The Clinical Utility of Strength Measures in Predicting Patient Progression Following ACLR

Background: Prognostic indicators of lack of strength progression or poor self-reported function may alter rehabilitation decision-making following anterior cruciate ligament reconstruction (ACLR). The torque-velocity relationship is a noninvasive measure of muscle function that is altered following ACLR, but its prognostic value has not been explored. Purpose: To compare the torque-velocity relationship of knee extensors (quadriceps) and flexors (hamstrings) between the ACLR and uninvolved limbs and to determine whether the torque-velocity relationship was prognostic of subsequent achievement of satisfactory strength. Study Design: Cohort study; Level of evidence, 3. Methods: Participants following ACLR with bone–patellar tendon–bone or hamstring autografts completed isokinetic knee extension and flexion at 90°/s and 180°/s bilaterally, the International Knee Documentation Committee (IKDC) form, and Knee injury and Osteoarthritis Outcome Score (KOOS) at approximately 5.5 and 8.3 months post-ACLR. The torque-velocity relationship was defined as the difference in torque production across velocities, and relationships were analyzed using 2 × 2 analyses of variance. Binomial logistic regressions were used to determine the association between the torque-velocity relationship, age, sex, and time postsurgery with satisfactory knee extension strength, IKDC, and KOOS at visit 2. Results: This study included 189 participants (22.4 ± 9.3 years; 55.0% female). There were significant increases in the quadriceps torque-velocity relationship from visit 1 (0.22 Nm/kg) to visit 2 (0.34 Nm/kg, P < .001) but no differences in the uninvolved limb ( P = .46) or for the hamstrings ( P = .20). When controlling for sex, age, and graft type, higher visit 1 quadriceps torque-velocity relationships were predictive of a higher likelihood of achieving satisfactory knee extension strength (≥1.23 Nm/kg; odds ratio [OR], 1.05; P = .04). The model was associated with an acceptable IKDC score (≥75.9, P = .01), but the only significant individual predictor was age (OR, 0.94; P < .01). The model was not associated with KOOS Sport score at visit 2 ( P = .24). Conclusion: Quadriceps torque-velocity relationships of the ACLR limbs increased across time but remained less than uninvolved limbs. Hamstrings torque-velocity relationships remained similar between limbs and across time. These findings indicate that the torque-velocity relationship of the quadriceps changed over time and was predictive of future satisfactory strength. Clinical Relevance: Clinicians may use a greater quadriceps torque-velocity relationship as a positive indication of a patient's ability to achieve satisfactory strength later in rehabilitation.