Figure 1: Trajectory of Injured Limb Knee Extension Torque by Injury Type*
Knee extensor and flexor muscle (ie, thigh) weaknesses are well-established consequences of anterior cruciate ligament (ACL) tears treated with ACL reconstruction (ACLR). To learn more, Canadian researchers assessed bilateral knee extensor and flexor concentric isokinetic peak torque at 90° per second semiannually in 186 youth (106 injured, 80 controls) for 2 years. Between group differences in strength over time were estimated with generalized estimating equations (95% confidence interval [CI]). Confounding was controlled using inverse probability weighting. Strength differences between those with ACL tears and those with non-ACL tear injuries as well as between male and female participants were explored.
Their results showed that compared to uninjured controls, injured limb knee extensor strength was lowest at baseline (−37.1 Nm; 95% CI, −45.3 to −28.9) and 6-month follow-up (−13.3 Nm; 95% CI, −20.4 to −6.2), with minimal strength gain beyond the 12-month follow-up (1.7 Nm; 95% CI, −14.3 to 17.6). Knee flexor strength of the injured limb was lowest at baseline (−24.6 Nm; 95% CI, −31.5 to −17.8), and there was minimal strength gain beyond 6 months (2.3 Nm; 95% CI, −7.7 to 12.3). The average residual deficit was similar to the knee extensors (10% to 11%) at 24 months. Exploratory analysis suggested no difference based on injury type or sex.
Figure 2: Trajectory of Injured Limb Knee Flexor Torque by Injury Type*
Injured limb knee extensor and flexor weakness was present after different youth sport-related knee joint injuries. Strength deficits peaked early after injury, improved over time, and plateaued after 12 months, with lingering deficits at 24 months. Thigh muscle strength trajectory was similar across injury types and sex.
Source: Losciale JM, Le CY, Jansen NEJ, et al. Strength Setbacks: The Impact of Youth Sport-Related Knee Joint Injuries on Thigh Muscle Strength. A 24-Month Prospective Cohort Study. J Orthop Sports Phys Ther. 2025;55(2):137-147. doi: 10.2519/jospt.2024.12663.
