The risk of sustaining a further knee injury is high for players who have sustained an injury to their anterior cruciate ligament (ACL). Various registry studies have shown a lifetime risk of up to 30%. This edition of the FastFact highlights a systematic review and meta-analysis that has investigated risk factors for future ACL injury in the contralateral (non-injured) knee in patients who have had an ACL reconstruction.¹

A total of 44 moderate-to-high quality studies were included in the review, with 35 studies being eligible for meta-analysis. Approximately 59 000 patients were involved in these studies. A total of seven risk factors for further injury were identified while two factors (decreased intercondylar notch width/width of the distal femur ratio and concomitant cartilage injury) were associated with a decreased risk of a subsequent ACL injury.

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. This was associated with an odds radio (OR) of 3.26 (95% CI 2.10–5.06). Clinicians have a duty of care to inform their patients (as well as their family and care givers) about this risk as well as strategies that might be employed to help reduce the risk of further injury. Females, patients younger than 18 years of age, those with an associated meniscal injury and those with a family history of ACL injury are all at an increased risk of sustaining a C-ACL. A potentially modifiable risk factor for further injury relates to the timing of the ACL reconstruction. Those receiving primary reconstruction within 3 months of injury appear to have an increased risk of C-ACL. It is possible that delaying surgery may allow more effective prehabilitation and that this might be protective. Players with a BMI of <25 may also be at an increased risk of further injury.

An area the study’s authors identified with little existing data, is the potential influence of various modifiable factors often addressed during injury prevention programmes. These factors include muscle strength, movement patterns and measures of knee stability. The study’s authors identify a range of limitations with their work. An important consideration for readers of this FastFact is whether the findings are generalisable to football players, especially those at the elite level, give the diverse range of study participants.

Reference
1. Cronström, A., Tengman, E. & Häger, C.K. Risk Factors for Contra-Lateral Secondary Anterior Cruciate Ligament Injury: A Systematic Review with Meta-Analysis. Sports Med (2021). https://doi.org/10.1007/s40279-020-01424-3