Purpose: Femoroacetabular impingement syndrome (FAIS) is a hip disorder where femoral head/neck asphericity and/or acetabulum over-coverage lead to hip pain, which is exacerbated by repetitive/sustained hip flexion (e.g. squatting). FAIS is associated with hip osteoarthritis onset, and is commonly treated with hip arthroscopy (addresses osseous deformities), and physiotherapist care (targets neuromuscular deficits and activity modification). The purpose of this study was to compare changes in kinematics and moments following hip arthroscopy and physiotherapist care during a deep squat task.

Methods: The Australian FASHIoN trial recruited 140 participants with FAIS from waiting lists for hip arthroscopy, and a subset (n=36) underwent biomechanical analysis. Participants were randomly assigned to hip arthroscopy (n=18) or 12 weeks of PHT (n=18). Three-dimensional body motion and ground reaction forces were measured before randomization (baseline) and at 12-months (follow-up) during four deep squat trials. Inverse kinematics and dynamics were performed in OpenSim to calculate joint angles and moments. Changes in trunk, pelvis, and lower limb angles (°), and external lower limb moments (Nm·kg/bodyweight·height[%]) were compared across the squat cycle between groups using independent t-tests, and within groups using paired t-tests via statistical parametric mapping (p<.05). Spatiotemporal variables (i.e., squat depth, descent and ascent velocity, and descent and ascent speed) were compared between- and within-groups using independent and paired t-tests, respectively, in SPSS.

Results: Hip sagittal, frontal, and transverse plane kinematics are displayed (Figure 1). We detected no between-group differences in 12-month changes in kinematics or moments. Compared to baseline, both groups at follow-up squatted with increased hip external rotation angles and to a greater depth (arthroscopy: mean difference -27.3% limb length [95% confidence interval -35.2, -19.5], p<0.001; PHT: mean difference -24.5% limb length [95% confidence interval -33.4, -15.6], p<0.001). Compared to baseline, the PHT group at follow-up had increased hip abduction during squat descent.

Conclusions: Changes in kinematics and moments during squatting following arthroscopy and PHT did not differ. Participants in both groups squatted with increased external rotation and to a greater depth. Chondrolabral damage is often located anterosuperiorly in FAIS patients, and increased external rotation during squatting may reduce anterior hip loading, potentially altering local hip cartilage stresses.