Knee Wear Simulator Research Articles

In vitro wear assessments of fixed and mobile UHMWPE total knee replacement

This work discusses the wear behaviour of two different ultra-high-molecular-weight-polyethylene tibial component designs. Mobile and fixed bearings were tested on a knee wear simulator for 5 million cycles using bovine calf serum as lubricant. We correlated the wear results with the chemical characterisation of the investigated materials: Fourier Transformed Infra Red Spectroscopy analyses, Differential Scanning Calorimetry and cross-link density measurements were used to assess the chemical features of this polyethylene.Mobile and fixed polyethylene inserts showed a different wear behaviour: the mobile designs components showed lower weight losses than the fixed components (109±6mg and 163±80mg, respectively). Significant statistical differences were observed in wear rate (P=0.035, Kolmogorov–Smirnov Test for two samples).From a molecular point of view, typical radiation-induced oxidation profiles were observed in all the tested polyethylene samples, but the overall degradation was more significant in the fixed bearing inserts and this is likely to play a role on the wear performances.

Effect of anterior–posterior and internal–external motion restraint during knee wear simulation on a posterior stabilised knee design

The objective of our study was to examine the effect of biphaseal AP translation and IE rotation restraint, using a system defined specifically for posterior stabilised knee designs, on wear, kinematics and particle release in comparison to linear motion restraint as required by the established ISO 14243-1:2002(E) protocol. In the ISOlinear groups, an AP motion restraint of 30N/mm and an IE rotation restraint of 0.6Nm/° were applied in the knee wear simulation. In the ISOgap biphaseal groups with PCL sacrificing implants, the restraining AP force was zero in a ±2.5mm range with, externally, a constant of 9.3N/mm applied proportionally to the AP translation of the tibia plateau, whereas the restraining IE torque was zero in a ±6° range with, externally, a constant of 0.13Nm/° applied proportionally to the IE rotation of the tibia plateau. Using the ISOgap biphaseal protocol on a posterior stabilised knee design, we found an increase of 41% in AP translation and of 131% in IE rotation, resulting in a 3.2-fold higher wear rate compared to the results obtained using the ISOlinear protocol. Changes in AP translation and IE rotation ligament motion restraints have a high impact on knee joint kinematics and wear behaviour of a fixed bearing posterior stabilised knee design.

The use of Raman spectroscopy in the analysis of UHMWPE uni-condylar bearing systems after run on a force and displacement control knee simulators

The complications associated with prosthetic failure and revision surgery still constitute the main clinical problem. The objective of wear evaluation is to determine the wear rate and its dependence on the test conditions. To obtain realistic results, a wear test can be performed to reproduce in vivo working conditions and compare the wear characteristics of various total knee prostheses designs.Two knee wear simulators with different input control mechanisms, displacement and force controlled, were used to assess the wear behavior of ultra-high molecular weight polyethylene uni-condylar knee prostheses. The differences in wear behavior were assessed using a state-of-art coordinate measuring machine; Raman spectroscopy was used to evaluate the possible crystallinity changes on the uni-condylar menisci induced by mechanical stress. These results were compared with available uni-condylar retrievals.Scratches were visible along the anterior-posterior direction emphasizing that the motion was constant during the movements under the displacement control simulation. On the contrary, different kinematics schemes were observed under the force controlled simulation. The structural Raman markers showed a good correlation with the coordinate measuring machine data, and in particular with the depth of the concavity formed upon in vitro testing or in vivo service. With regards to the in vitro tested components, the specimens tested under force controlled simulator, which underwent a higher volumetric loss, showed a higher increase of the amorphous content. At a molecular level, the wear mechanism did not appear significantly different for the three sets of specimens, with the exception of the amorphous content which, upon wear, increased in the in vitro tested components, while decreased in the retrievals.

Definition and evaluation of testing scenarios for knee wear simulation under conditions of highly demanding daily activities

