Knee Extensor Torque Variability Correlates With Impaired Functional Knee Kinetics After ACLR In Collegiate Athletes

Abstract

Quadriceps neuromuscular dysfunction is universal following anterior cruciate ligament reconstruction (ACLR). Quadriceps performance is often characterized by peak strength, but the ability to generate consistent knee extensor (KE) torque is not captured by maximal strength assessments and may be functionally significant. Torque steadiness (TS) quantifies the capacity to produce smooth and consistent contractile forces, but is not well-defined post-ACLR. PURPOSE: To evaluate KE TS in collegiate athletes 4, 6, and 12 months post-ACLR, and determine the associations between TS, strength, and knee joint kinetics during athletic tasks. METHODS: 13 Division I athletes (age 20.5 ± 1.0, BMI 26.3 ± 4.7, 6 male) completed maximal voluntary isometric KE contractions (MVIC), countermovement jumps (CMJ), and treadmill running (2.68 m/s) while 3D kinematics and ground reaction forces were recorded 4.1 ± 0.6 (4), 6.3 ± 0.6 (6) and 11.9 ± 1.1 (12) months post-surgery. TS was defined as the mean difference between raw KE torque and a lowpass filtered signal (4th order butterworth filter, 2 Hz cutoff) within a 4 second torque plateau window. Sagittal plane KE impulses were computed from the stance phase of running (RUN) and the concentric (CON) and landing (LAND) CMJ phases. Wilcoxon Signed-Ranks tests assessed between-limb comparisons at each interval, and Spearman’s correlation evaluated the associations between TS, MVIC, and KE impulses. RESULTS: Involved limb TS was significantly reduced at 4 (limb symmetry index (LSI): 36.8%, p = .002), 6 (LSI: 75.3%, p = .001), and 12 months post-surgery (LSI: 84.7%, p = .033). TS was significantly associated with RUN at 4 and 6 months post-surgery (rs = .881 and .865), CON at 4, 6, and 12 months (rs = .720, .587, and .708), and LAND at 6 and 12 months (rs = .678 and .564). MVIC was significantly correlated with RUN at 4 months (rs = .762) and CON at 4, 6, and 12 months (rs = .787, .587, and .689). TS and MVIC were not correlated at any interval (rs = -.335, -.346, and -.225). CONCLUSIONS: KE TS is reduced 4-12 months post-ACLR in collegiate athletes, and asymmetrical TS is generally strongly associated with asymmetrical KE kinetics. KE TS and strength appear to be unique characterizations of quadriceps performance post-ACLR. Interventions to improve KE TS post-ACLR are recommended to restore knee function.