The Influence of Quadriceps Strength and Rate of Torque Development on the Recovery of Knee Biomechanics During Running After Anterior Cruciate Ligament Reconstruction.

Background: After anterior cruciate ligament reconstruction (ACLR), altered surgical knee biomechanics during running is common. Although greater quadriceps strength is associated with more symmetrical running knee kinetics after ACLR, abnormal running mechanics persist even after resolution of quadriceps strength deficits. As running is a submaximal effort task characterized by limited time to develop knee extensor torque, quadriceps rate of torque development (RTD) may be more closely associated with recovery of running knee mechanics than peak torque (PT).

Purpose: To assess the influence of recovery in quadriceps PT and RTD symmetry on knee kinematic and kinetic symmetry during running over the initial 2 years after ACLR.

Study Design: Cohort study; Level of evidence, 3.

Methods: A total of 39 Division I collegiate athletes (106 testing sessions; 19 female) completed serial isometric performance testing and running analyses between 3 and 24 months after ACLR. Athletes performed maximal and rapid isometric knee extension efforts with each limb to assess PT and RTD between-limb symmetry indices (PT and RTD), respectively. Peak knee flexion difference (PKF) and peak knee extensor moment limb symmetry index (PKEM) during running were computed. Multivariable linear mixed-effects models assessed the influence of PT and RTD on PKF and PKEM over the initial 2 years after ACLR.

Results: Significant main effects of RTD ( < .001) and time (≤ .02) but not PT (≥ .24) were observed for both PKF and PKEM models. For a 10% increase in RTD, while controlling for PT and time, a 0.9° (95% CI, 0.5°-1.3°) reduction in PKF and a 3.5% (95% CI, 1.9%-5.1%) increase in PKEM are expected. For every month after ACLR, a 0.2° (95% CI, 0.1°-0.4°) reduction in PKF and a 1.3% (95% CI, 0.6%-2.0%) increase in PKEM are expected, controlling for PT and RTD.

Conclusion: Quadriceps RTD was more strongly associated with symmetrical knee biomechanics during running compared with PT or time throughout the first 2 years after ACLR.