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 compon ents were implanted according to manufacture's instructions with all p eripheral fins in contact with acetabular bone; as such, the acetabula r components were in a relatively Vertical position with a mean angle of inclination of 61.9 degrees. Three of these patients developed recu rrent dislocations necessitating revision of the acetabular component. In group B, 37 hips, a more horizontal orientation was used despite t he faa that all of the peripheral fins of the acetabular component did not engage acetabular bone; in this group the mean angle of inclinati on was 49.7 degrees. Only one of these hips recurrently dislocated and required revision. There were no problems in this group associated wi th provisional component stability caused by inadequate peripheral fix ation. Radiographs of all patients were obtained at 4 years after surg ery (range, 4.0-4.3 years). Pelvic osteolysis had occurred in 24% of h ips in group A and 13% of group B. Asymmetric polyethylene wear was ob served in 5.1% of the hips in group A; no hip in group B showed wear a symmetry. Acetabular component migration developed in 19% of group A h ips 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 follo w-up it is clear that significant problems can be encountered when thi s component is positioned in a relatively vertical position to facilit ate 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 dec reased incidence of pelvic osteolysis and fewer complications overall.