Hip Components Research Articles

Uncertainty determination for X-ray computed tomography wear assessment of polyethylene hip joint prostheses

Hip joint replacements have been successfully used in the field of orthopaedic medicine for over fifty years. Whilst clinical studies have shown encouraging long-term clinical performance, failure of these devices due to wear still occurs. The laboratory determination of wear rate is an important part of the pre-clinical validation of prostheses. The most commonly applied method for wear evaluation of prosthetic joint components is the gravimetric method. It is generally accurate and reliable but has certain limitations. In particular, gravimetric measurements cannot provide information about localization of wear damage and deformation over the component’s surface. As an alternative, tactile coordinate measuring machines are used to evaluate both volumetric wear and wear damage distribution over the worn surface. However, considering polymeric prosthetic components, these machines could induce unwanted damages and/or deformations due to clamping and probing forces leading to a large measurement uncertainty. X-ray computed tomography recently emerged as an advanced non-contact technique capable of performing dimensional measurements with high accuracy. Moreover, X-ray computed tomography can be used for volumetric wear measurement as well as for determination of local distribution of wear and deformations without any risk of further damaging or deforming polymeric components. Nevertheless, the uncertainty of such measurements has yet to be investigated. The purpose of the work was to determine the uncertainty in both volumetric wear measurements and assessment of local distribution of wear and deformations using X-ray computed tomography. More in depth, in this work, tomographic measurements were conducted on nine hip joint components made from three different types of ultrahigh molecular weight polyethylene. This investigation identified and quantified the main individual uncertainty contributions.

Masses of the components of SB2 binaries observed with Gaia – IV. Accurate SB2 orbits for 14 binaries and masses of three binaries*

The orbital motion of non-contact double-lined spectroscopic binaries (SB2), with periods of a few tens of days to several years, holds unique accurate informations on individual stellar masses, that only long-term monitoring can unlock. The combination of radial velocity measurements from high-resolution spectrographs and astrometric measurements from high-precision interferometers allows the derivation of SB2 components masses down to the percent precision. Since 2010, we observed a large sample of SB2 with the SOPHIE spectrograph at the Observatoire de Haute-Provence, aiming at the derivation of orbital elements with sufficient accuracy to obtain masses of components with relative errors as low as 1$\%$ when the astrometric measurements of the Gaia satellite will be taken into account. In this paper we present the results from six years of observations of 14 SB2 systems with periods ranging from 33 to 4185 days. Using the TODMOR algorithm we computed radial velocities from the spectra, and then derived the orbital elements of these binary systems. The minimum masses of the 28 stellar components are then obtained with a sample average accuracy of 1.0$\pm$0.2$\,\%$. Combining the radial velocities with existing interferometric measurements, we derived the masses of the primary and secondary components of HIP 61100, HIP 95995 and HIP 101382 with relative errors for components (A,B) of respectively (2.0, 1.7)$\,\%$, (3.7, 3.7)$\,\%$, and (0.2, 0.1)$\,\%$. Using the Cesam2k stellar evolution code, we could constrain the initial He-abundance, age and metallicity for HIP 61100 and HIP 95995.

Biomaterials for hip implants – important considerations relating to the choice of materials

Abstract This article is a review of important material requirements for hip biomaterials including their response to the body environment (biocompatibility), mechanical properties, wear resistance, fretting corrosion and availability as well as the price. The application of proper biomaterials for hip implants is one of the major focal points in this article. Background information is also provided on metals used in other prosthetic devices and implant components. Titanium and its alloys, cobalt base alloys and stainless steels (bio-steels) are used for load-bearing hip implants. These three groups of metallic materials will be introduced and discussed in detail. Metals and their alloys are crystalline materials since their properties depend on the crystal lattice, chemical and phase compositions, grain size, lattice defects, crystalline texture and residual micro- and macro-stresses. All these features of biomaterials are formed during technological manufacturing, such as metallurgical process, solidification, plastic deformation (rolling and forging), machining, heat treatment and coating. All these technological processes work in optimal conditions in order to achieve the optimal microstructure and mechanical, chemical and biological properties. Amongst the above-mentioned particular properties of biomaterials, fretting is a major concern as regards hip implants at the femoral head and neck taper interface. Additional important mechanisms of interaction between the implant and the human body must be taken into account, i.e. diffusion stream of foreign particles and atoms from the implant to body fluids, to the tissue and to the bone. These foreign particles and atoms are released from the implant to the body fluid, to the tissue and to the bone as wear product during use. All together they contribute to the wear, i.e. loss of weight, strength or volume of hip components. Wear rates of ultrahigh molecular weight polyethylene mated against Ti-6Al-4V are significantly greater than the ones for Co-Cr-Mo alloys. Therefore, thermochemical surface treatments like diffusion ion nitriding should be applied to increase the resistance of titanium alloys to wear. Austenitic stainless steels are also used for temporary applications, but they have lower resistance to pitting corrosion than titanium and cobalt alloys. The purpose of the paper is to introduce a group of metallic materials, which is often chosen for surgical hip implants. Conclusions of the paper refer to information which support important medical and patient decisions on hip implants. Also, the development of biomaterials, their treatments, properties, surface layers and coatings are considered. All these features develop over time and need synergy and experience in the progress of the biomedical, mechanical and materials science.

