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

(1) 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. (2) Methods: A prospective cohort of patients 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). (3) Results: Significant improvements were observed across all HOOS subscales at follow-up. Active hip ROM increased significantly in internal rotation, external rotation, and total rotation of the operated hip, whereas changes in hip flexion were minimal and no meaningful changes were observed in the non-operated hip. (4) 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.