Finite element analysis of polyethylene wear in total hip replacement: A literature review

Evaluation and prediction of wear play a key role in product design and material selection of total hip replacements, because wear debris is one of the main causes of loosening and failure. Multifactorial clinical or laboratory studies are high cost and require unfeasible timeframes for implant development. Simulation using finite element methods is an efficient and inexpensive alternative to predict wear and pre-screen various parameters. This article presents a comprehensive literature review of the state-of-the-art finite element modelling techniques that have been applied to evaluate wear in polyethylene hip replacement components. A number of knowledge gaps are identified including the need to develop appropriate wear coefficients and the analysis of daily living activities

Mechanical and Fatigue Behavior of Cellular Structure Ti-6Al-4V Alloy Femoral Stems: A Finite Element Analysis

Repetitive loads acting on the hip joint fluctuate according to the type of activities produced by the human body. Repetitive loading is one of the factors that leads to fatigue failure of the implanted stems. The objective of this study is to develop lightweight femoral stems with cubic porous structures that will survive under fatigue loading. Cubic porous structures with different volumetric porosities were designed and subjected to compressive loading using finite element analysis (FEA) to measure the elastic moduli, yield strength, and ultimate tensile strength. These porous structures were employed to design femoral stems containing mechanical properties under compressive loading close to the intact bone. Several arrangements of radial geometrical porous functionally graded (FG) and homogenous Ti-6Al-4V porous femoral stems were designed and grouped under three average porosities of 30%, 50%, and 70% respectively. The designed stems were simulated inside the femoral bone with physiological loads demonstrating three walking speeds of 1, 3, and 5 km/h using ABAQUS. Stresses at the layers of the functionally graded stem were measured and compared with the yield strength of the relevant porous structure to check the possibility of yielding under the subjected load. The Soderberg approach is employed to compute the safety factor (Nf > 1.0) for each design under each loading condition. Several designs were shortlisted as potential candidates for orthopedic implants. 2022 by the authors. Licensee MDPI, Basel, Switzerland.Funding: The APC was funded by QNRF grant no NPRP 8-876-2-375 from the Qatar National Research Fund (a member of Qatar Foundation). The findings achieved herein are solely the responsibility of the authors.Scopu

Utilisation du polypropylene extrudé par le procedé d’ECAE pour l’ameliorati1on du comportement mecanique de la cupule d’une prothese totale de hanche

L’augmentation de la durée de vie en service d’une cupule d’une prothèse totale de hanche, passe par l’amélioration de ses performances mécaniques. L’objectif de cet article est d’analyser, par simulation numérique basée sur la méthode des éléments, le comportement mécanique d’une cupule usinée dans un bloc de polypropylène (PP) extrudé à l'état solide à l’aide du procédé d'Extrusion Coudée à Aires Egales (ECAE). Nous présentons les résultats d'une modélisation, par éléments finis réalisée en utilisant le code d’éléments finis ANSYS, du comportement mécanique in-vitro de la cupule d'une prothèse totale de la hanche (PTH). Le polypropylène extrudé à l’état par le procédé d’ECAE a comportement élastoviscoplastiques dont les paramètres sont obtenus expérimentalement par des essais mécaniques de caractérisation. Les résultats obtenus montrent clairement, que l’utilisation du PP extrudé, a donné une meilleure répartition des contraintes-déformations au niveau de la cupule comparés à ceux donnés par un PP vierge. Ceci peut être expliqué par l’augmentation de la ductilité du matériau après une extrusion

