Bone remodelling inside a cemented resurfaced femoral head

BACKGROUND: 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. METHOD: 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. FINDINGS: 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. INTERPRETATION: 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.     

Effect of baseplate positioning on fixation of reverse total shoulder arthroplasty

BackgroundThe glenoid component in reverse total shoulder arthroplasty is recommended to be positioned inferiorly or with a downward tilt with the intention of reducing scapular notching. However, it is still unclear whether modifying the position of the glenoid prosthesis affects implant stability. The aim of this study was to determine the association between implant positioning and glenoid prosthesis fixation using Grammont reverse total shoulder arthroplasty.MethodsFour positions for the glenoid prosthesis were studied using the finite element method. The glenosphere was positioned as follows: 1) in the middle of the glenoid fossa, 2) flush with the inferior glenoid rim, 3) with an inferior overhang, 4) with a 15° inferior inclination. Bone-prosthesis micromotions and strain-induced bone adaptations were quantified during five daily activities.FindingsWhen the glenoid component was tilted inferiorly, the activities producing anterior-posterior shear forces (e.g. standing up from an armchair) caused an increase in peak micromotions. In the lateral-middle glenoid, inferior positioning caused a 64.6% reduction in bone apparent density. In the lateral-inferior glenoid, central positioning led to the most severe bone resorption, reaching 43.9%.InterpretationReducing activities which generate anterior-posterior shear forces on the shoulder joint will increase bone formation and may improve the primary stability of the implant when fixed in the position with an inferior tilt. Postoperative bone resorption is highly dependent on implant positioning. Understanding the relationship between bone resorption and implant positioning will help surgeons improve the long-term stability of reverse total shoulder arthroplasty.     

Numerical evaluation of bone remodelling and adaptation considering different hip prosthesis designs

BackgroundThe change in mechanical properties of femoral cortical bone tissue surrounding the stem of the hip endoprosthesis is one of the causes of implant instability. We present an analysis used to determine the best conditions for long-term functioning of the bone–implant system, which will lead to improvement of treatment results.MethodsIn the present paper, a finite element method coupled with a bone remodelling model is used to evaluate how different three-dimensional prosthesis models influence distribution of the density of bone tissue. The remodelling process begins after the density field is obtained from a computed tomography scan. Then, an isotropic Stanford model is employed to solve the bone remodelling process and verify bone tissue adaptation in relation to different prosthesis models.FindingsThe study results show that the long-stem models tend not to transmit loads to proximal regions of bone, which causes the stress-shielding effect. Short stems or application in the calcar region provide a favourable environment for transfer of loads to the proximal region, which allows for maintenance of bone density and, in some cases, for a positive variation, which causes absence of the aseptic loosening of an implant. In the case of hip resurfacing, bone mineral density changes slightly and is closest to an intact femur.InterpretationInstallation of an implant modifies density distribution and stress field in the bone. Thus, bone tissue is stimulated in a different way than before total hip replacement, which evidences Wolff's law, according to which bone tissue adapts itself to the loads imposed on it. The results suggest that potential stress shielding in the proximal femur and cortical hypertrophy in the distal femur may, in part, be reduced through the use of shorter stems, instead of long ones, provided stem fixation is adequate.     

Prediction of stemless humeral implant micromotion during upper limb activities

BackgroundAdequate primary stability is essential for the long term success of uncemented stemless shoulder implants. The goal of this study was to evaluate the micromotion of a stemless humeral implant during various upper limb activities.MethodsA finite element model was validated by reproducing experimental primary stability testing. Loading from an instrumented prosthesis representing a set of 29 upper limb activities were applied within the validated FE model. Peak micromotion and percentage area for different micromotion thresholds were considered.FindingsIn all simulated activities, at least 99% of the implant surface experienced micromotion below 150 μm. Micromotion depended strongly on loading with large discrepancies between upper limb activities. Carrying no external weight and keeping the arm at lower angles induced lower micromotion. Activities representative of demanding manual labor generally led to higher micromotion. Axilla crutches led to lower micromotion than forearm crutches. Micromotion increased when a wheelchair was used on slopes above 2% inclination.InterpretationMicromotions below the 150 μm threshold below which bone ingrowth occurs were measured over at least 99% of the implant surface for all simulated activities. Peak micromotion dependence on activity type demonstrates the need to consider physiologic in vivo loading and the full contact interface in primary stability evaluations. Focusing on activities with no hand weight and low arm motions during the rehabilitation period may enhance primary stability. For patients unable to walk without aids, axilla crutches and motorized wheelchairs might be more beneficial than forearm crutches and manual drive wheelchairs respectively.     

