Symmetries in muscle torque and landing kinematics are associated with maintenance of sports participation at 5 to 10 years after ACL reconstruction in young men

Background: Long-term maintenance of sports participation is important for young adults men undergoing ACL reconstruction. Identifying biomechanical characteristics in patients who achieve this goal can assist in elaborating rehabilitation programs and in identifying successful recovery but this has rarely been investigated. Purpose: To test the association between maintenance of sports participation at 5-to-10 years after ACL reconstruction and measures of force production and landing biomechanics in adult men. Study Design: Case series. Level of evidence, 4 Methods: Thirty men with isolated ACL reconstruction were examined. At 5-to-10 year follow-up, associations were tested between reported outcomes of sports maintenance and objective biomechanical measures. The biomechanical tests included isokinetic knee torques and lower limb kinetics and kinematics during landing tasks. Measurements for each limb were conducted separately and side-to-side symmetry indices (SI) were calculated. Subgroups included SI higher than (+)10% (i.e. extreme positive), SI lower than (-)10% (i.e. extreme negative), and SI between -10% and +10% (i.e. symmetric). Results: At follow-up, concentric knee torques in the operated limb correlated with Tegner and Marx scores (r =0.42 to 0.47, p <0.05). Regarding SI of knee torques, highest Tegner, Marx and KOOS scores were associated with symmetric as opposed to patients with extreme positive or extreme negative SI (p <0.05). As for landing kinematics, Tegner score negatively correlated with knee range of motion (ROM) in the operated limb (r =-0.38, p <0.05). With regard to SI, hip and knee ROM correlated with Tegner, IKDC and KOOS scores (r =0.41 to 0.51, p <0.05). Specifically, highest sports participation levels were associated with achieving symmetric hip and knee ROM but also with extreme positive SI as opposed to patients with extreme negative SI (p <0.03) indicating substantially higher ROM in the uninjured limb compared to the operated limb. Conclusion: At 5-to-10 years after ACL reconstruction, maintenance of sports participation is associated with symmetric side-to-side concentric knee torques and with producing greater attenuation of hip and knee ROM during drop jump landing in the operated limb. Therefore, eccentric load programs which can improve attenuation phase kinematics during landing tasks may be valuable in addition to concentric training and facilitate enhanced long-term outcomes.