Constrained Acetabular Components Used in Revision Total Hip Arthroplasty: A Registry Analysis

Abstract Background Constrained acetabular components have a mechanism to lock in the femoral head. They have been developed to control postoperative dislocation, particularly in revision total hip arthroplasty (THA). Although these components may reduce dislocation, there are durability concerns: with reports of locking mechanism failures and loosening. We wanted to determine the outcome of constrained components in controlling dislocation, and if these components had a higher rate of second revision when compared with standard nonconstrained components. Methods Revision THA procedures from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) with a recorded primary procedure and initial diagnosis of osteoarthritis were used to compare constrained and standard nonconstrained components. Kaplan-Meier estimates of survivorship were calculated, and hazard ratios using Cox proportional hazard models were used to compare groups. Results There were 9509 THA first-revision procedures and 700 constrained components. Constrained components had a significantly higher revision rate after 3 months when large-head metal-on-metal components were included (hazard ratio = 1.37; P = .005). When large-head metal-on-metal components were excluded, there was no difference in the rate of second revision between the 2 groups. When the analysis was limited to first revision for dislocation, constrained components had a higher second revision rate for further dislocation after 9 months. Conclusion Constrained acetabular components had similar second-revision rates when compared with standard nonconstrained components, both for all first-revision reasons and when used to treat dislocation. Although possibly used for the more difficult unstable hips, constrained components had a higher rate of second revision for further dislocation.