From 1982 to 1991, 251 bipolar hip arthroplasties were performed on 21
3 patients. Among them, 117 bipolar femoral prostheses were randomly s
elected to examine the behavior of abduction motion under weight-beari
ng loads. Roentgenographic motion study was performed at an average of
46.5 months after surgery (range, 2-110 months). One hundred one pros
theses used in dysplastic osteoarthritic, rheumatoid, and revised fail
ed total hip arthroplasy 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 statist
ical difference in the motion pattern between the two groups. The abdu
ction motion behavior of the bipolar femoral prostheses was not affect
ed by the length of the follow-up period, the diameter of the outer he
ads, or the position of the prostheses on immediate postoperative roen
tgenograms.