Prevention of ACL injuries targets youngest athletes

Some evidence suggests that neuromuscular training before puberty can help further reduce anterior cruciate ligament (ACL) injury rates. But young children respond differently to instruction than their older counterparts, which means early intervention requires some creativity.

By P.K. Daniel

A 10-year-old boy arrived at a Santa Monica, CA, sports medicine clinic with a knee injury. He had suffered a noncontact injury that occurred late in a soccer game. Diagnosis—partially torn anterior cruciate ligament (ACL).

The clinician described the boy as “a good little athlete.” He plays year-round soccer, going from American Youth Soccer Organization competition to club play. Then there’s the tournament season, followed by all-stars. His injury will require a three-month layoff and eventually neuromuscular training (NMT)—exercises designed to target motor control deficits.

The benefits of neuromuscular training for correcting bio­mechanical patterns associated with increased risk of ACL injury have been well documented.¹ But the vast majority of those studies have been done in adolescents and young adults. Now researchers and clinicians are exploring the potential rewards and challenges of implementing similar training programs in younger children.

The problem

The rate of ACL injuries in athletes younger than 18 years has increased in the past two decades.² The incidence of ACL injuries in skeletally immature patients is relatively low, but is growing as more children participate in organized sports and specialize at an early age.²

“The incidence curve is continually shifting to the left,” said Holly Silvers, MPT, director of research at the Santa Monica Orthopedic & Sports Medicine Research Foundation.

Silvers said ACL injury in children was practically unheard of 15 years ago, but she is treating it more and more. The reasons are multifold.

“Too many young athletes are specializing in one sport earlier and earlier, in addition to losing time in free play,” said Julie Eibensteiner, DPT, owner of Laurus Athletic Rehab & Performance in Minneapolis, MN. “As a result, kids are lacking the development of physical competence and ability to interact well with their physical environment and self regulate their physical activity.”

Although the documented evidence is limited, some of these same experts think children can benefit from integrative neuromuscular training.

“We [as a society] are not doing any preparatory conditioning for our youth,” said Greg Myer, PhD, research instructor of sports medicine at Cincinnati Children’s Hospital. “Our youth used to be outside. We used to have them playing. They used to develop these neuromotor control patterns naturally. Those opportunities are diminishing. There’s less opportunity for free play.”

Like Eibensteiner, Myer also blames an increase in sports specialization.

“I’m not a supporter of that because I value the components and the massive motor control adaptations that occur between sports,” he said. “If they are going to specialize early, they’re going to need this integrative neuromuscular training even more.”

Although both boys and girls experience almost equal numbers of ACL injuries, female adolescent athletes have the greatest risk. The incidence rate per total exposure for female athletes is four to six times higher than their male counterparts in similar sports.² Female athletes aged between 15 and 20 years account for the largest number of ACL injuries.²

Prior to the adolescent growth spurt there’s no observed difference in male and female athletes’ relative risk for ACL injury, but during puberty those rates increase sharply, especially in girls.² Decades of research have shown that the relative risk of ACL injuries, however, can be reduced by one-half to two-thirds through neuromuscular training. The American Academy of Pediatrics reported in April that ACL injury risk can be reduced by as much as 72%, especially in women aged 14 to 18 years.²

“You can absolutely reduce ACL injury rates pretty successfully and pretty consistently,” Silvers said.

Early intervention: A bit of a conundrum

With pubescence now occurring at earlier ages than in the past, and maturation not having a one-age-fits-all delivery, Silvers subscribes to early intervention. She also acknowledges the challenges.

“We have a bit of a conundrum,” she said. “Obviously, the earlier we get them the better. Before these patterns are well entrenched from a motor-plan perspective, before these things become habitual, we want to get them. But it’s very difficult to do that in an eight-year-old.”

The best time to implement preventive measures is debatable. Some suggest it is when neuromuscular risk factors are the highest—during early pubertal maturation. However, others argue this is too late.

“If you wait until after puberty, they’re already playing for several years at high risk because they have the increased mass, and that’s what’s tearing the ACL,” Myer said. “They may have had these control patterns—they were deficient when they were younger but they just weren’t large enough to tear their ACL.”

