

Date: 02-2006

DOI: 10.1243/095441105X93631

Abstract: Failure of the resurfaced femoral head may occur in the short term owing to femoral neck fracture or in the long term owing to aseptic loosening as a result of strain shielding. Resurfacing arthroplasties are not all the same. In particular, there is considerable debate regarding the role of the metaphyseal stem and cementing technique. This study examines the influence of various metaphyseal stem configurations (diameter, percentage length in contact with bone, and bonded versus debonded) and cement mantle thickness on the load transfer within the femoral head. Resurfacing resulted in significant strain shielding in the superior femoral head and elevated strain in the superior femoral neck. Although the increase in strain in the femoral neck was significant, the mean strains were below the yield strain for cancellous bone. Peak strains were observed above the yield strain, but they accounted for less than 1 per cent of the total head-neck bone volume and therefore were unlikely to result in femoral neck fracture. Increasing the stem diameter and increasing the percentage stem length in contact with bone both increased the degree of strain shielding. Bonding the metaphyseal stem produced the most dramatic strain shielding, which also extended into the head-neck junction. In contrast, varying the cement mantle thickness had a negligible effect on the load transfer.

Verification of Predicted Knee Replacement Kinematics During Simulated Gait in the Kansas Knee Simulator

Publisher: ASME International

Date: 07-2010

DOI: 10.1115/1.4001678

Abstract: Evaluating total knee replacement kinematics and contact pressure distributions is an important element of preclinical assessment of implant designs. Although physical testing is essential in the evaluation process, validated computational models can augment these experiments and efficiently evaluate perturbations of the design or surgical variables. The objective of the present study was to perform an initial kinematic verification of a dynamic finite element model of the Kansas knee simulator by comparing predicted tibio- and patellofemoral kinematics with experimental measurements during force-controlled gait simulation. A current semiconstrained, cruciate-retaining, fixed-bearing implant mounted in aluminum fixtures was utilized. An explicit finite element model of the simulator was developed from measured physical properties of the machine, and loading conditions were created from the measured experimental feedback data. The explicit finite element model allows both rigid body and fully deformable solutions to be chosen based on the application of interest. Six degrees-of-freedom kinematics were compared for both tibio- and patellofemoral joints during gait loading, with an average root mean square (rms) translational error of 1.1 mm and rotational rms error of 1.3 deg. Model sensitivity to interface friction and d ing present in the experimental joints was also evaluated and served as a secondary goal of this paper. Modifying the metal-polyethylene coefficient of friction from 0.1 to 0.01 varied the patellar flexion-extension and tibiofemoral anterior-posterior predictions by 7 deg and 2 mm, respectively, while other kinematic outputs were largely insensitive.

Influence of femur size and morphology on load transfer in the resurfaced femoral head: A large scale, multi-subject finite element study

Publisher: Elsevier BV

Date: 07-2012

DOI: 10.1016/J.JBIOMECH.2012.05.015

Abstract: Femoral resurfacing has become an increasingly popular procedure, especially for young, active patients. The procedure is known to alter load transfer through the proximal femur and this has been linked with the most commonly observed complication, neck fracture. An intriguing observation noted by registry data and clinical studies is an inverse relationship between implant size and revision rate. While computational analysis has become an established part of biomedical engineering, the majority of work uses a single or small set of bone models, with a single implant size, due to the constraints of time and data availability. Therefore, it has been infeasible to run a study incorporating natural inter-patient variability or the performance of smaller implants could not be meaningfully studied. In previous work a statistical model of the whole femur was used to generate large numbers of unique, realistic, FE-ready femur models describing both geometry and material properties. The current study demonstrates a methodology for virtually implanting and performing stress analysis of cemented femoral resurfacing components, with model specific sizing and orientation. Automated analysis of 400 generated femurs, in both implanted and intact configurations showed the strain changes induced by resurfacing. This produced a statistically meaningful number of results and allowed the examination of outliers. Results showed increased femoral neck strain changes potentially increasing the risk of neck fracture, associated with smaller, less dense femurs and smaller implant sizes agreeing with clinical observations. The study demonstrates a methodology for more comprehensive analyses, based on populations rather than in iduals.

Assessing contractile ability of the quadriceps muscle using ultrasound imaging

Publisher: Wiley

Date: 21-07-2010

DOI: 10.1002/MUS.21725

Abstract: Muscle dimension changes on ultrasound imaging (USI) indicate contractile activity. Quadriceps force and rectus femoris (RF) dimensions were examined to assess USI for estimating contraction level. In 15 healthy males, mean age 24.8 years, isometric quadriceps force was measured in 90° knee flexion during submaximal and maximal voluntary contractions (MVCs) and at MVC in extension. Mid-thigh cross-sectional area (CSA), depth and width, and surface electromyography (EMG) of RF were recorded. Muscle width decreased curvilinearly as both force and EMG increased. At MVC, width was 3.2 ± 0.5 cm, 25% smaller than at rest (4.4 ± 0.7 cm), and similar to MVC in extension (-23%). CSA decreased linearly to -18% at MVC. RF thickness increased by only 10% (at 30% to MVC). Similar width changes at MVC in flexion and extension indicate the clinical potential of USI for assessing quadriceps contractility. Sensitivity is limited to assessing strength to within 25% of MVC in young males.

Influence of an interpositional spacer on the behaviour of the tibiofemoral joint: A finite element study

Publisher: Elsevier BV

Date: 10-2008

DOI: 10.1016/J.CLINBIOMECH.2008.04.006

Abstract: Interpositional arthroplasty is considered by many surgeons for the treatment of isolated medial compartment osteoarthritis of the knee. In this procedure, an interpositional spacer is inserted into the medial compartment of the joint with no bone resection and no mechanical fixation. Major problems such as implant dislocation, severe pain or need for revision have been reported post-operatively. In this study, the kinematics of a knee implanted with an interpositional spacer made of either polyurethane or cobalt-chrome during walking, stair ascent and squatting cycles have been predicted and compared to the normal knee using finite element analysis. In addition, articular cartilage stress histories have been examined to obtain distributions of cumulative stress, a measure of the likelihood of articular cartilage degeneration. The insertion of a polyurethane interpositional spacer in the medial side of the knee did not affect knee kinematics as compared to the normal knee, but caused an increase of articular cartilage cumulative contact stress exposures in the medial compartment of the joint. The knee implanted with the Co-Cr spacer exhibited similar trends in knee kinematics, however significantly different ranges of motion were observed during some periods of the activity cycles, specifically during the first half of the walking cycle where lower ranges of motion were predicted. In addition, higher articular cartilage cumulative contact stress exposures were observed in both compartments of the knee. In both cases, cumulative contact stress exposures of the tibial articular cartilage were more affected than those of the femoral articular cartilage. These results suggest implant material as an important parameter in the design phase of interpositional spacers.

A semiautomated method to quantitatively assess osteolytic lesion volume and bone mineral density within acetabular regions of interest from CT

Publisher: Wiley

Date: 30-04-2021

DOI: 10.1002/JOR.25051

Abstract: The objectives of this study were to (1) develop a semiautomated method to obtain lesion volume and bone mineral density (BMD) in terms of Hounsfield units from pelvic computed tomography (CT) scans in three regions of interest, and (2) assess accuracy and reliability of the method based on cadaveric CT scans. Image artefacts due to metal implants reduce CT clarity and are more severe with more than one implant in situ. Therefore, accuracy and reliability tests were performed with varying numbers of total hip arthroplasties implanted. To test the accuracy of lesion size measurements, microcomputed tomography was used as a reference. Mean absolute error ranged from 36 to 284 mm 3 after five measurements. Intra‐ and inter‐operator reliability of the entire method was measured for a selection of parameters. All coefficient of variation values were good to excellent for CT scans of the native pelvic anatomy and a CT scans of the same pelvis with one and two implants in situ. Accuracy of quantifying lesion volume decreased with decreasing CT image clarity by 0.6%–3.6% mean absolute relative error. Reliability of lesion volume measurement decreased with decreasing CT clarity. This was also the case for reliability of BMD measurements in the region most disrupted by metal artefact. The presented method proposes an approach for quantifying bone loss which has been proven to be accurate, reliable, and clinically applicable.

Real time monitoring of progressive damage during loading of a simplified total hip stem construct using embedded acoustic emission sensors

Publisher: Elsevier BV

Date: 05-2011

DOI: 10.1016/J.MEDENGPHY.2010.10.025

Abstract: Acoustic emission (AE) is a non-destructive technique that is capable of passively monitoring failure of a construct with excellent temporal resolution. Previous investigations using AE to monitor the integrity of a total hip replacement (THR) have used surface mounted sensors however, the AE signal attenuates as it travels through materials and across interfaces. This study proposes that directly embedded sensors within the femoral stem of the implant will reduce signal attenuation effects and eliminate potential complications and variability associated with fixing the sensor to the s le. Data was collected during in vitro testing of implanted constructs, and information from both embedded and externally mounted AE sensors was compared and corroborated by micro-Computed Tomography (micro-CT) images taken before and after testing. The results of this study indicate that the embedded sensors gave a closer corroboration to observed damage using micro-CT and were less affected by unwanted noise sources. This has significant implications for the use of AE in assessing the state of THR constructs in vitro and it is hypothesised that directly embedded AE sensors may provide the first steps towards an in vivo, cost effective, user friendly, non-destructive system capable of continuously monitoring the condition of the implanted construct.

Predicting implant UHMWPE wear in-silico: A robust, adaptable computational–numerical framework for future theoretical models

Publisher: Elsevier BV

Date: 2012

DOI: 10.1016/J.WEAR.2011.08.020

Influence of loading and activity on the primary stability of cementless tibial trays

Publisher: Wiley

Date: 20-01-2012

DOI: 10.1002/JOR.22056

Abstract: Several potential advantages exist for cementless tibial fixation including preservation of bone stock and increased longevity of fixation. However, clinical results have been variable, with reports of extensive radiolucent lines, rapid early migration, and aseptic loosening. The primary stability of an implant depends on the micromotion of the bone-implant interface, which depends on the kinematics and kinetics of the replaced joint. Finite element analysis was used to examine the micromotion for different activities (walking, stair ascent, stair descent, stand-to-sit, and deep knee bend) for three commercially available tibial tray designs. Similar trends were observed for all three designs across the range of activities. Stair ascent and descent generated the highest micromotions, closely followed by level gait. Across these activities, the mean peak (maximum) micromotions measured across the entire resected surface ranged from 64 to 78 (186-239) µm for PFC Sigma, 61-72 (199-251) µm for LCS Complete Duofix, and 92-106 (229-264) µm for LCS Complete. The peak micromotions did not necessarily occur at the peak loads. For instance, the peak micromotions for level walking occurred when there were low axial forces, but moderate varus-valgus moments. This highlights the need to examine the whole gait cycle to properly determine the initial stability of tibial tray designs. By exploring a range of activities and interrogating the entire resected surface, it is possible to differentiate between the relative performance of different implant designs.

