Factors Associated With the Mechanism of ACL Tears in the National Football League: A Video-Based Analysis

Background: The factors associated with anterior cruciate ligament (ACL) injury mechanism in professional American football players are not well-understood. Hypothesis: It was hypothesized that football-related and player-specific factors, such as position and body mass index (BMI), are associated with ACL injury mechanism in these athletes. Study Design: Descriptive epidemiology study. Methods: Videos of ACL tears occurring in National Football League (NFL) games over 6 consecutive seasons from 2014 to 2019 were reviewed by 2 orthopaedic surgeons who specialize in sports medicine. For each injury, the role of contact (direct contact [contact to the injured knee/lower extremity], indirect contact [contact not involving the injured knee/lower extremity], or no contact) as well as playing situation and lower extremity position were recorded. Additional player characteristics, timing of injury, and surface information were obtained from NFL game-day and injury database statistics. Results: Of the 140 ACL tears, a minority occurred via direct contact to the injured lower extremity (30%), although this varied by position. Just over two-thirds (70%) of ACL tears in offensive linemen occurred via direct contact to the injured lower extremity, while wide receivers had no direct contact ACL tears. Elevated BMI was associated with a greater likelihood of ACL tears occurring via direct contact (53% in players with BMI ≥35 kg/m² vs 24% in players with BMI <35 kg/m²; P = <.01). Rookies had the lowest percentage of direct contact ACL tears (18%; P =.22). ACL tears that occurred during the middle 8 weeks of the regular season resulted more often from direct contact (38%; P =.06). ACL tears that occurred in the third quarter were the most likely to occur via direct contact (44%), while those that occurred in the fourth quarter were the least likely to occur via direct contact (13%; P <.01). Conclusion: Although most NFL players sustained ACL tears via a noncontact mechanism (ie, through indirect or no contact), players with an elevated BMI, especially on the offensive line, were more likely to injure their ACL through direct contact. Position-dependent variance in injury mechanism may help guide injury prevention efforts in these athletes.