Strain shielding for cemented hip implants

BackgroundLong-term survival of hip implants is of increasing relevance due to the rising life expectancy. The biomechanical effect of strain shielding as a result of implant insertion may lead to bone resorption, thus increasing risk for implant loosening and periprosthetic fractures. Patient-specific quantification of strain shielding could assist orthopedic surgeons in choosing the biomechanically most appropriate prosthesis.MethodsValidated quantitative CT-based finite element models of five femurs in intact and implanted states were considered to propose a systematic algorithm for strain shielding quantification. Three different strain measures were investigated and the most appropriate measure for strain shielding quantification is recommended. It is used to demonstrate a practical femur-specific implant selection among three common designs.FindingsStrain shielding measures demonstrated similar trends in all Gruen zones except zone 1, where the volumetric strain measure differed from von-Mises and maximum principal strains. The volumetric strain measure is in better agreement with clinical bone resorption records. It is also consistent with the biological mechanism of bone remodeling so it is recommended for strain shielding quantification. Applying the strain shielding algorithm on three different implants for a specific femur suggests that the collared design is preferable. Such quantitative biomechanical input is valuable for practical patient specific implant selection.InterpretationVolumetric strain should be considered for strain shielding examination. The presented methodology may potentially enable patient-specific pre-operative strain shielding evaluation so to minimize strain shielding. It should be further used in a longitudinal study so to correlate between strain shielding predictions and clinical bone resorption.     

Load response of an osseointegrated implant used in the treatment of unilateral transfemoral amputation: An early implant loosening case study

BackgroundOsseointegrated implants for transfemoral amputees facilitate direct load transfer between the prosthetic limb and femur; however, implant loosening is a common complication, and the associated implant-bone loads remain poorly understood. This case study aimed to use patient-specific computational modeling to evaluate bone-implant interface loading during standing and walking in a transfemoral amputee with an osseointegrated implant prior to prosthesis loosening and revision surgery.MethodsOne male transfemoral amputee with an osseointegrated implant was recruited (age: 59-yrs, weight: 83 kg) and computed tomography (CT) performed on the residual limb approximately 3 months prior to implant failure. Gait analyses were performed, and the CT images used to develop a finite element model of the patient's implant and surrounding bone. Simulations of static weight bearing, and over-ground walking were then performed.FindingsDuring standing, maximum and minimum principal strains in trabecular bone adjacent to the implant were 0.26% and −0.30%, respectively. Strains generated at the instant of contralateral toe-off and contralateral heel strike during walking were substantially higher and resulted in local trabecular bone yielding. Specifically, the maximum and minimum principal strains in the thin layer of trabecular bone surrounding the distal end of the implant were 1.15% and −0.98%, respectively.InterpretationLocalised yielding of trabecular bone at the interface between the femur and implant in transfemoral amputee osseointegrated prosthesis recipients may present a risk of implant loosening due to periprosthetic bone fracture during walking. Rehabilitation exercises should aim to produce implant-bone loading that stimulates bone remodelling to provide effective bone conditioning prior to ambulation.     

Stemless shoulder arthroplasty—current results and designs

Stemless shoulder arthroplasty was originally introduced in 2004 by a single manufacturer. Now, over a decade later, numerous designs are available outside the USA, but as yet, only one implant has been cleared by the Food and Drug Administration (FDA) and is available for use within the USA. Often referred to as “canal sparing,” these implants are designed for metaphyseal fixation to minimize humeral bone removal, avoid intraoperative and postoperative humeral fracture complications, and to decrease morbidity associated with revision operations. Recently, the second generation of stemless arthroplasty, a convertible implant allowing use in either anatomic or reverse arthroplasty configuration, was released for use outside the USA. This paper will review the available designs, reported results, and raise potential concerns for this emerging technology.     