The objective of our study was the definition of testing scenarios for knee wear simulation under various highly demanding daily activities of patients after total knee arthroplasty. This was mainly based on a review of published data on knee kinematics and kinetics followed by the evaluation of the accuracy and precision of a new experimental setup.We combined tibio-femoral load and kinematic data reported in the literature to develop deep squatting loading profiles for simulator input. A servo-hydraulic knee wear simulator was customised with a capability of a maximum flexion of 120°, a tibio-femoral load of 5000N, an anterior–posterior (AP) shear force of ±1000N and an internal–external (IE) rotational torque of ±50Nm to simulate highly demanding patient activities.During the evaluation of the newly configurated simulator the ability of the test machine to apply the required load and torque profiles and the flexion kinematics in a precise manner was examined by nominal–actual profile comparisons monitored periodically during subsequent knee wear simulation.For the flexion kinematics under displacement control a delayed actuator response of approximately 0.05s was inevitable due to the inertia of masses in movement of the coupled knee wear stations 1–3 during all applied activities. The axial load and IE torque is applied in an effective manner without substantial deviations between nominal and actual load and torque profiles.During the first third of the motion cycle a marked deviation between nominal and actual AP shear load profiles has to be noticed but without any expected measurable effect on the latter wear simulation due to the fact that the load values are well within the peak magnitude of the nominal load amplitude.In conclusion the described testing method will be an important tool to have more realistic knee wear simulations based on load conditions of the knee joint during activities of daily living.

Calf serum constituent fractions influence polyethylene wear and microbial growth in knee simulator testing

Calf serum lubricants consisting of various polypeptide constituent fractions are routinely used in knee wear simulators as part of the standardized test protocol. Three calf sera (bovine, new-born and alpha) were diluted as per the recommendation of ISO 14243-3 and used in displacement-controlled knee wear simulators to investigate their effects on polyethylene wear. Biochemical analyses included measuring total polypeptide degradation, electrophoretic profiles and low-molecular weight polypeptide concentrations to elucidate their involvement in the wear process. The effects of the various calf sera constituent fractions on microbial growth were also explored. The polyethylene wear rates and the results from the biochemical analyses for the three calf serum lubricants were all found to be statistically significantly different from each other. The lubricant derived from the alpha-calf serum was closest in constituent fractions to human synovial fluid. It also showed the lowest polyethylene wear rate (14.38 +/- 0.85 mm3/million cycles) and the lowest amount of polypeptide degradation (7.77 +/- 3.87%). Furthermore, the alpha-calf serum lubricant was associated with the least amount of change in the electrophoretic profile, the least change in low-molecular weight polypeptide concentration, and the lowest microbial growth in the presence of sodium azide (a microbial inhibitor conventionally used in implant wear testing). Replacing sodium azide with a broad spectrum antibiotic-antimycotic eradicated the microbial growth. Some speculation was entertained regarding the effect of alpha-calf serum on colloid-mediated boundary lubrication. Based on the results, it was recommended that ISO 14243-3 be modified to include guidelines on calf serum constituent fractions that would favour using alpha-calf serum in order to improve the fidelity of the simulation in knee implant wear testing.

Computational development of a polyethylene wear model for the articular and backside surfaces in modular total knee replacements

A computational model to predict polyethylene wear in modular total knee replacements was developed. The results from knee simulator wear tests were implemented with finite element simulations to identify the wear factors of Archard's wear law. The calculated wear factor for the articular and backside surface was 1.03±0.22×10−7mm3/Nm and 2.43±0.52×10−10mm3/Nm, respectively. The difference in wear factors was attributed to differences in wear mode and wear mechanisms between the articular (mainly two-body rolling/sliding wear mode with an abrasive/adhesive wear mechanism) and the backside surfaces (mainly fretting wear mode with an adhesive wear mechanism).

Prediction of backside micromotion in total knee replacements by finite element simulation

The micromotion at the interface between the polyethylene tibial insert and metal tibial tray [corrected] in modular total knee replacements [corrected] has been shown to contribute to wear particle-induced osteolysis and may [corrected] cause implant failure. Therefore, studying the design parameters that are involved in the backside wear process is an important task that may lead to improvement in new total knee replacements. In the present study, a finite element model was developed to predict the backside micromotion along the entire modular interface. Both the linear elastic constitutive model and non-linear J2-plasticity constitutive model were considered in the finite element model for polyethylene and were corroborated against published results obtained from displacement controlled knee simulator wear tests. The finite element simulation with the non-linear J2-plasticity constitutive model was able to predict backside micromotion [corrected] more accurately than the simulation with the linear elastic constitutive model. [corrected] The developed finite element model (including the non-linear J2-plasticity constitutive model) was then applied to assess the effects of the tibial tray locking mechanism design (dovetails versus fullperipheral [corrected] design) and different levels of interference fit on insert micromotion. The developed finite element model, implementing the non-linear J2-plasticity constitutive model, was shown to successfully predict clinical amounts of backside micromotion and could be used for the design and development of total knee replacements for the reduction of backside micromotion and polyethylene [corrected] wear.

