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

Background:   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.

Methods:   Cross-sectional study. Methods:   Research laboratory. Methods:   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). Methods:   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 (ρ = -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.