Watch your knees, girls. Anterior cruciate ligament (ACL) injuries are on the rise, and girls are more likely to get this injury than are their male friends.

Pediatrics, the journal for the American Academy of Pediatrics, reports that girls playing the same sport as boys are 2.5 to 6.2 times more likely to have an ACL injury than boys.

The highest risk is when girls are 12 and 13. Why? Puberty. This is the time when kids grow faster and their bodies can't always keep up, which is especially true in the leg's tibia and femur bones. For girls, hormones also make the ligaments more lax.

Boys go through puberty later, usually when they're 14 or 15. But in boys, the testosterone surge helps them increase muscular power and control, allowing them to better handle the rapid skeletal growth.

The number of kids with ACL injuries also is on the rise because more kids are focusing on one sport intensely all year with few breaks, experts said. This puts different stresses on the body than the old practice of kids playing a variety of sports with time off between seasons.

If your children are doing the same sport all year, they are overusing some muscles and not strengthening others, said Bethany Thoresen, director of rehabilitation services of Texas Orthopedics.

"It's too much," she said. "They are not ready for it."

Sports where kids stop suddenly and turn a different direction usually are the common offenders: soccer, gymnastics, volleyball and basketball. About 70 percent of the ACL injuries happen when there is no contact with another player.

Usually, the player will feel a pop in the knee and then see swelling, said Dr. Randall Schultz, an orthopedic surgeon with Texas Orthopedics. Sometimes it will hurt; other times, the pain might not be remarkable.

It's not something you have to go to the emergency room for, he said, but you should see a doctor within a few days to find out what's going on and what needs to be done. In the meantime, put ice on it and use crutches to try to stay off it, Schultz said.

Surgery is typical

Treatment approaches are changing. It used to be that the knee would be kept immobile, but now surgery is used to replace most torn ACLs. Post-surgery, athletes usually have six months of rehabilitation exercises before they can return to sports.

An ACL injury can have long-lasting effects. Athletes who have had one are 10 times more likely to have early-onset degenerative knee osteoarthritis. In addition, once a person has had an ACL injury, they are 15 percent more likely to have another.

"I have daughters that play sports. I'm worried about it," Schultz said.

A study of athletes older than 18 who have had an ACL injury found that only about half returned to the level of performance they had achieved before the injury.

Risk of ACL injury can be reduced, Thoresen said. Prevention is all about strengthening the knees and building core strength, as well as doing exercises to strengthen hips, quads, hamstrings and glutes. Pilates is great for that, she said.

Thoresen also recommends that kids who are active in sports see a physical therapist or trainer before an injury happens. The professional will look at how the kids jump and how much control they have with their muscles. After identifying areas of weakness, the trainers or therapists can show them exercises to strengthen those areas.