Anterior Cruciate Ligament Injury Mechanisms and the Kinetic Chain Linkage: The Effect of Proximal Joint Stiffness on Distal Knee Control During Bilateral Landings.

BACKGROUND: Neuromuscular deficits at the trunk and hip may contribute to dynamic knee valgus and anterior cruciate ligament injury mechanisms. However, comprehensive examination of neuromuscular patterns and their mechanical influence is lacking.
OBJECTIVES: To investigate the influence of lumbar spine joint rotational stiffness (JRS) and the gluteal musculature contribution to hip JRS on dynamic knee valgus.
METHODS: In this cross-sectional study, 18 university-aged women completed a drop vertical jump while we measured kinematics, kinetics, and 24 channels of electromyography (EMG) spanning the trunk and hip musculature. We classified each limb as high or low valgus, based on frontal plane knee displacement magnitude. We used anatomically detailed, EMG-driven biomechanical models to quantify lumbar spine JRS and muscle contributions to hip JRS.
RESULTS: Low-valgus limbs generated greater gluteus medius frontal JRS (P = .002; effect size, 1.3) and gluteus maximus transverse JRS (P = .003; effect size, 1.2) compared to high-valgus limbs. Participants with bilateral high-valgus collapse had substantially reduced lumbar spine sagittal JRS compared to the group with low valgus on both limbs (P = .05; effect size, 5.1). Those with low valgus on both limbs also had a peak lumbar spine flexion angle of 24° ± 4°, compared to the bilateral high-valgus group's angle of 38° ± 10° (P = .09; effect size, 1.8).
CONCLUSION: Participants who avoided high medial knee displacement had greater proximal JRS. Increased JRS at the lumbar spine and greater JRS contributions from the gluteal musculature are linked with preventing high medial knee displacement. J Orthop Sports Phys Ther 2019;49(8):601-610. Epub 26 May 2019. doi:10.2519/jospt.2019.8248.