Femoral neck-shaft angle can predict the anterior capsular thickness in patients with femoracetabular impingement syndrome.

PURPOSE: To measure the femoral neck-shaft angle (NSA) on computed tomography (CT) images in femoracetabular impingement syndrome (FAIS) patients and explore its relationship with the anterior capsular thickness (ACT). METHODS: A retrospective review of prospectively collected data from 2022 was performed. Inclusion criteria included: primary hip surgery, 18 to 55 years of age, and CT imaging of the hips. Exclusion criteria included: revision hip surgery, mild or borderline hip dysplasia, hip synovitis, and incomplete radiographs and medical records. NSA was measured on CT imaging. ACT was measured using magnetic resonance imaging (MRI). Multiple linear regression was performed to assess the association between ACT and related variables, including age, sex, body mass index (BMI), lateral center-edge angle (LCEA), alpha angle, Beighton test score (BTS), and NSA. RESULTS: A total of 150 patients were included. The mean age, BMI, and NSA were 35.8 ± 11.2 years, 22.8 ± 3.5, and 129.4° ± 7.7°, respectively. Eighty-five (56.7%) patients were females. Multivariable regression analysis revealed that NSA (P = 0.002) and sex (P = 0.001) were significantly negatively correlated with ACT. Age, BMI, LCEA angle, alpha angle, and BTS were not correlated with ACT. CONCLUSIONS: This study confirmed that NSA significantly predicts ACT. A decrease in the NSA by 1° increases the ACT by 0.24 mm. LEVEL OF EVIDENCE: Level III.