Do Neuromuscular Alterations Exist for Patients With Acetabular Labral Tears During Function?

Purpose: To determine if contact forces and electromyography (EMG) muscle amplitudes were altered during the lunge for patients with symptomatic labral tears compared with asymptomatic control subjects. Methods: Surface electromyography electrodes were placed over the gluteus medius, gluteus maximus, adductor longus, and rectus femoris muscles of the patients' involved limb and matched limb of asymptomatic controls. Subjects performed 3 trials of the lunge on a clinical force platform. An electrogoniometer tracked knee flexion motion during testing. Average root mean squared EMG muscle amplitudes for each muscle were calculated for the descent and ascent phases of the lunge, represented as a percentage of maximum activity (%MVIC). Peak knee flexion was calculated from the goniometer (degrees). The dependent variables from the force platform were lunge distance (%height), contact time (seconds), vertical impact force (%BW), and force impulse (%BW(star)s). Dependent variables were compared between groups using either independent samples t tests or Mann-Whitney U tests. Relations between dependent variables were assessed with Spearman Rho correlation coefficients. The level of significance was set at P <= .05. Results: Twenty-one patients with symptomatic unilateral labral tears (14 females, 7 males) and 17 asymptomatic control subjects (11 females, 6 males) participated in this study. Average gluteus maximus EMG muscle amplitudes were reduced for symptomatic labral patients compared with asymptomatic controls during lunge ascent (51.6 +/- 31.1 v 71.7 +/- 36.3 [mean difference (MD): 20.1% (-2.4%, 42.6%)], P = .042). Average vertical impact force was reduced (21.8 +/- 5.5 v 26.8 +/- 7.3 [MD: 5.1%BW (0.84%BW, 9.3%BW)], P = .02) and average contact time (1.8 +/- 0.4 v 1.5 +/- 0.4 [MD: 0.27 seconds (0.006 seconds, 0.54 seconds)], P = .045) and force impulse (188.4 +/- 42.4 v 162.6 +/- 33.3 [MD: 25.8%BW*s (0.3%BW*s, 51.4%BW*s)], P = .042) were increased for symptomatic labral patients compared with asymptomatic controls. Vertical impact force was inversely correlated with gluteus medius muscle amplitudes during lunge descent for symptomatic labral patients (r = -0.452, P = .045). Conclusions: Our study shows that contact forces and EMG muscle amplitudes are altered during the lunge for patients with symptomatic labral tears. The presence of a relation between muscle amplitudes and contact forces suggests that targeting muscle impairments may restore function in these patients. Level of Evidence: Level III, case-control study.