A dislocation of the inner head in bipolar prosthesis with a self-centering system: a case report.

We present a case of inner head dislocation 11 years after the replacement of a bipolar prosthesis with a self-centering system. An 84-year-old woman with osteoarthritis of the left hip underwent a replacement of the Bateman UPF-II bipolar prosthesis in 1987. She fell off a chair on April 19 1998, and felt a sudden sharp pain in the left hip. Roentgenograms revealed that the inner head was dislocated from the outer head. Moreover, on June 19, when she stood up from the floor, the dislocation recurred. On July 23, a revision surgery was carried out. When the outer head was removed from the acetabulum, the bearing insert was markedly worn by the impingement of the femoral stem neck. Because there was no evidence of loosening of the femoral stem, a cemented replacement of the acetabular component was performed. At a 2-year follow-up, she had mild hip pain, but had returned fully to daily living. Our review of current published studies reveals that most inner head dislocations occurred in osteoarthritic patients. Thus, the occurrence of dislocations may be more dependent on patient selection than on failure of the bipolar prosthesis itself.