THE USE OF A CEMENTED TRIPOLAR UNCONSTRAINTED ACETABULAR COMPONENT TO TREAT RECURRENT DISLOCATION. A MINIMUM 2-YEAR FOLLOW-UP STUDY

Introduction: Although a number of methods have been described to treat recurrent dislocation following total hip arthroplasty, this complication remains a challenging problem. The purpose of this retrospective study was to evaluate the minimum 2-year outcome in a consecutive series patients treated with a cemented tripolar unconstrained acetabular component for recurrent dislocation. Patients and Methods: Fifty-one patients presenting with recurrent dislocation following primary or revision total hip arthroplasty in the absence of an identifiable curable cause were treated with a cemented tripolar unconstrained acetabular component. There were thirty-nine females and twelve males with a mean age at the time of the index procedure of 71.3 years. A single acetabular component design was used consisting of a stainless steel outer shell with grooves for cement fixation with a highly polished inner surface. This shell articulated with a mobile intermediate component with an opening diameter smaller than the 22.2-mm femoral head. No locking ring or other mean of constraint was associated. Results: Of the fifty-one patients, forty-seven have had complete clinical and radiological evaluation data at a mean follow-up of 31.2 months (twenty-four to 56.3 months). The cemented unconstrained tripolar acetabular component restored complete stability of the hip in forty-nine patients (96%). The mean Merle d’Aubigne hip score was 15.8 ± 2.0 at the latest follow-up. Radiographic analysis revealed no or radiolucent lines less than 1 mm thick located in a single acetabular zone in forty-three of forty-seven hips (91.5%). The cumulative survival rate of the acetabular component at 36 months using revision for dislocation and/or mechanical failure as the end point was 93.3 ± 4.6% (95% confidence interval, 84.4% to 100%). Conclusion: A cemented tripolar unconstrained acetabular component was highly effective in the treatment of recurrent dislocation with none of the complications associated with constrained devices. However, because longer term follow-up is needed to warrant that dislocation and loosening rates will not increase, the use of such a device should be limited to strict indications.