Abstract
Introduction
Failure of total knee arthroplasty (TKA) is mainly caused by biological reactions against wear particles generated at the implant. So far, wear has been mainly attributed to polyethylene (PE) and much effort has been put into understanding and optimizing the wear mechanism of PE in recent years. However, evaluation of metal wear particles and ion release in TKR has been neglected so far although the implants present large metal surface areas. In the present study we aimed to analyse the wear performance of TKA and to study the kinetics of metal ion and particle release. We hypnotized that due to abrasion and corrosion TKA will release relevant levels of Cobalt (Co), Chromium (Cr), Molybdenum (Mo) and Titanium (Ti).
Methods
Implants were subjected to an in-vitro simulation applying physiological loadings and motions for 5 million walking cycles. Wear processes were determined gravimetrically and by measuring the release of Co, Cr, Mo and Ti ions using HR-ICP-MS. Surface alterations were determined through surface roughness measurements.
Results
An average PE wear rate of 7.28 mg/106 cycles (R=0.995;p≤0.001) was determined
After 5 million cycles the cumulative release of metals measured 1.63 ± 0.28mg for Co, 0.47 ± 0.06mg for Cr, 0.42 ± 0.06 mg for Mo and 1.28 ± 0.14mg for Ti. The metal release progressed linearly and the rate of sole surface corrosion was 0.06mg/106 cycles (R=0.993;p≤0.001), whereas the rate of articulation induced metal release was found to be 0.80mg/106 cycles (R=0.996;p≤0.001), (Fig. 1).
Discussion
For other metallic implant devices it is well known that metal wear products are able to interact with the immune system potentially leading to immunotoxic effects like hypersersensitivity or the formation of pseudotumors. To our knowledge, this is the first study that analysed the release of metallic wear products in TKA in vitro. We found that approx. 10% of the whole wear products are metallic and we believe that these particles and ions are relevant. Their effect regarding the clinical outcome of TKR will be analysed in further studies.
