First of its kind
The study is the first of its kind to examine ACL injuries by gender and across multiple sports, and the first large epidemiological study to focus on knee injuries among high school athletes in more than a decade.
All high schools with one or more National Athletic Trainers' Association-affiliated athletic trainers (ATs) were invited to participate in the National High School Sports-Related Injury Surveillance Study using the High School RIO TM program. A random sample was used to select schools from each of eight geographic regions to achieve a nationally representative sample of 100 schools. ATs reported practice and competition data for nine sports during the 2007/2008-2011/2012 academic years, five boys' (baseball, basketball, football, soccer and wrestling) and four girls' (basketball, soccer, softball and volleyball) sports.
Analyzing the data, the authors found that:
- ACL injuries accounted for 20.5% of all knee injuries and 3.0% of all injuries sustained by high school athletes in the nine sports studied.
- During the study, ATs reported 617 ACL injuries occurring in 9,452,180 athletic exposures or AEs, defined as 1 athlete participating in 1 practice or competition, for an overall rate of 6.5 ACL injuries per 100,000 AEs.
- Nationally, an estimated 124,626 ACL injuries in boys and 91,002 ACL injuries in girls were suffered by athletes playing the 9 sports studied.
- While girls and boys had similar rates of ACL injury overall, in sex-comparable sports (soccer, basketball, and baseball or softball):
- girls sustained more injuries than boys (209 versus 75, respectively);
- girls had a higher injury rate than boys (8.9 versus 2.6 per 100,000 AEs respectively)
- a higher proportion of ACL injuries sustained by girls than boys were of the non-contact variety, but the difference was not statistically significant;
- a higher percentage of ACL injuries suffered by boys' soccer players were due to player-to-surface contact compared by girls (21.% and 7.5%, respectively).
- The highest rates of ACL injuries per 100,000 AEs were in:
- girls' soccer (12.2);
- football (11.1); and
- girls' basketball (10.3)
- The lowest ACL injury rates were seen in boys' basketball (2.3) and baseball (0.7)
- 71.2% of boys' ACL injuries were sustained playing football, followed by soccer (17.2%), basketball (5.5%), wrestling (4.1%) and baseball (2.0%)
- Certain sports placed athletes at higher risk for ACL injuries than others:
- Boys were 4 times as likely to sustain an ACL injury while playing football as any other sport
- Girls were 2 times as likely to sustain an ACL injury playing soccer than any other girls' sport
- Girls were 4 times more likely to sustain an ACL injury playing either soccer or basketball compared to volleyball or softball.
- Girls most often injured their ACLs playing soccer (53.2%), followed by basketball (26.5%), softball (11.4%), and volleyball (8.;8%);
- Player-to-player contact was the most common injury mechanism (42.8%), followed by no contact (37.9%), player-to-surface contact (13.6%), player-playing apparatus contact (2.4%), and other (i.e. ball, base, goalpost etc.)(3.3%), but, as noted above, the injury mechanism varied by sport and gender;
- Athletes are 7 times more likely to sustain an ACL injury in competition rather than practice, significantly higher than the 2.7 to 3 times reported in previous studies.
- Of all ACL injuries:
- 87.6% were new
- 2.1% were recurrences from an injury sustained in the same academic year but from which the athlete had returned to play
- 7.9% were recurrences from an injury sustained ina previous academic year but from which an athlete had returned to play; and
- 2.4% were other/unknown
- 76.6% of the ACL injuries resulted in surgery, but the percentage varied by sport, ranging from 96.3% in boys' basketball to 61.1% in wrestling.
- Of those ACL injuries in which the outcome was reported:
- 46.4% resulted in medical disqualification for the season
- 15.4% required a 3-week or longer recovery time
- Of the 12.3% requiring less than a 3-week recovery time, 83.2% did not result in surgery, while 11.7% resulted in surgery which was postponed to enable the athlete to continue to play.
- ACL injury was assessed primarily by an AT in conjunction with a general physician or orthopaedic physican (or both), using a variety of diagnostic methods (evaluation, X-ray, MRI, CT scan, surgery)
- Those assessed by a physician were more likely to require surgery (80.5%) than those assessed by the AT alone (25.8%)
- Patients with ACL injuries assessed by the AT alone were more likely to return to play within 3 weeks (52.3%) compared to those assessed by a physician (8.9%)
Risk factors still unknown
Efforts to design effective target prevention programs have been hampered by a number of factors, the researchers said. While some ACL injury prevention programs have shown "great promise" (particularly in reducing the incidence of non-contact ACL injuries in female athletes), an understanding of their effectiveness, say researchers, "is still limited." In addition, they say, "we still lack a complete understanding of the modifiable risk factors for ACL injury."
"That said, coaches and ATs in sports with high rates of ACL injury should take special care to teach sport specific skills (e.g. planting and changing direction, jumping and landing) and address potential deficits in the neuromuscular strength and coordination of the stabilizing muscles about the knee joint through stretching, plyometrics and strength training drills."
"Plyometric exercises mimic many of the same motions an athlete will complete on the field," says Keith Cronin, PT, OCS, CSCS, a physical therapist in St. Louis and a MomsTEAM expert. "I like plyometric exercises as a means to evaluate joint positioning during the movement to determine if an athlete is at risk of hurting a joint, such as the knee."
"An athlete who can quickly change directions and respond to changing movements is not only a better athlete, but is less likely to sustain an injury. If mechanics are good, the athlete should do then sometimes (maybe 1-2 days a week as part of conditioning), but not overemphasize them, as too much heavy loading of the joints can cause damage. The purpose of sports training is to improve performance on the field. If the athlete grinds their body down training with plyometrics, performance is decreased and risk of injury increases."
In addition to prevention, the study recommends the use of screening tools to try to identify athletes at increased risk of ACL injury, such as through use of the tuck-jump exercise developed by researchers at Cincinnati Children's Hospital, which can identify lower extremity technical flaws during plyometric activity that may indicate a higher risk of ACL injury.
