PURPOSE: To investigate the association between maximal isometric gluteus medius (GM) strength and pelvic/hip control during running and single-leg landings and to evaluate the efficacy of 3D kinematic and kinetic measures of dynamic hip abductor control, compared with maximal strength, for assessing pelvic instability of the operated limb 5-7 months after anterior cruciate ligament (ACL) reconstruction. METHODS: A total of 644 patients were analysed 5-7 months after primary ACL reconstruction. Each subject performed the following exercises: running (run pelvic drop RPD), single-leg drop jump and single-leg hop, with 3D analysis synchronised to force platforms. Isometric abduction strength was assessed using the VALD system. Binary and ordinal logistic analyses (likelihood ratio LR type II test, false discovery rate FDR correction) identified predictors of proximal instability on the operated and contralateral sides. RESULTS: On the operated side, pelvic and trunk oscillations were the main predictors of greater pelvic drop (LR χ² = 96-174, p < 0.001), with less knee flexion. In the drop jump, greater pelvic tilt was associated with longer contact time (LR χ² = 42.7, p < 0.001), lower jump height and greater trunk inclination, indicating a rigid landing strategy. The isometric strength of the GM and quadriceps showed no significant associations with RPD except for the knee flexors that showed a modest effect on RPD (LR χ² = 6.09/6.4, p ≈ 0.013/0.04). On the healthy side, the same variables were present but with less intensity, suggesting stable compensatory behaviour. CONCLUSION: At 5-7 months after ACL reconstruction, proximal instability is specific to the operated limb and depends on deficits in coordination and neuromuscular timing rather than on strength deficiencies. Dynamic parameters describe pelvic stability more accurately than isometric strength. LEVEL OF EVIDENCE: Level III, retrospective cross-sectional study on a prospectively enrolled cohort.
Blancato et al. (Wed,) studied this question.