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 
rate was 15% (ipsilateral reinjury rate of 7% and contralateral injury rate of 8%). The secondary ACL injury rate for patients younger than 25 years was 21%. The secondary ACL injury rate for athletes who return to a sport was also 20%. Combining these risk factors, athletes younger than 25 years who return to sport have a secondary ACL injury rate of 23%.
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
