Abstract
Introduction
Primary stability of the Burch-Schneider ring (BSR) in case of acetabular revision is discussed controversial. In a retrospective two centre cohort study we analyzed the influence of the mode of screw fixation and the restoration of the center of rotation on migration, loosening and other radiographic parameters.
Material/Methods
Patients with a minimal radiographical follow-up of 2 years and suitable for EBRA analysis were included. In group 1 (46 patients) screws were placed through the cranial spherical part of the ring and covered by cement and cup, in group 2 (40 patients) screws were placed through the cranial flange. Preoperative bone defects were classified, the postoperative centre of rotation was determined. Changes of screws were recorded, migration exceeding >1mm was seen as significant.
Results
Demographic data and size of bone defect were comparable in both groups. No cups in group 1 and in group 2 were re-revised. In group 1 the centre of rotation was medialized mean 5.5 (SD 8.2) mm, in group 2 it was lateralised mean 11.0 (SD 10.3) mm (p<.001). Screw changes were observed in 5 (10.9%) patients in group 1 and 14 (35%) patients in group 2 (p=.009). Migration at 2 years was observed for 17 (37%) patients in group 1, mean migration was 1.0 (SD 1.0) mm. In group 2 21 (52.5%) patients showed migration at 2 years (p=.193), mean migration was 1.6 (SD 1.7) mm (p=.031).
Conclusion
Medialization of the implant and screw fixation with compression of the ring against the acetabular roof reduces migration and screw changes. The improved stability might be due to better osteointegration of the BSR and angular stability of the screws which are additionally fixed with cement.
