Abstract
PURPOSE: Periacetabular osteotomy (PAO) is an established treatment for hip dysplasia, known to affect the hip range of motion (ROM). However, the quantitative relationship between PAO-induced increase in lateral centre-edge angle (LCEA) and postoperative ROM remains undefined. This study aimed to determine the precise influence of increased LCEA on hip ROM following PAO. METHODS: Fifty computed tomography (CT)-based PAO simulations were performed on dysplastic hips, with corrections to LCEA values of 25° and 35°. Hip ROM was assessed in multiple planes using collision-based simulation endpoints. Linear regression and subgroup analyses evaluated the relationship between ΔLCEA and ROM changes. RESULTS: Increased lateral acetabular coverage, as measured by the change in LCEA, showed significant negative correlations with hip flexion and internal rotation (both p < 0.001). Linear regression analysis quantified these relationships, indicating that for every 1-degree increase in LCEA, internal rotation decreased by 1.003° (confidence interval [CI]: 0.7-1.3, p = 0.016) and flexion decreased by 1.36° (CI: 0.7-2.0, p < 0.001). Subgroup analysis further revealed that patients with lower preoperative ROM experienced more pronounced postoperative reductions in ROM. Notably, hips with < 20° preoperative internal rotation were at risk of fully losing internal rotation and having limited flexion if corrected to an LCEA of 35°. CONCLUSION: Greater correction of LCEA after PAO is associated with a measurable reduction in hip flexion and internal rotation. This study quantified these changes, finding a practical rule of thumb: for every 1-degree increase in LCEA, internal rotation decreases by approximately 1.003°, and hip flexion decreases by about 1.36°. Notably, hips with preoperative internal rotation less than 20° were identified as high-risk, as these hips were prone to fully losing internal rotation and experiencing limited flexion postoperatively. On the other hand, high internal rotation of >40° prior to PAO may be considered protective. To ensure residual ROM in hips at risk, the findings suggest accepting a lower target LCEA correction of 25°, on the lower end of the normal range. LEVEL OF EVIDENCE: Level III.