New research confirms what doctors working with young athletes already suspected: the number of anterior cruciate ligament (ACL) tears among youths, particularly high school students, has risen during the past 20 years.

Reviewing twenty years of billing data for the period 1994 to 2013 from an insurance company operating in a large metropolitan area, researchers found the overall incidence of ACL tears among 6- to 18-year-old patients increased by 2.3 percent per year.

Breaking down the increase based on gender, they found that males had an overall increase of 2.2 percent per year and experienced peak rates of ACL tears at age 17.  Females, meanwhile, saw an increase of 2.5 percent per year and experienced most ACL tears at age 16. All female age groups showed an increased incidence of ACL tears over the past 20 years, but among males, only the 15- to 16-year-olds had a significant rise.

The researchers also calculated the rate of ACL reconstructive surgery and found that it increased by 3 percent per year over the study period. 

"We hope these findings will help foster discussion both about how changes in pediatric athletic participation over the past 20 years may be impacting injury rates and how we can best develop youth injury prevention programs and athletic participation guidelines," said Marc A. Tompkins, MD, an assistant professor of orthopaedic surgery at the University of Minnesota. "The data would suggest, for example, that all female athletes and males in the 15-16 year ages would be good candidates for injury prevention programs," he said. 

Neuromuscular training programs reduce ACL injury risk 

Neurmuscular training (NMT) programs, including the FIFA 11+ program, a 20-minute series of warm-up exercises performed at the start of each training session and in a modified form before matches, and the PEP exercise program developed by the Santa Monica Orthopedic and Sports Medicine Research Foundation, a series of 19 warm-up, stretching, strengthening, plyometric, and sport-specific agility exercises that can be completed in less than 30 minutes without any specialized equipment, have both been proven effective in a series of studies in reducing ACL injuries, particularly of the non-contact variety, and especially among female athletes, who more prone to ACL tears.

A 2005 study of elite 14- to 18-year-old female soccer players, for instance, reported that ACL injuries went down 83% for girls on teams which used the PEP exercise program compared to girls on teams that did not; in the second year, the reduction in ACL injuries was 72%. 

A 2008 study of NCAA Division 1 female soccer players found that they  were at significantly reduced risk of ACL injuries, particularly those of the non-contact variety, if they performed the PEP warm-up program 3 times a week over the course of a 12-week regular season:

• Athletes with a history of previous ACL injury suffered ACL injuries at rate almost 5 times less than athletes not participating in PEP exercise program;
• The ACL injury rate for athletes without a history of prior ACL injury was approximately half for the PEP program participants;
• None of the female soccer players participating in the PEP program suffered an ACL injury during the second half of the season versus five who suffered such injuries who were not performing the PEP exercises.
• The reduction in ACL injury rates later in the season suggested that training had a cumulative benefit of the training. In fact, the study's authors suggested that the results may actually underestimate the program's potential impact because not all teams using PEP may have faithfully performed exercises.

Although each of the teams using the PEP exercise program had a dedicated athletic training staff, the success reported in the earlier study in reducing ACL injuries among 14- to 18-year-old competitive female club soccer players - who ordinarily do not benefit from direct oversight from certified athletic trainers (ATCs) or physical therapists - suggest that the program may benefit other age groups and levels of play where direct oversight by medical professionals is far less common.

And, while the program was specifically designed with soccer-specific drills, it also may be modified for use in other high-risk team sports such as volleyball, basketball, and girl's lacrosse. 

Window of opportunity? 

Research also suggests that pre- or early adolescence may be the best time to start NMT in order to reduce the number of ACL injuries female athletes suffer.

Performing a "meta-analysis" of data from 14 studies published between 1999 and 2012, researchers at Cinncinati Children's Hospital found a 72% risk reduction in female athletes under 18 years old versus a risk reduction of only 16% for those over age 18. The data indicated that pre- or early adolescents (mid-teens) showed the greatest risk reduction (72%) compared with late adolescents (late teens; 52% risk reduction).  

Unexpectedly, the study found that the odds a female athlete would suffer an ACL injury after NMT in early adulthood or their late teens were 3.6 and 1.7 times higher, respectively, than if they began NMT in their mid-teens.

The data "could indicate that the potential window of opportunity for optimized ACL injury risk reduction may be before the onset of neuromuscular deficits and peak knee injury incidence that occurs after the onset of maturation in female athletes and/or during the mid-teen years," said lead author, Gregory D. Myer, PhD, FACSM, CSCS, of the Division of Sports Medicine at Cincinnati Children's Hospital, and the Departments of Pediatrics and Orthopaedic Surgery, at the College of Medicine at the University of Cincinnati, and the Athletic Training Division, School of Allied Medical Professions at The Ohio State University in Columbus.  

The results "support the contention" - suggested in previous studies - "that younger athletes may be more receptive to NMT, which will lower their risk of injury," Myer writes, "compared with interventions implemented in late adolescents and early adult-aged female athletes.The higher risk of injury in postpubertal athletes has been attributed to several changes that occur thoughout the pubertal period, such as structural/anatomic changes, hormonal variations, and decreased strength." 

The study noted that another possible explanation for the great NMT effectiveness in the mid-teen age group may be variability in the "quality" of athletes participating in the cutting, pivoting, and jumping sports such as soccer, volleyball and basketball in the younger ages, so that targeting NMT to athletes who are at higher risk results in greater reduction of that risk.

American Academy of Pediatrics

Gilchrist J, Mandelbaum BR, Melancon H, Ryan GW, Silvers HJ, Giffen LY, et. al. A randomized controlled trial to prevent noncontact anterior cruciate ligament injury in female collegiate soccer players. Am J Sports Med 2008;36:1476-83. 

Mandelbaum BR, Silvers HJ, et al. Effectiveness of a neuromuscular and proprioceptive training program in preventing anterior cruciate ligament injuries in female athletes. Am J Sports Med. 2005;33:1003-10.  

Research paper #29890. "ACL Tears in School-Aged Children and Adolescents: Has There Been an Increased Incidence over the Last 20 Years?"  Beck NA, Lawrence JT, Nordin JD, DeFor TA, Tompkins M. Presented at American Academy of Pediatrics National Conference & Exhibition, October 24-27, Washington, DC.

Myer GD, Sugimoto D, Thomas S, Hewett T. The Influence of Age on the Effectiveness of Neuromuscular Training to Reduce Anterior Cruciate Ligament Injury in Female Athletes. Am. J. Sports Med. 2012; 20(10). DOI:10.1177/0363546512460637 (published online ahead of print October 8, 2012)(accessed October 15, 2012).