Neuromuscular Training May Be Effective for Reducing Anterior Cruciate Ligament Injuries in Female Athletes, Particularly Ages 14-18 Years
Resident Focus - Volume 11, Issue 3
As increasing numbers of adolescents and young adults participate in competitive, often year-round sports, the risk of injury is a growing concern. The anterior cruciate ligament (ACL) is the most commonly injured ligament of the knee, and the majority of these injuries are athletic-based. There are approximately 200,000 ACL injuries per year in the US, with an incidence of at least 1 in 3,500 people annually (Gordon MD, Steiner ME. Anterior cruciate ligament injuries. In: Garrick JG, ed. Orthopaedic Knowledge Update Sports Medicine 3. Rosemont, IL: American Academy of Orthopaedic Surgeons; 2004:169). Compared to male athletes, female athletes participating in the same sports have 4-6 times higher rates of ACL injuries. Experts have proposed that neuromuscular factors and deficits arising during puberty may play at least some part in this disparate rate of susceptibility. Neuromuscular Training (NMT) programs, which focus on strength, plyometrics, balance, proprioception, and the awareness of at-risk movements and positions, have been shown to decrease an athlete’s risk of injury. There is a current hypothesis that females’ injury-disposing changes occur at puberty. A group of authors decided to assess how age at initiation of NMT affects efficacy for preventing ACL injuries. In 2013 these authors published a systematic review of studies on NMT programs; this review took into account female athletes’ age at implementation, with the hypothesis that NMT effectiveness would be greatest in younger girls.
The review included 8 randomized, controlled trials and 6 nonrandomized studies comparing the incidence of ACL injuries in athletes who received NMT to those who did not. Most of the studies used a combination of neuromuscular interventions, including strength (often of hamstrings and core), plyometrics, stretching, balance, jump training, and agility. However, the NMT programs did differ from each other in the specific interventions that were used as well as in the intensity and duration of these interventions. Using injury data of female athletes from over 1,300 teams, the study authors performed a meta-analysis to find the odds ratios of ACL injury in subgroups stratified by age. The dichotomous age groups consisted of those older than 18 years and those 18 or younger; the tertile age groups consisted of mid-teens (14-18 years), late teens (18-20 years), and early adults (older than 20 years). Limitations of this review include follow-up periods that were often not explicit or varied as well as use of varying NMT interventions.
Overall, the meta-analysis of all 14 studies demonstrated significant injury reduction in those in preventive NMT groups compared with the controls (odds ratio [OR]0.54, 95% CI 0.35-0.83). In the dichotomized subgroup analyses, girls who received NMT while aged 18 years or younger had significantly reduced knee injuries (72% risk reduction; OR 0.28, 95% CI 0.18-0.42), while girls who received NMT at ages older than 18 years showed no significant ACL injury reduction (16% risk reduction; OR 0.84, 95% CI 0.56-1.26). Likewise, in the age-tertile subgroup analyses, only the girls aged 14-18 years showed significant ACL injury reduction (OR 0.28, 95% CI 0.18-0.42), while the other older groups did not (ages 18-20 years had OR 0.48, 95% CI 0.21-1.07; early adults over age 20 years had OR 1.01, 95% CI 0.62-1.64).
This meta-analysis indicates that NMT implementation may be most effective in female athletes aged 14-18 years, supporting the review’s initial hypothesis that the effectiveness of NMT would be greatest in younger participants. Since pubescent changes are what may lead to the neuromuscular deficits predisposing females to injury, NMT in younger athletes may help correct or minimize these deficits. Future studies should attempt to pinpoint the pubertally emergent neuromuscular deficits in females, in order to help determine an ideal, standardized NMT program for these athletes. In particular, data from girls aged less than 14 years should be included, as competitive sports are increasingly drawing younger participants, and they may benefit most from this training.