A dynamic model of polyethylene damage in dry total hip arthroplasties: wear and creep

The creep and wear of ultra-high-weight polyethylene hip prostheses under physiological conditions are studied in the present research work. Afully integrated contact-coupled dynamic model based upon multibody dynamics methodology is developed, allowing the evaluation of not only sliding distance, but also contact mechanics as well as cross-shear effects and both average pressure and in-service duration associated with the creep phenomenon. In vivo forces and motions of hip joint are used as input for the dynamic simulation, which result in more realistic contact point trajectory and contact pressure, and consequently wear and creep, compared to simplified inputs. The analysis also takes into account inertia forces due to hip motion, tribological properties of bearing bodies, and energy loss owing to contact-impact events. The principal molecular orientation (PMO) of the polyethylene cup is determined through an iterative algorithm and dynamic outcomes. Archard's wear law is also integrated into the multibody dynamics model for wear prediction in hip implants. Creep, besides wear, is attributed to polyethylene damage, which is investigated by implementing a creep model extracted from experimental data. The model is validated using clinical data and numerical results available from previously published studies. It is shown that creep plays a significant role in hip damage along with wear, both of which can be influenced by hip parameters, e.g., hip and clearance sizes. Moreover, the creep mechanism according to creep experiment is discussed, and contributing factors to the wear phenomenon are analyzed throughout this study

Finite element simulation of hip joint replacement under static and dynamic loading

The objective of this work is to develop methods for the structural analysis of orthopaedic implants. The central argument is that, if stress distributions are interpreted in the context of failure models of the component materials, significant advantages can be made in our ability to design these devices. The artificial hip joint is used throughout as an example. The finite element method was used as a structural analysis tool and its pplicability was discussed. Validity and accuracy were assessed and results were ompared with previous experimental and finite element studies. By comparing tress distributions with failure criteria for prosthesis and cement, the suitability of roposed design changes were assessed and guidelines for materials selection were resented. Prediction of bone stresses were also given for different prosthesis designs n the region of the artificial hip joint where bone adaption contributes to failure. hereafter the focus was on utilizing a new technique to develop a new hip prosthesis model. This study was divided into two parts according to the loading type. In this regard the stress field in the artificial hip components (prostheses, cement mantle, and bone) is analysed statically and dynamically to assess the implant longevity. In this static analysis all the simulations were conducted by assuming the peak loads during the normal gait at a particular time (static loads). The aim was to study the effects of a set of variables within which an optimal prosthesis design can be made by means of finite element analysis to qualify and quantify the stresses and the strains in natural and treated human femur for different cases of implantation. Until now, models developed to predict stresses in total hip replacements have been generally poorly validated. This could be because all the pre-clinical simulations were performed statically, that is by selecting the greatest load at a particular time of the activity cycle. The second part of the study was aimed to take into consideration, in designing total hip replacement, another factor belongs to the patient activity (stamping, jumping, walking, etc) and the effect of impact over the prosthesis head during these activity into the prosthesis performance. This study considered the prosthesis hip deformation with time, dynamic loads study. The elimination of impact cracking was considered by studying the effect of using “damper” trapped between the grooved prosthesis collar and the bone. Material selection of the total hip replacements was also investigated under the dynamic loading. The approaches of prosthesis fixation have been studied, too. This study was conducted by onstructing three-dimensional finite element model for a femur implanted with a cemented prosthesis with a representative physiological loading condition by using he LS-DYNA3D software

A computational approach to fretting wear prediction at the head-stem taper junction of total hip replacements

