Muscle function is associated with future patient-reported outcomes in young adults with ACL injury

BACKGROUND/AIM: Consequences of an anterior cruciate ligament (ACL) injury include worse patient-reported outcomes (PROs) and a decrease in activity level. Muscle function can be improved by targeted exercise. Our aims were to investigate cross-sectional and longitudinal associations among lower extremity muscle function and PROs after ACL injury. METHODS: Fifty-four participants (15 women, mean 30 years) with ACL injury or reconstruction, from the Knee Anterior Cruciate Ligament, Nonsurgical versus Surgical Treatment (KANON) trial (ISRCTN84752559), were assessed with hop performance, muscle power and postural orientation 3 years (SD 0.85) after ACL injury. PROs at 3 and 5 years after injury included Knee Injury and Osteoarthritis Outcome Score (KOOS) subscales Function in sport and recreation (KOOS Sport/rec) and Knee-related Quality of life (KOOS QoL), KOOS item Q3 (KOOS Q3), Tegner Activity Scale and Activity Rating Scale (ARS). Partial Spearman's rank-order correlation was used to analyse correlations between muscle function and PROs, controlling for gender and treatment. RESULTS: Numerous cross-sectional correlations were observed between muscle function and PROs (r(sp)≈0.3–0.5, p≤0.045). Worse hop performance and worse postural orientation were associated with worse KOOS scores 2 years later (r(sp)≥0.280, p≤0.045). Worse muscle power was associated with lower future ARS scores (r(sp)=0.281, p=0.044). CONCLUSIONS: The moderate associations suggest that improving muscle function during rehabilitation could improve present and future PROs.