Finite element analysis informed variable selection for femoral fracture risk prediction

Publisher: Elsevier BV

Date: 06-2021

DOI: 10.1016/J.JMBBM.2021.104434

Virtual trial to evaluate the robustness of cementless femoral stems to patient and surgical variation

Publisher: Elsevier BV

Date: 2019

DOI: 10.1016/J.JBIOMECH.2018.11.013

Abstract: Primary stability is essential for the success of cementless femoral stems. In this study, patient specific finite element (FE) models were used to assess changes in primary stability due to variability in patient anatomy, bone properties and stem alignment for two commonly used cementless femoral stems, Corail® and Summit® (DePuy Synthes, Warsaw, USA). Computed-tomography images of the femur were obtained for 8 males and 8 females. An automated algorithm was used to determine the stem position and size which minimized the endo-cortical space, and then span the plausible surgical envelope of implant positions constrained by the endo-cortical boundary. A total of 1952 models were generated and ran, each with a unique alignment scenario. Peak hip contact and muscle forces for stair climbing were scaled to the donor's body weight and applied to the model. The primary stability was assessed by comparing the implant micromotion and peri-prosthetic strains to thresholds (150 μm and 7000 µε, respectively) above which fibrous tissue differentiation and bone damage are expected to prevail. Despite the wide range of implant positions included, FE prediction were mostly below the thresholds (medians: Corail®: 20-74 µm and 1150-2884 µε, Summit®: 25-111 µm and 860-3010 µε), but sensitivity of micromotion and interfacial strains varied across femora, with the majority being sensitive (p < 0.0029) to average bone mineral density, cranio-caudal angle, post-implantation anteversion angle and lateral offset of the femur. The results confirm the relationship between implant position and primary stability was highly dependent on the patient and the stem design used.

The Distribution and Severity of Corrosion Damage at Eight Distinct Zones of Metallic Femoral Stem Implants

Publisher: MDPI AG

Date: 18-10-2018

DOI: 10.3390/MET8100840

Abstract: Metallic taper junctions of modular total hip replacement implants are analysed for corrosion damage using visual scoring based on different granularity levels that span from analysing the taper holistically to iding the taper into several distinct zones. This study aims to objectively explore the spatial distribution and the severity of corrosion damage onto the surface of metallic stem tapers. An ordinal logistic regression model was developed to find the odds of receiving a higher score at eight distinct zones of 137 retrieved stem tapers. A method to find the order of damage severity across the eight zones is introduced based on an overall test of statistical significance. The findings show that corrosion at the stem tapers occurred more commonly in the distal region in comparison with the proximal region. Also, the medial distal zone was found to possess the most severe corrosion damage among all the studied eight zones.

Assessment of the primary stability of revision tibial trays augmented with a cementless sleeve in AORI Type III defects

Publisher: Elsevier BV

Date: 12-2021

DOI: 10.1016/J.KNEE.2021.09.005

Abstract: Previous studies have evaluated the initial stability of uncemented tibial components in revision total knee replacement (rTKR) in the presence of an Anderson Orthopaedic Research Institute (AORI) Type II tibial defect. This study sought to evaluate similar metrics in the severe Type III (AORI TIII) defects with combined uncemented stem and sleeve fixation, specifically, the effect of varying the stem's length and tibial canal engagement upon stability and bone strain. Finite element models generated from the CT scans of 4 tibias with Type III defects were used to investigate the primary stability, in terms of the bone-implant composite peak micromotion (CPM) and microstrains (CPS), achieved after virtual implantations with and without stems. A stemless rTKR had increased metaphyseal CPM and CPS compared to all stemmed implants. Significant area of the bone supporting the stemless rTKR had CPS greater than bone yield (7000 με). Short engaging stems (≤150 mm construct length), could not achieve reliable engagement in the diaphysis (canal fill ≤ 50%), leading to insufficient reduction of CPS (≥5000 με). Longer engaging stems (170-220 mm construct length), were able to reliably engage the diaphysis (fill ratio ≥ 75%) resulting in CPS ≤ 5000 με. Although, non-engaging stems resulted in increased CPM and CPS compared to engaging stems, long non-engaging stems (170-220 mm construct) appeared to provide additional stability to the rTKR compared to stemless rTKR. The results indicate a likely correlation between uncemented stem engagement and metaphyseal CPS in Type III defects. Excessive strain within the supporting metaphyseal bone is likely to lead to rTKR migration and loosening.

Influence of head constraint and muscle forces on the strain distribution within the intact femur

Publisher: Elsevier BV

Date: 09-2000

DOI: 10.1016/S1350-4533(00)00056-4

Abstract: The aim of this study was to analyse the influence of muscle action and a horizontally constrained femoral head on the strain distribution within the intact femur. The strain distribution was measured for three loading configurations: joint reaction force only, joint reaction force plus abductors, and joint reaction force plus the abductors, vastus lateralis and iliopsoas. In each case the strains were recorded from 20 uniaxial strain gauges placed on the medial, lateral, anterior and posterior aspects of the proximal femur. Application of the abductor muscle force produced a marginal decrease in the strain levels on all aspects of the femur as compared with the joint reaction force alone. This is in contrast with previous studies which have simulated an unconstrained femoral head. The inclusion of vastus lateralis and iliopsoas further reduced the strain levels. A horizontally constrained femoral head produces smaller variation in the strain levels when muscle forces are applied. In vivo data, demonstrating negligible movement of the femoral head in one-legged stance, support the results of this study and suggest that in the absence of comprehensive muscle force data, a constrained femoral head may provide a more physiologically relevant loading condition.

Investigation into the affect of cementing techniques on load transfer in the resurfaced femoral head: A multi-femur finite element analysis

Publisher: Elsevier BV

Date: 05-2007

DOI: 10.1016/J.CLINBIOMECH.2006.12.001

Abstract: Femoral head resurfacing is a popular procedure for younger active hip replacement patients. Two major cementing techniques are used in femoral component fixation producing varying cement mantle thicknesses. Each technique has benefits, but it is not known if cement mantle thickness is detrimental to load transfer within the proximal femur. This study uses computer tomography based finite element analysis to determine the effect of cement mantle thickness on strain in the resurfaced femoral head. A group of 16 femurs were investigated to take into account inter-patient variation a factor often over-looked in such studies. Results showed strain in the proximal femoral head to decrease with increasing cement thickness, with a slight increase in strain in the posterior-superior neck. Cementing of the implant guide-pin produced marked reductions in strain in the head and neck except for the posterior-inferior neck where it increased slightly. The study concluded that a thicker cement mantle increases strain shielding within the superior resurfaced femoral head although short to medium term clinical trials do not suggest these factors to be of much concern. The analysis also found strain to increase around the inferior head-neck junction with a thinner mantle. Cementing the guide pin resulted in increased strain shielding whilst simultaneously shifting peak loads distally along the femoral neck. This work found that modelling a group of femurs was a useful tool for better interpreting the loading in the resurfaced femur.

Fretting Wear and Corrosion-Related Risk Factors in Total Hip Replacement: A Literature Review on Implant Retrieval Studies and National Joint Replacement Registry Reports

Publisher: MDPI AG

Date: 21-08-2023

DOI: 10.3390/PROSTHESIS5030055

Abstract: Fretting corrosion is a known failure mechanism of total hip replacement (THR) that can lead to revision surgery. Implant retrieval studies have thoroughly documented the occurrence of fretting corrosion in THR implants and its correlation with implant- and patient-related factors. Although implant retrieval studies benefit both clinicians and implant manufacturers, the limitations of these types of studies need to be acknowledged. For ex le, while some factors are routinely investigated for a possible correlation with failure due to fretting corrosion, other factors are often assumed to have no effect. To improve on these limitations, this review investigates the most significant patient- and implant-related risk factors for fretting corrosion of THR implants for both published retrieval studies and joint replacement registries. The findings and limitations are discussed critically. It is concluded that retrieval studies add significant insight into implant failure mechanisms and should be used in conjunction with joint replacement registry reports. It is suggested that the development of reliable predictive models based on implant failure risk factors and decision-making support systems could lead to enhanced implant longevity.

Biomechanical changes and recovery of gait function after total hip arthroplasty for osteoarthritis: a systematic review and meta-analysis

Publisher: Elsevier BV

Date: 07-2018

DOI: 10.1016/J.JOCA.2018.02.897

Abstract: To determine the change in walking gait biomechanics after total hip arthroplasty (THA) for osteoarthritis (OA) compared to the pre-operative gait status, and to compare the recovery of gait following THA with healthy in iduals. Systematic review with meta-analysis of studies investigating changes in gait biomechanics after THA compared to (1) preoperative levels and (2) healthy in iduals. Data were pooled at commonly reported time points and standardised mean differences (SMDs) were calculated in meta-analyses for spatiotemporal, kinematic and kinetic parameters. Seventy-four studies with a total of 2,477 patients were included. At 6 weeks postoperative, increases were evident for walking speed (SMD: 0.32, 95% confidence intervals (CI) 0.14, 0.50), stride length (SMD: 0.40, 95% CI 0.19, 0.61), step length (SMD: 0.41, 95% CI 0.23, 0.59), and transverse plane hip range of motion (ROM) (SMD: 0.36, 95% CI 0.05, 0.67) compared to pre-operative gait. Sagittal, coronal and transverse hip ROM was significantly increased at 3 months (SMDs: 0.50 to 1.07). At 12 months postoperative, patients demonstrated deficits compared with healthy in iduals for walking speed (SMD: -0.59, 95% CI -1.08 to -0.11), stride length (SMD: -1.27, 95% CI -1.63, -0.91), single limb support time (SMD: -0.82, 95% CI -1.23, -0.41) and sagittal plane hip ROM (SMD: -1.16, 95% CI -1.83, -0.49). Risk of bias scores ranged from seven to 24 out of 26. Following THA for OA, early improvements were demonstrated for spatiotemporal and kinematic gait patterns compared to the pre-operative levels. Deficits were still observed in THA patients compared to healthy in iduals at 12 months.

Measurement of strains experienced by viscerofugal nerve cell bodies during mechanosensitive firing using digital image correlation

Publisher: American Physiological Society

Date: 11-2016

DOI: 10.1152/AJPGI.00397.2015

Abstract: Mechanosensory neurons detect physical events in the local environments of the tissues that they innervate. Studies of mechanosensitivity of neurons or nerve endings in the gut have related their firing to strain, wall tension, or pressure. Digital image correlation (DIC) is a technique from materials engineering that can be adapted to measure the local physical environments of afferent neurons at high resolution. Flat-sheet preparations of guinea pig distal colon were set up with arrays of tissue markers in vitro. Firing of single viscerofugal neurons was identified in extracellular colonic nerve recordings. The locations of viscerofugal nerve cell bodies were inferred by mapping firing responses to focal application of the nicotinic receptor agonist 1,1-dimethyl-4-phenylpiperazinium iodide. Mechanosensory firing was recorded during load-evoked uniaxial or biaxial distensions. Distension caused movement of surface markers which was captured by video imaging. DIC tracked the markers, interpolating the mechanical state of the gut at the location of the viscerofugal nerve cell body. This technique revealed heterogeneous load-evoked strain within preparations. Local strains at viscerofugal nerve cell bodies were usually smaller than global strain measurements and correlated more closely with mechanosensitive firing. Both circumferential and longitudinal strain activated viscerofugal neurons. Simultaneous loading in circumferential and longitudinal axes caused the highest levels of viscerofugal neuron firing. Multiaxial strains, reflecting tissue shearing and changing area, linearly correlated with mechanosensory firing of viscerofugal neurons. Viscerofugal neurons were mechanically sensitive to both local circumferential and local longitudinal gut strain, and appear to lack directionality in their stretch sensitivity.

