ACL Tears: History and Overview History  Most ACL tears occur either with a twisting or hyperextension injury...often during some type of athletic or sporting activity.  Sometimes the injury occurs with contact (such as in a football game), but probably more often, a simple twist or hyperextension is responsible for the injury.  Often the knee swells within the first 15 minutes and the athlete is unable to continue play.  Sometimes ACL tears occur in less dramatic fashion.  Sometimes the athlete' s knee does not swell immediately and sometimes the athlete is able to continue play.  ACL tears can also occur with injuries such as stepping in a hole and other less obvious methods.  For more additional overview, click here for American Academy of Orthopaedic Surgeons link.