Sound side joint contact forces in below knee amputee gait with an ESAR prosthetic foot

The incidence of knee and hip joint osteoarthritis in subjects with below knee amputation (BK) appears significantly higher compared to unimpaired subjects, especially in the intact side. However, it is controversial if constant higher loads on the sound side are one of the major factors for an increased osteoarthritis (OA) incidence in subjects with BK, beside other risk factors, e.g. with respect to metabolism. The aim wasto investigate joint contact forces (JCF) calculated by a musculoskeletal model in the intact side and to compare it with those of unimpaired subjects and to further elucidate in how far increased knee JCF are associated with increased frontal plane knee moments. A group of seven subjects with BK amputation and a group of ten unimpaired subjects were recruited for this study. Gait data were measured by 3D motion capture and force plates. OpenSim software was applied to calculate JCF. Maximum joint angles, ground reaction forces, and moments as well as time distance parameters were determined and compared between groups showing no significant differences, with some JCF components of knee and hip even being slightly smaller in subjects with BK compared to the reference group. This positive finding may be due to the selected ESAR foot. However, other beneficial factors may also have influenced this positive result such as the general good health status of the subjects or the thorough and proper fitting and alignment of the prosthesis.

Scanning Electron Microscopy and Energy-Dispersive X-Ray Spectroscopy as a Valuable Tool to Investigate the Ultra-High-Molecular-Weight Polyethylene Wear Mechanisms and Debris in Hip Implants

BackgroundThe use of scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS) was investigated to understand the wear mechanisms from a metal-on-polyethylene bearing couple. Morphological features of femoral head acetabular liner, and isolated particles resulting from hip wear testing were evaluated. EDS was proposed to investigate the polymeric nature of the particles isolated from the wear testing. MethodsIn this work, 28-mm conventional ultra-high-molecular-weight polyethylene acetabular liners paired with metallic heads were tested in a hip wear simulator over 2 million cycles. SEM-EDS was employed to investigate wear mechanisms on hip implant components and associated wear debris. ResultsSEM showed worn surfaces for both hip components, and a significant volume of ultra-high-molecular-weight polyethylene wear particles resulting from hip wear testing. Particles were classified into 3 groups, which were then correlated to wear mechanisms. Group I had particles with smooth surfaces, group II consisted of particles with rough surfaces, and group III comprised aggregate-like particles.Group I EDS revealed that particles from groups I and II had a high C/O ratio raising a concern about the particle source. On the other hand, particles from group III had a low C/O ratio, supporting the hypothesis that they resulted from the wear of acetabular liner. Most of particles identified in group III were in the biologically active size range (0.3 to 20 μm). ConclusionThe use of optical and electron microscopy enabled the morphological characterization of worn surfaces and wear debris, while EDS was essential to elucidate the chemical composition of isolated debris.

Intra- and inter-observer agreement and reliability of bone mineral density measurements around acetabular cup: a porcine ex-vivo study using single- and dual-energy computed tomography.