Authors' response

Publisher: Elsevier BV

Date: 1997

DOI: 10.1016/S1350-4533(96)00044-6

Finite element based simulation of tribocorrosion at the head-neck junction of hip implants

Publisher: Elsevier BV

Date: 2022

DOI: 10.1016/J.TRIBOINT.2021.107284

An adaptive finite element simulation of fretting wear damage at the headneck taper junction of total hip replacement: The role of taper angle mismatch

Publisher: Elsevier BV

Date: 11-2017

DOI: 10.1016/J.JMBBM.2017.07.003

Abstract: An adaptive finite element simulation was developed to predict fretting wear in a head-neck taper junction of hip joint implant through a two dimensional (2D) model and based on the Archard wear equation. This model represents the most critical section of the head-neck junction which was identified from a 3D model of the junction subjected to one cycle of level gait loading. The 2D model was then used to investigate the effect of angular mismatch between the head and neck components on the material loss and fretting wear process over 4 million gait cycles of walking. Generally, junctions with distal angular mismatches showed a better resistance to fretting wear. The largest area loss in the neck after 4 million cycles of loading was 1.86E-02mm

A computational model for the prediction of total knee replacement kinematics in the sagittal plane

Publisher: Elsevier BV

Date: 04-2000

DOI: 10.1016/S0021-9290(99)00183-9

Abstract: A computational model has been developed using a current generation computer-aided engineering (CAE) package to predict total knee replacement (TKR) kinematic in the sagittal plane. The model includes friction and soft tissue restraint varying according to the flexion angle. The model was validated by comparing the outcomes of anterior-posterior (A-P) laxity tests of two contemporary knee replacements against data obtained from a knee simulating machine. It was also validated against predictions from a computer model reported in the literature. Results show good agreement in terms of A-P displacements. Further tests were performed to determined the influence of the soft tissue restraints varying with flexion angle. This work represents the first attempt to use a sophisticated commercial CAE package to predict TKR motions and the advantages of the modelling procedure chosen are discussed.

Finite element analysis of unicompartmental knee arthroplasty

Publisher: Elsevier BV

Date: 2010

DOI: 10.1016/J.MEDENGPHY.2009.10.002

Abstract: Concerns over accelerated damage to the untreated compartment of the knee following unicompartmental knee arthroplasty (UKA), as well as the relatively poor success rates observed for lateral as opposed to the medial arthroplasty, remain issues for attention. Finite element analysis (FEA) was used to assess changes to the kinematics and potential for cartilage damage across the knee joint in response to the implantation of the Oxford Mobile Bearing UKA. FE models of lateral and medial compartment arthroplasty were developed, in addition to a healthy natural knee model, to gauge changes incurred through the arthroplasty. Varus-valgus misalignments were introduced to the femoral components to simulate surgical inaccuracy or over-correction. Boundary conditions from the Stanmore knee simulator during the stance phase of level gait were used. AP translations of the tibia in the medial UKA models were comparable to the behaviour of the natural knee models (+/-0.6mm deviation from pre-operative motion). Following lateral UKA, 4.1mm additional posterior translation of the tibia was recorded than predicted for the natural knee. IE rotations of the medial UKA models were less consistent with the pre-operative knee model than the lateral UKA models (7.7 degrees vs. 3.6 degrees deviation). Varus misalignment of the femoral prosthesis was more influential than valgus for medial UKA kinematics, whereas in lateral UKA, a valgus misalignment of the femoral prosthesis was most influential on the kinematics. Resection of the cartilage in the medial compartment reduced the overall risk of progressive OA in the knee, whereas removing the cartilage from the lateral compartment, and in particular introducing a valgus femoral misalignment, increased the overall risk of progressive OA in the knee. Based on these results, under the conditions tested herein, both medial and lateral UKA can be said to induce kinematics of the knee which could be considered broadly comparable to those of the natural knee, and that even a 10 degrees varus-valgus misalignment of the femoral component may not induce highly irregular kinematics. However, elevated posterior translation of the tibia in lateral UKA and large excursions of the insert may explain the higher incidence of bearing dislocation observed in some clinical studies.

The Influence of Assembly Force on the Material Loss at the Metallic Head-Neck Junction of Hip Implants Subjected to Cyclic Fretting Wear

Publisher: MDPI AG

Date: 08-04-2019

DOI: 10.3390/MET9040422

Abstract: The impaction force required to assemble the head and stem components of hip implants is proven to play a major role in the mechanics of the taper junction. However, it is not clear if the assembly force could have an effect on fretting wear, which normally occurs at the junction. In this study, an adaptive finite element model was developed for a CoCr/CoCr head-neck junction with an angular mismatch of 0.01° in order to simulate the fretting wear process and predict the material loss under various assembly forces and over a high number of gait cycles. The junction was assembled with 2, 3, 4, and 5 kN and then subjected to 1,025,000 cycles of normal walking gait loading. The findings showed that material removal due to fretting wear increased when raising the assembly force. High assembly forces induced greater contact pressures over larger contact regions at the interface, which, in turn, resulted in more material loss and wear damage to the surface when compared to lower assembly forces. Although a high assembly force (greater than 4 kN) can further improve the initial strength and stability of the taper junction, it appears that it also increases the degree of fretting wear. Further studies are needed to investigate the assembly force in the other taper designs, angular mismatches, and material combinations.

Targeted computational probabilistic corroboration of experimental knee wear simulator: The importance of accounting for variability

Publisher: Elsevier BV

Date: 04-2011

DOI: 10.1016/J.MEDENGPHY.2010.10.015

Abstract: Experimental testing is widely used to predict wear of total knee replacement (TKR) devices. Computational models cannot replace this essential in vitro testing, but they do have complementary strengths and capabilities, which make in silico models a valuable support tool for experimental wear investigations. For effective exploitation, these two separate domains should be closely corroborated together this requires extensive data-sharing and cross-checking at every stage of simulation and testing. However, isolated deterministic corroborations provide only a partial perspective in vitro testing is inherently variable, and relatively small changes in the environmental and kinematic conditions at the articulating interface can account for considerable variation in the reported wear rates. Understanding these variations will be key to managing uncertainty in the tests, resulting in a 'cleaner' investigation environment for further refining current theories of wear. This study demonstrates the value of probabilistic in silico methods by describing a specific, targeted corroboration of the AMTI knee wear simulator, using rigid body dynamics software models. A deterministic model of the simulator under displacement-control was created for investigation. Firstly, a large s le of experimental data (N>100) was collated, and a probabilistic computational study (N>1000 trials) was used to compare the kinetic performance envelopes for in vitro and in silico models, to more fully corroborate the mechanical model. Secondly, corresponding theoretical wear-rate predictions were compared to the experimentally reported wear data, to assess the robustness of current wear theories to uncertainty (as distinct from the mechanical variability). The results reveal a good corroboration for the physical mechanics of the wear test rig however they demonstrate that the distributions for wear are not currently well-predicted. The probabilistic domain is found to be far more sensitive at distinguishing between different wear theories. As such we recommend that in future, researchers move towards probabilistic studies as a preferred framework for investigations into implant wear.

Statistical Properties of a Virtual Cohort for In Silico Trials Generated with a Statistical Anatomy Atlas

Publisher: Springer Science and Business Media LLC

Date: 06-09-2023

DOI: 10.1007/S10439-022-03050-8

Abstract: Osteoporosis-related hip fragility fractures are a catastrophic event for patient lives but are not frequently observed in prospective studies, and therefore phase III clinical trials using fractures as primary clinical endpoint require thousands of patients enrolled for several years to reach statistical significance. A novel answer to the large number of subjects needed to reach the desired evidence level is offered by In Silico Trials, that is, the simulation of a clinical trial on a large cohort of virtual patients, monitoring the biomarkers of interest. In this work we investigated if statistical aliasing from a custom anatomy atlas could be used to expand the patient cohort while retaining the original biomechanical characteristics. We used a pair-matched cohort of 94 post-menopausal women (at the time of the CT scan, 47 fractured and 47 not fractured) to create a statistical anatomy atlas through principal component analysis, and up-s led the atlas in order to obtain over 1000 synthetic patient models. We applied the biomechanical computed tomography pipeline to the resulting virtual cohort and compared its fracture risk distribution with that of the original physical cohort. While the distribution of femoral strength values in the non-fractured sub-group was nearly identical to that of the original physical cohort, that of the fractured sub-group was lower than in the physical cohort. Nonetheless, by using the classification threshold used for the original population, the synthetic population was still ided into two parts of approximatively equal number.

Initial stability of ankle arthrodesis with three-screw fixation. A finite element analysis

Publisher: Elsevier BV

Date: 08-2004

DOI: 10.1016/J.CLINBIOMECH.2004.04.014

Influence of stems and metaphyseal sleeve on primary stability of cementless revision tibial trays used to reconstruct AORI IIB defects

Publisher: Wiley

Date: 07-04-2019

DOI: 10.1002/JOR.24232

Abstract: Metaphyseal augments, such as sleeves, have been introduced to augment the fixation of revision total knee replacement (rTKR) components, and can be used with or without a stem. The effect of sleeve size in combination with stems on the primary stability and load transfer of a rTKR implant in AORI type IIB defects where the defect involves both condyles are poorly understood. The aim of this study was to examine the primary stability of revision tibial tray augmented with a sleeve in an AORI type IIB defect which involves both condyles with loss of cortical and cancellous bone. Finite element models were generated from computed tomography (CT) scans of nine in iduals. All the bones used in the study had an AORI type IIB defect. The cohort included eight females (mean weight: 64 kg, height: 1.6 m). Material properties were s led from CT data and assigned to the FE model. Joint contact forces for level gait, stair descent, and squat were applied. Stemless sleeved implants under various loading conditions were shown to have adequate primary stability in all AORI type IIB defects investigated. Adding a stem only marginally improved the primary stability of the implant but reduced the strain in the metaphysis compared to stemless implants. Once good initial mechanical stability was established with a sleeve, there was no benefit, in terms of primary stability or bone strains, from increasing sleeve size. This study suggests that metaphyseal sleeves, without a stem, can provide the required primary stability required by a rTKR tibial implant, to reconstruct an AORI type IIB defect. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Effect of Varus/Valgus Malalignment on Bone Strains in the Proximal Tibia After TKR: An Explicit Finite Element Study

