The Torque-Velocity Relationship and Second ACL Injury Risk

Context Anterior cruciate ligament (ACL) injury results in an elevated risk of reinjury despite surgical ACL reconstruction (ACLR). According to the torque-velocity relationship, muscle contraction velocity and torque production should be inversely related, but this is altered following ACLR. Objective To determine the prognostic ability of the torque-velocity relationship to predict future ACL injury in patients recovering from primary ACLR. Design Descriptive laboratory study. Setting Research laboratory. Patients or Other Participants Primary unilateral ACLR patients (n = 579, 50% female), on average, aged 23.5 ± 10.3 years, 1.73 ± 0.10 m, 75.8 ± 17.8 kg, 6.9 ± 2.0 months post-ACLR, participated in this study. Main Outcome Measure(s) Participants completed isokinetic knee extension at 90°/s and 180°/s bilaterally. Peak torque normalized to body mass was used to calculate the torque-velocity relationship. Reinjury outcomes were determined following surgery via follow-up phone calls and medical record reviews with a minimum follow-up time point of 2 years post-surgery. Any subsequent ACL injury to either limb was classified as a reinjury. Results Approximately 14.0% (81/579) of patients suffered reinjury. Reinjury rates were similar by sex ( p = .97) and graft type ( p = .82). A 1 Nm/kg increase in the quadriceps torque-velocity relationship was associated with increased odds of sustaining a reinjury (odds ratio: 3.52; 95% confidence interval (CI) = 1.03, 12.00; p = .045). Each year older participants were was associated with a 6% decrease in reinjury risk (odds ratio: 0.94; 95% CI = 0.91, 0.98; p < .01). Conclusions The quadriceps torque-velocity relationship was predictive of subsequent ACL injury following ACLR and had higher odds of subsequent injury compared with single velocity testing. Increased strength may have influenced return to sport decision making and increased exposure to risk at an earlier point post-ACLR. This may indicate that clinicians should consider increased surveillance of strong young patients and additional modifiable risk factors to enhance reinjury prediction.