Effect of augmented cup fixation on stability, wear, and osteolysis: a 5-year follow-up of total hip arthroplasty with RSA

To evaluate different modes of cementless fixation of hemispherical cups, we operated on 87 hips in 81 patients using 4 different means of cup fixation. The hips were randomly assigned to fixation with press-fit technique only (PF), or with augmentation with screws (S), pegs (P), or hydroxyapatite (HA) coating. The patients were evaluated with radiostereometric analysis (RSA) for cup migration and wear, conventional radiography for osteolysis, and Harris Hip Score for clinical outcome over 5 years. The fixation of the cups did not differ between the groups, but HA showed a tendency to decrease proximal migration. HA-coated cups displayed the best interface with hardly any signs of radiolucent lines, indicating a superior sealing effect of the HA coating. Cups with screws or pegs had more radiolucent lines and osteolytic lesions than the other groups. Radiolucent lines were correlated to higher proximal migration, young age, and female gender (r2=.2). The wear rate of the ethylene oxide-sterilized polyethylene liner was high (0.2 mm/y) but did not differ between the groups. Two cups with a perioperative fracture of the acetabular rim showed large initial migration but stabilized thereafter.