Publisher: ASME International

Date: 18-09-2006

DOI: 10.1115/1.2401177

Abstract: Malalignment is the main cause of tibial component loosening. Implants that migrate rapidly in the first two post-operative years are likely to present aseptic loosening. It has been suggested that cancellous bone stresses can be correlated with tibial component migration. A recent study has shown that patient-specific finite element (FE) models have the power to predict the short-term behavior of tibial trays. The stresses generated within the implanted tibia are dependent on the kinematics of the joint however, previous studies have ignored the kinematics and only applied static loads. Using explicit FE, it is possible to simultaneously predict the kinematics and stresses during a gait cycle. The aim of this study was to examine the cancellous bone strains during the stance phase of the gait cycle, for varying degrees of varus/valgus eccentric loading using explicit FE. A patient-specific model of a proximal tibia was created from CT scan images, including heterogeneous bone properties. The proximal tibia was implanted with a commercial total knee replacement (TKR) model. The stance phase of gait was simulated and the applied loads and boundary conditions were based on those used for the Stanmore knee simulator. Eccentric loading was simulated. As well as examining the tibial bone strains (minimum and maximum principal strain), the kinematics of the bone-implant construct are also reported. The maximum anterior–posterior displacements and internal–external rotations were produced by the model with 20mm offset. The peak minimum and maximum principal strain values increased as the load was shifted laterally, reaching a maximum magnitude for −20mm offset. This suggests that when in varus, the load transferred to the bone is shifted medially, and as the bone supporting this load is stiffer, the resulting peak bone strains are lower than when the load is shifted laterally (valgus). For this particular patient, the TKR design analyzed produced the highest cancellous bone strains when in valgus. This study has provided an insight in the variations produced in bone strain distribution when the axial load is applied eccentrically. To the authors’ knowledge, this is the first time that the bone strain distribution of a proximal implanted tibia has been examined, also accounting for the kinematics of the tibio–femoral joint as part of the simulation. This approach gives greater insight into the overall performance of TKR.

Statistical modelling of the whole human femur incorporating geometric and material properties

Publisher: Elsevier BV

Date: 2010

DOI: 10.1016/J.MEDENGPHY.2009.10.008

Abstract: When analysing the performance of orthopaedic implants the vast majority of computational studies use either a single or limited number of bone models. The results are then extrapolated to the population as a whole, overlooking the inherent and large interpatient variability in bone quality and geometry. This paper describes the creation of a three dimensional, statistical, finite element analysis (FEA) ready model of the femur using principal component analysis. To achieve this a registration scheme based on elastic surface matching and a mesh morphing algorithm has been developed. This method is fully automated enabling registration and generation of high resolution models. The variation in both geometry and material properties was extracted from 46 computer tomography scans and captured by the statistical model. Analysis of mesh quality showed this was maintained throughout the model generation and s ling process. Reconstruction of the training femurs showed 35 eigenmodes were required for accurate reproduction. A set of unique, anatomically realistic femur models were generated using the statistical model, with a variation comparable to that seen in the population. This study illustrates a methodology with the potential to generate femur models incorporating material properties for large scale multi-femur finite element studies.

Assessment of the Effect of Mesh Density on the Material Property Discretisation Within QCT Based FE Models: A Practical Example Using the Implanted Proximal Tibia

Publisher: Informa UK Limited

Date: 02-2003

DOI: 10.1080/1025584031000064470

A new finding on the in-vivo crevice corrosion damage in a CoCrMo hip implant

Publisher: Elsevier BV

Date: 10-2017

DOI: 10.1016/J.MSEC.2017.05.086

Abstract: A detailed investigation was performed to characterize the fretting wear and corrosion damage to the neck component of a CoCrMo stem from a metal-on-polyethylene implant retrieved after 99months. The stem was a low-carbon (0.07wt%) wrought Co-28Cr-6Mo alloy with no secondary carbide phases in the matrix (γ-phase). The original design of the neck surface contained an intentionally fabricated knurled profile with a valley-to-peak range of approximately 11μm. Roughness measurements indicated that the tip of the knurled profile was significantly damaged, especially in the distal medial region of the neck, with up to a 22% reduction in the mean peak-to-valley height (R

Patient and surgical variability in the primary stability of cementless acetabular cups: A finite element study

Publisher: Wiley

Date: 04-03-2020

DOI: 10.1002/JOR.24636

Influence of geometry and materials on the axial and torsional strength of the head–neck taper junction in modular hip replacements: A finite element study

Publisher: Elsevier BV

Date: 07-2016

DOI: 10.1016/J.JMBBM.2015.12.044

Abstract: The assembly force is important in establishing the mechanical environment at the head-neck taper junction of modular hip replacements. Previous experimental results of the assembled taper junctions with different material combinations (Co-28Cr-6Mo and Ti-6Al-4V) reported similar axial strengths (pull-off loads), but lower torsional strengths (twist-off moments) for the CoCr/CoCr junction. However, mechanics of the junction and the strength behaviour have not been understood yet. A three dimensional finite element model of an isolated femoral head-neck junction was developed to explore the assembly and disassembly procedures, particularly the axial and torsional strengths for different material combinations and geometries. Under the same assembly load, the contacting length between the CoCr head and titanium neck was greater than that of in CoCr/CoCr. The contact length in the titanium neck was more sensitive to the assembly force when compared to the CoCr neck. For instance, with increasing the assembly force from 1890 to 3700N, the contact length increased by 88% for CoCr/Ti and 59% for CoCr/CoCr junctions. The torsional strength of the junction was related to the lateral deformation of the neck material due to the applied moment. The angular mismatch existing between the head and neck components was found to play the main role in the torsional strength of the junction. The smaller mismatch angle the higher torsional strength. It is suggested to consider reducing the mismatch angle, particularly in CoCr/CoCr junctions, and ensure a sufficiently high assembly force is applied by impaction for this combination.

A combined finite element method and continuum damage mechanics approach to simulate the in vitro fatigue behavior of human cortical bone

Publisher: Springer Science and Business Media LLC

Date: 1999

DOI: 10.1023/A:1008960630142

Abstract: The fatigue of bone, in particular the associated modulus degradation and accumulation of permanent strain, has been implicated as the cause of femoral neck fractures and the migration of total joint replacements. The objective of this study was to develop a technique to simulate the tensile fatigue behavior of human cortical bone. A combined continuum damage mechanics (CDM) and finite element analysis (FEA) approach was used to predict the number of cycles to failure, modulus degradation and accumulation of permanent strain of human cortical bone specimens. The simulation of fatigue testing of eight dumb-bell specimens of cortical bone were performed and the predictions compared with existing experimental data. The predictions from the finite element models were in close agreement with the experimental data. The models predicted similar development of modulus degradation and permanent strain as observed in the experimental tests. The technique is capable of predicting the accumulation of permanent strain without the need for simulating every single load step. These findings suggest that the complex fatigue behavior of human cortical bone can be simulated using the described approach and forms the first step for simulating the more complex mechanisms associated with femoral neck fractures and implant migration.

Mathematical modelling of skeletal repair

Publisher: Elsevier BV

Date: 2004

DOI: 10.1016/J.BBRC.2003.11.171

Abstract: Tissue engineering offers significant promise as a viable alternative to current clinical strategies for replacement of damaged tissue as a consequence of disease or trauma. Since mathematical modelling is a valuable tool in the analysis of complex systems, appropriate use of mathematical models has tremendous potential for advancing the understanding of the physical processes involved in such tissue reconstruction. In this review, the potential benefits, and limitations, of theoretical modelling in tissue engineering applications are examined with specific emphasis on tissue engineering of bone. A central tissue engineering approach is the in vivo implantation of a biomimetic scaffold seeded with an appropriate population of stem or progenitor cells. This review will therefore consider the theory behind a number of key factors affecting the success of such a strategy including: stem cell or progenitor population expansion and differentiation ex vivo cell adhesion and migration, and the effective design of scaffolds and delivery of nutrient to avascular structures. The focus will be on current work in this area, as well as on highlighting limitations and suggesting possible directions for future work to advance health-care for all.

Effect of Bone Material Properties on the Initial Stability of a Cementless Hip Stem: A Finite Element Study

Publisher: SAGE Publications

Date: 04-2005

DOI: 10.1243/095441105X34293

Abstract: In previous finite element studies of cementless hip stems reported in the literature, the effect of bone quality on the initial micromotion and interface bone strain has been rarely reported. In this study, the effect of varying cortical and cancellous bone modulus on initial stem micromotion and interface bone strain was examined and the potential consequence of these changes on bone ingrowth and implant migration was reported. A finite element (FE) model of a total hip replacement (THR) was created and the Young's moduli of cortical and cancellous bone were systematically varied to study the relative effect of the quality of both types of bone on the initial stability of a cementless THR. It was found that the initial micromotion and interface bone strain in a THR was significantly affected by the overall stiffness of the femur. In other words, both the reduction of the modulus of cortical and cancellous bone caused an increase in the initial micromotion and interface bone strain. This suggests that for FE studies to be truly predictive, a range of bone quality must be examined to study the performance envelope of a particular stem and to allow comparison with clinical results.

Evaluating the primary stability of standard vs lateralised cementless femoral stems – A finite element study using a diverse patient cohort

Publisher: Elsevier BV

Date: 11-2018

DOI: 10.1016/J.CLINBIOMECH.2018.09.002

Abstract: Restoring the original femoral offset is desirable for total hip replacements as it preserves the original muscle lever arm and soft tissue tensions. This can be achieved through lateralised stems, however, the effect of variation in the hip centre offset on the primary stability remains unclear. Finite element analysis was used to compare the primary stability of lateralised and standard designs for a cementless femoral stem (Corail®) across a representative cohort of male and female femora (N = 31 femora age from 50 to 80 years old). Each femur model was implanted with three designs of the Corail® stem, each designed to achieve a different degree of lateralisation. An automated algorithm was used to select the size and position that achieve maximum metaphyseal fit for each of the designs. Joint contact and muscle forces simulating the peak forces during level gait and stair climbing were scaled to the body mass of each subject. The study found that differences in restoring the native femoral offset introduce marginal differences in micromotion (differences in peak micromotion 3000 με) was achieved for some subjects when lateralized stems were used. Findings of this study suggest that, with the appropriate size and alignment, the standard offset design is likely to be sufficient for primary stability, in most cases. Nonetheless, appropriate use of lateralised stems has the potential reduce the risk of peri-prosthetic bone damage. This highlights the importance of appropriate implant selection during the surgical planning stage.

