Returning to a high activity level was the risk factor with the highest odds for sustaining a contra-lateral anterior cruciate ligament (C-ACL) injury following primary unilateral ACL injury.

In addition, females, individuals younger than 18 years, those with a family history of ACL injury and those receiving primary reconstruction within 3 months of injury had an increased risk of C-ACL.

Very few studies were identified investigating the potential influence of modifiable factors, including muscle strength, movement patterns and knee stability on the risk of C-ACL injury.