919 EP006 – Tired of re-injury: adolescent females cleared for return after ACL reconstruction make strength gains but lack the muscular endurance of their adolescent peers

Background The ACL is the most injured ligament in the knee, and the rate is rising in the female adolescent population. Return to play (RTP) guidelines often consider the strength of ACL injured patients with respect to their contralateral limb, but rarely with respect to their adolescent peers, nor is muscular endurance commonly assessed at RTP. Objective To compare the muscular endurance of female adolescent ACLr patients at RTP with their uninjured peers. Participants 21 females (Age=16.0 ±1.5) with a ACL repair (ACLr), and 21 control (CON) female participants (Age=14.3±1.9) Main outcomes Isokinetic knee flexor and extensor torque. Testing of the ACLr participants occurred following clearance for full RTP. All participants performed 44 maximal repetitions of isokinetic concentric knee flexion and extension on a Biodex dynamometer at 90deg/s. Electromyography was recorded from their quadriceps following the SENIAM guidelines. The change in knee extension torque and quadriceps muscle activation was measured as the percent difference between the mean of repetitions 5 to 10, and the mean of repetitions 39 to 44. Results The ACLr participants displayed a greater decrease in knee flexion torque (p=0.047, d= 0.633) and a greater increase in quadriceps activation (p<0.001, d=1.212) from start to finish compared to the uninjured CON participants. Conclusion Despite having undergone rehabilitation and being cleared for RTP, female ACLr participants produced significantly greater quadriceps activation to output similar torque levels, indicating a lack of muscular endurance compared to their uninjured peers. Typical maximal strength tests will not uncover these functional deficits in the ACL injured population at RTP assessment. Furthermore, this lack of muscular endurance may place these athletes at increased risk of injury and could help explain the high rates of re-injury in the adolescent female population.