Primary stability of a cementless acetabular cup in a cohort of patient-specific Finite Element models

Publisher: Wiley

Date: 12-09-2017

DOI: 10.1002/JOR.23709

Abstract: The primary stability achieved during total hip arthroplasty determines the long-term success of cementless acetabular cups. Pre-clinical finite element testing of cups typically use a model of a single patient and assume the results can be extrapolated to the general population. This study explored the variability in predicted primary stability of a Pinnacle

Factors affecting the static shear strength of the prosthetic stem-bone cement interface

Publisher: Springer Science and Business Media LLC

Date: 2003

DOI: 10.1023/A:1021501520479

Abstract: Debonding of the stem-cement interface has been implicated in the initiation of failure of cemented femoral stems. The objective of this work was to examine some of the parameters which influence the interface static shear strength, including surface finish, cement type, pre-treatments and porosity. Surface finish was found to have the greatest effect on the interface strength. Increasing the surface roughness by a factor of 100 increases the interface shear strength by a factor of 20. However, increasing the surface roughness above a certain value was found to have no additional affect. This was due to failure in the cement itself rather than at the cement-stem interface. There were significant differences between some of the different cement types regarding the interface strength. Pre-heating the stem produced a six fold reduction in cement porosity at the stem-cement interface, however, resulting in only a minor influence on the static interface strength. Generally, no significant correlation was found between the cement porosity and the static interfacial shear strength.

Finite element analysis of a total ankle replacement during the stance phase of gait

Publisher: Elsevier BV

Date: 2006

DOI: 10.1016/J.JBIOMECH.2005.04.010

Abstract: Total ankle replacement (TAR) designs have still several important issues to be addressed before the treatment becomes fully acceptable clinically. Very little is known about the performance, in terms of the contact pressures and kinematics of TAR when subjected to daily activities such as level gait. For this purpose, an explicit finite element model of a novel 3-component TAR was developed, which incorporated a previously validated mechanical model of the ankle ligament apparatus. The intermediate mobile polyethylene meniscal bearing was modelled as an elastic-plastic continuum while the articulating surfaces of the tibial and talar metal components as rigid bodies. Overall kinematics, contact pressures and ligament forces were analysed during passive, i.e. virtually unloaded, and active, i.e. stance phase of gait, conditions. Simulation of passive motion predicted similar kinematics as reported previously in an analytical four-bar linkage model. The meniscal bearing was observed to move 5.6 mm posteriorly during the simulated stance and the corresponding antero-posterior displacement of the talar component was 8.3 mm. The predicted pattern and the amount (10.6 degrees ) of internal-external rotation of the ankle complex were found to be in good agreement with corresponding in vivo measurements on normal ankles. A peak contact pressure of 16.8 MPa was observed, with majority of contact pressures below 10 MPa. For most ligaments, reaction forces remain within corresponding physiological ranges. A first realistic representation of the biomechanical behaviour of the human ankle when replaced by prosthetic joints is provided. The applied methodology can potentially be applied to other TAR designs.

Iliopsoas tendonitis after total hip arthroplasty

Publisher: British Editorial Society of Bone & Joint Surgery

Date: 2023

DOI: 10.1302/2633-1462.41.BJO-2022-0147.R1

Abstract: Iliopsoas impingement occurs in 4% to 30% of patients after undergoing total hip arthroplasty (THA). Despite a relatively high incidence, there are few attempts at modelling impingement between the iliopsoas and acetabular component, and no attempts at modelling this in a representative cohort of subjects. The purpose of this study was to develop a novel computational model for quantifying the impingement between the iliopsoas and acetabular component and validate its utility in a case-controlled investigation. This was a retrospective cohort study of patients who underwent THA surgery that included 23 symptomatic patients diagnosed with iliopsoas tendonitis, and 23 patients not diagnosed with iliopsoas tendonitis. All patients received postoperative CT imaging, postoperative standing radiography, and had minimum six months’ follow-up. 3D models of each patient’s prosthetic and bony anatomy were generated, landmarked, and simulated in a novel iliopsoas impingement detection model in supine and standing pelvic positions. Logistic regression models were implemented to determine if the probability of pain could be significantly predicted. Receiver operating characteristic curves were generated to determine the model’s sensitivity, specificity, and area under the curve (AUC). Highly significant differences between the symptomatic and asymptomatic cohorts were observed for iliopsoas impingement. Logistic regression models determined that the impingement values significantly predicted the probability of groin pain. The simulation had a sensitivity of 74%, specificity of 100%, and an AUC of 0.86. We developed a computational model that can quantify iliopsoas impingement and verified its accuracy in a case-controlled investigation. This tool has the potential to be used preoperatively, to guide decisions about optimal cup placement, and postoperatively, to assist in the diagnosis of iliopsoas tendonitis. Cite this article: Bone Jt Open 2023 (1):3–12.

Efficient computational method for assessing the effects of implant positioning in cementless total hip replacements

Publisher: Elsevier BV

Date: 04-2011

DOI: 10.1016/J.JBIOMECH.2010.12.027

Abstract: The present work describes a statistical investigation into the effects of implant positioning on the initial stability of a cementless total hip replacement (THR). Mesh morphing was combined with design of computer experiments to automatically construct Finite Element (FE) meshes for a range of pre-defined femur-implant configurations and to predict implant micromotions under joint contact and muscle loading. Computed micromotions, in turn, are postprocessed using a Bayesian approach to: (a) compute the main effects of implant orientation angles, (b) predict the sensitivities of the considered implant performance metrics with respect to implant ante-retroversion, varus-valgus and antero-posterior orientation angles and (c) identify implant positions that maximise and minimise each metric. It is found that the percentage of implant area with micromotion greater than 50 μm, average and maximum micromotions are all more sensitive to antero-posterior orientation than ante-retroversion and varus-valgus orientation. Sensitivities, combined with the main effect results, suggest that bone is less likely to grow if the implant is increasingly moved from the neutral position towards the anterior part of the femur, where the highest micromotions occur. The computed implant best position leads to a percentage of implant area with micromotion greater than 50 μm of 1.14 when using this metric compared to 14.6 and 5.95 in the worst and neutrally positioned implant cases. In contrast, when the implant average/maximum micromotion is used to assess the THR performance, the implant best position corresponds to average/maximum micromotion of 9 μm/59 μm, compared to 20 μm/114 μm and 13 μm/71 μm in the worst and neutral positions, respectively. The proposed computational framework can be extended further to study the effects of uncertainty and variability in anatomy, bone mechanical properties, loading or bone-implant interface contact conditions.

A finite element study on the mechanical response of the head-neck interface of hip implants under realistic forces and moments of daily activities: Part 2

Publisher: Elsevier BV

Date: 2018

DOI: 10.1016/J.JMBBM.2017.08.038

Abstract: A finite element model was developed to investigate the effect of loading regimes caused by various daily activities on the mechanical behaviour of the head-neck taper junction in modular hip replacements. The activities included stair up, stair down, sit to stand, stand to sit, one leg standing and knee bending. To present the real mechanical environment of the junction, in addition to the force components, the frictional moments produced by the frictional sliding of the head and cup were applied to a CoCr/CoCr junction having a 12/14 taper with a proximal mismatch angle of 0.024°. This study revealed that stair up with the highest fretting work per unit of length (1.62 × 10

Application of an interface failure model to predict fatigue crack growth in an implanted metallic femoral stem

Publisher: Elsevier BV

Date: 03-2004

DOI: 10.1016/S0169-2607(03)00042-7

Damage accumulation, fatigue and creep behaviour of vacuum mixed bone cement

Publisher: Elsevier BV

Date: 09-2005

DOI: 10.1016/J.BIOMATERIALS.2005.02.009

Abstract: The behaviour of bone cement under fatigue loading is of interest to assess the long-term in vivo performance. In this study, uniaxial tensile fatigue tests were performed on CMW-1 bone cement. Acoustic emission sensors and an extensometer were attached to monitor damage accumulation and creep deformation respectively. The S-N data exhibited the scatter synonymous with bone cement fatigue, with large pores generally responsible for premature failure at 20 MPa specimens failed between 2 x 10(3) and 2 x 10(4) load cycles, while at 7 MPa specimens failed from 3 x 10(5) load cycles but others were still intact after 3 x 10(6) load cycles. Acoustic emission data revealed a non-linear accumulation of damage with respect to time, with increasing non-linearity at higher stress levels. The damage accumulation process was not continuous, but occurred in bursts separated by periods of inactivity. Damage in the specimen was located by acoustic emissions, and allowed the failure site to be predicted. Acoustic emission data were also used to predict when failure was not imminent. When this was the case at 3 million load cycles, the tests were terminated. Creep strain was plotted against the number of load cycles and a linear relationship was found when a double logarithmic scale was employed. This is the first time a brand of cement has been characterised in such detail, i.e. fatigue life, creep and damage accumulation. Results are presented in a manner that allows direct comparison with published data for other cements. The data can also be used to characterise CMW-1 in computational simulations of the damage accumulation process. Further evidence is provided for the condition-monitoring capabilities of the acoustic emission technique in orthopaedic applications.

The Role of the Assembly Force in the Tribocorrosion Behaviour of Hip Implant Head-Neck Junctions: An Adaptive Finite Element Approach

Publisher: MDPI AG

Date: 11-2022

DOI: 10.3390/BIOENGINEERING9110629

Abstract: The cyclic loading, in the corrosive medium of the human body, results in tribocorrosion at the interface of the head-neck taper junction of hip implants. The resulting metal ions and wear debris adversely affect the local tissues. The force applied by surgeons to assemble the junction has proven to play a major role in the mechanics of the taper junction which, in turn, can influence the tribocorrosion damage. Recently, finite element method has been used to predict the material loss at the head-neck interface. However, in most finite element studies, the contribution of electrochemical corrosion has been ignored. Therefore, a detailed study to investigate the influence of the assembly force on the tribocorrosive behaviour of the head-neck junction, which considers both the mechanical and chemical material removal, is of paramount interest. In this study, a finite-element-based algorithm was used to investigate the effect of assembly force on the tribocorrosion damage at the junction interface, for over four million cycles of simulated level gait. The patterns of the material removal in the modelling results were compared with the damage patterns observed in a group of retrieved modular hip implants. The results of this study showed that for different cases, chemical wear was in the range of 25–50% of the total material loss, after four million cycles. A minimum assembly force (4 kN for the studied cases) was needed to maintain the interlock in the junction. The computational model was able to predict the damage pattern at the retrieved head-neck interface.

Development of a statistical model of knee kinetics for applications in pre-clinical testing

Publisher: Elsevier BV

Date: 2012

DOI: 10.1016/J.JBIOMECH.2011.09.009

Abstract: Pre-clinical computational testing of total knee replacements (TKRs) often only considers a single patient model with simplified applied loads. In studies of multiple patients, most only take into account geometric differences, especially in studies on the knee. Limited availability of kinetic data means that it is difficult to account for inter-patient variability. Principal component analysis (PCA) based statistical models have been used to capture the variation of a set of data and generate new instances of the data. This study presents a method to create a statistical model of kinetic waveform data. A PCA based statistical model was created of the tibiofemoral joint loads for level gait of preoperative TKR patients using data predicted from a musculoskeletal model. A reconstruction test showed that, using principal components (PCs) representing 95% variance, the median root-mean-squared (RMS) error was <0.1 body weight (BW) for the forces and <0.001 BWm for the moments. Leave-one-out tests were also performed and although the median RMS error increased for each load in comparison to the reconstruction error (maximum was 0.2 BW for the axial force and 0.012 BWm for the varus-valgus moment) these were considered within an acceptable limit. The purpose of creating a statistical model is to be able to s le a large set of data representing a population from a small set of clinical data. Such models can potentially be used in population based studies of TKRs incorporating inter-patient variability.

