High risk of new knee injury in elite footballers with previous anterior cruciate ligament injury

Background: Anterior cruciate ligament (ACL) injury is a severeevent for a footballer, but it is unclear if the knee injuryrate is higher on returning to football after ACL injury. Objective: To study the risk of knee injury in elite footballerswith a history of ACL injury compared with those without. Method: The Swedish male professional league (310 players) wasstudied during 2001. Players with a history of ACL injury atthe study start were identified. Exposure to football and alltime loss injuries during the season were recorded prospectively. Results: Twenty four players (8%) had a history of 28 ACL injuriesin 27 knees (one rerupture). These players had a higher incidenceof new knee injury of any type than the players without ACLinjury (mean (SD) 4.2 (3.7) v 1.0 (0.7) injuries per 1000 hours,p = 0.02). The risk of suffering a knee overuse injury wassignificantly higher regardless of whether the player (relativerisk 4.8, 95% confidence interval 2.0 to 11.2) or the knee (relativerisk 7.9, 95% confidence interval 3.4 to 18.5) was used as theunit of analysis. No interactive effects of age or any otheranthropometric data were seen. Conclusion: The risk of new knee injury, especially overuseinjury, was significantly increased on return to elite footballafter ACL injury regardless of whether the player or the kneewas used as the unit of analysis