Most studies on polyethylene wear are retrieval analyses. To evaluate the process of wear and the factors that might have influence on it, wear should be analyzed in vivo. In Chapter 5 the methods to quantify wear of the SKI prosthesis in vivo are described. Because the SKI prosthesis has a raised metal border on the tibial tray, it can be fluoroscopically centralized, with the X-ray beam perfectly parallel to the tibial tray. To determine the reliability of measuring the amount of wear radiographically, we calculated the intraclass correlation coefficient between measurements on a radiograph and with a Vernier calliper of different unused tibial inserts. The PE thickness of the SKI prosthesis could be determined radiographically with accuracy (intraclass correlation coefficient 0.999).

With the accurate measurements of the PE thickness radiographically, factors that may influence the wear and wear rate could be studied in vivo, including alignment of the prosthesis in the bone and alignment of the leg.