A normal knee has three joint areas or compartments, a ligament on the inside of the knee (medial collateral ligament), a ligament on the outside of the knee (lateral collateral ligament), and 2 ligaments in the middle of the knee (anterior and posterior cruciate ligaments). The ligaments keep the knee from bending or twisting further than it should and are even stronger than the growth plates in children. Because of this, children and adolescents who were still growing (skeletally immature) were historically thought to only be capable of sustaining a growth plate fracture and not a ligamentous injury.

Although knee ligament injuries were once thought to be rare in growing children, they are now found with increasing frequency. The reasons for this are multiple: more and more children are participating in sporting events, physicians are becoming much more adept at identifying ligamentous injuries, and there is improved diagnostic equipment available to patients of all ages (such as MRI scanners).

ACL ruptures, in particular, are becoming more common. ACL ruptures can be divided into those that have a bony avulsion and those with a complete intra-substance tear. Bony avulsions can be repaired surgically with a traditional incision or arthroscopically (with a small camera). Treatment for a complete intra-substance rupture depends on the injury to other ligaments in the knee and the skeletal maturity of the patient. If the patient has a repairable meniscal tear, in most circumstances it should be reconstructed at the same time as the ACL. But, if the patient is skeletally immature, reconstruction risks altering the normal longitudinal and angular growth of the femur. Most patients are managed non-operatively with activity modification unless they have a repairable meniscal tear or instability with routine activities; reconstruction is then performed once they are skeletally mature. There is not enough information available to decide how and when to reconstruct a skeletally immature patient. Surgeons are beginning to push the envelope in this respect because many kids have trouble curtailing their physical activities.

More Information:
Johns Hopkins Sports Medicine Information: http://www.hopkinsmedicine.org/orthopedicsurgery/sports/acl/index.html
Arthroscopy.com: http://www.arthroscopy.com/sp05018.htm