Wear in total knee arthroplasty-just a question of polyethylene?

Purpose Biological reactions against wear particles are a common cause for revision in total knee arthroplasty. To date, wear has mainly been attributed to polyethylene. However, the implants have large metallic surfaces that also could potentially lead to metal wear products (metal ions and debris). The aim of this study was to determine the local release of cobalt, chromium, molybdenum and titanium in total knee arthroplasty during a standard knee wear test. Four moderately conforming fixed-bearing implants were subjected to physiological loadings and motions for 5x10(6) walking cycles in a knee wear simulator. Polyethylene wear was determined gravimetrically and the release of metallic wear products was measured using high resolution-inductively coupled plasma-mass spectrometry. A polyethylene wear rate of 7.28 +/- 0.27 mg/10(6) cycles was determined and the cumulative mass of released metals measured 1.63 +/- 0.28 mg for cobalt, 0.47 +/- 0.06 mg for chromium, 0.42 +/- 0.06 mg for molybdenum and 1.28 +/- 0.14 mg for titanium. For other metallic implants such as metal-on-metal total hip arthroplasty, the metal wear products can interact with the immune system, potentially leading to immunotoxic effects. In this study about 12 % by weight of the wear products were metallic, and these particles and ions may become clinically relevant for patients sensitive to these materials in particular. Non-metallic materials (e.g. ceramics or suitable coatings) may be considered for an alternative treatment for those patients.