Eccentric rotational acetabular osteotomy (ERAO) enhances acetabular coverage and optimizes joint contact pressure in patients with hip dysplasia (HD); however, postoperative range of motion (ROM) may be restricted due to bony impingement. The impact of this procedure on anterior ROM in males remains unknown. ROM depends on both acetabular morphology and femoral neck anteversion (FNA); hence, this study aimed to address the following questions: (1)Does sex affect the achievement of functional ROM (flexion ≥105 ° and internal rotation ≥20 ° at 90 ° flexion) after virtual ERAO standardized to lateral center-edge angle (LCEA) 30 ° and anterior center-edge angle (ACEA) 55°? (2)Is FNA lower in males compared to females with hip dysplasia? (3)Does FNA correlate with post-ERAO ROM in males with hip dysplasia? (4)What is the threshold value of FNA below which males are at risk of inadequate ROM after ERAO?

We hypothesized that males, who generally exhibit lower FNA, would demonstrate reduced anterior hip ROM even after ERAO despite achieving comparable acetabular coverage.

A total of 24 male and 98 female hips with HD treated between 2016 and 2018 were analyzed. Virtual ERAO was performed on preoperative CT models, targeting an LCEA of 30 ° and an ACEA of 55 °. Postoperative acetabular coverage, FNA, and neck-shaft angle (NSA) were measured. ROM simulations were used to quantify the maximum flexion and internal rotation at 90 ° flexion. Sex-related differences and correlations were assessed, and receiver operating characteristic (ROC) analysis was performed to determine the FNA threshold for failure to achieve functional ROM. ROM estimation was based on CT-derived bony contact; soft tissue constraints were not modeled.

After standardized virtual ERAO, males demonstrated higher failure rates in achieving functional ROM than females, with flexion <105 ° observed in 8 of 24 hips (33.3%) compared with 11 of 98 hips (11.2%) (p = 0.012), and internal rotation <20 ° in 8 of 24 hips (33.3%) compared with 13 of 98 hips (13.6%). Postoperative acetabular coverage and NSA did not differ significantly between sexes, whereas FNA was significantly lower in males (13.7 ± 14.0 °) than in females (21.5 ± 13.1 °). FNA correlated with flexion (r = 0.69) and internal rotation (r = 0.52). An FNA of ≤0.0 ° was predictive of failure to achieve functional ROM, with an AUC of 0.78, a sensitivity of 0.57, and a specificity of 0.94.

Low FNA, which was more prevalent in males with hip dysplasia, was associated with reduced anterior ROM following virtual ERAO, and males also exhibited higher failure rates in achieving functional ROM. These findings suggest that femoral morphology—particularly FNA—should be considered during ERAO planning in male patients. However, given the limited sensitivity of the FNA ≤0 ° threshold and the exploratory nature of this virtual simulation analysis, these results should be regarded as hypothesis generating and validated in clinical ERAO cohorts before clinical application.

III; case-control study.