[An experimental study on the suitability of the prosthetic head to the acetabulum].

Central migration is a serious postoperative complication of the femoral head replacement and one of its causes is incongruity of the femoral head prosthesis. The present experiment was undertaken to investigate the influence of femoral head prostheses of varying size, constructed entirely of stainless steel, upon the acetabular cartilage. Dogs had their femoral head replaced with a smaller prosthesis (smaller prosthesis group), a larger prosthesis (larger prosthesis group) or a virtually congruous prosthesis (diameter discrepancy: less than 2 mm; congruous prosthesis group) and were examined both roentgenographically and histologically for subsequent changes in the acetabulum. As a result, acetabular changes were found to be more profound in both the smaller and larger prosthesis groups, especially the latter, than in the congruous prosthesis group. These results, even though not directly applicable to human clinical situations, may be interpreted as implicating incongruousness in diameter of the head of the prosthesis as one of factors causative of central migration of femoral head prostheses.