BackgroundPeriprosthetic bone loss is considered to be a potentially contributing factor in aseptic loosening of acetabular hip components, but no studies have shown this association. The lack of association might be caused by insufficient image quality because of metal artifacts and challenges in measuring bone density (BMD) in complex anatomic structures which might be overcome using dual-energy computed tomography (DECT).PurposeTo test inter- and intra-observer agreement and reliability of in-house segmentation software measuring BMD adjacent to acetabular cup and to compare measurements performed with single-energy CT (SECT) and DECT in cemented and cementless cups.Material and MethodsTwenty-four acetabular cups inserted in porcine hip specimens were scanned with SECT and DECT. Bone density was measured in a three-dimensional volume adjacent to the cup. Double measurements were performed.ResultsBMD derived from SECT was approximately four times higher than that of DECT. In both scan modes, intraclass correlation coefficient (ICC) was >0.90 with no differences between repeated measurements, except for uncemented cups where a statistically significant difference of 11 mg/cm3 was found with DECT. DECT showed narrower limits of agreement than SECT. Inter-observer analysis showed small differences.ConclusionBMD can be estimated with high intra- and inter-observer reliability with SECT and DECT around acetabular cups using custom software. The intra- and inter-observer agreement of DECT is superior to that of SECT and better in the cementless concept. Good intra- and inter-observer reliability can be obtained in both cemented and cementless cups using the segmentation software. SECT and DECT cannot be used interchangeably.

Wear mechanisms and surface topography of artificial hip joint components at the subsequent stages of tribological tests

It is virtually impossible to follow through changes in surface topography and analyse wear mechanisms of the friction components of a hip joint prosthesis under in vivo conditions. Only under laboratory conditions can analysis of operation process of friction pairs be undertaken. Research on wear mechanisms and formation of surface topography at the subsequent stages of operation process (during in vitro testing) analyzed in this work is a new approach to the current problem concerning investigation and analysis of the lifespan of an artificial hip joint.The paper presents issues of artificial hip joint wear mechanisms and methods for studying changes in the surface topography of a ball-and-socket friction pair at the subsequent stages of tribological research.The subjects of research were co-acting components of an artificial hip joint: a metallic ball and a polymeric socket. Tribological tests were performed with a hip joint simulator replicating the physiological movements and working conditions of the natural hip joint. After each stage of tribological tests, the surface texture of friction pair components was measured using a white light interference microscopy. In addition, the surface topography was examined before and after the operation process, using a coordinate measuring machine as well as an optical microscope.Based on the results, changes in surface topography (its functional properties) occurring at the subsequent stages of tribological tests were assessed. The wear mechanisms of the interacting components, i.e. abrasion, fatigue and adhesion, were identified.

Influence of Power Delivery Timing on the Energetics and Biomechanics of Humans Wearing a Hip Exoskeleton.

A broad goal in the field of powered lower limb exoskeletons is to reduce the metabolic cost of walking. Ankle exoskeletons have successfully achieved this goal by correctly timing a plantarflexor torque during late stance phase. Hip exoskeletons have the potential to assist with both flexion and extension during walking gait, but the optimal timing for maximally reducing metabolic cost is unknown. The focus of our study was to determine the best assistance timing for applying hip assistance through a pneumatic exoskeleton on human subjects. Ten non-impaired subjects walked with a powered hip exoskeleton, and both hip flexion and extension assistance were separately provided at different actuation timings using a simple burst controller. The largest average across-subject reduction in metabolic cost for hip extension was at 90% of the gait cycle (just prior to heel contact) and for hip flexion was at 50% of the gait cycle; this resulted in an 8.4 and 6.1% metabolic reduction, respectively, compared to walking with the unpowered exoskeleton. However, the ideal timing for both flexion and extension assistance varied across subjects. When selecting the assistance timing that maximally reduced metabolic cost for each subject, average metabolic cost for hip extension was 10.3% lower and hip flexion was 9.7% lower than the unpowered condition. When taking into account user preference, we found that subject preference did not correlate with metabolic cost. This indicated that user feedback was a poor method of determining the most metabolically efficient assistance power timing. The findings of this study are relevant to developers of exoskeletons that have a powered hip component to assist during human walking gait.

Comparative Characteristic of Strength of Different Approaches to Cement Fixation of Therapeutic Component of Hip Joint in Endoprosthesis from Computer Modeling Positions

Improvement of cement consolidation technologies of the components of the hip joint endoprosthesis is carried out not only based on the analysis of clinical and X-ray data, but also by computer modeling. The purpose of the study was to study the stress-strain state of the virtual endoprosthetized hip joint with various variants of the acetabular cement anchoring. The finite element method was used as a theoretical basis. The ANSYS computer program was used to construct the desired model. For calculations, a version of the model, this includes three segments: the acetabular component, the cement mantle and the spongy bone was created.