Wear of Polyethylene Against Oxidized Zirconium Femoral Components: Effect of Aggressive Kinematic Conditions and Malalignment in Total Knee Arthroplasty

Metallic femoral components with ceramic articulating surfaces can substantially lower polyethylene (PE) wear during walking activities under conditions of normal knee alignment. It is unknown whether these types of components can maintain low wear rates under conditions of knee malalignment and the harsher kinematics associated with younger, athletically active patients. Wear was measured in non–cross-linked, ethylene oxide–sterilized PE inserts against oxidized zirconium or cobalt-chrome femoral components in a knee wear simulator. The vertical load was modified to replicate knee varus malalignment of 3°, and the range of tibial rotation was increased to 20°. Mean gravimetric and volumetric wear rate over 5 million cycles was 55% lower in the oxidized zirconium group. An oxidized zirconium femoral component can significantly reduce PE wear under simulated conditions of athletically active patients with modestly malaligned total knee arthroplasty prostheses.

Mobile or fixed unicompartmental knee prostheses? In-vitro wear assessments to solve this dilemma

The unicompartmental knee prosthesis is an attractive alternative to total knee arthroplasty. Current UKP devices can be subdivided into two groups based on different design principles: fixed bearing knees, where the ultra-high molecular weight polyethylene meniscal component snap or press fits into the tibial tray, and mobile bearing designs which facilitate movement of the insert relative to the tray. The present study was aimed at comparing the in-vitro wear behaviour of fixed and mobile unicompartmental knee menisci under two configurations: the femoral components were cemented into a custom-made metallic block or, as a novelty of the present study, into a synthetic femur (i.e. under conditions which should better reproduce the in-vivo behaviour). Analyses were performed using a displacement-control knee wear simulator with “three-plus-one” stations. All the kinematics tests were set in accordance with the ISO 14243-1,2,3.Fixed and mobile polyethylene menisci showed a different wear behaviour: the fixation-frame influenced directional load transfer through each component in a qualitative and quantitative way. In fact, gravimetric results showed that under the metal block holder fixation, mobile components worn more than fixed components (weight losses of 8.7±2.0mg and 2.6±1.09mg, respectively); on the other hand, under the synthetic femur configuration, differences in wear behaviour were less pronounced and mobile menisci underwent a slightly lower weight loss than fixed components (4.5±2.2mg vs. 6.7±1.4mg). This different trend was explained in relation to the kinematic schemes of the two fixation methods.Raman spectroscopy, used to evaluate the UHMWPE crystallinity changes induced by mechanical stress, showed that mobile menisci specimens were more affected than the fixed components in both their superior and inferior surfaces, independent of the fixation-frame.In conclusion, if tested under conditions which should better reproduce the in-vivo behaviour, mobile UKPs did not show a worse wear behaviour than fixed components in terms of weight losses, although UHMWPE changes at the molecular scale could be detrimental.

Commissioning of a displacement-controlled knee wear simulator and exploration of some issues related to the lubricant

A six-station displacement-controlled knee simulator with separately controlled left (L) and right (R) banks (three wear implants per bank) was commissioned for a total of three million cycles (Mc) following ISO 14243-3. A commissioning protocol was applied to compare the polyethylene wear among the six wear stations by exchanging the implants between wear stations. Changes in lubricant characteristics during wear testing, such as polypeptide degradation, low-molecular-weight polypeptide concentration, and possible microbial contamination were also assessed. The total mean wear rate for the implants was 23.60 +/- 1.96 mm3/Mc and this was of a similar magnitude to the mean wear rate for the same implant tested under similar conditions by DePuy Orthopaedics Inc. (Warsaw, IN). Repeated run-in wear was observed when the implants were exchanged between wear stations, suggesting that implants should be subjected to the same wear station throughout the duration of a wear test. The total polypeptide degradation for the implants measured 30.53 +/- 3.96 percent; the low-molecular-weight polypeptide concentration of the "used" lubricant for implants (0.131 +/- 0.012 g/L) was 3.3 times greater than the mean polypeptide concentration of the fresh, "unused" lubricant (0.039 +/- 0.004 g/L). This increase in low-molecular weight polypeptide concentration was suggested to be attributable to protein shear in the articulation of the implant, the circulation of the lubricant, and some proteolytic activity. Sodium azide was ineffective in maintaining a sterile environment for wear testing as a single, highly motile Gram-negative micro-organism was identified in the lubricant from wear tests.