Wear is one of the main reasons for failure of modular total hip replacements. Recent evidence suggests that fretting wear occurs at the taper junction which provides fixation between the prosthesis femoral head and stem components. The fine metallic wear debris that is released can lead to adverse soft-tissue reactions which can necessitate a revision surgery. The present study proposes a computational methodology utilising an energy wear law and a 3D finite element model to predict fretting wear at the taper junction. The method is novel in that it simulates the weakening of the initial taper ‘fixation’ (created at impaction of the head onto the stem in surgery) due to the wearing process. The taper fixation is modelled using a contact analysis with overlapped meshes at the taper junction. The reduction in fixation is modelled by progressive removal of the overlap between components based on calculated wear. The fretting wear analysis approach has been shown to model the evolution of wear effectively; however, it has been shown that accurate, quantitative values for wear are critically dependant on mesh refinement, wear scaling factor and fraction, wear coefficient used and knowledge of the device loading history. The method has been implemented with a 3D finite element model of the taper junction of a commercial total hip replacement. This has been used to determine taper wear patterns, wear damage and wear rates which have been shown to be consistant with those found from observation and measurement of retrieved prostheses. The numerical method could be used to consider the effect of design changes and clinical technique on subsequent fretting wear in modular prosthetic devices

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

MODIFYING AND EXPANDING THE SIMULATION OF WEAR IN THE SPHERICAL JOINT WITH A POLYMERIC COMPONENT OF THE TOTAL HIP PROSTHESIS

The existing model of wear, based on the classical Archard equation, in the spherical joint of a total hip prosthesis comprising an acetabular cup of ultra-high molecular weight polyethylene (UHMWPE) in combination with a metal or ceramic femoral head is modified and expanded. With this model, studies are conducted using the finite element analysis in terms of cumulative linear and volumetric wear for the ISO 14242-1 demands and additionally for the conditions during walking gait. Also they are carried out for the head diameter of 28 mm at the constant and the variable wear factor, where the variable wear factor is adopted from the modified formula for the dependence on the contact pressure

Wear analysis of hip explants, dual mobility concept: Comparison of quantitative and qualitative analyses

International audienceTotal hip replacement (THR) fails mainly because of wear. It is of interest to analyze wear to be able to increase the longevity of the hip implants. One way to achieve it is to use instruments on explants but the most suitable depends on the application. This paper aims at comparing several methods of surface analysis in the particular application of wear determination in a series of dual mobility explants. Wear measurement could help understand the wear mechanism only partially known. A CMM, Coordinate Measuring Machine, is used to get 3D points representing the explants, then Pro/Engineer ® and Matlab ® are used to calculate wear. A mechanical (SOMICRONIC®) and an optical profilometer (Bruker nanoscope Wyko® NT 9100, ex. Veeco) are used to access roughness parameters. The comparisons of the two software showed similar results for wear calculation except in a few cases where differences are due to the theoretical volumes calculation. The comparison of the two profiling techniques resulted in similar results particularly for Sa and Sdr. The comparison of the results showed that wear is present for four explants; it is relevant with the observed characteristics. The mechanical profilometer showed better accuracy than the optical one which enable to conclude that it must not be neglected for that particular application, even if measurements need more time

1st EFORT European Consensus: Medical & Scientific Research Requirements for the Clinical Introduction of Artificial Joint Arthroplasty Devices

Innovations in Orthopaedics and Traumatology have contributed to the achievement of a high-quality level of care in musculoskeletal disorders and injuries over the past decades. The applications of new implants as well as diagnostic and therapeutic techniques in addition to implementation of clinical research, have significantly improved patient outcomes, reduced complication rates and length of hospital stay in many areas. However, the regulatory framework is extensive, and there is a lack of understanding and clarity in daily practice what the meaning of clinical & pre‐clinical evidence as required by the MDR is. Thus, understanding and clarity are of utmost importance for introduction of new implants and implant-related instrumentation in combination with surgical technique to ensure a safe use of implants and treatment of patients. Therefore EFORT launched IPSI, The Implant and Patient Safety Initiative, which starting from an inaugural workshop in 2021 issued a set of recommendations, notably through a subsequent Delphi Process involving the National Member Societies of EFORT, European Specialty Societies as well as International Experts. These recommendations provide surgeons, researchers, implant manufacturers as well as patients and health authorities with a consensus of the development, implementation, and dissemination of innovation in the field of arthroplasty. The intended key outcomes of this 1st EFORT European Consensus on “Medical & Scientific Research Requirements for the Clinical Introduction of Artificial Joint Arthroplasty Devices”are consented, practical pathways to maintain innovation and optimisation of orthopaedic products and workflows within the boundaries of MDR 2017/745. Open Access practical guidelines based on adequate, state of the art pre-clinical and clinical evaluation methodologies for the introduction of joint replacements and implant-related instrumentation shall provide hands-on orientation for orthopaedic surgeons, research institutes and laboratories, orthopaedic device manufacturers, Notified Bodies but also for National Institutes and authorities, patient representatives and further stakeholders. We would like to acknowledge and thank the Scientific Committee members, all International Expert Delegates, the Delegates from European National & Specialty Societies and the Editorial Team for their outstanding contributions and support during this EFORT European Consensus

