Intrinsic and extrinsic risk factors for anterior cruciate ligament injuryin Australian footballers

The aim of this study was to examine the interaction between intrinsic (pla yer-related) and extrinsic (environment-related) variables as risk factors for anterior cruciate ligament injury in Australian football. Between 1992 and 1999, 100,820 player-match exposures were analyzed for risk of anterior cruciate ligament injury using logistic regression analysis. There were 63 surgically proven noncontact anterior cruciate ligament injuries. The stro ngest risk factors were a player history of anterior cruciate ligament reco nstruction either in the previous 12 months (relative risk [RR], 11.33; 95% confidence interval [CI], 4.02 to 31.91) or before the previous 12 months (RR, 4.44; 95% CI, 2.46 to 8.01). Weather conditions that were associated w ith dry field conditions-high water evaporation in the month before the mat ch (RR, 2.55; 95% CI, 1.44 to 4.52) and low rainfall in the year before the match (RR, 2.87; 95% CI, 1.30 to 6.32)-were also significantly associated with these injuries. The increased risk of injury in the first 12 months af ter reconstruction was associated with the reconstructed knee, whereas afte r 12 months there was an even distribution of new injuries to the reconstru cted knee and contralateral knee. A history of anterior cruciate ligament r econstruction is a risk factor for further injury. Weather conditions of hi gh evaporation and low rainfall before matches are associated with nonconta ct anterior cruciate ligament injury.