Risk factors for lateralization or superiorization of the center of the femoral head in eccentric rotational acetabular osteotomy.

PURPOSE: This study aimed to clarify the factors that cause the lateralization and superiorization of the femoral head after eccentric rotational acetabular osteotomy (ERAO) by examining the three-dimensional morphology of the osteotomy site using computed tomography (CT). METHODS: This study included 52 patients who underwent ERAO for hip dysplasia. Postoperatively, the center of the femoral head was measured for lateralization and superiorization. We defined the iliac and sciatic osteotomy angles in the coronal and axial CT planes, respectively. The surgical factors for lateralization and superiorization were analysed using multiple logistic regression analysis. We also analysed the relationship between the femoral head relocation and clinical outcomes (as assessed using Japanese Orthopaedic Association (JOA) scores). RESULTS: Thirty-five patients had hips with lateralized femoral heads, and 25 patients' femoral heads were superiorized. Logistic regression analysis revealed that a higher osteotomy angle of the ilium in the coronal plane served as a significant predictor of superiorization of the femoral head. Similarly, a larger osteotomy angle of the ischium in the axial plane and the amount of change in the lateral centre edge angle were identified as predictors of lateralization. A weak negative correlation was observed between the amount of lateralization and the JOA score. CONCLUSION: Large osteotomy angles in the superior and posterior aspects of the acetabulum carry a risk of superiorization and lateralization of the center of the femoral head. Surgeons should be aware of the need to chisel through the internal plate to achieve the results described in the ERAO theory. STUDY DESIGN: A single-center, retrospective study.