The In Vivo Biological Response to Intra-Articular Injected Polycarbonate Urethane Wear Debris Particles

Wear particles invariably form due to contact and friction between articulating surfaces in orthopedic prosthetic joint replacements. Polycarbonate urethane (PCU) has shown low wear rates and invoked minimal local biological response to wear debris in various orthopedic applications. However, controlled preclinical studies have not yet studied the biological response to PCU particles in synovial joints. This study aims to evaluate the biological response to mostly submicron-sized PCU wear particles in synovial joints in a rabbit model representing a worst-case scenario. PCU and ultra-high-molecular-weight-polyethene (UHMWPE) particles were generated in vitro, and particle characterization was performed using scanning electron microscopy (SEM) images. Fifteen New Zealand white rabbits, divided into three groups, received bilateral injections in the knee joint with 10 mg/mL PCU, UHMWPE particles, or saline (all 0.2 mL). After 3 months, the biological response in the joint was evaluated by histopathological reactivity scoring. The generated PCU and UHMWPE wear particles were mainly in the biologically active size range with an average equivalent circle diameter (ECD) of 0.31 mu m (+/- 0.48) and 6.99 mu m (+/- 16.32), respectively. There was a minimal to non-existing biological response (score <= 0.5) to PCU (0.5 +/- 1.0), UHMWPE particles (0.6 +/- 1.3) and saline (0.0 +/- 0.0). Also, the wear particles did not disperse from the injection site. The results of this study support the use of PCU as a bearing surface in orthopedic prosthetic joint replacements by indicating that even in the likelihood that wear particles are generated, they are not likely to trigger a strong inflammatory response.