Dual-mobility components obviate the need for constrained components in revision total hip arthroplasty–Affirms

Dual-mobility hip components provide an additional articular surface, with the goals of improving range of motion and overall stability. In many European centers, these components are used for primary total hip arthroplasty. However, their greatest utility may be to prevent and treat recurrent dislocation after revision total hip arthroplasty. Several retrospective series have shown satisfactory results for this indication at medium-term follow-up. There are important concerns with these components, including intraprosthetic dislocation and polyethylene wear causing chronic dislocation, but these are rare phenomena. At present, dual-mobility components are the preferred solution to manage recurrent dislocation in revision surgery.

Reconciling in vivo and in vitro kinetics of the polymorphic transformation in zirconia-toughened alumina for hip joints: II. Theory

In this paper, an updated analytical model for the kinetics of the tetragonal to monoclinic (t→m) polymorphic transformation in ZTA composites for hip joints is proposed and discussed. The model builds upon the so-called Mehl-Avrami-Johnson (MAJ) description of transformation kinetics, which combines two overlapping processes: nucleation of monoclinic sites, and their successive growth. Dependencies on two specific factors are introduced in the model, namely the initial fraction of monoclinic polymorph as received from the manufacturer, and the presence of different types of transition-metal stains (e.g., Ti, CoCr, and Fe) on the ZTA surface. These two factors were studied because clear indications of their potential roles on the environmental stability of implantable ZTA components were found in previous phenomenological analyses of retrievals. Nucleation and growth of monoclinic domains are two key processes whose interplay decides the actual kinetics of the overall transformation process according to two main parameters: an apparent activation energy value function of time and temperature, and a nuclei growth exponent. These parameters were clearly altered by the presence of transition metal contamination, whose effect was incorporated into the model to explain exacerbations of surface degradation. In accordance with a general analytical description of transformation kinetics for isothermal or isochronal evolutions in terms of time and temperature, the modified model of the MAJ description assesses the effect of the initial monoclinic fraction. The updated model has been validated using systematic in vitro experiments, and appears to partly reconcile in vitro and in vivo data of t→m transformation discrepancies in ZTA hip components.

Detection of incorrect manufacturer labelling of hip components

We describe the case of a 53-year-old man who underwent a left metal-on-metal hip resurfacing in 2015. Component size mismatch (CSM) was suspected because of the patient’s immediate post-operative mechanical symptoms and high metal ion levels. Surgical notes indicated the appropriate combinations of implants were used. However, we detected a mismatch using computed tomography. Revision was performed and subsequent measurements of explanted components confirmed the mismatch. To our knowledge, this case is the first report of a CT method being used in a patient to pre-operatively identify CSM.

Numerical Modelling of Surface Texturing of UHMWPE under Influence of Normal Load

The reduced wear rate of hip-joint bearing components is the main issues in biotribology researches for the biomedical implants. Ultra-high molecular weight polyethylene (UHMWPE) is extensively used as a bearing material because of having its great properties of friction and wear. Surface texturing can be selected as a method of enhancing tribology properties of engineering surfaces. In this present study, surface texturing examination was performed by 3D finite element method under influence of normal load. Stress distribution of UHMWPE surface under the influence of texturing with the variation in diameter cavities and separation was investigated. The result showed that the surface texturing provided the higher stress distribution of the lower separation in the cylindrical cavities.

Masses of the components of SB2 binaries observed withGaia– III. Accurate SB2 orbits for 10 binaries and masses of HIP 87895

In anticipation of the Gaia astrometric mission, a large sample of spectroscopic binaries has been observed since 2010 with the SOPHIE spectrograph at the Haute--Provence Observatory. Our aim is to derive the orbital elements of double-lined spectroscopic binaries (SB2s) with an accuracy sufficient to finally obtain the masses of the components with relative errors as small as 1 % when the astrometric measurements of Gaia are taken into account. In this paper we present the results from five years of observations of 10 SB2 systems with periods ranging from 37 to 881 days. Using the TODMOR algorithm we computed radial velocities from the spectra, and then derived the orbital elements of these binary systems. The minimum masses of the components are then obtained with an accuracy better than 1.2 % for the ten binaries. Combining the radial velocities with existing interferometric measurements, we derived the masses of the primary and secondary components of HIP 87895 with an accuracy of 0.98 % and 1.2 % respectively.

