Joint motion of bipolar femoral prostheses.

From 1982 to 1992, 251 bipolar hip arthroplasties were performed on 213 patients. Among them, 117 bipolar femoral prostheses were randomly selected to examine the behavior of abduction motion under weight-bearing loads. Roentgenographic motion study was performed at an average of 46.5 months after surgery (range, 2-110 months). One hundred one prostheses used in dysplastic osteoarthritic, rheumatoid, and revised failed total hip arthroplasty patients moved 18.2% at the outer bearing and 81.8% at the inner bearing, while 16 prostheses used in femoral neck fracture and osteonecrosis of the femoral head patients moved 49.7% at the inner bearing and 50.3% at the outer bearing. There was a statistical difference in the motion pattern between the two groups. The abduction motion behavior of the bipolar femoral prostheses was not affected by the length of the follow-up period, the diameter of the outer heads, or the position of the prostheses on immediate postoperative roentgenograms.