Does Kinematic Alignment Increase Polyethylene Wear Compared With Mechanically Aligned Components? A Wear Simulation Study.

BACKGROUND: Kinematic alignment is an alternative approach to mechanical alignment. Kinematic alignment can restore the joint line to its prearthritic condition, and its advocates have suggested it may be associated with other benefits. But this alignment approach often results in tibial components that are placed in varus and femoral components that are placed in valgus alignment, which may result in an increased risk of component loosening because of wear. Like malaligned implant components, kinematically aligned knee implants could increase wear in vivo, but we lack comparative data about wear behavior between these approaches. QUESTIONS/PURPOSES: (1) Do the different alignment approaches (kinematic, mechanical, and purposefully malaligned components) result in different wear rates in a wear simulator? (2) Do the different alignment approaches lead to different worn areas on the polyethylene inserts in a wear simulator? (3) Do the different alignment approaches result in different joint kinematics in a wear simulator? METHODS: Mechanical alignment was simulated in a force-controlled manner with a virtual ligament structure according to the International Organization for Standardization (ISO 14243-1) using a knee wear simulator. To simulate kinematic alignment, flexion-extension motion, internal-external torque, and the joint line were tilted by 4°, using a novel mechanical setup, without changing the force axis. The setup includes bearings with inclinations of 4° so that the joint axis of 4° is determined. To verify the angle of 4°, a digital spirit level was used. To simulate malalignment, we tilted the implant and, therefore, the joint axis by 4° using a wedge with an angle of 4° without tilting the torque axes of the simulator. This leads to a purposefully malaligned tibial varus and femoral valgus of 4°. For each condition, three cruciate-retaining knee implants were tested for 3.0 x 10 6 cycles, and one additional implant was used as soak control. Gravimetric wear analyses were performed every 0.5 x 10 6 cycles to determine the linear wear rate of each group by linear regression. The wear area was measured after 3.0 x 10 6 cycles by outlining the worn areas on the polyethylene inserts, then photographing the inserts and determining the worn areas using imaging software. The joint kinematics (AP translation and internal-external rotation) were recorded by the knee simulator software and analyzed during each of the six simulation intervals. RESULTS: Comparing the wear rates of the different groups, no difference could be found between the mechanical alignment and the kinematic alignment (3.8 ± 0.5 mg/million cycles versus 4.1 ± 0.2 mg/million cycles; p > 0.99). However, there was a lower wear rate in the malaligned group (2.7 ± 0.2 mg/million cycles) than in the other two groups (p < 0.01). When comparing the total wear areas of the polyethylene inserts among the three different alignment groups, the lowest worn area could be found for the malaligned group (716 ± 19 mm 2 ; p ≤ 0.003), but there was no difference between kinematic alignment and mechanical alignment (823 ± 19 mm 2 versus 825 ± 26 mm 2 ; p > 0.99). Comparing the AP translation, no difference was found between the mechanical alignment, the kinematic alignment, and the malalignment group (6.6 ± 0.1 mm versus 6.9 ± 0.2 mm versus 6.8 ± 0.3 mm; p = 0.06). In addition, the internal-external rotation between mechanical alignment, kinematic alignment, and malalignment also revealed no difference (9.9° ± 0.4° versus 10.2° ± 0.1° versus 10.1° ± 0.6°; p = 0.44). CONCLUSION: In the current wear simulation study, the wear rates of mechanical alignment and kinematic alignment of 4° were in a comparable range. CLINICAL RELEVANCE: The results suggest that kinematic alignment with up to 4° of component inclination may give the surgeon confidence that the reconstruction will have good wear-related performance when using a modern cruciate-retaining implant. The malaligned group had the lowest wear rate, which may be a function of the smaller worn area on the inserts compared with the other two alignment groups. This smaller articulation area between the femoral condyles and polyethylene insert could increase the risk of delamination of malaligned components over longer test durations and during high-load activities. For that reason, and because malalignment can cause nonwear-related revisions, malalignment should be avoided. Further in vitro and clinical studies must prove whether the wear simulation of different alignments can predict the wear behavior in vivo.

