Good Diagnostic Performance of Early Migration as a Predictor of Late Aseptic Loosening of Acetabular Cups Results from Ten Years of Follow-up with Roentgen Stereophotogrammetric Analysis (RSA)

Background: Excessive early migration of femoral stems following total hip arthroplasty and tibial components following total knee arthroplasty is associated with their long-term survival and allows reliable early evaluation of implant performance. However, a similar relationship involving acetabular components following hip arthroplasty has not been evaluated. This prospective, long-term study with clinical and Roentgen stereophotogrammetric analysis (RSA) follow-up establishes the existence of this relationship and its associated diagnostic performance. Methods: Thirty-nine consecutive patients (forty-one hips) who underwent total hip arthroplasty with a cemented Exeter stem and a cemented Exeter all-polyethylene cup had prospective clinical and RSA follow-up. Patients were evaluated postoperatively at six weeks, at three, six, and twelve months, and annually thereafter. Conventional anteroposterior and lateral radiographs were made at six weeks and at two, five, and ten years postoperatively as well as when indicated. The mean duration of follow-up (and standard deviation) was 9.4 +/- 3.2 years. No patients were lost to follow-up; fifteen patients died during the follow-up period. Results: Eleven acetabular components were observed to be loose on conventional radiographs after a mean of seventy-six months (range, twelve to 140 months). During the first two postoperative years, the failed acetabular components showed markedly greater and more rapid cranial translation and sagittal rotation. Both cranial translation (hazard ratio = 19.9 [95% confidence interval, 4.94 to 80.0], p < 0.001) and sagittal rotation (hazard ratio = 11.1 [95% confidence interval, 2.83 to 43.9], p = 0.001) were strong risk factors for late aseptic loosening. Eight of the eleven failed components showed a distinctive pattern of excessive cranial translation combined with excessive sagittal rotation. The associated diagnostic performance of two-year cranial translation and/or sagittal rotation for predicting late aseptic loosening of the acetabular component was good (area under the receiver operating characteristic curve, 0.88 [95% confidence interval, 0.74 to 1.00; p < 0.0011 and 0.84 [95% confidence interval, 0.68 to 1.00; p = 0.001], respectively). Conclusions: Early migration, as measured by RSA at two years postoperatively, has good diagnostic capabilities for the detection of acetabular components at risk for future aseptic loosening, and this method appears to be an appropriate means of assessing the performance of new implants or implant-related changes.