Volume 3, Issue 6 (June 2006)
The Effects of Implant Temperature on Lubricant Protein Precipitation and Polyethylene Wear in Joint Simulation Studies
Implant temperature increases as soon as a wear test starts. Frictional heating is the main reason for the temperature increase. Factors that affect the magnitude of the increase include the thermal conductivity of the implant materials, testing speed, and serum volume of the test chamber. High implant temperature can cause precipitation of soluble proteins in the serum lubricant. The protein precipitates can form a film at the wear interface and may affect laboratory wear evaluation of polyethylene liners. The effects of the implant temperature (of cobalt-chromium and zirconia femoral components) and the amount of protein precipitation from serum lubricant on the wear of UHMWPE liners has been demonstrated in a previous study using an external temperature control device. Furthermore, the nonlinear relationship of the implant temperature and the polyethylene wear has been discussed in another study, using moderately crosslinked UHMWPE liners tested against cobalt-chromium, zirconia, and alumina/zirconia composite femoral components at various temperatures. The results from both studies demonstrated that the temperature around the hip joint implants during a simulation can affect the wear rate of polyethylene. One guideline for minimizing the thermal effects on in vitro testing include circulation of coolant at an appropriate temperature to avoid overheating (due to nonstop running of the simulator) thus preventing excessive protein precipitation. This recommendation should help producing wear surfaces and wear debris that are more comparable to in vivo outcomes.