上颌中切牙种植体的应力改变及骨吸收变化

目的：观察上颌中切牙种植体植入方向在与牙冠长轴不同夹角情况下,种植体骨界面应力变化值和最大安全角度的临界值,以此来指导种植前设计。方法：应用有限元法分析不同倾斜角度对种植体骨界面应力峰值影响。结合临床病例,使用X线头影测量分析,测算出患者理想牙冠长轴的位置,以此轴线与种植体长轴的夹角作为倾斜角度分析在不同角度下种植体的骨界面应力变化和中切牙种植病例的周围骨吸收情况。倾斜角0°-20°范围内边缘骨吸收值和种植体骨界面应力值均在正常范围内,适合使用角度基台修复;倾斜角大于20°或25°以上时,应力值有明显升高趋势,种植体唇侧颈部应力集中区骨吸收明显。结论：建议做牙槽骨改建手术,改变种植体植入角度。     

Ipsilateral shoulder and elbow replacements: on the risk of periprosthetic fracture

Background. Ipsilateral shoulder and elbow replacements may leave only a short segment of bone bridging the two implants in the humerus. The potential for high stress concentrations as a result of this geometry has been a concern with regard to periprosthetic fracture, especially with osteoporotic bone. The study aims to determine the optimum length of the bone-bridge between shoulder and elbow humeral implants, and to assess the effect of filling the canal with cement.

Methods. A three-dimensional finite element model was used to compare the stresses between a humerus with a solitary prosthesis and a humerus with both proximal and distal cemented prostheses. The length of the bone-bridge and the effect of filling the canal with cement were studied under bending and torsion.

Findings. Gradual load transfer from prosthesis to bone was observed for all cases, and no stress concentration was evident. The length of the bone-bridge had no deleterious effect on stresses in the humerus, and filling the canal with cement did not appreciably decrease the loads carried by the humerus.

Interpretation. The length of the bone-bridge between stem tips has little effect on the resultant stresses in the humerus. Filling the canal with cement adds little benefit to the structural integrity of the humerus. Ipsilateral shoulder and elbow prostheses may be considered independent of one another in terms of risk of periprosthetic fracture.     

The sclerotic line: Why it appears under knee replacements (a study based on the Oxford Knee)

BackgroundRadiolucent lines and sclerotic margins are often seen on knee radiographs taken a year or longer after knee replacement surgery. Histology has shown that the radiolucent zone is predominantly fibrocartilage and the sclerotic margin is lamellar bone. The reasons for their existence are not clearly understood.MethodsA three-dimensional finite element model of the medial half of the proximal 75 mm of a tibia implanted with a knee replacement was created and run over 365 iterations simulating 1 year of in vivo post implant remodelling. After each iteration, new material properties were calculated for all elements of the model using established bone remodelling and tissue differentiation rules. For comparison with patient anteroposterior radiographs, “synthetic anteroposterior radiographs” were generated by reverse calculating radiographic densities from material properties of the model after 365 iterations. Von Mises stress of elements in the bone where the sclerotic line is usually seen were calculated after 365 iterations. These values were compared with the same entities assuming no remodelling.FindingsThe mean von Mises stress in the sclerotic region was higher when remodelling was assumed than when not, suggesting that the presence of the soft tissue (radiolucent line) increased the stress in the underlying bone.InterpretationThe sclerotic line is caused by the stiffening of bone due to the relatively larger loads seen by the bone just beneath the soft tissue (radiolucent line) adjoining knee replacements.     

