A scoping review of subsequent anterior cruciate ligament (ACL) injury in football (Soccer): incidence, associations, and implications

Background Athletes returning to sport following anterior cruciate ligament reconstruction (ACLR) are at increased risk of subsequent ipsilateral reinjury to the graft and contralateral new injury to the native ACL. The objectives of this scoping review were to provide a football-specific evidence synthesis of (1) the extent of the subsequent ACL injury problem; (2) variables associated with subsequent ACL injury and identification of modifiable variables; (3) the implications for future football participation and knee health outcomes; and (4) the effectiveness of injury-prevention measures. Methods A scoping review methodology was employed that adhered to the PRISMA Extension for Scoping Reviews reporting guidelines. Six databases were searched in November 2024 to January 2004. Incidence proportion data were quantitatively synthesised with a random-effects meta-analysis, with all other data being qualitatively synthesised. Results The search retrieved 3597 records and produced 60 eligible studies. Publications since 2018 represented 80% of included studies. Twelve studies of professionals (1,222 players) and 12 studies of amateurs (2,508 players) revealed pooled total incidence proportion for subsequent ACL injury of 18.6% (95% CI 15.3 to 22.4%) and 21.0% (95% CI 16.9 to 25.8%), respectively. Ipsilateral and contralateral knees appeared equally affected in professionals (Ipsilateral 9.8%; Contralateral 9.2%) and amateurs (Ipsilateral 10.6%; Contralateral 11.0%). Returning to football, female sex, and younger age, were identified most frequently as having a positive association with subsequent ACL injury. Following subsequent ACLR, a similar proportion of players return to football and in a similar timeframe as following index ACLR, but with greater reductions in football participation and patient reported outcomes in subsequent years. No studies reported on the effectiveness of injury prevention measures. Conclusions Approximately one-in-five football players with index ACLR experienced a subsequent ACL injury. Knowledge gaps identified include the implications of subsequent ACL injury on long-term knee health and the effectiveness of secondary prevention measures.