Long-term muscle weakness may increase the risk of knee reinjury after anterior cruciate ligament reconstruction (ACLR) and of osteoarthritis. The incidence of secondary injuries after ACLR and the predictive value of preoperative and postoperative limb symmetry index (LSI) and estimated preinjury capacity (EPIC) index were studied for predicting the risk of reinjury in a retrospective study. Sixty-three recreational and professional athletes after ACLR with hamstring autograft were followed for secondary injury in the period from 2012 to 2014, 5 years after ACLR. Peak torque values of knee extensor and flexor muscle strength of the involved and uninvolved limb were measured with an isokinetic dynamometer at 60 degrees per second before ACLR and 6 months after ACLR and were used to calculate LSI and EPIC index. The results suggest that the preoperative LSI and EPIC indexes predict a secondary ACL injury better than the postoperative LSI for extensor muscles which is often used as a criterion to determine the time for returning to normal sports activities. Individuals with secondary ACL injuries suffer greater loss of knee extensor muscle strength of the uninvolved limb between preoperative and postoperative ACLR testing compared to the individuals without secondary injury.

Background: Healthcare restrictions on non-urgent services during the COVID-19 pandemic led to limited access to rehabilitation and delayed treatment, potentially affecting early and mid-term recovery following anterior cruciate ligament reconstruction (ACLR). However, little is known about its specific consequences on muscle strength recovery in recreational and amateur athletes. Objectives: This study aimed to compare short-term clinical outcomes in ACLR patients before, during, and after the pandemic, spanning from 2020 to 2022. Methods: We conducted a retrospective review of 126 patients who underwent ACLR using a hamstring tendon autograft. Patients were grouped based on the timing of surgery and matched for gender. Clinical outcomes and muscle strength parameters were evaluated using an isokinetic dynamometer. Results: Male patients exhibited no significant differences in muscle strength across all time frames (control, 2020, 2021, and 2022). In contrast, female patients who underwent surgery in 2020 and 2021 showed higher extension asymmetry index deficits (Q-AI: 34.09 ± 14.59% and 36.47 ± 16.36%, respectively) and increased flexion deficits in 2021 (H-AI: 25.14 ± 11.41%). Significant differences were observed in quadriceps and hamstring peak torque values, both absolute and normalized. By 2022, the female group exhibited a reduced extension deficit (Q-AI: 18.64 ± 14.49%) comparable to pre-pandemic levels (Q-AI: 19.84 ± 12.37%), indicating a recovery of knee extensor strength. Conclusion: Our study showed gender-specific differences in muscle strength recovery after ACLR during the COVID-19 pandemic, with females showing poorer outcomes than males at 5 months post-operation. Larger studies with extended follow-up are needed to clarify the pandemic’s impact and gender-specific responses.