A recent systemic review looked at second ACL injuries among young athletes. These injuries included tears of the surgical leg or the opposite, uninjured knee. Overall, the total second ACL reinjury
This combined data indicates that nearly 1 in 4 young athletic patients who sustain an ACL injury, and return to high-risk sports, will go on to sustain another ACL injury at some point in their career, and they will likely sustain it early in the return-to-play period.
Source: American Journal of Sports Medicine, Published online January 15, 2016