Wear rate evaluation of a novel polycarbonate-urethane cushion form bearing for artificial hip joints

There is growing interest in the use of compliant materials as an alternative to hard bearing materials such as polyethylene, metal and ceramics in artificial joints. Cushion form bearings based on polycarbonate-urethane (PCU) mimic the natural synovial joint more closely by promoting fluid-film lubrication. In the current study, we used a physiological simulator to evaluate the wear characteristics of a compliant PCU acetabular buffer, coupled against a cobalt-chrome femoral head. The wear rate was evaluated over 8 million cycles gravimetrically, as well as by wear particle isolation using filtration and bio-ferrography (BF). The gravimetric and BF methods showed a wear rate of 9.9-12.5mg per million cycles, whereas filtration resulted in a lower wear rate of 5.8mg per million cycles. Bio-ferrography was proven to be an effective method for the determination of wear characteristics of the PCU acetabular buffer. Specifically, it was found to be more sensitive towards the detection of wear particles compared to the conventional filtration method, and less prone to environmental fluctuations than the gravimetric method. PCU demonstrated a low particle generation rate (1-5×10⁶ particles per million cycles), with the majority (96.6%) of wear particle mass lying above the biologically active range, 0.2-10μm. Thus, PCU offers a substantial advantage over traditional bearing materials, not only in its low wear rate, but also in its osteolytic potential.