Benefits of an anatomical reconstruction of the humeral head during shoulder arthroplasty: a finite element analysis

OBJECTIVE: To study the influence of the shape of the prosthetic humeral head on shoulder biomechanics and then to evaluate the benefits of an anatomical reconstruction of the humeral head after shoulder arthroplasty. DESIGN: A 3D numerical model of a healthy shoulder was reconstructed. The model included the proximal humerus, the scapula and, for stability purposes, the subscapularis, infraspinatus and supraspinatus rotator cuff muscles. BACKGROUND: Shoulder prostheses used nowadays, called third generation, allow for a better adaptation of the implant to the anatomy of the proximal humerus than previously used implants. However, no biomechanical study has shown the benefits of this anatomical reconstruction of the humeral head. METHODS: The model was used to compare the biomechanics of a shoulder without implant with the biomechanics of the same shoulder after humeral hemiarthroplasty. Two humeral components were tested: a second-generation prosthesis and an implant with an anatomically reconstructed humeral head. RESULTS: The anatomical reconstruction of the humeral head restored the physiological motions and limited eccentric loading of the glenoid. Conversely, the second-generation implant produced contact forces in the superior extremity of the glenoid surface leading to bone stresses up to 8 times higher than for the intact shoulder. CONCLUSIONS: This analysis provided insights into the mechanical effects of different reconstructions of the humeral head and highlighted the advantages of anatomical reconstructions of the humeral head during shoulder arthroplasty.     

Evaluation of femoral strains with cementless proximal-fill femoral implants of varied stem length

Background

The design intent of proximally-filling lateral flare femoral stems is to load the endosteal surface of the proximal femur both laterally and medially, to achieve normal bone strains. However, the long stem can contact the femoral cortex and may offload the proximal region to some extent. Therefore, in this study, we sought to determine if reducing the stem length, would result in physiologic strain patterns.

Methods

Using the PhotoStress® method we analyzed 13 femurs intact and with three different stem length implants: stemless, ultra-short and short. The test rig loaded the femoral head by simulating the mid-stance single leg support phase of gait with the ilio-tibial band and the hip abductor forces. The strain distribution with each stem length implant was then compared to the intact strain distribution to determine which was most similar.

Findings

As the stem length increased the femurs exhibited a typical pattern of reduced proximal strain and increased distal strain. However, there was some variation in this pattern indicating that the exact stem position and the location of its interaction with the endosteal surface of bone was not the same in each femur.

Interpretation

The stemless design provided the best match compared to the native femur and therefore has the greatest potential to address the shortcomings of a stemmed femoral implant. However, the ultra-short implant also exhibited a strain distribution that closely emulated the intact femur, and may represent the best option as there are still several questions pertaining to stability and alignment of a stemless implant.     

上颌前牙区即刻种植后骨量变化：水平向吸收是否影响骨结合

背景：目前大量的动物实验和临床研究已证实即刻种植和延期种植同样可获得成功的骨结合,但即刻种植是否能够减少或预防拔牙窝牙槽嵴的生理性骨吸收一直是学者们争论的焦点.目的：利用锥束CT测量评估上颌前牙区即刻种植的近期骨组织变化.方法：选取上颌前牙无法保留适合采取即刻种植的患者18例18颗患牙.于种植当天、6个月、1年行锥束CT检查,分别测量距离种植体肩台4,6,8mm处牙槽嵴唇侧骨壁的厚度,以及缺失牙牙槽嵴唇颊侧近、远中骨高度.结果与结论：种植后6个月,牙槽嵴唇颊侧骨板近、远中吸收高度分别为（1.83±0.05） mm和（1.50±0.04） mm,距离种植体肩台4,6,8 mm处牙槽嵴唇侧骨板吸收分别为（1.72±0.30） mm,（1.65±0.26） mm,（1.55±.25） mm;1年后牙槽嵴唇颊侧骨板近、远中吸收高度分别为（0.85±0.04） mm和（0.78±0.05） mm,距离种植体肩台4,6,8 mm处牙槽嵴唇侧水平吸收（0.52±0.20） mm,（0.45±0.16） mm,（0.32±0.15） mm.结果表明即刻种植后唇侧骨壁会发生水平向吸收,但是不影响种植体的骨结合,1年后骨组织吸收基本稳定.     

