The Charnley versus the Spectron hip prosthesis - Radiographic evaluation of a randomized, prospective study of 2 different hip implants

A total of 410 hips were randomized to treatment with either a Charnley (20 6 hips) or a Spectron (204 hips) total hip arthroplasty. The patients were operated on by a standardized procedure using a contemporary cementing tech nique and were followed after 1, 3, 5 to 6, and 10 years. The postoperative radiographs showed a significantly increased rate of malalignment and cons equently low grade of cement mantle quality of the Charnley stem compared t o the Spectron. No differences concerning cement mantle quality or position ing were found between the Charnley ogee cup and the metal-backed Spectron. Evaluation of the follow-up radiographs revealed 10 loose Charnley stems a nd I loose Spectron stem and 4 loose Charnley ogee cups and 23 loose Spectr on metal-backed cups. The differences of revision rate for the femoral and acetabular components of the 2 prostheses were significant (P = .03, Charnl ey femoral component more frequent: P = .03, Spectron acetabular component more frequent). The radiographic evaluation strengthened this disparity Poo r wear characteristics of the metal-backed Spectron cup are perhaps the mai n reason for the highly significant difference in mechanical failure rate b etween the 2 cups. We therefore propose that metal-backing of cemented cups should be avoided, at least when combined with larger femoral heads. The d ifficulty in positioning the Charnley stem with an adequate cement mantle, especially in the absence of trochanteric ostectomy, might explain the infe rior Charnley stem longevity in this study.