Association Between Lower Limb Kinematics During Single Leg Squat and Patient-Reported Outcomes After Hip Arthroscopy for Femoroacetabular Impingement Syndrome

Background: Typically, 3 months is an early postoperative time point at which patients with femoroacetabular impingement syndrome (FAIS) demonstrate clinically meaningful improvement, while 6 months represents an important midterm stage for recovery and return to sport. Purpose: To assess continuous changes in the kinematics of the involved and uninvolved lower limbs in patients with FAIS at 3 and 6 months after hip arthroscopy as well as to examine their relationships with International Hip Outcome Tool–33 (iHOT-33) and Copenhagen Hip and Groin Outcome Score Sport subscale (HAGOS-Sport) scores. Study Design: Cohort study; Level of evidence, 2. Methods: The study included 15 patients who underwent hip arthroscopy between March 2024 and November 2024 as well as a healthy control group of 15 participants, matched to the patients by sex, age, and body mass index, recruited from the community. All participants performed the single-leg squat (SLS), and kinematic data were collected using an 8-camera motion capture system. One-way analysis of variance was used to compare baseline, 3-month postoperative, and 6-month postoperative kinematic data of the FAIS group with those of the healthy control group. Post hoc comparisons were conducted using the Tukey test to determine between-group differences. Correlation analysis was performed to assess the relationship between changes in the hip flexion angle and changes in iHOT-33 and HAGOS-Sport scores. Results: At 3 months postoperatively, the involved limb hip flexion angle ( P = .021), hip adduction angle ( P = .0011), knee flexion angle ( P = .016), and change in the center of mass ( P = .0034) were reduced compared with the healthy control group. At 6 months postoperatively, no significant kinematic differences were observed between the FAIS and healthy control groups. Correlations between changes in the iHOT-33 score at 3 months and changes in the hip flexion angle at 6 months were positive ( r = 0.64; P = .0094), and changes in the iHOT-33 score at 6 months were also positively correlated with changes in the hip flexion angle at 6 months ( r = 0.53; P = .041). Conclusion: Patients with FAIS exhibited abnormal kinematics during the SLS at 3 months postoperatively, which showed improvement by 6 months. Furthermore, improvement in sagittal-plane angles of the hip at 6 months postoperatively was correlated with the iHOT-33 score, supporting our hypothesis. Clinicians should not overlook functional recovery after hip arthroscopy for FAIS.