PROGRESSIVE MIGRATION IN BIPOLAR ARTHROPLASTY FOR OSTEOARTHRITIS OF THE HIP SECONDARY TO CONGENITAL DISLOCATION

Seventy-one hips with osteoarthritis secondary to congenital dislocati on underwent bipolar arthroplasty with autologous bone grafting (graft ed group) or without bone grafting (ungrafted group). Clinical and rad iographic followup was performed; the average followup was 5.7 years ( range, 3-11.3 years). At followup, the mean Merle d'Aubigne and Postel score was 14.3 points. Excellent or good results were achieved in onl y 50% of all cases. The mean extent of prosthetic head migration was 6 .5 mm in the grafted group and 4.7 mm in the ungrafted group. Progress ive migration occurred in 68% of the grafted group and in 43% of the u ngrafted group. There was a significant negative correlation between t he extent of migration of the outer head and the coverage of the outer head by the original acetabulum (R = 0.53). In the grafted group, the revision rate for failure of the outer head of the prosthesis was 60% at 6 years postoperatively. In the grafted group, progressive migrati on was more extensive and more frequently than in the ungrafted group. Extensive migration was also observed when there was adequate coverag e of the outer head by host bone in the ungrafted group. In conclusion , bipolar arthroplasty is not recommended for osteoarthritis secondary to congenital hip dislocation because of the poor clinical outcome, h igh risk of significant progressive migration, and high revision rate.