Wear investigation based on a novel, anatomic shoulder prosthesis with bearing materials inversion.

INTRODUCTION: In shoulder arthroplasty, ultra-high-molecular-weight polyethylene is used as standard material for glenoid components. The emergence of wear particles and their influence on the aseptic loosening of joint replacements are well known. The aim of the present study is to investigate the wear behaviour of the implant combinations as well as the size and morphology of the released wear particles from novel anatomic shoulder prosthesis. Here, the main interest lies on the influence of material inversion and different conformities on wear behaviour. METHODS: Wear simulation was performed using a force-controlled joint simulator. The Modular-Shoulder-System from Permedica S.p.A. Orthopaedics was studied. Polyethylene wear was determined gravimetrically and was characterised by particle analysis. An abduction-adduction motion of 0°-90° lifting a load of 2 kg superimposed by an ante-/retroversion was chosen as the activity. In addition, an extreme test was performed to simulate subluxation of the joint. RESULTS: The results showed a wear reduction of approximately 70% and a significant decrease in the total number of wear particles due to the material inversion on the bearing materials. No reduction of wear could be determined by varying the conformity of the bearing partners. In the simulated subluxation, the material inversion shows an increase in wear. CONCLUSION: Compared to similarly investigated systems, the Modular-Shoulder-System shows a reduction in wear. This reduction shows that material inversion may lead to a wear reduction. However, if subluxation of the humeral head occurs more frequently, increased material wear can be expected with the Modular-Shoulder-System. An influence of the conformity on the wear behaviour could not be determined.

Quantitative Measurements of Backside Wear in Acetabular Hip Joint Replacement: Conventional Polyethylene Versus Cross-Linked Polyethylene.

As shown in previous studies, the modification of conventional polyethylene (CPE) to cross-linked polyethylene (XLPE) and the contribution of antioxidants result in a reduction in total wear. The aim of this study was to evaluate XLPE inserts with vitamin E and CPE regarding their resistance to the backside wear mechanism. A cementless hip cup system (Plasmafit® Plus 7, Aesculap) was dynamically loaded using CPE and XLPE inserts. The backside wear was isolated, generated and collected using the two-chamber principle. The chambers were filled with ultrapure water. After 2 × 106 cycles, the fluids were examined for wear particles according to a particle analysis. Using XLPE inserts, the backside wear was significantly reduced by 35%. While XLPE backside wear particles are significantly larger than CPE particles, they do not differ in their morphology. This study confirms the greater resistance to backside wear of XLPE compared to CPE. It can be assumed that the improved fatigue resistance of the vitamin E-stabilized XLPE inserts demonstrates XLPE's effectiveness against micro-motion and the resulting changing tensions in interface areas like surface breakdown, pitting and the release of very small particles.

Comparison of Different Locking Mechanisms in Total Hip Arthroplasty: Relative Motion between Cup and Inlay.

The resulting inflammatory reaction to polyethylene (PE) wear debris, which may result in osteolysis, is still considered to be a main reason for aseptic loosening. In addition to the primary wear in hip joint replacements caused by head-insert articulation, relative motions between the PE liner and the metal cup may cause additional wear. In order to limit this motion, various locking mechanisms were used. We investigated three different locking mechanisms (Aesculap, DePuy, and Zimmer Biomet) to address the resulting relative motion between the acetabular cup and PE liner and the maximum disassembly force. A standardized setting with increasing load levels was used in combination with optically based three-dimensional measurements. In addition the maximum disassembly forces were evaluated according to the ASTM F1820-13 standard. Our data showed significant differences between the groups, with a maximum relative motion at the maximum load level (3.5 kN) of 86.5 ± 32.7 µm. The maximum axial disassembly force was 473.8 ± 94.6 N. The in vitro study showed that various locking mechanisms may influence cup-inlay stability.

Carbon-fibre-reinforced PEEK: An alternative material for flexion bushings of rotating hinged knee joints?

