Among high school athletes, football players and female soccer players are most likely to injure their anterior cruciate ligament (ACL), a new study finds.
Those injuries often require surgery and months of rehab, and can put young athletes at risk for arthritis years down the road.
The ACL is located in the middle of the knee joint. It most commonly gets torn when the knee is overextended, such as when a basketball player pivots or lands from a jump.
Past research has shown the highest number of ACL surgeries are done among high school-aged kids, Dr. Dean C. Taylor said.
"The ability to control the joints through the muscles and nerves doesn't catch up as quickly as the growth of the bones and the joints. As a result, there are still coordination issues, there are still issues of learning how to control their bodies," he said.
An orthopedic surgeon at Duke University Medical Center in Durham, North Carolina, and retired U.S. Army Colonel, Taylor was not involved in the new study.
The report confirms earlier findings that among boys and girls playing the same sport, girls have a higher risk of ACL injury. That could be due to differences in their build, muscle development or hormones.
But researchers said it's important to focus on ACL injury prevention for boys, too - especially because a high rate of injuries is seen among young football players.
Given how many kids play football across the country, a doctor is more likely to see a young football player with an ACL injury than a female soccer or basketball player, said Dawn Comstock, from the Colorado School of Public Health in Aurora.
Comstock and her colleagues from Nationwide Children's Hospital in Columbus, Ohio, studied a nationally-representative group of 100 high schools over five years.
At each school, athletic trainers reported on practice and game time and any new ACL injuries on nine different teams: football, volleyball, wrestling, baseball, softball and boys' and girls' soccer and basketball.
There were a total of 617 ACL injuries during the study period. That translates to an estimated 216,000 injuries in those sports across the U.S. during the same time.
Football players accounted for 286 of the injuries. The researchers calculated there were 11 ACL injuries for every 100,000 times a single football player participated in a game or practice.
Similarly, there were 12 ACL injuries for every 100,000 "athlete-exposures" for girls' soccer, and 10 per 100,000 for girls' basketball.
Injury rates were below five injuries per 100,000 athlete-exposures for all other sports, the researchers wrote in the Journal of Athletic Training.
High school athletes were seven times more likely to injure their ACL during games than during practice. And about three-quarters of the injuries required surgery.
Taylor said it's important that ACL tears are treated quickly. Kids who continue to play on an injured ligament can cause more damage that ultimately makes surgery more complicated.
In addition, he said, "We need to do a better job of injury prevention." But the best way to protect against ACL injuries isn't clear.
Possible answers are rule changes in football or conditioning and training exercises for players, he said.
Because mechanisms of injury differ between sports - with most football ACL injuries resulting from player-to-player contact, for instance - prevention strategies will have to differ as well, Comstock said.
"ACL injury prevention is really not going to be a simple one-size-fits-all cure," she said.
For now, Taylor suggested athletes work on improving their agility and strengthening their hamstring muscles, which can change the forces on the knee ligaments.