Knee Simulator Wear of Vitamin E Stabilized Irradiated Ultrahigh Molecular Weight Polyethylene

Wear and damage of ultrahigh molecular weight polyethylene (UHMWPE) tibial inserts used in total knee arthroplasty are accelerated by oxidation. Radiation crosslinking reduces wear but produces residual free radicals adversely affecting stability. One alternative to stabilize radiation-crosslinked UHMWPE is to infuse the material with vitamin E (vit E). We investigated the properties of 100-kGy e-beam–irradiated UHMWPE that was subsequently doped with vitamin E in comparison with conventional UHMWPE. Both polymers were sterilized with gamma irradiation in vacuum packaging. Vitamin E–doped UHMWPE showed lower wear before and after aging (2.4 ± 0.5 and 2.5 ± 0.8 mg/million cycle, respectively, vs 26.9 ± 3.5 and 40.8 ± 3.0 mg/million cycle for conventional UHMWPE). Conventional UHMWPE showed oxidation after accelerated aging, and its mechanical properties were adversely affected, whereas vit E–doped UHMWPE showed no oxidation or changes in its mechanical properties. Vitamin E stabilization of radiation-crosslinked UHMWPE resulted in low wear and high oxidation resistance; it is an alternative load-bearing material for total knee applications.

In Vitro Knee Wear, Kinematics, and Particle Morphology Among Different Bearing Geometries in a Mobile Bearing Knee System

Abstract Excellent clinical long term results were reported from individual clinical centers for both of the two fundamental design principles—fixed and mobile bearing knee designs. Several pre-clinical studies are dealing with a direct comparison between fixed and mobile bearing knee replacements, but to our knowledge there is no published data comparing the in vitro wear and kinematic behaviour of mobile bearing designs with floating, rotating and posterior stabilized gliding surfaces. The objective of our study was to evaluate the influence of the tibio-femoral bearing type on abrasive wear, tibio-femoral kinematics and particle release for a mobile bearing knee system with three different design alternatives. Wear simulator testing on 12 e.motion® TKA devices (Aesculap, Germany) was performed according to ISO 14243-1. The knee replacements were tested for 5 million cycles on a customized 4 station knee wear simulator (Endolab, Germany) in the bearing configurations floating platform (FP), ultra-concruent rotating platform (UC) and posterior stabilized (PS). The amount of wear in the polyethylene gliding surfaces was estimated to 4.4±0.9 mg/million cycles (FP design) to 2.3±0.1 mg/million cycles (UC) and 5.2±1.0 mg/million cycles (PS). The amplitudes of A/P displacement during 5 million cycles showed a mean value of 3.7±0.33 mm (FP design), 2.3±0.14 mm (UC) and 2.9±0.26 mm (PS). For the I/E rotation angle, the amplitudes of the recorded mean values were 6.3°±0.82° (FP design), 3.7±0.41° (UC) and 4.9°±0.48° (PS). The polyethylene particle release (mean size and morphology) is comparable for the mobile bearing articulations FP, UC, and PS. The present study demonstrates the influence of different mobile bearing types on abrasive wear, tibio-femoral kinematics, and particle release under elimination of bearing material influences.

The wear of fixed and mobile bearing unicompartmental knee replacements

Unicompartmental knee replacements (UKR) are an option for surgical intervention for the treatment of single-compartment osteoarthritis. The aim of this study was to compare the wear of a low-conformity fixed-bearing UKR with a conforming mobile bearing UKR under two kinematic conditions, to investigate the effect of implant design and kinematics on wear performance in a physiological knee wear simulator. Under both sets of kinematic conditions, the relatively low-conforming fixed UKR showed lower wear, compared with the more conforming anterior-posterior sliding mobile bearing. However, it should be noted that differences in materials between the two designs also contribute to the relative wear performance of the bearings. The combined wear of the medial and lateral bearings of the fixed-bearing UKR as a 'total knee' were significantly reduced compared with a fixed-bearing total knee replacement studied under the same kinematic conditions.