BACKGROUND: For prosthetic knee joints of the hinged type, typically polyethylene (PE) flexion bushings are used between axis and femoral component to prevent metallic wear. Nevertheless, PE-wear can lead to periprosthetic osteolysis followed by aseptic loosening of the implant. Based on high creep and wear resistance carbon-fibre-reinforced polyether ether ketones (CFR-PEEKs) could provide an alternative material to ultra-high-molecular-weight polyethylene (UHMWPE) for this bearing type. METHODS: Flexion bushings of four different materials were investigated (CFR-PEEK pitch fibres, CFR-PEEK PAN fibres, virgin PEEK without carbon fibres and UHMWPE) using a bushing tester. For determination of the polymeric and metallic wear, gravimetric measurements and particle analyses were performed. RESULTS: The polymeric wear rates of CFR-PEEK PAN (6.657 ±â€¯0.714 mg/106 cycles) and CFR-PEEK pitch (32.085 ±â€¯2.748 mg/106 cycles) were significantly higher compared to the polymeric wear rates of virgin PEEK (0.764 ±â€¯0.283 mg/106 cycles) or UHMWPE (-0.015 ±â€¯0.011 mg/106 cycles) (p < .001). In addition, the metallic wear rates were significantly higher when using bushings made of CFR-PEEK PAN (3.373 ±â€¯0.214 mg/106 cycles) and CFR-PEEK pitch (3.604 ±â€¯0.355 mg/106 cycles), than when using bushings made of virgin PEEK (0.177 ±â€¯0.049 mg/106 cycles) or UHMWPE (0.031 ±â€¯0.011 mg/106 cycles) (p < .001). The mean particle size of the two CFR-PEEK groups was significantly smaller compared to the virgin PEEK and UHMWPE group (p < .001). CONCLUSION: According to these results, the clinical use of CFR-PEEK in combination with CoCr could lead to higher wear rates and this should be avoided. Virgin PEEK may still be considered as an alternative to UHMWPE to use it for flexion bushings in a hinged knee joint.

Particle analysis of shape factors according to American Society for Testing and Materials.

Polyethylene wear is one of the major factors influencing the survivorship of joint replacements. Depending on the number, size and morphology of the polyethylene particles, biological responses of the periprosthetic soft tissue in terms of inflammatory processes can occur, leading to loosening of the implant. Various parameters are used to analyze wear particles, which are usually determined by examining scanning electron microscopy (SEM) images with a particle analysis program. In this study, three different software solutions for particle analysis (self-developed Particleanalyzer_HD, Leica QWin and ImageJ) were compared regarding particle number, size and morphology. These solutions were also compared to the American Society for Testing and Materials (ASTM) F1877-16 specifications regarding particle morphology. SEM image analysis revealed no differences for the equivalent circle diameter (p = 0.969). However, a significant difference was found for the aspect ratio between the Particleanalyzer_HD and the other two software solutions (p < 0.001) and between Leica QWin and the other two software solutions regarding the roundness (p < 0.001). Only the Particleanalyzer_HD showed an excellent agreement with the ASTM standard for both morphology parameters (intraclass correlation = 1.000). Only the Particleanalyzer_HD calculated the two morphology parameters according to the ASTM standard. A comparison of the particle morphology between different studies is barely possible, as different algorithms for particle analysis are used. It is strongly recommended that the calculation according to the ASTM standard is used to improve future comparability of findings from wear analysis studies. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:225-233, 2020.

Titanium Acetabular Component Deformation under Cyclic Loading.