A General Wear Algorithm for Wear Predictions in Total Hip Replacements

Total hip replacements are known to be one of the most successful orthopaedic interventions of all time when the hip joint becomes damaged due to disease or trauma. Currently, these hip prostheses have a lifespan of approximately 15 years, however, according to the National Joint Registry (NJR) in for England, Wales, Northern Ireland, and the Isle of Man for 2021, 8% of implanted prostheses fail prematurely with wear being one of the main reasons for these failures. Wear occurs at the contacting surfaces of the hip prosthesis and is inevitable due to the surfaces being in constant contact throughout its lifespan. Current experimental methods to assess wear at the contacting surfaces are expensive, time-consuming and complicated. Computational wear modelling is an alternative method which is faster and cheaper compared to experimental methods and can be used to improve prosthesis design and increase overall longevity. The focus of this research is to develop a wear algorithm which can accurately predict wear at both the bearing surface and taper junction, including linear and volumetric wear damage. In this research, a new computational method, to predict wear at the articulating bearing surface and the taper junction surfaces of total hip prosthesis, is proposed. The method incorporates wear laws into a commercial finite element package to predict wear at the articulating bearing surface and the taper junction. The assessment of wear in this research is based on wear at the bearing surface and fretting wear at the taper junction as the primary mechanism causing surface damage. This method is unique in that it simulates both the articulating bearing surface wear and taper junction fretting wear within the same analysis with individual surface characteristics. The method is capable of modelling the fixation of the femoral head onto the femoral stem during surgery. This method has been used to investigate different design, and clinical recommendations with results consistent with wear damage observed within current literature. This research has investigated the impact of body weight on the wear of the contacting surfaces of the THR prosthesis. The results showed that a reduction in body weight from 140kg to 100kg would decrease wear up to 30% and significantly improve the longevity of the prosthesis. The impact of adding bicycling on the wear at the contacting surfaces of the THR prosthesis was also investigated. By adding bicycling up to 80km per week, the results show that there was a significant increase in the amount of wear observed, however, the health benefits may outweigh the risks. These studies will allow for clinical recommendations post-THR to help patients return to an active lifestyle. The method has also investigated different design parameters, such as the different femoral head sizes on the wear on the contacting surfaces on the THR prosthesis. Four different femoral head sizes (22mm, 28mm, 32mm and 36mm) were investigated. The results showed that increasing the femoral head size would increase the volumetric wear at the bearing surface; however, the risk of dislocation decreased. This study would allow for further design modifications to further increase the lifespan of the THR prosthesis. The results obtained from the computational method were found to be consistent with wear damage observed within current literature and the method is able to model the wear evolution effectively. The computational method here can be used in conjunction with experimental testing to create a longer lasting hip prosthesis through design, materials and surgical approaches

DESIGN OF FULLY POROUS FUNCTIONALLY GRADED TI-6AL-4V FEMORAL STEM FOR STRESS SHIELDING AND IMPLANT'S STABILITY

The main objective of this study is to design titanium alloy femoral stems with cubic porous structures that will be able to reduce stress-shielding and promote stem stability. Stress-shielding is one of the factors that contributes toward aseptic loosening, which eventually leads to the failure of implants. These porous structure designs were accommodated into the titanium alloy femoral stem as homogeneous and functionally graded porous structures. First, the cubic cellular structures were simulated under compressive loading to measure the yield and modulus of elasticity for various porosity ranges. This allowed the selection of porosity range to design the femoral stems having stiffness in compressive loading identical to that of an intact femur bone. This was done to reduce the stress shielding effects. Based on the selected porosity range, fifteen different arrangements of radial geometrical functionally graded (FG) designs were developed with average porosities of 30, 50, and 70% respectively. The finite element models developed with physiological loads presenting three different walking speeds (1, 3, and 5 km/hrs.), where the average human body weight was assumed. Stresses at the bone Gruen zones were measured to check the percentage of stress transfer to the bone for each porous stem design and were compared with the bulk/dense stem. Micromotion for each design was measured to find the acceptable designs that enable the bone tissue ingrowth (stability of implant). It was found that stems with 70% average porosity had similar stiffness to the intact bone. Besides this, the functionally graded (FG) porous stems tend to transfer higher stress values to the bone compared to bulk/dense stems for all physiological loads associated with three studied walking speeds. Micromotion values increased as the porosity and physiological loads / walking speed increased, creating a constraint on the amount of porosity that can be introduced in the stem design. Finally, the Fatigue factor of safety of the designed stems was calculated at the studied walking speeds to find the appropriate designs for hip implants. Several FG stems designs were shortlisted as recommended candidates for hip implants

Evaluating footwear “in the wild”: Examining wrap and lace trail shoe closures during trail running

Trail running participation has grown over the last two decades. As a result, there have been an increasing number of studies examining the sport. Despite these increases, there is a lack of understanding regarding the effects of footwear on trail running biomechanics in ecologically valid conditions. The purpose of our study was to evaluate how a Wrap vs. Lace closure (on the same shoe) impacts running biomechanics on a trail. Thirty subjects ran a trail loop in each shoe while wearing a global positioning system (GPS) watch, heart rate monitor, inertial measurement units (IMUs), and plantar pressure insoles. The Wrap closure reduced peak foot eversion velocity (measured via IMU), which has been associated with fit. The Wrap closure also increased heel contact area, which is also associated with fit. This increase may be associated with the subjective preference for the Wrap. Lastly, runners had a small but significant increase in running speed in the Wrap shoe with no differences in heart rate nor subjective exertion. In total, the Wrap closure fit better than the Lace closure on a variety of terrain. This study demonstrates the feasibility of detecting meaningful biomechanical differences between footwear features in the wild using statistical tools and study design. Evaluating footwear in ecologically valid environments often creates additional variance in the data. This variance should not be treated as noise; instead, it is critical to capture this additional variance and challenges of ecologically valid terrain if we hope to use biomechanics to impact the development of new products