Comparative analysis of dual-phase 18F-fluoride PET/CT and three phase bone scintigraphy in the evaluation of septic (or painful) hip prostheses: A prospective study.

The preoperative differentiation of aseptic and septic loosening of hip prostheses remains a diagnostic challenge for clinicians and many molecular imaging techniques have been evaluated. The objective of current study was to establish the clinical utility of dual phase 18F-fluoride PET/CT (DPFP) in diagnosing implant loosening, differentiation between septic and aseptic loosening and to compare the diagnostic accuracy of DPFP and three-phase bone scan (TPBS). In this prospective study, we evaluated 57 hip components in 45 patients (bilateral prostheses in 12 patients, 45 painful and 12 asymptomatic contralateral hip components) with dual phase fluoride PET/CT and TPBS. Findings of skeletal scintigraphy and PET/CT were evaluated by two expert nuclear medicine physicians, blinded with clinical findings and final diagnosis. The patterns of tracer uptake and maximum standardized uptake value (SUVmax) were noted for each joint. The final diagnosis was based on intraoperative findings, histopathological or microbiological examinations. Out of twelve non-painful hips, DPFP correctly identified no loosening in 11 hips while TPBS detected in 10 hips. In the remaining 45 hips with radiological proven loosening to rule out sepsis, DPFP had a sensitivity, specificity, PPV, NPV and accuracy of 75%, 97%, 92%, 88% and 88% respectively while TPBS revealed 81%, 86%, 76%, 89% and 82% respectively. DPFP had shown a higher specificity and PPV as compared to the TPBS in the evaluation of painful hip prostheses. The pattern of tracer uptake may help in the differentiation between the two entities. We also noted a significant difference between SUVmax values of septic and aseptic loosening. The results suggested that DPFP has considerable potential in differentiating septic from aseptic loosening of hip prostheses and more specific to rule out sepsis than TPBS. It may be employed before revision arthroplasty to evaluate implant for loosening and sepsis in loosened implant.

Delayed cementless total hip arthroplasty for neglected dislocation of hip combined with complex acetabular fracture and deficient bone stock

Total hip arthroplasty (THA) for an untreated acetabular fracture is technically challenging and the long-term result is not so favorable. A 45-year-old female patient with untreated column and comminuted posterior wall fracture of the acetabulum was treated in our institution by reconstruction of the posterior wall using iliac strut autograft and plate stabilization of the posterior column with cancellous grafting and cementless THA in a single stage. At 3 years’ follow-up, the patient was independently mobile without limb length discrepancy. Radiological evaluation showed well integrated components and bone grafts. No evidence of aseptic loosening or osteolysis was found. This report aims to emphasize that bony acetabular reconstruction allows the use of primary hip components, which improves prosthesis longevity and preserves bone stock for a future revision.

Failure analysis of retrieved PE-UHMW acetabular liners

Ultra-high molecular weight polyethylene (PE-UHMW) acetabular liners have a limited lifespan in a patient’s body. There are many factors affecting the performance of the implant and furthermore the properties of the polymeric material are changing after implantation. In this work material changes according to structure and morphology and their implication on mechanical properties are in focus. The physical and mechanical properties of ten crosslinked (xL) PE-UHMW and nine conventional (conv) gamma-sterilized PE-UHMW hip components, used as sliding surface in total hip joint replacement, with different in-vivo times are compared. The evaluation of the retrieved acetabular liners is performed in view of crosslinking and conventional gamma-sterilization but also in terms of the influence of gender concerning alteration in properties. The oxidative degradation in the PE-UHMW is investigated by means of Fourier Transformed Infrared Spectroscopy (FTIR). The characterization of the morphology is carried out via differential scanning calorimetry (DSC). A depth profile of the micro-hardness and elastic modulus is taken over the cross-section of the components in order to find the influence of chemical constitution and morphology on the micro-mechanical properties. It could be shown that crosslinking and oxidative degradation influence the degree of crystallinity of the polymer. Oxidation occurs for both types of the material due to in-vivo time. Higher degree of crystallinity can be correlated to higher hardness and indentation modulus. No unequivocal superiority of crosslinked over conventional liners can be observed. The influence of sex concerning alteration of the evaluated properties matters but need to be further investigated.