Acetabular cup deformation may affect liner/cup congruency, clearance and/or osseointegration. It is unclear, whether deformation of the acetabular components occurs during load and to what extent. To evaluate this, revision multi-hole cups were implanted into six cadaver hemipelvises in two scenarios: without acetabular defect (ND); with a large acetabular defect (LD) that was treated with an augment. In the LD scenario, the cup and augment were attached to the bone and each other with screws. Subsequently, the implanted hemipelvises were loaded under a physiologic partial-weight-bearing modality. The deformation of the acetabular components was determined using a best-fit algorithm. The statistical evaluation involved repeated-measures ANOVA. The mean elastic distension of the ND cup was 292.9 µm (SD 12.2 µm); in the LD scenario, 43.7 µm (SD 11.2 µm); the mean maximal augment distension was 79.6 µm (SD 21.6 µm). A significant difference between the maximal distension of the cups in both scenarios was noted (F(1, 10) = 11.404; p = 0.007). No significant difference was noted between the compression of the ND and LD cups, nor between LD cups and LD augments. The LD cup displayed significantly lower elastic distension than the ND cup, most likely due to increased stiffness from the affixed augment and screw fixation.

Backside wear, particle migration and effectiveness of screw hole plugs in acetabular hip joint replacement with cross-linked polyethylene.

In total hip arthroplasty, osteolysis of the acetabulum often occurs at the backside of cups in the area of screw holes, indicating a clinically relevant amount of polyethylene (PE) wear particles in this area. In order to avoid a possible migration of wear particles to the acetabulum-bone, screw hole plugs are provided for some implant systems. The aims of this study were to quantitatively determine backside wear and to investigate the migration behaviour of articulation-related wear particles in a cup system with open and closed screw holes by plugs. Titanium cup systems with backside holes for screw fixations were sinusoidally loaded with 2.7 kN. The articulation area was separated from the backside area of the cup. A defined amount of articulation-generated particles was added to the fluid of the articulation chamber. The fluids in the two chambers were separately filtered after 2 × 106 cycles for a particle analysis. Backside wear with noticeably small (65.6 ±â€¯4.2 nm) and round PE particles was identified. With both open and closed screw holes, a migration of the articulating wear particles from the articulation area behind the cup could be observed. Backside wear was estimated to be below 1% of the articulated wear. Screw hole plugs did not effectively prevent the migration of PE wear particles behind the investigated cups. STATEMENT OF SIGNIFICANCE: Backside wear occurs in a proven cup-system. Furthermore, it was quantitatively observed that articulation-generated wear products could migrate from the articulating area along the cup/liner-interface through the screw holes behind the cup. An almost unimpeded particle migration to the acetabulum-bone, in conjunction with very small backside wear particles, could produce a clinically relevant amount of PE with respect to pelvic lysis. These findings highlight the importance of management to avoid particle migration in artificial hip cups. Therefore, primarily the use of screw hole plugs, as far as available for the respective cup-system, is recommended. The aim of avoiding particle migration by plugs, but also by using a sophisticated anchoring mechanism between cup and PE liner should continue in future.

Electrocautery Damage Can Reduce Implant Fatigue Strength: Cases and in Vitro Investigation.

BACKGROUND: The risk of femoral stem fracture after total hip replacement is low and can often be associated with a specific implant system or other factors that may reduce the fatigue strength. Additionally, damage to a metal component during revision surgery by an electrocautery device may further affect the fatigue behavior. METHODS: Two clinical cases of stem failure after revision of fractured ceramic components are presented; the retrieved components were analyzed for the cause of failure. In vitro cyclic load-to-failure testing of titanium alloy femoral stems after electrocautery application at 2 different locations (at the base and about midway on the femoral neck) was performed using a stepwise increase in load until implant fracture occurred. In addition, a detailed characterization of the local material structure around the electrocautery marks was performed. RESULTS: Superficial discoloration and melting marks were found on the retrieved components, including at the location of crack initiation in the anterolateral region, which may have reduced the fatigue strength of the material. In addition, elemental analysis indicated material transfer from the electrocautery tip. Damage to the surface by the electrocautery device significantly reduced the in vitro load to failure by up to 47% compared with that of undamaged femoral neck specimens. Material analysis revealed a relevant modification in microstructure, with an extension of approximately 2.7 mm and a depth of 550 µm, which could be divided in 3 structural zones. CONCLUSIONS: Intraoperative electrocautery device contact with the implant during surgical revision of a total hip replacement cannot always be avoided. However, on the basis of our findings, the risk of implant failure is increased due to a change in microstructure and a potential reduction of the implant's fatigue strength. Surgeons and manufacturers of electrocautery devices should be aware of this concern. CLINICAL RELEVANCE: During revision surgery, contact between an electrocautery device and the femoral component should be avoided to reduce the chance of subsequent femoral neck fracture.

