ACL Research Retreat V: An Update on ACL Injury Risk and Prevention, March 25–27, 2010, Greensboro, NC

Multiple factors, whether individually or in combination, likely contribute to noncontact anterior cruciate ligament (ACL) injury. Although research has increased our understanding of contributing factors, much remains unknown, and continued research is needed. To that end, the fifth ACL Research Retreat was held at the University of North Carolina at Greensboro, March 25–27, 2010. The retreat's ongoing mission is to (1) present and discuss the most recent research on ACL injury risk and prevention and (2) identify new research directives aimed at understanding the epidemiology, risk factors, and prevention of noncontact ACL injury. This year, 75 clinicians and researchers representing 6 countries participated.All the keynote presenters are expert scientists engaged in cutting-edge research on ACL injury risk and prevention. Edward Wojtys, MD; Stephen W. Marshall, PhD; Darin A. Padua, PhD, ATC; and Christopher M. Powers, PT, PhD, focused on issues related to clinical and research considerations for ACL-injured pediatric and adolescent athletes, current trends in injury epidemiology, and new directions in risk-factor assessment and efficacy of injury-prevention programs. Forty podium and poster presentations were organized into thematic sessions: risk-factor assessment (specifically factors associated with spinal and trunk control, muscle strength and fatigue, anatomical and hormonal factors, and landing and cutting strategies), injury mechanisms, risk-factor screening, and prevention. A meeting hallmark is the substantial time provided for group discussion after each keynote address and thematic podium session. To close the meeting, participants revisited and updated the consensus statement from the 2008 ACL Research Retreat IV1 and charted new directions for future research. Following are the updated consensus statement, keynote presentation summaries, and abstracts organized by topic and presentation order.As at past retreats, the consensus statement was updated and further refined based on the input of all participants at the meeting's end. Participants were divided into 3 interest groups: hormonal and anatomical risk factors, neuromechanical contributions to ACL injury, and risk factor screening and prevention. Within each group, the relevant sections of the previous consensus document were discussed and updated as to (1) what we know based on new evidence emerging in the literature and presented at the retreat, (2) what remains unknown about these factors, and (3) the important directions for future research needed to address these unknowns. Each group then presented its working draft to all participants for further discussion, and drafts were circulated after the meeting for final comment.From these discussions, some global observations, themes, and recommendations emerged that deserve special note. First, in response to general themes raised previously,1 we seem to be moving away from the purely descriptive sex-comparison studies that have tended to dominate the literature toward a better understanding of the underlying mechanisms associated with the observed sex differences and, more directly, ACL injury risk and prevention. However, a more integrated approach in our research is still desperately needed to better characterize the multifactorial nature of the ACL injury enigma: examine all relevant anatomical (eg, posture, structure, body composition) and structural (eg, tibial slope, condylar geometry) factors, as well as the associated neuromechanical outcomes (eg, integrated findings from kinetic, kinematic, and neuromuscular measures) used in assessing these risk factors. Studying multiple factors is particularly challenging, given the relatively low incidence of ACL injury. Thus, traditional risk-factor designs (eg, prospective cohort studies) are needed but may not advance our scientific understanding of the ACL injury mechanism rapidly enough to permit these injuries to be prevented. To offset these challenges, we must develop open-source databases (eg, video registries, software models) to pool our resources. Generating complementary new measurement paradigms is also important, both to more quickly advance our scientific understanding of the ACL injury mechanism and related risk factors and to gain a more integrated understanding of this complex, multifactorial problem. Continued emphasis on computer and cadaveric modeling will allow multifactorial manipulation that is not possible in vivo, and state-of-the-art robotic simulations will help us to better understand complex relationships among muscle force production, joint and ligament morphology, and resultant ACL strain. More functional in vivo testing conditions are needed to describe cognitive, supraspinal, and spinal contributions to knee joint and ACL loading within the truly random movement environment of game play. The roles of behavior and cognition have to date received relatively little attention, yet the work of previous researchers2,3 and the keynote presentation by Chris Powers provide compelling evidence of the need to explore these areas. Addressing these and other unknowns is critical to the continued development and refinement of injury-prevention programs. Although most prevention programs to date have focused on eliminating certain movements (eg, valgus maneuvers) as a solution to the problem, the evidence supporting any one mechanism alone is quite weak. Thus, although these programs have shown some success and should continue, the ideal ACL injury-prevention program may not be realized until we have a better grasp on this complex, multifactorial problem.Another general consideration raised at the retreat was increasing our focus on the youth athlete and taking more of a public health approach in our injury-risk screening and injury-prevention strategies in this population. The best time to identify and counter risk is posited to be during the adolescent years, but we still know very little about when relevant risk factors emerge, when intervention should be initiated, and how we can improve participation in, compliance with, and effectiveness of ACL injury-prevention programs in this critical target population. Children and adolescents perform athletic tasks differently than adults,4–7 and recent findings8,9 suggest that the response to injury-prevention programs may differ across age groups. Additionally, the continuing trends of inactivity and obesity (eg, loss of physical education classes in US schools) are of great concern with respect to their effect on acquisition of general motor programs, skill development, and prospective ACL injury risk. Another important public health concern is the consequences of ACL injury so early in life in both the short (eg, lost school time) and long term (eg, osteoarthritis, inactivity). Therefore, we call for a better understanding of the prospective risk factors for ACL injury in the maturing youth population; improved understanding of the cognitive, behavioral, and socioeconomic factors that influence the successful implementation of ACL injury-awareness and injury-prevention programs in youth sport participants; and a movement toward more translational approaches to implementing ACL injury-prevention programs into community settings to maximize public health.Although only 2 years have passed since the last ACL retreat, a number of advancements in our knowledge of ACL injury risk and prevention have reshaped the important unknowns and future directions we need to take. These changes are reflected in the revised consensus statement. We hope that the insights and proceedings from this meeting will continue to strengthen the foundation upon which quality research and clinical interventions in ACL injury risk and prevention can be advanced.The ACL Research Retreat V was hosted by the Department of Kinesiology at the University of North Carolina at Greensboro. We gratefully acknowledge Innovative Sports Training, Inc; the Department of Kinesiology, School of Health and Human Performance, and the Office of the Provost and Executive Vice Chancellor of the University of North Carolina at Greensboro for their sponsorship and support of the meeting.