Efficient human force transmission tailored for the individual cyclist

Publisher: Elsevier BV

Date: 06-2010

DOI: 10.1016/J.PROENG.2010.04.029

Influence of varying stem and metaphyseal sleeve size on the primary stability of cementless revision tibial trays used to reconstruct AORI IIA defects. A simulation study

Publisher: Wiley

Date: 13-02-2018

DOI: 10.1002/JOR.23851

Abstract: Traditionally, diaphyseal stems have been utilized to augment the stability of revision total knee replacement (rTKR) implants. More recently metaphyseal augments, such as sleeves, have been introduced to further augment component fixation. The effect of augments such as stems and sleeves have on the primary stability of a rTKR implant is poorly understood, however it has important implications on the complexity, costs and survivorship of the procedure. Finite element analysis was used to investigate the primary stability and strain distribution of various size stems and sleeves used in conjunction with a cementless revision tibial tray. The model was built from computer tomography images of a single healthy tibia obtained from an 81-year-old patient to which an Anderson Orthopaedic Research Institute (AORI) IIA defect was virtually added. The influences of varying body mass index (BMI) and bone modulus were also investigated. Stemless sleeves were found to provided adequate primary implant stability (average implant micro-motion <50 μm) for the studied defect. Addition of a stem did not enhance the primary stability. Furthermore, this study found that varying BMI and bone modulus had a considerable effect on strain distribution but negligible effect on micro-motion in the sleeve area. In conclusion, the addition of diaphyseal stem to a metaphyseal sleeve had little benefit in enhancing the primary stability of tibial trays augmented when simulating reconstructions of AORI IIA tibial defects. Additional studies are required to determine the relative benefit of the diaphyseal stem when using metaphyseal sleeves defects with more extensive bone loss. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1876-1886, 2018.

Strain patterns during tensile, compressive, and shear fatigue of human cortical bone and implications for bone biomechanics

Publisher: Wiley

Date: 30-06-2006

DOI: 10.1002/JBM.A.30796

Abstract: It is a common theme in basic bone biomechanics and in biomechanical applications that much of the behavior can be determined and is dictated by the level of strain, whether this pertains to bone physiology, bone remodeling, osseoinduction, osseointegration, or the development of damage. The development of damage, demonstrated by stiffness loss measurements, has already been reported in detail in the literature. However, the systematic study of the development of "plastic" (residual) strains, which are associated with the inelastic mechanical behavior of bone tissue, has generally been overlooked. The present study compares the rates at which the elastic (e(a)) and plastic components (e(p)) of strain developed during tensile, compressive, and shear fatigue in human cortical bone of six in iduals aged between 53 and 79 years. The overall hypothesis of this investigation is that there is a common underlying factor in the damage-related behavior of bone, which may allow us to link together the various aspects of the damage related behavior of bone. The rate of development of plastic strain (Deltae(p)/DeltaN) and the rate of growth in elastic strain litude (Deltae(a)/DeltaN) are described as a function of the stress (sigma), and/or stress normalized by the modulus of elasticity (sigma/E). The implications of our findings are discussed with respect to simple models/mechanisms, which may underlie the observed behavior.

An intelligent system for image-based rating of corrosion severity at stem taper of retrieved hip replacement implants

Publisher: Elsevier BV

Date: 11-2018

DOI: 10.1016/J.MEDENGPHY.2018.08.002

Abstract: Visual scoring of damage at taper junctions is the sole method to quantify corrosion in large-scale retrieval studies of failed hip replacement implants. This study introduces an intelligent image analysis-based method that objectively rates corrosion at stem taper of retrieved hip implants according to the well-known Goldberg scoring method. A Support Vector Machine classifier was used that takes in vectors of global and local textural features and assigns scores to the corresponding images. Bayesian optimisation fine-tunes the hyperparameters of the classifier to minimise the cross-validation error.

Glenohumeral kinematics following total shoulder arthroplasty: A finite element investigation

Publisher: Wiley

Date: 2006

DOI: 10.1002/JOR.20290

Abstract: The osseous geometry of the glenohumeral joint is naturally nonconforming and minimally constrained, and the joint's stability is maintained by action of the rotator cuff muscles. Damage to these muscles is often associated with joint degeneration, and a variety of glenoid prostheses have been developed to impart varying degrees of stability postoperatively. The issues of conformity and constraint within the artificial shoulder have been addressed through in vivo and in vitro studies, although few computational models have been presented. The current investigation presents the results of three-dimensional finite element analyses of the total shoulder joint and the effects of design parameters upon glenohumeral interaction. Conformity was shown not to influence the loads required to destabilize the joint, although it was the principal factor determining the magnitude of humeral head translation. Constraint was found to correlate linearly with the forces required to dislocate the humeral head, with higher constraint leading to slightly greater humeral migration at the point of joint instability. The model predicts that patients with a dysfunctional supraspinatus would experience frequent eccentric loading of the glenoid, especially in the superior direction, which would likely lead to increased fixation stresses, and hence, a greater chance of loosening. For candidates with an intact rotator cuff, the models developed in this study predict that angular constraints of at least 14 degrees and 6.5 degrees in the superoinferior and anteroposterior axes are required to provide stable unloaded abduction of the humerus, with larger constraints of 18 degrees and 10 degrees necessitated by a dysfunctional supraspinatus. The tools developed during this study can be used to determine the capacity for different implant designs to provide resistance to excessive glenohumeral translations and reduce the potential for instability of the joint, allowing surgeons to optimize postoperative functional gains on a patient by patient basis.

Accounting for Inclusions and Voids Allows the Prediction of Tensile Fatigue Life of Bone Cement

Publisher: ASME International

Date: 09-04-2009

DOI: 10.1115/1.3049518

Abstract: Previous attempts by researchers to predict the fatigue behavior of bone cement have been capable of predicting the location of final failure in complex geometries but incapable of predicting cement fatigue life to the right order of magnitude of loading cycles. This has been attributed to a failure to model the internal defects present in bone cement and their associated stress singularities. In this study, dog-bone-shaped specimens of bone cement were micro-computed-tomography (μCT) scanned to generate computational finite element (FE) models before uniaxial tensile fatigue testing. Acoustic emission (AE) monitoring was used to locate damage events in real time during tensile fatigue tests and to facilitate a comparison with the damage predicted in FE simulations of the same tests. By tracking both acoustic emissions and predicted damage back to μCT scans, barium sulfate (BaSO4) agglomerates were found not to be significant in determining fatigue life (p=0.0604) of specimens. Both the experimental and numerical studies showed that diffuse damage occurred throughout the gauge length. A good linear correlation (R2=0.70, p=0.0252) was found between the experimental and the predicted tensile fatigue life. Although the FE models were not always able to predict the correct failure location, damage was predicted in simulations at areas identified as experiencing damage using AE monitoring.

Modelling Human Locomotion to Inform Exercise Prescription for Osteoporosis

Publisher: Springer Science and Business Media LLC

Date: 25-04-2020

DOI: 10.1007/S11914-020-00592-5

Abstract: We review the literature on hip fracture mechanics and models of hip strain during exercise to postulate the exercise regimen for best promoting hip strength. The superior neck is a common location for hip fracture and a relevant exercise target for osteoporosis. Current modelling studies showed that fast walking and stair ambulation, but not necessarily running, optimally load the femoral neck and therefore theoretically would mitigate the natural age-related bone decline, being easily integrated into routine daily activity. High intensity jumps and hopping have been shown to promote anabolic response by inducing high strain in the superior anterior neck. Multidirectional exercises may cause beneficial non-habitual strain patterns across the entire femoral neck. Resistance knee flexion and hip extension exercises can induce high strain in the superior neck when performed using maximal resistance loadings in the average population. Exercise can stimulate an anabolic response of the femoral neck either by causing higher than normal bone strain over the entire hip region or by causing bending of the neck and localized strain in the superior cortex. Digital technologies have enabled studying interdependences between anatomy, bone distribution, exercise, strain and metabolism and may soon enable personalized prescription of exercise for optimal hip strength.

Simulation of a knee replacement during a gait cycle using explicit finite element analysis

Publisher: Elsevier BV

Date: 03-2005

DOI: 10.1016/J.JBIOMECH.2004.04.002

Finite Element Analysis of Poor Distal Contact of the Femoral Component of a Cementless Hip Endoprosthesis

Publisher: SAGE Publications

Date: 12-1993

DOI: 10.1243/PIME_PROC_1993_207_304_02

Abstract: The difficulty of achieving good distal contact between a cementless hip endoprosthesis and the femur is well established. This finite element study investigates the effect on the stress distribution within the femur due to varying lengths of distal gap. Three-dimensional anatomical models of two different sized femurs were generated, based upon computer tomograph scans of two cadaveric specimens. A further six models were derived from each original model, with distal gaps varying from 10 to 60 mm in length. The resulting stress distributions within these were compared to the uniform contact models. The extent to which femoral geometry was an influencing factor on the stress distribution within the bone was also studied. Lack of distal contact with the prosthesis was found not to affect the proximal stress distribution within the femur, for distal gap lengths of up to 60 mm. In the region of no distal contact, the stress within the femur was at normal physiological levels associated with the applied loading and boundary conditions. The femoral geometry was found to have little influence on the stress distribution within the cortical bone. Although localized variations were noted, both femurs exhibited the same general stress distribution pattern.

A large scale finite element study of a cementless osseointegrated tibial tray

Publisher: Elsevier BV

Date: 07-2013

DOI: 10.1016/J.JBIOMECH.2013.04.021

Abstract: The aim of this study was to investigate the performance of a cementless osseointegrated tibial tray (P.F.C. ® Sigma®, Depuy® Inc, USA) in a general population using finite element (FE) analysis. Computational testing of total knee replacements (TKRs) typically only use a model of a single patient and assume the results can be extrapolated to the general population. In this study, two statistical models (SMs) were used one of the shape and elastic modulus of the tibia, and one of the tibiofemoral joint loads over a gait cycle, to generate a population of FE models. A method was developed to automatically size, position and implant the tibial tray in each tibia, and 328 models were successfully implanted and analysed. The peak strain in the bone of the resected surface was examined and the percentage surface area of bone above yield strain (PSAY) was used to determine the risk of failure of a model. Using an arbitrary threshold of 10% PSAY, the models were ided into two groups ('higher risk' and 'lower risk') in order to explore factors that may influence potential failure. In this study, 17% of models were in the 'higher risk' group and it was found that these models had a lower elastic modulus (mean 275.7MPa), a higher weight (mean 85.3kg), and larger peak loads, of which the axial force was the most significant. This study showed the mean peak strain of the resected surface and PSAY were not significantly different between implant sizes.