Backside wear in acetabular hip joint replacement.

INTRODUCTION: Besides head-insert articulation in hip joint replacements, micro-motions between the backside of assembled polyethylene acetabular liners and the metal cup may cause additional wear. Pelvic osteolysis frequently occurs in the region of screw holes, and cup loosening hints to clinically relevant amounts of polyethylene backside wear. It has yet to be confirmed whether backside wear particles differ in size and morphology compared to articulating wear. Previous methods have been limited to subjective assessment of backside surface damages without consideration of wear debris. The aim of this study was to develop and validate a method for quantitative in vitro measurements of polyethylene backside wear in artificial hip cups and to characterize these wear particles for the first time. METHODS: Titanium cup-systems (Plasmafit®Plus7, Aesculap, UHMWPE liner) were sinusoidally loaded (2.5 kN) and a torque of 5 Nm was simultaneously applied. The front and rear side of the cup were separated to isolate backside wear. After 2 × 106 cycles the surrounding fluid was filtered and a particle analysis was performed. RESULTS: Backside wear had a particles size of 64.1 ±â€¯1.9 nm and was verified as round and oval particles with partly rough outlines. An estimated total number of particles of 1.26 × 109 ±â€¯1.67 × 108 per 106 cycles was determined. CONCLUSION: Backside wear was estimated to be several times lower than published values of articulating wear. However, polyethylene backside wear particles represented significantly smaller particles with partly roughened outlines than articulating wear particles and may therefore cause higher biological response in macrophage-mediated bone resorption compared to articulated particles. STATEMENT OF SIGNIFICANCE: Within this study, an analytical method for quantitative measuring polyethylene backside wear of artificial hip cups was successfully developed and validated for the first time. It could be shown that backside wear is still present, even in modern cup-systems. These findings can be further used for investigations of the osteolytic potential of polyethylene particles, for evaluating and improving new implant systems and to evaluate the effectiveness of screw hole plugs to prevent the particle migration to the acetabulum.

The subchondral bone layer and glenoid implant design are relevant for primary stability in glenoid arthroplasty.

BACKGROUND: Clinical studies suggest that reaming of the subchondral bone layer to achieve good implant seating is a risk factor for glenoid loosening. This study aims to evaluate (1) the importance of the subchondral bone layer and (2) the influence of the design of the glenoid component. METHODS: Different techniques for preparation of an A1 glenoid were compared: (1) preserving the subchondral bone layer; (2) removal of the subchondral bone layer; (3) implantation of a glenoid component that does not adapt to the native anatomy. Artificial glenoid bones (n = 5 each) were used with a highly standardized preparation and implantation protocol. Biomechanical testing was performed during simulated physiological shoulder motion. Using a high-resolution optical system, the micromotions between implant and bone were measured up to 10,000 motion cycles. RESULTS: At the 10,000 cycle measuring point, significantly more micromotions were found in the subchondral layer removed group than in the subchondral layer preserved group (p = 0.0427). The number of micromotions in the nonadapted group was significantly higher than in the subchondral layer preserved group (p = 0.0003) or the subchondral layer removed group (p = 0.0207). CONCLUSION: Conservative reaming proved important to diminish the micromotions of the glenoid component. Implantation of a glenoid component that matches with the bony underlying glenoid can help to preserve the subchondral bone layer without sacrificing proper implant seating.

Influence of joint kinematics on polyethylene wear in anatomic shoulder joint arthroplasty.

