Wear analysis of retrieved ceramic-on-ceramic articulations in total hip arthroplasty: Femoral head makes contact with the rim of the socket outside of the bearing surface.

We investigated articular bearing surfaces retrieved from three patients with ceramic-on-ceramic total hip arthroplasties using high-quality alumina. The duration of implantation was 3.5, 3.0, and 2.5 years, respectively. Dislocation of the hip joint after implantation did not occur in any patients. The retrieved prostheses were examined by stereomicroscopy and scanning electron microscopy (SEM). In the main load-bearing area, no wear marks were seen in any sockets. However, in all three cases, stripe scars were observed at the rim of the alumina inlay under stereomicroscopy, despite the lack of indentation in the socket and the stem, which suggests impingement. Such scars were not observed on the load-bearing surface. Under SEM, the scars showed excessive wear, including material excavation, that has not been observed in conventional hip simulator experiments. These findings are similar to those of experiments in which a simulator was programmed to distract the femoral head from the socket. The present results suggest that the femoral head can separate from the socket without neck-socket impingement in vivo.