Squatting biomechanics following physiotherapist-led care or hip arthroscopy for femoroacetabular impingement syndrome: a secondary analysis from a randomised controlled trial

Background: Femoroacetabular impingement syndrome (FAIS) can cause hip pain and chondrolabral damage that may be managed non-operatively or surgically. Squatting motions require large degrees of hip flexion and underpin many daily and sporting tasks but may cause hip impingement and provoke pain. Differential effects of physiotherapist-led care and arthroscopy on biomechanics during squatting have not been examined previously. This study explored differences in 12-month changes in kinematics and moments during squatting between patients with FAIS treated with a physiotherapist-led intervention (Personalised Hip Therapy, PHT) and arthroscopy. Methods: A subsample (n = 36) of participants with FAIS enrolled in a multi-centre, pragmatic, two-arm superiority randomised controlled trial underwent three-dimensional motion analysis during squatting at baseline and 12-months following random allocation to PHT (n = 17) or arthroscopy (n = 19). Changes in time-series and peak trunk, pelvis, and hip biomechanics, and squat velocity and maximum depth were explored between treatment groups. Results: No significant differences in 12-month changes were detected between PHT and arthroscopy groups. Compared to baseline, the arthroscopy group squatted slower at follow-up (descent: mean difference −0.04 m∙s⁻¹ (95%CI [−0.09 to 0.01]); ascent: −0.05 m∙s⁻¹ [−0.11 to 0.01]%). No differences in squat depth were detected between or within groups. After adjusting for speed, trunk flexion was greater in both treatment groups at follow-up compared to baseline (descent: PHT 7.50^◦ [−14.02 to −0.98]%; ascent: PHT 7.29^◦ [−14.69 to 0.12]%, arthroscopy 16.32^◦ [−32.95 to 0.30]%). Compared to baseline, both treatment groups exhibited reduced anterior pelvic tilt (descent: PHT 8.30^◦ [0.21–16.39]%, arthroscopy −10.95^◦ [−5.54 to 16.34]%; ascent: PHT −7.98^◦ [−0.38 to 16.35]%, arthroscopy −10.82^◦ [3.82–17.81]%), hip flexion (descent: PHT −11.86^◦ [1.67–22.05]%, arthroscopy −16.78^◦ [8.55–22.01]%; ascent: PHT −12.86^◦ [1.30–24.42]%, arthroscopy −16.53^◦ [6.72–26.35]%), and knee flexion (descent: PHT −6.62^◦ [0.56– 12.67]%; ascent: PHT −8.24^◦ [2.38–14.10]%, arthroscopy −8.00^◦ [−0.02 to 16.03]%). Compared to baseline, the PHT group exhibited more plantarflexion during squat ascent at follow-up (−3.58^◦ [−0.12 to 7.29]%). Compared to baseline, both groups exhibited lower external hip flexion moments at follow-up (descent: PHT −0.55 N∙m/BW∙HT[%] [0.05–1.05]%, arthroscopy −0.84 N∙m/BW∙HT[%] [0.06–1.61]%; ascent: PHT −0.464 N∙m/BW∙HT[%] [−0.002 to 0.93]%, arthroscopy −0.90 N∙m/BW∙HT[%] [0.13–1.67]%). Conclusion: Exploratory data suggest at 12-months follow-up, neither PHT or hip arthroscopy are superior at eliciting changes in trunk, pelvis, or lower-limb biomechanics. Both treatments may induce changes in kinematics and moments, however the implications of these changes are unknown.