On the Importance of Considering Porosity When Simulating the Fatigue of Bone Cement

Publisher: ASME International

Date: 26-01-2005

DOI: 10.1115/1.1934182

Abstract: Fatigue cracking in the cement mantle of total hip replacement has been identified as a possible cause of implant loosening. Retrieval studies and in vitro tests have found porosity in the cement may facilitate fatigue cracking of the mantle. The fatigue process has been simulated computationally using a finite element/continuum damage mechanics (FE/CDM) method and used as a preclinical testing tool, but has not considered the effects of porosity. In this study, experimental tensile and four-point bend fatigue tests were performed. The tensile fatigue S-N data were used to drive the computational simulation (FE/CDM) of fatigue in finite element models of the tensile and four-point bend specimens. Porosity was simulated in the finite element models according to the theory of elasticity and using Monte Carlo methods. The computational fatigue simulations generated variability in the fatigue life at any given stress level, due to each model having a unique porosity distribution. The fracture site also varied between specimens. Experimental validation was achieved for four-point bend loading, but only when porosity was included. This demonstrates that the computational simulation of fatigue, driven by uniaxial S-N data can be used to simulate nonuniaxial loadcases. Further simulations of bone cement fatigue should include porosity to better represent the realities of experimental models.

Finite element modelling of glenohumeral kinematics following total shoulder arthroplasty

Publisher: Elsevier BV

Date: 2006

DOI: 10.1016/J.JBIOMECH.2005.07.031

Abstract: Due to the shallowness of the glenohumeral joint, a challenging but essential requirement of a glenohumeral prosthesis is the prevention of joint dislocation. Weak glenoid bone stock and frequent dysfunction of the rotator cuff, both of which are common with rheumatoid arthritis, make it particularly difficult to achieve this design goal. Although a variety of prosthetic designs are commercially available only a few experimental studies have investigated the kinematics and dislocation characteristics of design variations. Analytical or numerical methods, which are predictive and more cost-effective, are, apart from simple rigid-body analyses, non-existent. The current investigation presents the results of a finite element analysis of the kinematics of a total shoulder joint validated using recently published experimental data for the same prostheses. The finite element model determined the loading required to dislocate the humeral head, and the corresponding translations, to within 4% of the experimental data. The finite element method compared dramatically better to the experimental data (mean difference=2.9%) than did rigid-body predictions (mean difference=37%). The goal of this study was to develop an accurate method that in future studies can be used for further investigations of the effect of design parameters on dislocation, particularly in the case of a dysfunctional rotator cuff. Inherently, the method also evaluates the glenoid fixation stresses in the relatively weak glenoid bone stock. Hence, design characteristics can be simultaneously optimised against dislocation as well as glenoid loosening.

Computational modelling of cell spreading and tissue regeneration in porous scaffolds

Publisher: Elsevier BV

Date: 04-2007

DOI: 10.1016/J.BIOMATERIALS.2006.12.008

Abstract: Improved biological and mechanical functionality of musculoskeletal tissue-engineered constructs is required for clinical application, which can only be achieved by comprehensive multidisciplinary research. This review focuses on the contribution of computational modelling as a framework for obtaining an integrated understanding of key processes, which include: nutrient transport and utilization, matrix formation, cell population dynamics, cell attachment and migration, and local cell-cell interactions. Such an integrated perspective of these key aspects will be critical to open up new directions in tissue engineering research, as significant progress can be made by combining existing computational and experimental methods. Furthermore, theoretical modelling has enormous potential in applications ranging from the interpretation of experimental results and the identification of the main governing processes, to the optimization of practical tissue engineering protocols with implications therein for an increasing ageing population.

The role of muscle forces and gait cycle discretization when assessing acetabular cup primary stability: A finite element study

Publisher: Elsevier BV

Date: 03-2023

DOI: 10.1016/J.CMPB.2023.107351

What is the relationship between metal-on-metal and ceramic-on-metal tribocorrosive behaviours? An experimental study on Ti‐6Al‐4 V/CoCrMo interface

Publisher: Elsevier BV

Date: 10-2022

DOI: 10.1016/J.TRIBOINT.2022.107720

The Tribocorrosion Behaviour of Ti-6Al-4 V Alloy: The Role of Both Normal Force and Electrochemical Potential

Publisher: Springer Science and Business Media LLC

Date: 21-06-2022

DOI: 10.1007/S11249-022-01624-0

Abstract: The tribocorrosion behaviour of Ti-6Al-4 V exposed to phosphate buffered saline was investigated under a range of normal forces in both cathodic and anodic regions to provide a basis for properly deriving the tribological constants of this alloy. To achieve this, a new customised tribotester was designed and manufactured to rub the Ti-6Al-4 V disks against zirconia balls. The tests were conducted at a sliding frequency of 1 Hz and a sliding distance of 4.8 mm under various normal forces and potentials as 17.5, 10.8, 6, 3.5 N, and − 1.2, − 0.6, 0, 0.4, 0.8 V/V Ag/AgCl , respectively. The damaged surfaces were characterised by scanning electron microscopy and energy-dispersive X-ray spectroscopy, profilometer, and micro-hardness tester. The post analyses confirmed the appearance of some minor cracks together with third-body wear particles. No significant changes in the hardness were detected after the tribocorrosion tests. The results of profilometry and electrochemical current indicated that in the anodic region the chemical losses accounted for a significant proportion (up to 36%) of the total loss. The proportional chemical loss increased with the potential however, neither direct nor reverse relationship was found with the normal force. Overall, in the anodic domain, the material loss increased with the potential level due to the formation of oxide layer which may induce more shear cutting. In the cathodic domain, hydrogen embrittlement changed the properties of the interface and thus, the amount of material loss. Both the mechanical and chemical wear were described by an existing tribocorrosion theory thereby, the theory was equipped with its tribocorrosive constants for future analyses on the tribocorrosion of this alloy extensively used in various applications including biomedical implants.

Changes in 24-Hour Physical Activity Patterns and Walking Gait Biomechanics After Primary Total Hip Arthroplasty

Publisher: Ovid Technologies (Wolters Kluwer Health)

Date: 27-05-2021

DOI: 10.2106/JBJS.20.01679

Abstract: This article was updated on July 19, 2021, because of a previous error. On page 1172, in the Results section entitled “Sedentary Activity,” the sentence that had read “Postoperatively, 32% at 1 year and 14% at 2 years were sedentary for hours per day.” now reads “Postoperatively, 32% at 1 year and 41% at 2 years were sedentary for hours per day.” Despite marked improvements in self-reported pain, perceived functional ability, and gait function following primary total hip arthroplasty (THA), it remains unclear whether these improvements translate into improved physical activity and sleep behaviors. The aim of this study was to determine the change in 24-hour activity profile (waking activities and sleep) and laboratory-based gait function from preoperatively to 2 years following the THA. Fifty-one patients undergoing primary THA at a single public hospital were recruited. All THAs were performed using a posterior surgical approach with the same prosthesis type. A wrist-worn accelerometer was used to capture 24-hour activity profiles preoperatively and at 1 and 2 years postoperatively. Three-dimensional gait analysis was performed to determine changes in temporospatial and kinematic parameters of the hip and pelvis. Patients showed improvements in all temporospatial and kinematic parameters with time. Preoperatively, patients were sedentary or asleep for a mean time (and standard deviation) of 19.5 ± 2.2 hours per day. This remained unchanged up to 2 years postoperatively (19.6 ± 1.3 hours per day). Sleep efficiency remained suboptimal ( %) at all time points and was worse at 2 years (77% ± 10%) compared with preoperatively (84% ± 5%). More than one-quarter of the s le were sedentary for hours per day at 1 year (32%) and 2 years (41%), which was greater than the preoperative percentage (21%). Patients accumulated their activity performing light activities however, patients performed less light activity at 2 years compared with preoperative levels. No significant differences (p = 0.935) were observed for moderate or vigorous activity across time. Together with improvements in self-reported pain and perceived physical function, patients had significantly improved gait function postoperatively. However, despite the opportunity for patients to be more physically active postoperatively, patients were more sedentary, slept worse, and performed less physical activity at 2 years compared with preoperative levels. Therapeutic Level IV . See Instructions for Authors for a complete description of levels of evidence.

In-silico wear prediction for knee replacements—methodology and corroboration

Publisher: Elsevier BV

Date: 07-2009

DOI: 10.1016/J.JBIOMECH.2009.04.022

Abstract: The capability to predict in-vivo wear of knee replacements is a valuable pre-clinical analysis tool for implant designers. Traditionally, time-consuming experimental tests provided the principal means of investigating wear. Today, computational models offer an alternative. However, the validity of these models has not been demonstrated across a range of designs and test conditions, and several different formulas are in contention for estimating wear rates, limiting confidence in the predictive power of these in-silico models. This study collates and retrospectively simulates a wide range of experimental wear tests using fast rigid-body computational models with extant wear prediction algorithms, to assess the performance of current in-silico wear prediction tools. The number of tests corroborated gives a broader, more general assessment of the performance of these wear-prediction tools, and provides better estimates of the wear 'constants' used in computational models. High-speed rigid-body modelling allows a range of alternative algorithms to be evaluated. Whilst most cross-shear (CS)-based models perform comparably, the 'A/A+B' wear model appears to offer the best predictive power amongst existing wear algorithms. However, the range and variability of experimental data leaves considerable uncertainty in the results. More experimental data with reduced variability and more detailed reporting of studies will be necessary to corroborate these models with greater confidence. With simulation times reduced to only a few minutes, these models are ideally suited to large-volume 'design of experiment' or probabilistic studies (which are essential if pre-clinical assessment tools are to begin addressing the degree of variation observed clinically and in explanted components).

The MAP Client: User-Friendly Musculoskeletal Modelling Workflows

Publisher: Springer International Publishing

Date: 2014

DOI: 10.1007/978-3-319-12057-7_21

Predicting wear of UHMWPE: Decreasing wear rate following a change in direction

Publisher: Elsevier BV

Date: 09-2011

DOI: 10.1016/J.WEAR.2011.06.006

A novel training-free method for real-time prediction of femoral strain

Publisher: Elsevier BV

Date: 03-2019

DOI: 10.1016/J.JBIOMECH.2019.01.057

Abstract: Surrogate methods for rapid calculation of femoral strain are limited by the scope of the training data. We compared a newly developed training-free method based on the superposition principle (Superposition Principle Method, SPM) and popular surrogate methods for calculating femoral strain during activity. Finite-element calculations of femoral strain, muscle, and joint forces for five different activity types were obtained previously. Multi-linear regression, multivariate adaptive regression splines, and Gaussian process were trained for 50, 100, 200, and 300 random s les generated using Latin Hypercube (LH) and Design of Experiment (DOE) s ling. The SPM method used weighted linear combinations of 173 activity-independent finite-element analyses accounting for each muscle and hip contact force. Across the surrogate methods, we found that 200 DOE s les consistently provided low error (RMSE < 100 µε), with model construction time ranging from 3.8 to 63.3 h and prediction time ranging from 6 to 1236 s per activity. The SPM method provided the lowest error (RMSE = 40 µε), the fastest model construction time (3.2 h) and the second fastest prediction time per activity (36 s) after Multi-linear Regression (6 s). The SPM method will enable large numerical studies of femoral strain and will narrow the gap between bone strain prediction and real-time clinical applications.

