Impaired Quadriceps Rate of Torque Development and Knee Mechanics after Anterior Cruciate Ligament Reconstruction with Patellar Tendon Autograft

Background: Rate of torque development (RTD) measures the ability of a muscle to produce torque quickly. Decreased quadriceps RTD may impair performance of sporting tasks after surgery. Currently, little is known about variations in quadriceps RTD between anterior cruciate ligament (ACL)-reconstructed and noninjured limbs. Purpose: To determine the differences in RTD of the quadriceps, the rate and timing of knee extensor moment (KEM) development, and knee flexion excursion during running after ACL reconstruction with patellar tendon autograft. Study Design: Cross-sectional study; Level of evidence, 3. Methods: This study involved 21 patients (11 female) 6 months after ACL reconstruction with patellar tendon autograft (median [IQR]: age, 18 [16-20] years; mass, 68.18 [61.34-75] kg; height, 1.74 [1.66-1.78] m). Patients performed four 5-second maximal voluntary isometric strength trials of both limbs on an isokinetic dynamometer. RTD was calculated as the mean slope of the torque-time curve between 20% and 80% of total time to peak torque. Then, patients underwent 3-dimensional motion analysis while running on an instrumented treadmill at a self-selected running speed (mean ± SD, 2.68 ± 0.28 m/s). The rate of knee extensor moment (RKEM) was calculated as the mean slope of the moment curve between 10% and 30% of stance phase. Between-limb comparisons were determined with a paired t test for peak KEM, RKEM, knee flexion excursion during 10% to 30% of stance, and time to generate KEM. Results: In the reconstructed limb, deficits in the peak rate of quadriceps torque development compared with the noninjured limb existed both isometrically (RTD, 257.56 vs 569.11 Nm/s; P <.001) and dynamically (RKEM, 16.47 vs 22.38 Nm/kg·m·s; P <.001). The reconstructed limb also generated a KEM later in the stance phase compared with the noninjured limb (11.37% vs 9.61% stance; P <.001) and underwent less knee flexion excursion (15.5° vs 19.8°; P <.001). Conclusion: After ACL reconstruction with patellar tendon autograft, patients have lower RTD and RKEM in the reconstructed limb. Deviations in RTD and the timing of the KEM can change the way the knee is loaded and can potentially increase injury risk and future development of posttraumatic osteoarthritis. Rehabilitation should consider exercises designed to improve RTD and prepare the limb for the demands of sport performance.