The question is whether this prevention training can be successfully applied to younger athletes.

Some researchers, including Myer, have suggested that neuromuscular training intervention needs to be incorporated as early as possible. However, the research is still out on how effective NMT is among younger children.

“The solution is you have to start early,” said Myer. “You have to start training younger kids before they hit puberty, and then provide them complementary and supplementary preparatory conditioning as they go through puberty. Then they come out the backside with a stable neuromuscular profile that [we can continue to fine-tune through training]. That way you’re not starting from scratch at a very difficult stage.”

Too often, kids are going from being inactive to jumping into competitive sports programs without integrative neuromuscular training, Myer said.

“They’re not doing these training programs that build that profile of safety and enhance their movement mechanics and motor skills,” he said.

Myer acknowledged that at the maturation level everything goes haywire, but suggested that having a solid neuromuscular foundation before puberty sets in can still be helpful.

“Even what they’ve developed, they have to relearn it and manage those large changes in their anatomy and control measures, and they have to be able to adapt,” he said. “The issue is if they’ve never learned these mechanics prior to puberty, you have to teach them during that period—the phase when it’s most difficult and control is hardest. So that’s not the best solution.”

Skepticism

Tim Hewett, PhD, director of the Ohio State University Health and Performance Institute in Columbus, isn’t convinced that this training is transferable to a child who doesn’t already have the problem. An 8-year-old isn’t yet experiencing what he described as a “post­puberty machine-motor mismatch.” When girls go through puberty they get bigger without the corresponding muscle power. Their motor isn’t powerful enough to manage the machine at a level that keeps the body at great neuromotor control in very high-velocity, high-force, high-torque situations.²

“You have to have that mismatch to teach how to control it or how to increase the power, increase the control,” said Hewett. “If you do it prior to that taking place, I have doubts whether it would be effective. A pill doesn’t work until you actually have the condition.”

Hewett said the research shows that just at or after the adolescent growth spurt is when you want to institute the neuromotor training.

“I don’t think we can prepare someone in advance of that,” he said. “It’s optimistic to say let’s get to them early and make sure this doesn’t happen. I don’t know that we can alter that pattern.”

The research

A 2009 study led by Lindsey DiStefano, PhD, ATC, assistant professor in the Department of Kinesiology at the University of Connecticut in Storrs, may support that. The study involved an injury prevention program focused on landing biomechanics, after which the older children (aged 14-17 years) showed more gains than the younger children (aged 10-13 years).³

However, Myer said some research suggests kids can benefit from integrative neuromuscular training. He was part of a research group led by Avery Faigenbaum, MD, a world leader in exercise training in children, that looked at fitness performance in 7-year-olds.⁴ Integrative neuromuscular training was performed two times a week over an eight-week period for the first 15 minutes of physical education (PE) class. Forty children (24 girls) participated.

The boys performed better than the girls at baseline in the push-up, standing long jump, single-legged hop, shuttle run, and .8-km run. However, the girls responded better to the integrative neuromuscular training effects relative to the control group on the curl-up, long jump, single-legged hop, and .8-km run. The boys did not demonstrate similar improvements from the intervention.¹¹

This likely indicates that girls were more responsive to the intervention, Myer said. It might also suggest that boys need increased intensity, or a higher-level stimulus, to influence adapta­tions, he said, noting that this was not tested in the study.

“That tells me it’s in those early stages that [the girls] can start to adapt,” said Myer, a study coauthor. “We had huge gains in their power and performance.”

The study, published in the March-April issue of the Journal of Athletic Training, concluded that NMT is an effective and time-efficient addition to PE for enhancing motor skills and promoting physical activity in children.⁴

The authors did a follow-up study⁵ with the same kids for another eight-week period. During this period there was a cessation in integrative neuromuscular training due to school vacation. Substantial decreases in performance were observed. A child’s neuromuscular profile, Myer said, is highly plastic, modifiable, and responsive to its environment.⁵

“They respond to the stimuli very well,” said Myer. “Children need to be exposed to a high level of motor control developmental strategies as they’re maturing and can actually achieve their neuromuscular control potential.”