Computer aided stress analysis of the femur with prosthetic hip stem utilizing computed tomography

A computer aided design and analysis method, utilizing computed tomography (CT) is developed, which together with a finite element program determines the stress and deformation patterns in the femur with hip prosthesis. The CT scan data file provides the geometry and the material parameters for the generated finite element model. The three-dimensional finite element model of the femur with hip prosthesis is automatically generated from the CT data file by a preprocessing procedure. The preprocessor includes a CT image display, edge detector, nodes generation, prosthesis simulator, mesh generator and model display. The loading conditions applied on the finite element model are determined from existing gait analysis including joint force and muscle force. Formatted input data for ANSYS (Swanson Analysis Systems Inc.) finite element program is generated by the preprocessor. In this research, the influence on the stress pattern of different prosthetic materials and fixation, such as cobalt-chromium alloy or titanium alloy prosthesis, also cemented or porous-coated prosthesis are studied. A comparison of the stress patterns for the three different femora is made and a radiographic follow-up study in two cases is carried out at 14 months and 12 months postoperation for analyzing the bone remodeling process. As a result of the calculated stress patterns in the femur with prosthesis, it is found that the cobalt-chromium alloy prosthesis unloads the calcar cortical bone and the titanium alloy prosthesis decreases the stress within the prosthetic stem except for the proximal side. The highest calculated stress is approximately 12% of the fatigue limit for cobalt-chromium alloy prosthesis, and approximately 4% for the titanium alloy prosthesis. Comparing the porous coating model with the cemented model, the porous coating model leads to decreased bone stresses, reduced stress concentrations in bone surrounding the prosthesis and more uniformly distributed stress to the surrounding bone tissue. For the effect of stiffness and Poisson\u27s ratio of the porous coating layer, lower elastic modulus and Poisson\u27s ratio will reduce the interface stress between cancellous bone and the porous coating layer. The average stress of the fractured femur with prosthesis is approximately twice the amount of the femur with prosthesis in the proximal and distal side of the prosthetic stem. Furthermore the average stress of the male femur with prosthesis is about 4% lower than the female femur with prosthesis. In regards to stress changes in the postoperative femur, the bone remodeling results indicate that bone resorption of the cortex around the proximal prosthesis would increase the stress in the proximal prosthetic stem and femoral surface slightly while decreasing the stress of the midregion. Bone hypertrophy around the distal prosthesis would decrease the stress up to 35% in the distal prosthetic stem and femoral surface

Spatial Sensors for Quantitative Assessment of Retrieved Arthroplasty Bearings

Evaluation of retrieved joint arthroplasty bearings provides unique evidence related to the physiological environment in which bearing materials are expected to perform. This dissertation describes the development of novel spatial sensors and measurement strategies for standardized, quantitative assessments of arthroplasty bearings, including total knee replacements, unicompartmental knee replacements, and total hip replacements. The approach is to assess bearings that endured a finite duration of function in patients, with particular emphasis on expanding our understanding of the biomechanical conditions specific to bearing function and wear in the physiological environment. Several quantifiable parameters are identified that prove comparable to pre-clinical in vitro tibological evaluations, including knee wear simulation and analytical modeling. These comparisons provide clinical relevance to the existing methodologies, helping to verify that the biomechanical simulations accurately represent the in vivo conditions they are meant to simulate. The broad objective of this dissertation is to improve the longevity and function of arthroplasty bearing materials and designs. Assessments from the retrieved prostheses are discussed within the context of developing comprehensive approaches for the prospective evaluation of new materials and designs in joint replacements