BACKGROUND: Despite the positive results in total shoulder arthroplasties (TSAs), a higher revision rate is documented compared with total hip and knee replacements. Wear is the possible main cause of TSA failure in the long-term. This study investigated the effect of joint kinematics and the influence of the rotator cuff on the polyethylene wear performance in an anatomic TSA. METHODS: Lifting a load of 2 kg with an abduction/adduction of 0° to 90° was simulated for 2 × 106 cycles as a primary motion using a fully kinematic joint simulator. A combined rotation in anteversion-retroversion of ±5° and ±10° was also simulated. The force in the superior-inferior direction and the axial joint compression were applied under force control based on in vivo data of the shoulder. A soft tissue restraint model was used to simulate an intact and an insufficient rotator cuff. RESULTS: The highest wear rate in the intact rotator cuff group was 58.90 ± 1.20 mg/106 cycles with a combined rotation of ±10°. When an insufficient rotator cuff was simulated, the highest polyethylene wear rate determined was 79.67 ± 4.18 mg/106 cycles. CONCLUSIONS: This study confirms a high dependency of the polyethylene wear behavior and dimension on the joint kinematics in total shoulder replacement. This can be explained by an increasing cross-shear stress on the polyethylene component. The results obtained indicate that additional combined kinematics are an indispensable part of wear tests on anatomic shoulder replacements.

Replacement options for the B2 glenoid in osteoarthritis of the shoulder: a biomechanical study.

BACKGROUND: Glenoid replacement in cases of severe glenoid retroversion (RV) or eccentric wear is challenging. The aim of this study was to evaluate different treatment methods under standardized conditions to assist surgeons in the decision-making process. METHODS: Three treatment options for severe glenoid RV (15°) were compared: (1) no RV correction; (2) complete RV correction; (3) no RV correction and implantation of a posterior augmented glenoid (PAG). A highly standardized implantation protocol using artificial glenoid bones (five per group) was chosen, and a physiologic shoulder movement was applied in a biomechanical setting. Micromotions (MM) between glenoid components and bone were quantified using an optical 3D measuring system. RESULTS: In the uncorrected retroversion group, three instances of subluxation of the prosthetic head occurred between 2000 and 4000 cycles. At 2000 cycles, significantly more MM were observed in the uncorrected RV group than in the corrected RV group (p < 0.0001) or to the augmented group (p < 0.0001). At 10|000 cycles, more MM were observed in the posterior augmented group than in the corrected RV group (p < 0.0001). CONCLUSION: If sufficient bone stock is available, retroversion correction should be favored. Posterior augmented glenoids seem to be a suitable treatment option if complete correction of the retroversion is not possible without compromising the glenoid vault. Without correction of the retroversion, high failure rates were observed.

Mixing of Head-Stem Components in Total Hip Arthroplasty.

BACKGROUND: Implant manufacturers proclaim that the tapers of modular total hip arthroplasty are not standardized and can vary from manufacturer to manufacturer. That is why the combination of various components from different manufacturers ("Mix and Match") is not permitted. In this study, different taper combinations were investigated experimentally to assess the effect of "Mix and Match" regarding the taper connection strength. METHODS: Torque-off tests using hip stems and metal femoral heads from 6 different implant manufacturers were performed. First the components were tested as intended and afterwards the stems were combined with metal heads from other manufacturers. RESULTS: There was no significant difference in taper connection strength when stems from the manufacturers Link, Smith & Nephew, and Zimmer were combined with heads from other manufacturers. The Biomet stems showed a significantly reduced taper connection strength if femoral heads of Aesculap, DePuy, or Smith & Nephew were used. On the contrary, the DePuy stems in combination with the originally intended femoral heads showed a significantly lower taper connection strength compared to the use of heads from Link, Biomet, and Zimmer. The same was observed for the Aesculap stems in combination with Zimmer heads. CONCLUSION: The results of this study suggest that mixing components from different manufacturers may affect the taper connection strength and could reduce the stability. As safety should be a high priority in patient treatment, any potential risks should be avoided. Therefore, mixing and matching of heads and femoral stems from different manufacturers cannot be recommended.

Three-dimensional friction measurement during hip simulation.