Mass Gain Behaviour of Tibial Polyethylene Inserts during Soak Testing

Fluid adsorption and the associated mass gain behaviour in tibial inserts of total knee replacements was investigated in polyethylene (PE) manufactured from extruded GUR 1050 resin. Repeatedly removing the PE inserts from the soak fluid for gravimetric assessment (including cleaning, desiccation, and weighing) increased the mass gain. Soaking PE inserts for 46 days or 92 days seemed to give about the same mass gain. PE inserts that were soaked at 37 degrees C gained more mass than PE inserts soaked at room-temperature. Gas-plasma sterilized PE inserts gained less mass than gamma-in-air sterilized PE inserts. No statistically significant differences were detected in mass gain between PE inserts that were of 10mm and 14mm thickness. The mass gain of PE inserts was higher in protein-rich soak fluid compared with low-ion distilled water. Prior to knee simulator wear testing, tibial PE inserts should be conditioned in the same medium and under the same test conditions (gravimetric assessment frequency, fluid protein content, and fluid temperature). This approach would help improve the accuracy and precision of the gravimetrically determined PE wear rate during knee simulator wear testing.

Targeted computational probabilistic corroboration of experimental knee wear simulator: The importance of accounting for variability

Experimental testing is widely used to predict wear of total knee replacement (TKR) devices. Computational models cannot replace this essential in vitro testing, but they do have complementary strengths and capabilities, which make in silico models a valuable support tool for experimental wear investigations. For effective exploitation, these two separate domains should be closely corroborated together; this requires extensive data-sharing and cross-checking at every stage of simulation and testing. However, isolated deterministic corroborations provide only a partial perspective; in vitro testing is inherently variable, and relatively small changes in the environmental and kinematic conditions at the articulating interface can account for considerable variation in the reported wear rates. Understanding these variations will be key to managing uncertainty in the tests, resulting in a ‘cleaner’ investigation environment for further refining current theories of wear. This study demonstrates the value of probabilistic in silico methods by describing a specific, targeted corroboration of the AMTI knee wear simulator, using rigid body dynamics software models. A deterministic model of the simulator under displacement-control was created for investigation. Firstly, a large sample of experimental data ( N > 100) was collated, and a probabilistic computational study ( N > 1000 trials) was used to compare the kinetic performance envelopes for in vitro and in silico models, to more fully corroborate the mechanical model. Secondly, corresponding theoretical wear-rate predictions were compared to the experimentally reported wear data, to assess the robustness of current wear theories to uncertainty (as distinct from the mechanical variability). The results reveal a good corroboration for the physical mechanics of the wear test rig; however they demonstrate that the distributions for wear are not currently well-predicted. The probabilistic domain is found to be far more sensitive at distinguishing between different wear theories. As such we recommend that in future, researchers move towards probabilistic studies as a preferred framework for investigations into implant wear.

Can the method of fixation influence the wear behaviour of ZrN coated unicompartmental mobile knee prostheses?

Background Modern unicompartmental knee prostheses represent a valid alternative to total knee replacement. It is known that variations in clinical alignment lead to altered biomechanics and abnormal wear. The aim of this study was to assess the influence, on wear behaviour, of two different cementing interfaces of the femoral components tested on a knee joint wear simulator. Methods The wear tests were run in a knee wear simulator at a frequency of 1.1 Hz for 3 million cycles in accordance with ISO 14243-3. Twelve commercial mobile GUR 1020 UHMWPE meniscus specimens articulated in between 12 cobalt–chromium–molybdenum alloy femoral and tibial components covered by a multi-layer of chromium nitride and a final layer of zirconium nitride ceramic coating to prevent ion release from the substrate. Two wear tests were performed: in the first test, each femoral component was cemented into a custom made metallic-block shaped to perfectly host it. In the second test, synthetic composite femurs received the femoral components on the basis of guidelines used in current surgery. Findings The two cementing interfaces showed a significantly different wear behaviour, quantified as mean weight loss ( P < 0.001). Scanning electron microscope examinations of new and tested metallic components showed macro- and micro-pores of few microns on both configurations. Interpretation The wear pattern observed at 3 million cycles showed differences between the two methods of fixation for the meniscus femoral components.

Biochemical comparisons of osteoarthritic human synovial fluid with calf sera used in knee simulator wear testing