Ceramic-on-Poly Femoral Head Fractures: What's Going On?

As outlined in our January 16, 2013, editorial , “The Case Report Redefined with JBJS Case Connector ,” one important role of JBJS Case Connector is to alert the orthopaedic community about a potentially problematic device or therapy. When two or more such cases with similar mechanisms appear, we will identify the procedure or implant as a “watchable” intervention. While this system is not statistically conclusive and may or may not be supported by other published case reports or registry data, the intention is to sharpen the focus of clinicians on the potential for similar problems and thereby enhance clinical outcomes and patient safety. The “Watch” designation may also encourage others to report related difficulties and enlist the orthopaedic community to either demonstrate that these are isolated, unrelated cases or sharpen the focus further on rigorously evaluating the intervention. Where appropriate, we may identify brand, model, or implant-lot specifics. In total hip arthroplasty (THA), a fractured ceramic head is a catastrophic but thankfully very rare event. Most case reports of ceramic head fractures involve ceramic-on-ceramic articulations, but this “Watch” describes three cases of femoral head fractures involving ceramic-on-polyethylene bearings. Moreover, the fractures occurred in association with little or no postsurgical trauma. Ceramic hip components are often chosen for younger patients in an effort to minimize long-term wear. On the downside, unlike metal, ceramic components can fracture. Ceramic femoral head fractures arise from four main factors: trauma; material or manufacturing defects; non-compatible, damaged, or contaminated femoral stem/head taper connections; or other suboptimal surgical techniques. The ceramics industry has a more-than-forty-year track record of continuous improvement in hip-component manufacturing. CeramTec, the main U.S. player in this arena, first introduced ceramic hip components in 1974; those first-generation femoral heads had a fracture rate of 0.026%. By 2003, when CeramTec introduced its fourth-generation BIOLOX …

Preliminary Study on the Biocompatibility of Stainless Steel 316L and UHMWPE Material

Stainless steel AISI 316L (SS316L) and ultra-high molecular weight polyethylene (UHMWPE) are widely used materials for artificial hip joint components. The SS316L material is typically used for the acetabular cup, femoral head and the stem, while the UHMWPE material is used for the acetabular liner in an artificial hip joint. The aim of this work is to study the biocompatibility of SS316L and UHMWPE materials by implanting and installing these materials in the tissues of rabbits. The tissues around the implants were examined after eight weeks of the installment. Results showed that the reaction of the rabbit tissues around the implants was positive. It was concluded that the SS316L and the UHMWPE materials are biocompatible and the applications of these materials for implants seems conceivable.

Trunnion Troubles in Modular Hip Implants.

As outlined in our January 16, 2013 editorial, “The Case Report Redefined with JBJS Case Connector , ” one important role of JBJS Case Connector is to alert the orthopaedic community about a potentially problematic device or therapy. When two or more such cases with similar mechanisms appear, we will identify the procedure or implant as a “watchable” intervention. While this system is not statistically conclusive and may or may not be supported by other published case reports or registry data, the intention is to sharpen the focus of clinicians on the potential for similar problems and thereby enhance clinical outcomes and patient safety. The “Watch” designation may also encourage others to report related difficulties and enlist the orthopaedic community to either demonstrate that these are isolated, unrelated cases or sharpen the focus further on rigorously evaluating the intervention. Where appropriate, we may identify brand, model, or implant-lot specifics. Of the five Watch articles that have been published in JBJS Case Connector, three—including this one—have focused on total hip arthroplasty (THA). Our very first Watch in September 2013 discouraged surgeons who implant dual-mobility hips from using a “mix-and-match” strategy with components from different manufacturers. Our January 2014 Watch about THA cautioned hip surgeons to be wary about using long-necked and skirted-head modular hip designs. In both of those Watch articles, we emphasized how head-neck modularity has helped orthopaedists achieve important biomechanical objectives—such as adjusting version, limb length, and offset—to maximize implant function and longevity. Modularity also facilitates easier revisions and lowers inventory costs. But we also made the point that modularity increases the number of interfaces at which corrosion can occur, making prosthetic materials more vulnerable to compression, shear forces, and bending stresses. The arthroplasty community currently feels that the advantages gained from modularity outweigh the risks, but we …