Characterizing Knee Extensor Function After Acl Reconstruction Through The Torque-velocity Relationship

Patients post-ACL reconstruction (ACLR) experience persistent quadriceps strength deficits. While knee extensor strength symmetry post-ACLR offers insight to performance capacity, evaluating the torque-velocity relationship (TVR) may holistically describe muscle function thereby better informing rehabilitation progression. PURPOSE: To characterize knee extensor function after ACLR through the TVR. METHODS: Thirty-two patients (Sex: 17F, 15 M; Age: 28 ± 11 years) underwent bilateral strength testing during the post operative rehabilitation period, prior to release to unrestricted physical activity. Patients completed 6 maximal effort repetitions of isokinetic concentric knee extension at 60, 120, and 240°/s with 30s rest between sets. Subjective knee function was evaluated with the IKDC patient reported outcome instrument. The TVR was determined for each limb by calculating the best fit line slope for the peak knee extension torques across velocities. TVR symmetry was calculated by ACLR/CONTRA *100%. Paired samples t-tests were used to compare TVR between limbs. Correlation coefficients were used to determine associations between TVR or symmetry with IKDC score. Statistical analyses were stratified based on time post-surgery (4, 6, and 8 months). RESULTS: The ACLR limb TVR was significantly smaller (flatter, negative slope) than the CONTRA limb TVR at all time points (Table 1). At 4 months, a greater IKDC score was correlated with smaller ACLR TVR, but greater CONTRA TVR. At 8 months, a greater IKDC score was correlated with greater CONTRA TVR. Symmetry was not correlated with IKDC at any time point (Table 1). CONCLUSIONS: Smaller ACLR limb TVR compared to CONTRA limb suggests altered knee extensor function post-ACLR. Table 1. - Means ± SD for IKDC score, ACLR and CONTRA torque-velocity, and symmetry. * = significant difference between limbs (p < .05). ^ = significant correlation with IKDC score (p<.05). 4 months (n=22) 6 months (n=14) 8 months (n=13) IKDC Score Mean ± SD 66.04±2.50% 81.36±11.74% 78.34±14.36% ACLR Mean Slope ± SD -0.14±0.13* -0.28±0.16 -0.22±0.13 r -.56^ -.23 .01 CONTRA Mean Slope ± SD -0.59±0.21* -0.55±0.38 -0.65±0.12 r -.57^ -.15 -.60^ Symmetry Mean Slope ± SD 25.41±24.64% 46.07±7.49% 33.23±18.31% r .34 .37 -.20