Effect of acetabular component orientation on recurrent dislocation, pelvic osteolysis, polyethylene wear, and component migration.

We retrospectively reviewed 75 total hip arthroplasties to examine the effect of acetabular component position. In group A, 38 of the components were implanted according to manufacture's instructions with all peripheral fins in contact with acetabular bone; as such, the acetabular components were in a relatively vertical position with a mean angle of inclination of 61.9 degrees. Three of these patients developed recurrent dislocations necessitating revision of the acetabular component. In group B, 37 hips, a more horizontal orientation was used despite the fact that all of the peripheral fins of the acetabular component did not engage acetabular bone; in this group the mean angle of inclination was 49.7 degrees. Only one of these hips recurrently dislocated and required revision. There were no problems in this group associated with provisional component stability caused by inadequate peripheral fixation. Radiographs of all patients were obtained at 4 years after surgery (range, 4.0-4.3 years). Pelvic osteolysis had occurred in 24% of hips in group A and 13% of group B. Asymmetric polyethylene wear was observed in 5.1% of the hips in group A; no hip in group B showed wear asymmetry. Acetabular component migration developed in 19% of group A hips and 5% of group B hips. The Mayo clinical hip score was excellent in both groups: group A 71/80, group B 73/80. At an intermediate follow-up it is clear that significant problems can be encountered when this component is positioned in a relatively vertical position to facilitate engaging all four peripheral fins in bone. We have addressed this problem by placing the cup in a more anatomic position of inclination while maintaining provisional rim fixation. This has resulted in a decreased incidence of pelvic osteolysis and fewer complications overall.