Post-loosening mechanical behavior of femoral resurfacing prostheses

The survival rate of femoral surface replacements has been low relative to conventional total hip replacements. The purpose of this investigation was to determine whether the early clinical loosening can be explained by mechanical causes. Using linear and nonlinear finite element methods, the pre- and post-failure load-transfer characteristics of the femoral surface replacement were analysed, and stress patterns and relative motions at the implant/bone interface were evaluated for a particular hip-loading cycle. Using histology of revision material as a guideline, implant loosening, bone resorption and fibrous interface formation were introduced in the model and their mechanical consequences analysed. The results suggest that the high failure rates are not correlated directly with the chances for primary mechanical failure of the implant-bone interface, but rather indirectly with the sensitivity of the implant design to implant loosening and the propagation of bone resorption and fibrous tissue formation. This mechanism appears to be governed by the proliferation of relative motions between implant and bone. We conclude that the 'secondary stability' of implants in general and their capacity to obtain a stable post-loosening configuration is an important design criterion for long-term survival.     

Biomechanical evaluation of pyrocarbon proximal interphalangeal joint arthroplasty: An in-vitro analysis

BackgroundPyrocarbon proximal interphalangeal joint arthroplasty provided patients with excellent pain relief and joint motion, however, overall implant complications have been very variable, with some good outcomes at short-medium-term follow-up and some bad outcomes at longer-term follow-up. Implant loosening with migration, dislocation and implant fracture were the main reported clinical complications. The aim of the present work was to test the hypothesis that the magnitude proximal interphalangeal joint cyclic loads in daily hand functions generates stress-strain behaviour which may be associated with a risk of pyrocarbon component loosening in the long-term.MethodsThis study was performed using synthetic proximal and middle phalanges to experimentally predict the cortex strain behaviour and implant stability considering different load conditions for both intact and implanted states. Finite element models were developed to assess the structural behaviour of cancellous-bone and pyrocarbon components, these models were validated against experimentally measured cortex strains.FindingsCortex strains showed a significant increase at dorsal side and reduction at palmar side between intact and implanted states. Cancellous-bone adjacent to the condylar implant base components suffers a two to threefold strain increase, comparing with the intact condition.InterpretationThe use of pyrocarbon implant changes the biomechanical behaviour of the joint phalanges and is associated with a potential risk of support cancellous-bone suffer fatigue failure in mid to long term due to the strain increase for cyclic loads in the range of daily hand activities, this risk is more prominent than the risk of bone resorption due to strain-shielding effect.     

Biomechanics of short hip endoprostheses — The risk of bone failure increases with decreasing implant size

Background

Short uncemented metaphyseally anchored femoral endoprostheses are becoming popular and are proposed to be less invasive than longer conventional implants. However, it is proposed here that shortening femoral endoprostheses can increase the risk of periprosthestic fracture.

Methods

A simple analytical model of a femoral hip implant was developed to estimate the risk of bone overload for varying implant size, implantation geometry, implantation force and bone quality. The load capacity of a particular short implant design in poor quality cadaveric bone specimens was also measured experimentally, to validate the model.

Findings

The model demonstrated a high risk of bone overload for a short endoprosthesis in poor quality bone. The experimental results and a clinical example of failure, to which the model was applied, supported this finding. Bone stresses increased with decreasing implant length and diameter, varus implantation, incomplete seating and high implantation forces, approaching the strength of good quality bone in extreme cases.

Interpretation

Correct implantation and patient selection is essential for short femoral endoprostheses.     

Relationship between bone adaptation and in-vivo mechanical stimulus in biological reconstructions after bone tumor: A biomechanical modeling analysis

BackgroundBiomechanical interpretations of bone adaptation in biological reconstructions following bone tumors would be crucial for orthopedic oncologists, particularly if based on quantitative observations. This would help plan for surgical treatments, rehabilitative programs and communication with the patients. We aimed to analyze the biomechanical adaptation of a femoral reconstruction after Ewing sarcoma according to an increasingly-used surgical technique, and to relate in-progress bone resorption to the mechanical stimulus induced by different motor activities.MethodsWe created a multiscale musculoskeletal and finite element model from CT scans and motion analysis data at a 76-month follow-up of a patient, to analyze muscle and joint loads, and to compare the mechanical competence of the reconstructed bone with the contralateral limb, in the current real condition and in a possible revision surgery that removed proximal screws.FindingsOur results showed strategies of muscle coordination that led to differences in joint loads between limbs more marked in more demanding motor activities, and generally larger in the contralateral limb. The operated femur presented a markedly low ratio of physiological strain due to load-sharing with the metal implant, particularly in the lateral aspect. The possible revision surgery would help restore a physiological strain configuration, while the safety of the reconstruction would not be threatened.InterpretationWe suggest that bone resorption is related to load-sharing and to the internal forces exerted during movement, and the mechanical stimulus should be improved by adopting modifications in the surgical treatment and by promoting physical therapy aimed at specific muscle strengthening.     