A multi-platform comparison of efficient probabilistic methods in the prediction of total knee replacement mechanics

Publisher: Informa UK Limited

Date: 12-2010

DOI: 10.1080/10255840903476463

Abstract: Explicit finite element (FE) and multi-body dynamics (MBD) models have been developed to evaluate total knee replacement (TKR) mechanics as a complement to experimental methods. In conjunction with these models, probabilistic methods have been implemented to predict performance bounds and identify important parameters, subject to uncertainty in component alignment and experimental conditions. Probabilistic methods, such as advanced mean value (AMV) and response surface method (RSM), provide an efficient alternative to the gold standard Monte Carlo simulation technique(MCST). The objective of the current study was to benchmark models from three platforms (two FE and one MBD) using various probabilistic methods by predicting the influence of alignment variability and experimental parameters on TKR mechanics in simulated gait. Predicted kinematics envelopes were on average about 2.6mm for tibial anterior-posterior translation, 2.98 for tibial internal–external rotation and 1.9 MPa for tibial peak contact pressure for the various platforms and methods. Based on this good agreement with the MCST, the efficient probabilistic techniques may prove useful in the fast evaluation of new implant designs, including considerations of uncertainty, e.g. misalignment.

The importance of tibial alignment

Publisher: Elsevier BV

Date: 12-2000

DOI: 10.1054/ARTH.2000.17941

Abstract: The influence of the tibial plateau orientation on cancellous bone stress was examined by finite element analysis for a cemented device. The objectives of the study were i) to examine the effect of the plateau-ankle angle on the cancellous bone stress, ii) to analyze the significance of the anteroposterior angles of the tibial component on these stresses, and iii) to compare the finite element predictions with clinical data. In general, positioning the tibial plateau in valgus resulted in lower cancellous bone stresses. These results support previous clinical studies, which suggest that overall alignment in valgus results in lower migration rates and lower incidence of loosening.

Similar damage initiation but different failure behavior in trabecular and cortical bone tissue

Publisher: Elsevier BV

Date: 11-2011

DOI: 10.1016/J.JMBBM.2011.05.036

Abstract: The mechanical properties of bone tissue are reflected in its micro- and nanostructure as well as in its composition. Numerous studies have compared the elastic mechanical properties of cortical and trabecular bone tissue and concluded that cortical bone tissue is stiffer than trabecular bone tissue. This study compared the progression of microdamage leading to fracture and the related local strains during this process in trabecular and cortical bone tissue. Unmachined single bovine trabeculae and similarly-sized cortical bovine bone s les were mechanically tested in three-point bending and concomitantly imaged to assess local strains using a digital image correlation technique. The bone whitening effect was used to detect microdamage formation and propagation. This study found that cortical bone tissue exhibits significantly lower maximum strains (trabecular 36.6%±14% vs. cortical 22.9%±7.4%) and less accumulated damage (trabecular 16100±8800 pix/mm2 vs. cortical 8000±3400 pix/mm2) at failure. However, no difference was detected for the maximum local strain at whitening onset (trabecular 5.8%±2.6% vs. cortical 7.2%±3.1%). The differences in elastic modulus and mineral distribution in the two tissues were investigated, using nanoindentation and micro-Raman imaging, to explain the different mechanical properties found. While cortical bone was found to be overall stiffer and more highly mineralized, no apparent differences were noted in the distribution of modulus values or mineral density along the specimen diameter. Therefore, differences in the mechanical behavior of trabecular and cortical bone tissue are likely to be in large part due to microstructural (i.e. orientation and distribution of cement lines) and collagen related compositional differences.

Finite Element Simulation of the Fatigue Behaviour of Cancellous Bone

Publisher: Springer Science and Business Media LLC

Date: 2002

DOI: 10.1023/A:1020848007201

Could passive knee laxity be related to active gait mechanics? An exploratory computational biomechanical study using probabilistic methods

Publisher: Informa UK Limited

Date: 12-2009

DOI: 10.1080/10255840902895994

Abstract: Improving total knee replacement (TKR) requires better understanding of the many factors influencing clinical outcomes. Recently, probabilistic studies have investigated the influence of variability for in idual TKR activities. This study demonstrates conceptually how probabilistic studies might further provide a framework to explore relationships not just within but between multiple different activities, e.g. intra-operative passive laxity drawer loading and post-operative active gait. Two implants were compared using simulated ISO-gait and passive laxity loading, with factors including mal-positioning and soft-tissue constraint varied using Monte-Carlo analysis. The results illustrate that correlations between different activities can be quantified this demonstration study suggests further research is justified (with detailed clinically representative models) to explore the relationship between passive and active mechanics for specific in vivo conditions. Probabilistics is a key enabling methodology for achieving this goal. In future, exploring correlations between different activities may facilitate a better holistic understanding of TKR function.

Joint loading asymmetries in knee replacement patients observed both pre- and six months post-operation

Publisher: Elsevier BV

Date: 10-2013

DOI: 10.1016/J.CLINBIOMECH.2013.07.014

Abstract: Studies have highlighted asymmetries in knee joint moments in in iduals with osteoarthritis and joint replacements. However, there is a need to investigate the forces at the knee joints to establish the extent of loading asymmetries. Twenty healthy (mean age, 62 range, 55-79 years) and 34 pre- to post-knee arthroplasty (mean age, 64 range, 39-79 years) participants performed gait and sit-stand activities in a motion capture laboratory. Knee joint forces and moments were predicted using inverse dynamics and used to calculate peak loading and impulse data which were normalized to body weight. Comparisons were made between affected and contralateral limbs, and changes from pre- to post-knee arthroplasty. Pre-knee arthroplasty peak vertical knee forces were greater in the contralateral limb compared to the affected limb during both gait 3.5 vs. 3.2 ∗ body weight and sit-stand 1.8 vs. 1.5 ∗ body weight. During gait, peak knee adduction moment asymmetries significantly changed from pre- to post-knee arthroplasty (-0.3 to 0.8 ∗ % body weight ∗ m ∗ height), although differences in vertical knee forces remained. There were no significant changes in loading during sit-stand from pre- to post-knee arthroplasty. The healthy participants showed no noteworthy asymmetries. This study showed loading asymmetries in knee forces between affected and contralateral limbs both pre- and post-knee arthroplasty. Continued over reliance of the contralateral limb could lead to pathology.

Torsional stability of primary total knee replacement tibial prostheses

Publisher: Elsevier BV

Date: 08-1999

DOI: 10.1016/S0883-5403(99)90085-2

Abstract: The significance of torsional loads on the tibial component of total knee replacement prostheses is not clearly established. This study investigated the micromotion induced by torsion, under physiologic loads. Three forms of fixation were sequentially tested in cadaveric tibiae: press-fit, press-fit plus 4 peripheral corticocancellous screws, and horizontally cemented. The implanted tibia was loaded with an axial force between 0.5 and 2.2 kN and a cyclic torque of +/- 5 Nm. The relative motion between the prosthesis and the bone was measured. Our results show little difference between the 3 methods of fixation at high axial loads. At low axial loads, however, the press-fit prosthesis may permit micromotions high enough to interfere (theoretically) with bone ingrowth. Motion is reduced when the same prosthesis is augmented with screws. The cemented prosthesis produces the lowest average micromotion. Our study indicates that rotational micromotion is unlikely to contribute to the failure of ingrowth into the uncemented tibial prosthesis under normal physiologic loads. At low axial loads, which may be encountered in the immediate postoperative period, ingrowth may be compromised. Thus, initial rotational stability is an important consideration in uncemented total knee replacement design and postoperative management. In poor-quality tibiae, cementation may be the only method of fixation to provide sufficient torsional stability.

Queen Mary And Westfield College

Location: United Kingdom of Great Britain and Northern Ireland

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Flinders University

Location: Australia

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University Of Southampton

Location: United Kingdom of Great Britain and Northern Ireland

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University Of Dundee

Location: United Kingdom of Great Britain and Northern Ireland

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University Of Wales College Cardiff

Location: United Kingdom of Great Britain and Northern Ireland

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SYMBIOSIS: Synergy Between Mathematics, Bio- And Nano-engineering At Southampton University

Start Date: 2008

End Date: 2011

Funder: Engineering and Physical Sciences Research Council

Virtual Testing Of Orthopaedic Devices As Part Of The Design And Development Process: Strategies To Account For Patient And Surgical Variability

Start Date: 2013

End Date: 2016

Funder: Australian Research Council

Using Theoretical Simulation To Direct Bone Tissue Engineering

Start Date: 2006

End Date: 2009

Funder: Biotechnology and Biological Sciences Research Council

Development Of A World-class Facility For Three Dimensional Dynamic Testing

Start Date: 2015

End Date: 2015

Funder: Australian Research Council

Decision Support Software For Orthopaedic Surgery

Start Date: 2006

End Date: 2009

Funder: European Commission

High Performance And Robust Systems (HIPARSYS)

Start Date: 2006

End Date: 2009

Funder: Innovate UK

Large-volume, Multi-use Micro-computed Tomography

Start Date: 2018

End Date: 2018

Funder: Australian Research Council

Computational Methods To Predict The Robustness Of Cementless Total Hip Replacements

Start Date: 2007

End Date: 2010

Funder: Engineering and Physical Sciences Research Council

Enhanced Patient Safety By Computational Modelling From Clinically Available X-rays To Minimise The Risk Of Overload And Instability For Optimised Function And Joint Longevity

Start Date: 2010

End Date: 2012

Funder: European Commission

The Virtual Human Knee

Start Date: 2018

End Date: 2020

Funder: Australian Research Council

ARC Training Centre For Medical Implant Technologies

Start Date: 2018

End Date: 2021

Funder: Australian Research Council

Linkage Projects - Grant ID: LP130100122

Start Date: 07-2013

End Date: 11-2017

Amount: $270,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP180103146

Start Date: 05-2018

End Date: 09-2021

Amount: $368,636.00

Funder: Australian Research Council

Industrial Transformation Training Centres - Grant ID: IC180100024

Start Date: 09-2019

End Date: 07-2025

Amount: $4,000,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE180100136

Start Date: 09-2018

End Date: 09-2019

Amount: $557,389.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE150100094

Start Date: 06-2015

End Date: 12-2018

Amount: $400,000.00

Funder: Australian Research Council