Acetabular Revisions. Risk Factors and Prediction of Re-revision

Abstract: Hip replacement is a successful intervention when treating patients with hip osteoarthritis. Approximately 10% of all patients undergoing primary hip replacement surgery require further surgical interventions (revisions) during their lifetime. Acetabular component (cup) failure is the most common reason for a revision. Cemented fixation in acetabular revision surgery was a common method until the mid-1980s. Low survival rates reported for cemented revision cups and encouraging results. There are, however, no studies comparing the results of revision surgery based on the method of fixation for the acetabular component. In 2006, a highly porous trabecular metal (TM) tantalum cup was introduced in the Swedish market and, in 2013, this cup was the most commonly used acetabular revision component in Sweden. The primary aim of this thesis was to compare cemented and uncemented fixation in acetabular revisions using radiostereometric analysis (RSA). Further, a comparative analysis of the TM cup and other cup designs frequently used in acetabular revisions was performed. Data from the SHAR, on 18,593 first-time revisions, were used in the first study to analyse differences relating to the risk of re-revision between cemented and uncemented cups. The overall risk of acetabular component failure did not differ between the two modes of fixation. In this analysis, cemented revision cups were re-revised more often due to aseptic loosening but less often due to dislocation. In Paper II, TM cups were compared with the other two cups most frequently used in first-time revisions recorded in the SHAR. The short-term re-revision rate of the TM design did not differ from that of the other two designs. The third paper addressed the influence of proximal migration on the risk of aseptic loosening. An analysis of 312 acetabular revisions followed with RSA for two to 20 years showed that proximal migration measured with RSA can be used a predictor of aseptic loosening of the acetabular component. In the fourth paper, 45 patients (47 hips) undergoing surgery with cemented or uncemented fixation were followed prospectively for 17 years. Radiostereometry was used to monitor the migration and rotation of acetabular components. Cups installed using cemented fixation showed a higher rate of early migration. In a randomised prospective study (Paper V), the RSA migration pattern of the TM cup was compared with that of a cemented cup in hips with large bone defects. The TM design showed less proximal migration compared with the cemented design, indicating a lower risk of aseptic loosening when the TM cup is used in hips with large bone defects. To summarise, there was no difference in the overall risk of re-revision based on the method of fixation, according to data from the SHAR. Proximal migration measured with RSA is a predictor of late aseptic loosening in acetabular revisions. The TM cup shows promising short-term results in the SHAR. The low early proximal migration of the TM design suggests that it has the potential to reduce the risk of late aseptic loosening in revision surgery, but this remains to be demonstrated in clinical studies with longer follow-up.