Risk Factors for Anterior Cruciate Ligament Injury in High School and College Athletes Becky Woodford-Rogers, ATC, PT Lynne Cyphert, PT Craig R. Denegar, PhD, ATC, PT Abstract: The anterior cnrciate (ACL) is the most frequently ruptured ligament of the knee. Some authors have sug- gested that excessive internal tibial rota- tion concomitant with hyperpronation of the subtalarjoint duringstance and inher- ent knee joint laxity may predispose an athlete to knee injury. Over a period of 2 years, we identified 14ACL-injured foot- ball players and eight ACL-injured fe- male basketball players and gymnasts. We matched them by sport, team, posi- tion, and level ofcompetition with 22 ath- letes without history ofACL injury. Mea- sures of navicular drop, calcaneal alignment, and anterior knee joint laxity with a K7-1000 were obtained from the uninjured knee of the ACL-injured ath- letes and compared with measures ob- tainedfrom theACL-noninjured athletes. ACL-injured athletes had greater amounts of navicular drop, suggesting greater subtalar pronaton and greater anterior knee joint laxity. Discriminant analysis and multiple regression indi- cated that these variables correctly pre- dicted injury status for 87.5% of the fe- males and for 70.5% of all cases. These Becky Woodford-Rogers is Orthopaedic Coordinator at Aurora Presbyterian Hos- pital in Aurora, CO 80011. Lynne Cyphert is a staff physical therapist at North Hills Passavant Hospital in Pitts- burgh, PA 15237. Craig R. Denegar is an associate professor in the School of Physical Therapy at Slip- pery Rock University in Slippery Rock, PA 16057. results suggest that the more an athlete pronates and the greater the anterior knee joint laxity, the greater the associa- tion with ACL injury. T nhe anterior cruciate ligament (ACL) is the most frequently rup- tured ligament of the knee.12 The mechanism of ACL injury is often de- scribed as noncontact. Previous authors have reported that 78%2° and 71%4 of ACL-injured patients described noncon- tact mechanisms of injury. It has been suggested that excessive intemal tibial ro- tation concomitant with hyperpronation of the subtalar joint during stance4 and inherent knee joint laxity17 may predis- pose an athlete to ACL injury. While much has been written on injury to the anterior cruciate ligament, little at- tention has been devoted to understand- ing the mechanism of injury.9 A greater understanding of the mechanics of injury are needed as we work to prevent, and improve treatment of, injuries to the ACL.9 We conducted this investigation to develop a better understanding of the risks of ACL injury. For, if our efforts of prevention are to succeed to their fullest potential, we must be able to identify those athletes at greatest risk. The purposes of our study were: 1) to determine if clinical measurements used to assess pronation and anterior translation of the tibia on the femur dis- criminate between-ACL injured and ACL-noninjured athletes matched for sport, team, and position, and 2) to identify those measures which are the strongest discriminators between the two groups. Methods We assessed the uninjured lower ex- tremity of 14 ACL-injured male high school and college football players and eight ACL-injured female high school- and college gymnasts (n = 6) and bas- ketball players (n = 2) using clinical measures indicative of pronation and anterior displacement of the tibia on the femur. All of the ACL-injured fe- males and 10 of the males clearly de- scribed a noncontact mechanism of in- jury. We also selected an equal number of athletes, matched for sport, position, and playing time, without history of ACL injury, and assessed both lower extremities. All subjects provided in- formed consent in compliance with uni- versity guidelines. Data collection was conducted in two phases during a 2-year period. In the first phase, 14 high school and col- lege football players (19.1 + 6.0 years, 73.2 + 3.3 in, 211.0 + 47.9 lb) with a history of unilateral ACL injury, con- firmed arthroscopically or during ar- throtomy, were identified. We matched the injured athletes with 14 football players (18.1 + 1.6 years, 72.3 + 2.9 in, 199.6 + 36.6 lb) without history of a knee injury more severe than a first de- gree sprain, by team, position, and ex- tent of participation. In the second year of data collection, we identified and matched eight ACL- injured female athletes (six gymnasts and two basketball players) (19.5 + 1.7 years, 64.6 + 3.7 in, 128.0 + 17.0 lb) with eight uninjured athletes (19.0 ± 1.2 years, 63.3 + 2.6 ins, 126.9 ± 12.8 lbs) by sport, injured leg, and level of competition. We obtained measures of calcaneal alignment changes in stance, navicular drop, and anterior translation of the tibia on the femur bilaterally from the ACL- noninjured athletes and from the ACL- uninjured lower extremity of the ACL- injured athletes. We selected the uninjured lower extremity so that all mea- sures came from the same extremity and so that athletes whose weight bearing was restricted secondary to surgery could be included in the study. Calcaneal alignment was assessed in a nonweight-bearing position by having the athlete lie prone and place the con- tralateral leg in the figure 4 position (see Figure). The lower one third of the leg was bisected from the musculoten- dinous junction of the triceps surae to the Achilles tendon. The medial and lateral tubercles of the calcaneus were Journal of Athletic Training 343