Acetabular Component Migration Following Revision Total Hip Replacement
Background: The most common reason for revision of the acetabular component after total hip replacement (THR) is loosening. Identifying a surrogate, such as early migration, that could predict the long-term performance of revision acetabular components and techniques is important given the introduction of new implants and techniques. Radiostereometric Analysis (RSA) and Ein-Bild Roentgen Analyse (EBRA-Cup) are the only validated methods to measure component migration that can predict long-term survivorship of primary THR implants. The advantage of EBRA-Cup is that it can be performed retrospectively, and therefore, is currently arguably the best method to establish thresholds for component migration that predict component loosening. The advantage of RSA is that it is the most accurate method to measure component migration and the current gold standard. If EBRA-Cup established thresholds of migration could be applied to RSA measurements, RSA could be used to predict loosening of revision acetabular components and therefore assess the early performance of various components as well as the effect that variation in technique can have on the performance of components. Aims: The aims of this thesis were: (1) to undertake a scoping review of all studies that used RSA, to measure the migration of acetabular components used at revision THR. (2) To determine the amount of acetabular component proximal translation and sagittal rotation as measured by EBRA-Cup after revision THR to predict and (3) diagnose aseptic loosing at re-revision surgery. (4) To determine the accuracy of EBRA-Cup measurements of uncemented acetabular component migration after revision THR, and (5) to compare the number of cases identified using EBRA-Cup and RSA as having proximally migrated above and below 1mm at 2 years post-operatively. (6) To compare the migration of the revision acetabular system thought to have the best results to treat severe bone defects, using porous tantalum acetabular components, with the EBRA established migration thresholds, and (7) to determine the effect that modifying the surgical technique to implant the porous acetabular components in these cases has on the amount of early component migration. Methods: (1) A systematic search was performed on PubMed, Scopus and Embase to identify all publications that measured the migration of acetabular components following revision THR using RSA. (2/3) EBRA-Cup was used to retrospectively measure the migration of 94 uncemented acetabular components used at revision THR, until re-revision surgery. The cohort was divided into two patient groups: Group A, included revision acetabular components that were found to be not loose at re-revision THR (52 components); and Group B, the revision acetabular components that were found to be loose at re-revision (42 components). (4/5) The migration of 76 revision acetabular components was measured, and compared, using both RSA and EBRA-Cup and using radiographs taken at the same time points. (6/7) RSA was utilized to measure the migration of 55 porous tantalum components used to treat severe, Paprosky III, acetabular defects at revision surgery. The component migration after a surgical technique change was compared to those preceding. Results: (1) The systematic literature search found seventeen publications. Uncemented acetabular components and components used to treat smaller defects had lower amounts of early migration. Several recommendations were made to improve the reporting of future RSA results to allow comparison between publications and to allow future systematic reviews and meta-analyses. (2) The mean proximal translation and sagittal rotation, measured by EBRA-Cup, were significantly higher for acetabular components that were found loose compared with those that were not loose at re-revision (p < 0.02). Proximal translation > 1.0 mm within 24 months had a positive predictive value (PPV) of 90% and a specificity of 94%, but a sensitivity of 64%, for a revision acetabular component to be loose at re-revision. (3) Thresholds of 2.5 mm proximal translation or 2° sagittal rotation (EBRA-Cup) in combination with radiolucency criteria had a sensitivity of 93% and specificity of 88% to diagnose aseptic loosening. (4/5) EBRA-Cup can accurately measure migration of uncemented acetabular components used at revision THR. The presence of pelvic discontinuity, significantly influenced the accuracy of EBRA-Cup measurements. EBRA-Cup and RSA had good agreement on classification of components that migrated above or below 1mm at 2 years, with 100% sensitivity and 87% specificity. (6) Of the 55 components used to reconstruct Paprosky III acetabular defects, 7 migrated more than the early threshold that predicts later loosening (>1 mm) and of these 5 had been re-revised for loosening at the time of the latest follow-up. (7) At 2 years, the absolute median proximal translation of components with enhanced inferior fixation was |0.3| mm (range, |0.1| to |0.9| mm), which was significantly lower than |0.4| mm (range, |0.03| to |16.4| mm) for those without enhanced inferior fixation (p = 0.04). Conclusion: Improved reporting of RSA migration results of acetabular components used at revision THR is required. A 1mm threshold of early proximal migration reliably predicts re-revision for aseptic loosening of acetabular components used at revision THR. Furthermore, using the same method, thresholds of migration were established that are diagnostic of aseptic loosening of acetabular components used at revision THR at any time point. EBRA-Cup measurements of acetabular component migration following revision THR was shown to be accurate when compared with RSA measurements. The use of these thresholds in a prospective cohort of patients that underwent reconstruction of severe acetabular defects was shown to be effective to improve the surgical technique and early stability of the acetabular components investigated.
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