Abstract
Introduction: Reduction of ultra high molecular weight polyethylene (UHMWPE) surface wear in total knee replacement (TKR) bearings may delay the onset of osteolysis and subsequent loosening of components. The aim of this study was to compare the effect of bearing material on UHMWPE wear using a physiological knee simulator.
Methods: LCS Rotating Platform (RP) mobile bearing TKRs (DePuy) were investigated with standard and custom insert materials (Table 1). Testing was completed on a six-station force/displacement controlled knee simulator (frequency 1 Hz). Kinematic inputs consisted of 0 – 58° extension-flexion [1], maximum 2600 N axial force [1], -262 to 110 N anterior-posterior force [1] and ± 5° internal-external rotation [2]. The test lubricant was 25% (v/v) bovine serum with 0.1% (m/v) sodium azide solution in sterile water. Six components of each material were tested for up to five million cycles. The mean wear rates of the inserts were determined gravimetrically after every million cycles.
Results and Discussion: The higher molecular weight 1050 GP exhibited a higher wear rate than 1020 NI but the difference was not statistically significant (p > 0.05) (Fig. 1). The medium level of crosslinking in the Marathon GP inserts significantly reduced wear in comparison to the uncrosslinked 1050 GP material (p < 0.05) and moderate crosslinking in the 1020 GVF also decreased wear compared with the 1020 NI base material although this was not statistically significant. However, these differences would not be considered to be clinically significant. In addition, further work should be completed to assess the biological activity of the crosslinked materials as increased biological response may negate the benefit of decreased volumetric wear. All RP materials exhibited significantly reduced wear rates (p < 0.05) in comparison to fixed bearing TKR tested under equivalent high kinematic conditions [3]. The RP translates complex motions into more unidirectional motions, benefiting from reduced wear due to decreased cross-shear on the UHMWPE compared with more multidirectional fixed bearing TKR. Therefore, TKR design is an important factor for reduction of UHMWPE wear.
Correspondence should be addressed to Carlos Widgerowitz, Honorary Secretary BORS, Division of Surgery and Oncology, Section of Orthopaedic and Trauma Surgery, Ninewells Hospital and Medical School, Tort Centre, Dundee DD1 9SY, Scotland.
References
[1] ISO 14243 (1999) Google Scholar
[2] Lafortune MA et al (1992) J Biomech, 25, 347–357 Google Scholar
[3] McEwen HMJ et al (2001) J Mats Sci Mats in Med, 12, 1049–1052 Google Scholar