Injury outcome data studies have not been completed. Myer said he is currently involved in a randomized controlled trial of the same type of PE-based intervention in younger versus older children. The responders, Myer hypothesized, are going to be most prevalent among the younger kids.

“That said, I think the programs are effective in older kids, and they are effective in males, but I think our best money is going to be training younger athletes,” Myer said.

Challenges

But there are challenges, such as attention and compliance.

“Compliance is a huge factor in the effectiveness of the neuromuscular training programs,” said Eibensteiner. “Those who are more compliant have significantly less risk of injury.”

Silvers is in favor of introducing the subject of neuromuscular training to kids and making them more body aware.

“We just want to start the education and initiate the conversation,” she said.

Her foundation is in the sixth year of a 10-year study on early intervention funded by the National Institutes of Health. It involves 250 children from across Southern California’s Coast Soccer League, one of the largest soccer leagues in the country. The children were aged 8 and 9 years at the outset of the study and will be followed until they are aged 18 and 19 years.

Silvers and colleagues also utilized Coast Soccer League participants when the group developed the Prevent injury, Enhance Performance (PEP) Program in 2000 to reduce ACL injury risk.¹³ The prepractice program consists of a warm-up, stretching, strengthening, plyometrics, and sport-specific agility drills to address potential deficits in the strength and coordination of the stabilizing muscles around the knee. PEP was initially intended for those aged 12 years and older. However, an addendum for those younger than 12 is now available.

PEP includes drills using cones. Adaptations for younger children include shorter distances between the cones, jumping over only visual lines on the field or a flat 2-inch cone, and landing with two legs instead of one. The emphasis during plyometric activities is on the landing technique, not the height of the object they jump over. Performing the exercises with the correct technique in the allotted time frame is emphasized over repetition.

There are different approaches when incorporating neuromuscular training for children. The training has to adapt to their learning capacities. Keeping kids’ attention through a simple, progressive, and fun approach is recommended.

“Training younger children is focused on feedback and their mental capacity,” said Myer. “For the very youngest kids we use balloons to help control their focus. As they get a little bit older, we can take away that supportive tool.”

The children hold the balloons while squatting, lunging, and moving in different directions to enhance muscle strength as well as agility, balance, and coordination, Myer said. The balloons help by slowing down the children’s catching and kicking movements, enabling them to master the new skills and experience success.⁴

Silvers’ programs don’t involve balloons, balls, or other equipment. She doesn’t want any distractions for the short period of eight to 15 minutes.

“We just want them to be aware of [their bodies] in space,” she said. “As they get older you can layer the program, make it more challenging. In the beginning, keep it simple.”

FIFA 11+ is an injury prevention program designed for soccer players aged 14 years and older. The program has proven to reduce overall injury rates⁷ and lower extremity injuries significantly.^7-9 Hewett has been working on a child-friendly version of FIFA 11+ with neurosurgeon Jiri Dvorak, MD, who is the chair of FIFA’s Medical and Research Centre (F-MARC) and FIFA’s chief medical officer professor, and Mario Bizzini, PhD, also of F-MARC.

The three-year study is less than a year old. It is targeting several thousand kids between the U-9 and U-14 age groups. The training is simplified and focuses more on play while still addressing the same neuromotor deficits. Randomized controlled trials in Germany are currently being conducted.

“Theoretically, it’ll work,” Hewett said. “Truthfully, we don’t really know, but it’s definitely worth a try. It still gets at these potential imbalances of ligament dominance, quadriceps dominance, leg dominance, trunk dominance. It teaches better neuromotor control of the body, posterior kinetic chain activation, control of hip and knee joint. It really focuses on the kids not allowing their hip and knee to collapse in but in a simpler, more play-like approach.”

Another challenge is ensuring these no-cost or low-cost programs are implemented with high fidelity. The American Academy of Orthopaedic Surgeons has joined other organizations, such as the National Athletic Trainers Association, in promoting injury prevention among kids through a campaign called STOP (Sports Trauma and Overuse Prevention). The message is being conveyed through public service announcements, social media, and other mediums in a multidisciplinary approach.

To assist with the proper implementation, many of these neuromuscular training programs are available digitally, either online through streaming video or in CD form. An app for smartphones is currently being developed for the PEP program.