Quadriceps Neuromuscular Function and Jump-Landing Sagittal-Plane Knee Biomechanics After Anterior Cruciate Ligament Reconstruction

Context: Aberrant biomechanics may affect force attenuation at the knee during dynamic activities, potentially increasing the risk of sustaining a knee injury or hastening the development of osteoarthritis after anterior cruciate ligament reconstruction (ACLR). Impaired quadriceps neuromuscular function has been hypothesized to influence the development of aberrant biomechanics. Objective: To determine the association between quadriceps neuromuscular function (strength, voluntary activation, and spinal-reflex and corticomotor excitability) and sagittal-plane knee biomechanics during jump landings in individuals with ACLR. Design: Cross-sectional study. Setting: Research laboratory. Patients or Other Participants: Twenty-eight individuals with unilateral ACLR (7 men, 21 women; age = 22.4 +/- 3.7 years, height = 1.69 +/- 0.10 m, mass = 69.4 +/- 10.1 kg, time postsurgery = 52 +/- 42 months). Main Outcome Measure(s): We quantified quadriceps spinal-reflex excitability via the Hoffmann reflex normalized to maximal muscle response (H : M ratio), corticomotor excitability via active motor threshold, strength as knee-extension maximal voluntary isometric contraction (MVIC), and voluntary activation using the central activation ratio (CAR). In a separate session, sagittal-plane kinetics (peak vertical ground reaction force [vGRF] and peak internal knee-extension moment) and kinematics (knee-flexion angle at initial contact, peak knee-flexion angle, and knee-flexion excursion) were collected during the loading phase of a jump-landing task. Separate bivariate associations were performed between the neuromuscular and biomechanical variables. Results: In the ACLR limb, greater MVIC was associated with greater peak knee-flexion angle (r = 0.38, P = .045) and less peak vGRF (r = -0.41, P = .03). Greater CAR was associated with greater peak internal knee-extension moment (q = -0.38, P = .045), and greater H: M ratios were associated with greater peak vGRF (r = 0.45, P = .02). Conclusions: Greater quadriceps MVIC and CAR may provide better energy attenuation during a jump-landing task. Individuals with greater peak vGRF in the ACLR limb possibly require greater spinal-reflex excitability to attenuate greater loading during dynamic movements.