Active Range of Motion in Non-Impingement Directions After Hip Arthroscopy for Femoroacetabular Impingement Syndrome

Background: Femoroacetabular impingement syndrome (FAIS) is a common cause of hip pain and functional limitation in young and physically active individuals. Although hip arthroscopy is an established treatment when conservative management fails, objective data on early postoperative changes in active hip range of motion (ROM) remain limited. This study aimed to evaluate changes in active hip ROM three months after arthroscopic treatment for FAIS using inertial measurement units (IMUs) and to investigate their relationship with patient-reported outcomes. Methods: A prospective cohort of forty-two patients (mean age 36 ± 9 years; 64% male) undergoing hip arthroscopy for FAIS was assessed preoperatively and at a three-month follow-up. Active hip ROM-including flexion, internal rotation, external rotation, and total rotation-was measured using IMU sensors, while subjective outcomes were evaluated using the Hip disability and Osteoarthritis Outcome Score (HOOS). Results: Significant improvements were observed across all HOOS subscales at follow-up (all p < 0.001). The HOOS Total score increased from 57 ± 15 to 83 ± 11. Clinical recovery, defined by the Minimal Important Change (MIC), was achieved by 74% of patients for Symptoms, 81% for Pain, 81% for ADL, 83% for Sport, and 67% for Quality of Life (QOL). Active hip ROM in the operated hip increased significantly for internal rotation (19.6° ± 11.9° to 26° ± 8°), external rotation (37° ± 10° to 40° ± 8°), and total rotation (57° ± 15° to 67° ± 12°). Changes in hip flexion were not clinically meaningful (98° to 100°), and no changes were observed in the non-operated hip. Spearman's analysis showed weak and inconsistent correlations between active ROM and HOOSs (r ranging from -0.34 to 0.31). Conclusions: Hip arthroscopy for FAIS leads to early improvements in both patient-reported outcomes and active hip mobility, particularly in rotational movements, although the relationship between ROM and subjective outcomes appears weak.