AN ANALYSIS OF THREE MOBILE KNEE BEARINGS RETRIEVED AT THE TIME OF REVISION SURGERY

Abstract

Introduction: The transition from fixed bearing to mobile bearing total replacements represents a recent trend in Australia with the introduction of many new designs. The complex kinematics of mobile bearing designs coupled with the importance of proper surgical techniques including soft tissue balancing presents a number of factors that may influence the short and long-term success of these implants. There have been few reports in the literature on the performance of many of the new mobile bearing design with regards to initial wear of the polyethylene (PE) insert.

Aim: To investigate the patterns of wear on three mobile bearing knee PE inserts that had been retrieved soon after implantation.

Methods: Three mobile bearing knee PE inserts were retrieved at the time of revision surgery and submitted to our laboratory for examination. The proximal and distal articulating surfaces were examined by measuring surface roughness (Ra) using a Surfanalyzer (5400 (Federal Products Co., Providence, RI, USA) following ISO 97. Optical microscopy and scanning electron microscope (SEM) analyses were used to locate and identify patterns of wear.

Results: The average time in service for the PE inserts was 18.6 months. The maximum Ra values were noted on the anterior-lateral side for all implants. Optical and SEM analysis revealed wear mechanisms that included burnishing, scratches, pitting and cold flow. Damage to the distal surface was noted in all samples with extensive wear tracks noted in the LCS and TRAC knees.

Conclusion: The surface roughness analyses showed asymmetrical wear on the distal PE interfaces as well as wear on the proximal PE interfaces. The presence of embedded particles and debris suggests a third-body mechanism. Dislocation and general instability may have exacerbated the early signs of wear in these components.