Analysis of prosthetic femoral heads retrieved at autopsy

This study examined 24 prosthetic femoral heads retrieved at autopsy from patients with clinically and radiographically successful arthroplasties. Four alumina ceramic and 20 cobalt chrome heads in service for an average of 8.5 years were examined with a contact and a laser stylus profilometer. The authors documented general increases in surface roughness of the cobalt chrome and ceramic femoral heads attributable to in vivo articulation and also observed wear polishing around the apical region of the cobalt chrome heads. The roughness of the prosthetic femoral heads was compared with the polyethylene wear in the matching liners. No relationship was found between femoral head roughness values and polyethylene wear or component duration in situ. The only variable related to the pattern of head roughness and polyethylene wear was the presence of embedded particle debris in the polyethylene liner. Roughness parameters for cobalt chrome heads without embedded debris in the polyethylene liner were fairly uniform around the head. Roughness values, which were higher for heads associated with debris, had a decreasing gradient of surface roughness from the equator to the apex. In addition, the polyethylene wear rate for cups with embedded particle debris in the liner was significantly greater than the wear rate for cups without embedded debris. This study also showed a strong correlation between surface roughness values measured with the contact profilometer and values measured with the noncontact laser profilometer. However, laser profilometer values were four to six times higher, indicating that roughness parameters measured by the two different profilometers cannot be compared directly. Findings of this study point consistently to the influence of third body wear particles on prosthetic femoral head roughness and polyethylene wear. These results stress the importance of minimizing all foreign body debris in maintaining a well functioning articular couple.