Return-to-sport assessment for preventing ACL re-injury: An experimental and musculoskeletal modeling approach

Abstract This study aimed to propose a return-to-sport procedure for preventing a second anterior cruciate ligament (ACL) injury in football (soccer) players. Six professional male football players, three of whom had undergone ACL reconstruction (ACLR), performed normal overground walking gait tests. Muscle activations and forces, knee joint kinematic and kinetic parameters, and ACL loading were obtained using electromyography (EMG) and OpenSim musculoskeletal analysis. Asymmetry in muscle activation between the dominant and non-dominant legs was observed in both the ACLR and control groups and was more pronounced in the ACLR subjects. Significant limb asymmetries were also observed in the gait cycle of the ACLR subjects. These asymmetries after ACLR were associated with increased ACL loading and, consequently, a higher risk of ACL re-injury. Therefore, an injury risk index (IRI) was introduced to assess the risk of a second ACL injury based on the maximum ACL graft force during the gait cycle. The IRI was significantly higher in the ACLR group than in the control group. Based on these findings and the proposed index, a return-to-sport procedure was developed that accounts for ACL loading in both the injured and contralateral legs. This procedure may help physicians prescribe specific rehabilitation programs for football players after ACLR and reduce the risk of ACL re-injury. The results also suggest that rehabilitation programs after ACLR should specifically target the quadriceps and gastrocnemius muscles to reduce lower-limb asymmetries.