This is an excerpt from Preventing Noncontact ACL Injuries eBook by Human Kinetics.
While an ACL injury can be a result of direct contact with another player or an object to the lower extremity, it has been reported that approximately 70% of ACL injuries result from situations that do not involve direct contact (Boden et al. 2000; McNair, Marshall, and Matheson 1990). It is clear that given adequate force, a direct blow to the lower extremity could result in an ACL injury. However, a mechanism that does not result from such contact may be more difficult to define. Such mechanisms are typically associated with evasive maneuvers that involve some form of deceleration, change of direction, or landing (Boden et al. 2000; Olsen et al. 2004; Cochrane et al. 2007). ACL injury mechanisms that are not the result of direct contact to the knee are of particular interest because their etiology is not clear.
It is important to further distinguish injuries that occur concurrently with contact to a part of the body other than the lower extremity. This type of injury mechanism is referred to as indirect contact. Most statistics reporting injury mechanism do not address issues related to indirect contact. However, the consequence of such contact was highlighted by Olsen and colleagues (2004) after analyzing videotapes of 20 ACL injuries captured during team handball competitions. They found that 6 of 19 injuries, typically classified as noncontact, involved some type of contact to the body by another player. The perturbation caused by this contact may have unexpectedly altered the individual's lower-extremity alignment, center of mass, or direction of movement in a manner that she was not prepared to manage. This has particular implications for training programs because there is a need to prepare athletes for such perturbations. For the purposes of designing a training program, we will be focusing on the noncontact ACL injuries with the understanding that this includes mechanisms related to indirect contact as well.
To gain perspective on the extent of this problem, we will review what is known in regard to injury incidence in the general population, within sports, between sexes, and across age groups. Additional information regarding the occurrence of noncontact ACL injuries in sports that are considered to be high risk for knee injury will be presented. Together this information will help direct intervention strategies toward populations at elevated risk for injury.
The number of anterior cruciate ligament injures in the general population is thought to be relatively low. Determining the overall incidence of anterior cruciate ligament injury in the general population is difficult given the limited availability of accurate data. However, an analysis of the 2003 National Ambulatory Care Database provided some insight into this issue. These data estimate that cruciate ligament injuries accounted for approximately one million hospital outpatient department, emergency room, and physician office visits in the United States in 2003. While this may seem high, one must consider that the total population of the United States was close to 290 million and the total number of visits for unintentional injuries was between 90 and 136 million for the same year (Hewett 2007). One must be careful not to interpret these data as a reflection of incidence of ACL injury for a couple reasons. First, these data are referring to both anterior and posterior cruciate ligament injuries. Additionally, the numbers represent office visits, which would include initial and follow-up visits. Because cruciate ligament injuries typically require more than one visit with the doctor, these data would be more representative of the overall burden on the health care system.