Postoperative Changes in Femoral Rotation Angle and Their Influencing Factors Following Total Hip Arthroplasty via...

Background/Objectives: This study aimed to evaluate the femoral rotation angle (FRA) before and after THA using a single approach and to identify its influencing factors through three-dimensional measurements. Methods: This retrospective study analyzed patients undergoing 108 primary unilateral THA via the anterolateral-supine approach (ALSA) from May to October 2023. Patients with hip contractures, femoral deformities, or other specific conditions were excluded for precise FRA measurements. Preoperative and postoperative CT scans were used for measurements of the FRA, anteversion, leg lengthening, and global offset. FRA was defined as the angle between the posterior condylar line and the line connecting the bilateral anterosuperior iliac spines, with external rotation as positive. Multiple linear regression, adjusted for age, sex, body mass index, and stem design, assessed the influence of anteversion change, leg lengthening, global offset change, and soft tissue release on the difference in FRA. Results: The mean FRA changed significantly from -2.8° preoperatively to -11.8° postoperatively (p < 0.001), demonstrating an average internal rotation of 9.0° after THA. Anteversion increased by a mean of 9.0° (p < 0.001), leg length increased by 9.0 mm (p < 0.001), and global offset decreased by 1.7 mm (p < 0.001). Multivariate analysis revealed that anteversion change (β = -0.41, p < 0.001) and global offset change (β = 0.40, p = 0.022) were significantly associated with FRA differences. Leg lengthening and ischiofemoral ligament or conjoint tendon resection were not significant (p = 0.089, p = 0.917, and p = 0.750, respectively). Conclusions: ALSA THA significantly rotates the femur internally, associated with an increase in anteversion and a decrease in global offset.