TM种植体骨界面应力分布的有限元分析

背景：种植体形态是决定种植体骨界面应力分布的重要因素之一。探讨顺应人体正常颌骨解削形态的TM种植体骨界面的应力分布特征对临床医生选择和设计种植体有指导意义。目的：观察集中荷载作用下TM种植体及其周围骨组织应力分布的特征。方法：通过逆向工程技术,将二维下颌骨CT图片转化为三维实体模型,并建立3种包含不同锥度的TM种植体真实下颌骨B/2类骨质的有限元模型,利用有限元技术研究两种加载方式下TM种植体骨界面应力分布特征。结果与结论：垂直加载时,对于锥度较大的TM种植体周边密质骨承受较小的应力;斜向加载时,对于锥度较大的TM种植体周边密质骨和松质骨承受较大的应力;种植体颈部,密质骨上缘与种植体接触处和种植体底部松质骨出现明显应力集中现象,斜向荷载下种植体骨界面的应力分布显著高于垂直荷载下的应力分布。从1/2长度开始变化的TM种植体骨界面在垂直荷载下表现出较好的应力分布特征。     

TM种植体骨界面应力分布的有限元分析

背景:种植体形态是决定种植体骨界面应力分布的重要因素之一。探讨顺应人体正常颌骨解剖形态的TM种植体骨界面的应力分布特征对临床医生选择和设计种植体有指导意义。目的:观察集中荷载作用下TM种植体及其周围骨组织应力分布的特征。方法:通过逆向工程技术,将二维下颌骨CT图片转化为三维实体模型,并建立3种包含不同锥度的TM种植体真实下颌骨B/2类骨质的有限元模型,利用有限元技术研究两种加载方式下TM种植体骨界面应力分布特征。结果与结论:垂直加载时,对于锥度较大的TM种植体周边密质骨承受较小的应力;斜向加载时,对于锥度较大的TM种植体周边密质骨和松质骨承受较大的应力;种植体颈部,密质骨上缘与种植体接触处和种植体底部松质骨出现明显应力集中现象,斜向荷载下种植体骨界面的应力分布显著高于垂直荷载下的应力分布。从1/2长度开始变化的TM种植体骨界面在垂直荷载下表现出较好的应力分布特征。     

Fixed and mobile-bearing total ankle prostheses: Effect on tibial bone strain

BackgroundTotal ankle replacement is associated to a high revision rate. To improve implant survival, the potential advantage of prostheses with fixed bearing compared to mobile bearing is unclear. The objective of this study was to test the hypothesis that fixed and mobile bearing prostheses are associated with different biomechanical quantities typically associated to implant failure.MethodsWith a validated finite element model, we compared three cases: a prosthesis with a fixed bearing, a prosthesis with a mobile bearing in a centered position, and a prosthesis with mobile bearing in an eccentric position. Both prostheses were obtained from the same manufacturer. They were tested on seven tibias with maximum axial compression force during walking. We tested the hypothesis that there was a difference of bone strain, bone-implant interfacial stress, and bone support between the three cases. We also evaluated, for the three cases, the correlations between bone support, bone strain and bone-implant interfacial stress.FindingsThere were no statistically significant differences between the three cases. Overall, bone support was mainly trabecular, and less effective in the posterior side. Bone strain and bone-implant interfacial stress were strongly correlated to bone support.InterpretationsEven if slight differences are observed between fixed and mobile bearing, it is not enough to put forward the superiority of one of these implants regarding their reaction to axial compression. When associated to the published clinical results, our study provides no argument to warn surgeons against the use of two-components fixed bearing implants.