Total hip arthroplasty for acute acetabular fractures through the replace-in-situ philosophy: radiological assessment of component stability

Aims: The aim of this study was to determine the early stability of acetabular components of total hip arthroplasty (THA) treating acute acetabular fractures through a replace-in-situ technique, using standard radiological assessment techniques as well as radiostereometric analysis (RSA), the gold standard for assessment of implant stability. Methods: We prospectively investigated 29 patients who underwent THA to manage an acute acetabular fracture in which patients underwent postoperative in-clinic radiological assessment of acetabular component stability, and detailed measurements using both RSA and manual techniques. The latter were performed based on pelvic reference landmarks located below and above the fracture. Greater than 3 mm of proximal translation and/or 5° of rotation around the sagittal axis were considered diagnostic of a loose acetabular component. Results: The median proximal translation and sagittal rotation of the cohort was 0.5 mm (IQR 0.3 to 0.9) and 0.8° (IQR -0.6° to 1.1°), respectively, as measured by RSA at two years. Acetabular components in the most unstable acetabular fracture patterns were found to migrate more immediately post-surgery. There was a disparity between different measurement techniques. Accurate RSA measurements correctly identified two components that were deemed to be clinically loose, and the diagnostic performance of RSA migration measurements was improved when migration within the first six months was excluded. Visual assessment of radiographs in clinic underestimated – and manual radiological measurements overestimated – acetabular component loosening in these complex cases. Conclusion: The replace-in-situ technique led to acceptable early acetabular component stability in the majority of cases (27/29, 93%), a good result considering the complexity of these reconstructions. Accurate measurements of acetabular component migration are recommended in these cases, as pelvic landmark identification on consecutive plain radiographs is influenced by both pelvic projection on plain radiographs and fracture fragment migration during healing. Cite this article: Bone Jt Open 2025;6(10):1282–1294.