Osteoarthritic human synovial fluid was obtained from the knees of 20 patients and was compared with four different calf sera solutions frequently used as lubricants in knee simulator wear testing. Assuming that the fluid after arthroplasty was the same as the fluid in patients with osteoarthritis, the total protein concentration, protein constituent fractions, osmolality, trace element concentrations, and the thermal stability obtained via differential scanning calorimetry were determined. Human synovial fluid, with an average total protein concentration of 34 g/L, was significantly different from all undiluted calf sera. However, alpha-calf serum and iron-supplemented alpha-calf serum were closest in protein constituent fractions (albumin, alpha-1-globulin, alpha-2-globulin, ss-globulin, and gamma-globulin) to human synovial fluid. Diluting calf sera with low-ion distilled water to a total protein concentration of 17 g/L (as recommended by ISO 14243) produced non-clinically relevant total protein concentration and osmolality levels. Performing the same dilution of iron-supplemented alpha-calf serum with phosphate-buffered saline solution and 1.5 g/L hyaluronic acid produced an artificial lubricant with both a clinically relevant level of osmolality and clinically relevant thermal stability as seen in human synovial fluid from patients with osteoarthritis. The present study suggested that alpha-calf serum, phosphate-buffered saline solution and hyaluronic acid were essential constituents of an artificial lubricant to mimic the major biochemical properties of human synovial fluid for simulator wear testing of total knee replacements.

Highly Crosslinked Polyethylene in Posterior-Stabilized Total Knee Arthroplasty: In Vitro Performance Evaluation of Wear, Delamination, and Tibial Post Durability

Recent advances in total knee arthroplasty (TKA) include the development of highly crosslinked polyethylene (HXPE). To assess the suitability of using HXPE in posterior-stabilized TKA, knee simulator wear testing and a novel tibial post durability test were performed on a modern posterior-stabilized implant design with both conventional polyethylene (CPE) and HXPE materials. The laboratory testing reproduced clinically relevant wear and tibial post damage mechanisms. For the designs tested, wear volume was reduced by 67% to 75% for aged HXPE compared with aged CPE. Components of HXPE also demonstrated superior tibial post durability compared with the CPE design, despite the use of unaged material to represent best-case CPE tibial post strength. With appropriate design considerations, HXPE can be successfully incorporated into a posterior-stabilized TKA.

Biotribology of alternative bearing materials for unicompartmental knee arthroplasty

The objective of our wear simulator study was to evaluate the suitability of two different carbon fibre-reinforced poly-ether-ether-ketone (CFR-PEEK) materials for fixed bearing unicompartmental knee articulations with low congruency. In vitro wear simulation was performed according to ISO 14243-1:2002 (E) with the clinically introduced Univation F fixed bearing unicompartmental knee design (Aesculap AG, Tuttlingen, Germany) made of UHMWPE/CoCr29Mo6 in a direct comparison to experimental gliding surfaces made of CFR-PEEK pitch and CFR-PEEK PAN. Gliding surfaces of each bearing material (n=6+2) were gamma-irradiated, artificially aged and tested for 5 million cycles with a customized four-station knee wear simulator (EndoLab, Thansau, Germany). Volumetric wear assessment, optical surface characterization and an estimation of particle size and morphology were performed. The volumetric wear rate of the reference PE1-6 was 8.6 +/- 2.17 mm(3) per million cycles, compared to 5.1+/-2.29 mm(3) per million cycles for PITCH1-6 and 5.2 +/- 6.92 mm(3) per million cycles for PAN1-6; these differences were not statistically significant. From our observations, we conclude that CFR-PEEK PAN is obviously unsuitable as a bearing material for fixed bearing knee articulations with low congruency, and CFR-PEEK pitch also cannot be recommended as it remains doubtful wether it reduces wear compared to polyethylene. In the fixed bearing unicompartmental knee arthroplasty examined, application threshold conditions for the biotribiological behaviour of CFR-PEEK bearing materials have been established. Further in vitro wear simulations are necessary to establish knee design criteria in order to take advantage of the biotribiological properties of CFR-PEEK pitch for its beneficial use to patients.

Effect of joint laxity on polyethylene wear in total knee replacement

Experimental simulator studies are frequently performed to evaluate wear behavior in total knee replacement. It is vital that the simulation conditions match the physiological situation as closely as possible. To date, few experimental wear studies have examined the effects of joint laxity on wear and joint kinematics and the absence of the anterior cruciate ligament has not been sufficiently taken into account in simulator wear studies. The aim of this study was to investigate different ligament and soft tissue models with respect to wear and kinematics. A virtual soft tissue control system was used to simulate different motion restraints in a force-controlled knee wear simulator. The application of more realistic and sophisticated ligament models that considered the absence of anterior cruciate ligament lead to a significant increase in polyethylene wear ( p=0.02) and joint kinematics ( p<0.01). We recommend the use of more complex ligament models to appropriately simulate the function of the human knee joint and to evaluate the wear behavior of total knee replacements. A feasible simulation model is presented.