Anterior cruciate ligament injury after more than 20 years. II. Concentric and eccentric knee muscle strength

The long‐term consequences on knee muscle strength some decades after rupture of the anterior cruciate ligament (ACL) are not established. The aims of our study were to examine peak torque more than 20 years after ACL injury and to compare their knee muscle strength to that of healthy controls. We tested 70 individuals with unilateral ACL injury 23 ± 2 years after injury, whereof 33 (21 men) were treated with physiotherapy in combination with ACL reconstruction (ACL_R) and 37 (23 men) with physiotherapy alone (ACL_PT). These were compared with 33 age‐ and gender‐matched controls (21 men). A Kin‐Com^® dynamometer (90°/s) was used to measure peak torque in knee flexion and extension in both concentric and eccentric contractions. Knee extension peak torque, concentric and eccentric, was ～10% lower for the injured leg compared with the non‐injured leg for both ACL_R (P < 0.001; P < 0.001) and ACL_PT (P = 0.007; P = 0.002). The ACL_PT group also showed reduced eccentric knee flexion torque of the injured leg (P = 0.008). The strength of the non‐injured leg in both ACL groups was equal to that of controls. No difference was seen for those with no‐or‐low degree of knee osteoarthritis compared to those with moderate‐to‐high degree of osteoarthritis. ACL injury may lead to a persistent reduction of peak torque in the injured leg, which needs to be considered across the lifespan.