The Medium Term Outcome of the Omnifit Constrained Acetabular Cup

Recurrent dislocation requiring revision surgery occurs in approximately 4% of primary total hip arthroplasties (THAs). To reduce this risk, or to treat those patients who recurrently dislocate, a constrained acetabular component may be used, however there are concerns over the success of such components due to increased mechanical stresses. The purpose of this study was to analyse the survivorship and radiological results for the Omnifit constrained acetabular component, providing a longer patient reported outcome follow-up than previous studies.

117 patients (median age 82 years) underwent a THA with an Omnifit constrained acetabular component. Of these, 45 were primary replacements and 72 were revisions. Survivorship analysis was performed and patients were assessed both radiologically and functionally.

At follow-up, 53 patients (45.3%) had died at a median time of 33 months from operation. The median overall follow-up was 7.0 (5.5–8.2) years. Survivors (median age 83 years) reported a median Oxford Hip Score (OHS) of 16.6 (0–48), 87.8% were satisfied with their surgery. 45 (91.8%) of the acetabular components were stable radiologically, 48 (96%) of the femoral components were stable (5 uncemented, 43 cemented) and two possibly unstable. Four of the 117 patients underwent further surgery. Only one required revision of the prosthesis and this was for a periprosthetic fracture.

In the medium term the Omnifit constrained acetabular component prevents dislocation and does not cause excessive loosening of either the acetabular or femoral components in our patient population. Our results support the use of the Omnifit constrained acetabular component in elderly patients at risk of dislocation with low functional demand.