The anterior cruciate ligament (ACL) helps to connect the end of the thigh bone (femur) to the top of the shin bone (tibia). The ACL helps to “stabilize” the knee, or keeps it from “giving way”.
Although we usually hear about ACL injuries in adults playing sports such as football, in which the players are hit in the knee by another player, there is an increasing incidence of ACL injuries in kids and teenagers. This is because more kids and teenagers are playing competitive sports at a high level at a younger age.
Teenagers are more likely than kids to injure their ACLs. In addition, girls are 3-8 times more likely than boys to have this injury, when playing the same sport. Also, most ACL injuries actually happen when there is not a hit from another player: these occur when planting and twisting on the leg, such as when playing soccer, or landing a jump, such as in basketball. Soccer and basketball are the sports that have the highest rate of ACL injuries among girls.
The growing incidence of athletes of all ages with ACL injuries related to sports has prompted parents, coaches, researchers, doctors, trainers, and physical therapists to look into why these injuries happen, and, especially, why they are so much more common in girls. The hope is that if we know why the injuries happen, they can be prevented.
A lot of research has looked into why girls are so much more likely than boys to hurt their ACLs. Some people have looked at the size of the knee (“femoral notch”), the size of the ACL, the differences in how a girl’s leg is aligned (for example, girls are more likely to be “knock-kneed”), and maybe some role for female hormones. All of these may have some impact on ACL injuries.
However, the most likely reason, and the one that we can try to fix, is how girls (and all females) use the muscles in their legs during sports and how they land from jumps. The muscles in front of the thigh that help to straighten the knee (the “quadriceps”) tend to be stronger and tighten more quickly than the muscles in back of the thigh that bend the knee (the “hamstrings”) females. Females naturally land from jumps with their legs straight, at both the hip and knee. All of these put more stress on the ACL.
Athletes with ACL injuries will have acute onset of knee pain and swelling. They may not be able to put weight on that leg. They may note that the knee feels “unstable”.
Why are we so concerned about ACL injuries? Torn ACLs can lead to “giving way” of the knee, which can lead to more injuries. ACL injuries can negatively affect sports activities, especially in high level sports. They can also affect school performance in some children or may lead to the loss of a sports-related scholarship. ACL injuries are serious. If you think that your child or teenager has an ACL tear, let their coach, athletic trainer, pediatrician, or orthopaedic surgeon know as soon as possible.
Although these injuries can be addressed with exercises (with physical therapists and athletic trainers) and/or with surgery (by an orthopaedic surgeon), these injuries have a lot of consequences. If the athlete and her/his family decide not to have surgery, the child will be asked to restrict her/his activities, wear a brace, and participate in therapy with an athletic trainer or physical therapist. If the athlete and/ her/his family decide to have surgery, the athlete should not expect to return to sports for 7-9 months.
The first phase of therapy focuses in getting the knee to straighten and bend (“range of motion”), getting the muscles in the leg stronger, and returning to normal (not sports-related) activities. The next phases add in activities that are related to sports, such as running and jumping. Not all athletes are the same in how fast they make progress.
As with all injuries, prevention is always better. This is especially true of ACL injuries, not only because of the immediate pain and issues with playing sports, but also because of what happens later on. At the time of the injury, other tissues in the knee, including the menisci (“shock absorbers”) and the articular cartilage (the tissue that lines the bones of the joint and allows the bones to easily move past each other when the joints move) can be damaged. Even in young people, the articular cartilage can’t heal. This leads to the arthritis of the knee, often 10-15 years after the injury.
Females are not only more likely to develop osteoarthritis after an ACL injury, they also do so sooner after the injury than do males. This happens even if the athlete has had surgery and completed the exercises that were discussed earlier.
The risk of chronic pain and loss of function due to arthritis of the knee makes preventing ACL injuries very important. Talk with your athlete’s coach or athletic trainer about ways to prevent ACL injuries. As the cause of these injuries is different between males and females, the way to prevent them is also different. Prevention activities include strengthening and stretching exercises and, most importantly, how to pivot and land from jumps in ways that don’t put stress on the ACL.
For more information, visit the websites of the American Academy of Pediatrics, Your Orthopaedic Connection, National Athletic Trainers’ Association, American Physical Therapy Association, American College for Sports Medicine, American Medical Women's Association, or the Ruth Jackson Orthopaedic Society.
Watch this video on ACL injuries in female athletes from the American Academy of Pediatrics.
This story is brought to you as part of World Pediatric Bone and Joint (PB&J) Day, celebrated on October 19, which is part of Bone and Joint Action Week (Oct. 12 - 20).
The United States Bone and Joint Initiative (USBJI) and its Pediatric Specialty Group thank the following for writing this article: Julie Neumann, MD, K Allan Jarratt DPT, Michael T Busch, MD, Kimberly Templeton, MD, Jill C Flanagan, MD.