Biomechanical study of rigid ankle-foot orthoses in the treatment of stroke patients

Error on title page, date of award is 2021.Rigid Ankle-Foot Orthoses (AFOs) are commonly prescribed for stroke patients who exhibit equinovarus deformity as an orthotic intervention. The main purpose of prescribing a rigid AFO is to provide appropriate control of unwanted ankle and foot motions in any plane. To achieve the optimal effects of the AFO, appropriate stiffness and alignment optimisation (tuning) should be considered. The AFO provides moments (referred to as the orthotic moments) to control ankle motion. Orthotic moments are different from the moments generated by ground reaction forces, the later are known as total ankle moments. Reviewing the literature showed limited research in this area. The aims of this study are to investigate the biomechanical effects of using rigid AFO (before and after tuning) and to investigate the orthotic moment during walking in stroke patients. Gait data were collected from six stroke participants (2 females, 4 males) and six healthy participants (3 females, 3 males) using a Motekforce Link dual belt instrumented treadmill and a Vicon 3-dimensional motion analysis system. Each participant was fitted with a custom made rigid AFO instrumented using four strain gauges. Walking at a self-selected speed was investigated while wearing: (1) Standard shoes only (2) Rigid AFO with standard shoes (3) Rigid Tuned-AFO with standard shoes. Lower limb temporal-spatial, kinetic and kinematic parameters, and electromyographic activity (Delsys TrignoTM) of the knee muscles were compared among the test conditions. The orthotic moments were also quantified using the strain gauges data combined with gait analysis. Repeated measures ANOVA and Friedman’s ANOVA were used for statistical analysis. The rigid AFO showed immediate improvement in the temporal-spatial parameters and the kinematics and the kinetics of post stroke gait. Greater improvement in knee kinematics and kinetics was achieved when tuning the rigid AFO. The rigid AFO (before and after tuning) increased quadriceps muscle activity and reduced hamstring muscle activity compared to walking with standard shoes only. Tuning a rigid AFO further increased quadriceps muscle activity and reduced hamstring muscle activity compared to AFO before tuning. Strain gauges data combined with gait analysis can be used in evaluating the orthotic moment around the ankle in sagittal and frontal planes. Tuning a rigid AFO had no clear changes in the orthotic moment, and it did not alter the anatomical moments at the ankle joint in sagittal and at the subtalar joint in frontal plane.Rigid Ankle-Foot Orthoses (AFOs) are commonly prescribed for stroke patients who exhibit equinovarus deformity as an orthotic intervention. The main purpose of prescribing a rigid AFO is to provide appropriate control of unwanted ankle and foot motions in any plane. To achieve the optimal effects of the AFO, appropriate stiffness and alignment optimisation (tuning) should be considered. The AFO provides moments (referred to as the orthotic moments) to control ankle motion. Orthotic moments are different from the moments generated by ground reaction forces, the later are known as total ankle moments. Reviewing the literature showed limited research in this area. The aims of this study are to investigate the biomechanical effects of using rigid AFO (before and after tuning) and to investigate the orthotic moment during walking in stroke patients. Gait data were collected from six stroke participants (2 females, 4 males) and six healthy participants (3 females, 3 males) using a Motekforce Link dual belt instrumented treadmill and a Vicon 3-dimensional motion analysis system. Each participant was fitted with a custom made rigid AFO instrumented using four strain gauges. Walking at a self-selected speed was investigated while wearing: (1) Standard shoes only (2) Rigid AFO with standard shoes (3) Rigid Tuned-AFO with standard shoes. Lower limb temporal-spatial, kinetic and kinematic parameters, and electromyographic activity (Delsys TrignoTM) of the knee muscles were compared among the test conditions. The orthotic moments were also quantified using the strain gauges data combined with gait analysis. Repeated measures ANOVA and Friedman’s ANOVA were used for statistical analysis. The rigid AFO showed immediate improvement in the temporal-spatial parameters and the kinematics and the kinetics of post stroke gait. Greater improvement in knee kinematics and kinetics was achieved when tuning the rigid AFO. The rigid AFO (before and after tuning) increased quadriceps muscle activity and reduced hamstring muscle activity compared to walking with standard shoes only. Tuning a rigid AFO further increased quadriceps muscle activity and reduced hamstring muscle activity compared to AFO before tuning. Strain gauges data combined with gait analysis can be used in evaluating the orthotic moment around the ankle in sagittal and frontal planes. Tuning a rigid AFO had no clear changes in the orthotic moment, and it did not alter the anatomical moments at the ankle joint in sagittal and at the subtalar joint in frontal plane