OSTEOLYSIS BEHIND MODERN CEMENTLESS ACETABULAR COMPONENTS IN TOTAL HIP ARTHROPLASTY

Abstract

Introduction: Cementless acetabular components have been associated with a higher rate of pelvic osteolysis compared to cemented components. Modular locking mechanisms and wear against screw heads and holes have been implicated in the production of polyethylene particles. Pressure waves and particle access to the pelvis are facilitated by screw holes. The patients in this study had a cementless, modular cup with screw fixation but not in all holes. Therefore factors thought to contribute to osteolysis were present.

Methods: 178 consecutive patients (198 hips) underwent primary THA using the EPF cementless cup (Plus Orthopaedics AG, Switzerland). 30 patients (31 hips) had died, 5 hips were revised, 8 were lost to follow up and 9 were unable to attend for radiographs. 126 patients (145 hips) were followed up clinically (Harris Hip Score) and radiographically. Mean follow up was 8.0 years (6.3–9.4). AP, lateral and Judet view radiographs were analysed for osteolysis. Polyethylene wear rates were determined using a validated 2D method (Martell).

Results: The mean HHS was 89.0 (44.4–99.9). Osteolysis was seen in 19 hips (13.1%). In only 6 hips (4.1%) osteolysis was evident on the AP radiograph. In 13 hips (9.0%) osteolysis was only seen on lateral or Judet view radiographs. No cups were considered to be loose. Mean linear polyethylene wear rate was 0.10 +/− 0.06 mm/yr. Mean volumetric polyethylene wear rate was 43.2 +/− 28.2 mm³/yr. There was no significant difference between wear rates in hips with osteolysis compared to no osteolysis. Only 1 revision was for aseptic loosening.

Discussion: The EPF cup produced good clinical results, and appeared radiologically stable at 8 years. Wear rates are similar to other studies of cementless cups. The osteolysis rate is low given this “worst case scenario” especially considering the increased likelihood of detecting osteolysis with multiple radiographic views.