Increased correction of lateral centre edge angle after periacetabular osteotomy is associated with a reduction in hip flexion and internal rotation: A three-dimensional computed tomography simulation study.

Abstract

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. 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. Increased lateral acetabular coverage, as measured by the change in LCEA, showed significant negative correlations with hip flexion and internal rotation (both <i>p</i> < 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, <i>p</i> = 0.016) and flexion decreased by 1.36° (CI: 0.7-2.0, <i>p</i> < 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°. 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 III.