OBJECTIVES: Wear of total hip replacements has been the focus of many studies. However, frictional effects, such as high loading on intramodular connections or the interface to the bone, as well as friction associated squeaking have recently increased interest about the amount of friction that is generated during daily activities. The aim of this study was thus to establish and validate a three-dimensional friction setup under standardized conditions. MATERIALS AND METHODS: A standard hip simulator was modified to allow for high precision measurements of small frictional effects in the hip during three-dimensional hip articulation. The setup was verified by an ideal hydrostatic bearing and validated with a static-load physical pendulum and an extension-flexion rotation with a dynamic load profile. Additionally, a pendulum model was proposed for screening measurement of frictional effects based on the damping behavior of the angular oscillation without the need for any force/moment transducer. Finally, three-dimensional friction measurements have been realized for ceramic-on-polyethylene bearings of three different sizes (28, 36 and 40 mm). RESULTS: A precision of less than 0.2 Nm during three-dimensional friction measurements was reported, while increased frictional torque (resultant as well as taper torque) was measured for larger head diameters. These effects have been confirmed by simple pendulum tests and the theoretical model. A comparison with current literature about friction measurements is presented. CONCLUSIONS: This investigation of friction is able to provide more information about a field that has been dominated by the reduction of wear. It should be considered in future pre-clinical testing protocols given by international organizations of standardization.

Influence of humeral head material on wear performance in anatomic shoulder joint arthroplasty.

BACKGROUND: The number of total shoulder arthroplasties has increased in the past years, with encouraging results. However, the survival of anatomic total shoulder arthroplasty (aTSA) is lower compared with that of knee and hip replacements. Wear-associated problems like loosening are well-known causes of long-term failure of aTSA. The main purpose of this study was to investigate the wear behavior of ceramic-polyethylene bearings compared with the standard metal-polyethylene bearings. Because there is a lack of valid experimental wear testing methods, the secondary aim was to develop a validated wear simulation. METHODS: The wear assessment was performed using a force-controlled joint simulator for 3 × 106 cycles, and polyethylene wear was assessed gravimetrically and by particle analysis. Kinetic and kinematic data were adopted from in vivo loading measurements and from several clinical studies on shoulder joint kinematics. The reaction of the rotator cuff was simulated on the basis of a virtual soft tissue model. As activity, an abduction-adduction motion of 0°-90° lifting a load of 2 kg superimposed by an anteversion-retroversion has been chosen. RESULTS: The studied aTSA resulted in a polyethylene wear rate of 62.75 ± 1.60 mg/106 cycles in combination with metallic heads. The ceramic heads significantly reduced the wear rate by 26.7% to 45.99 ± 1.31 mg/106. There were no relevant differences in terms of the particle characteristics. CONCLUSION: This is the first study that experimentally studied the wear behavior of aTSA based on patient-related and biomechanical data under load-controlled conditions. Regarding polyethylene wear, the analyzed aTSA could benefit from ceramic humeral heads.

Same Same but Different? 12/14 Stem and Head Tapers in Total Hip Arthroplasty.

BACKGROUND: Taper corrosion has been identified to be a major concern in total hip arthroplasty during the past years. So far, the mechanisms that lead to taper corrosion in modular taper junctions are not fully understood. However, it has been shown that corrosion is also influenced by the geometry and topography of the taper, and these parameters vary among the implant manufacturers. The purpose of this study was to investigate the variations of common stem and head tapers regarding design and surface characteristics. METHODS: An analysis of selected commercially available 12/14 stem and head tapers was performed. As geometric parameters, the taper angle, the opening taper diameter, and the taper length were measured using a coordinate measuring machine. Several topographic parameters were determined using a tactile roughness measurement instrument. RESULTS: Although all investigated tapers are so-called 12/14 tapers, this study showed that the stem and head tapers differ among the manufacturers. The stem tapers were clearly different in both geometry and topography, and the range in variation of the topographic parameter was greater than it was for the geometric parameter. In contrast, the head tapers were different in their geometry, although not in topography. CONCLUSION: Ultimately, this study provides an overview on the characteristics and variations of modular hip taper connections, and in addition, a new classification system regarding the surface finish is presented. These findings could be further considered in experimental corrosion or retrieval studies.