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Diagnosing the Knee Injury

By Dr. Eric W. Edmonds

Most young athletes and parents have heard of common knee injuries including a torn ACL (anterior cruciate ligament) or even a torn meniscus, which many professional athletes encounter in the course of their careers. But, there are actually four main ligaments in the knee that are at risk for injury.

In the center of the knee is the ACL and the counter-directed PCL. On the outside (away from the other leg) is the LCL (lateral collateral ligament) and on the inside (side toward the other leg) is the MCL (medial collateral ligament).

Ligaments attach bones to bones, and the MCL is designed to stabilize the knee by preventing the shin bone from moving to the side (creating a knocked-knee look) relative to the thigh bone. MCL injuries can occur by direct contact or by non-contact (when an athlete is running or jumping and then suddenly slows and changes direction or twists). This injury can occur at any age.

MCL injuries are known to be associated with ACL and meniscus tears, as well as growth plate fractures of the shin bone. Like most injuries to a ligament, the MCL tears can be graded based on the severity of injury. The easiest way to understand this grading system is to consider grade 1 injuries a stretch, grade 2 injuries a partial tear and grade 3 injuries a complete tear.

The symptoms of an isolated MCL tear include pain on the inner side of the knee, often with swelling, and potentially a sense that the knee will “give out.” A physical exam by a medical professional will often help distinguish it from other knee injuries and can often make the diagnosis.

Treatment is an initial period of ice and compression to reduce swelling and pain. Depending on the severity of injury or the grade of tear, there are a few different treatment options.

Young kids that sustain grade 1, possibly grade 2, injuries tend to never get evaluated by medical professionals because they are usually better in two weeks. Pre-adolescent kids are unlikely to sustain higher-grade injuries because their growth plates will usually break first. However, teenagers will often sustain higher-grade tears.

Crutches and a brace locking the knee straight is important in the treatment for these athletes. This will allow the MCL to heal in the appropriate position and slow the teenager down. If an associated injury is found on MRI, then surgery may be required; but, isolated MCL tears rarely require surgery. Physical therapy will be important to start after about a month in the knee immobilizer. After six weeks of therapy, most young athletes will be able to return to sport.

In general, a significant MCL injury (grade 2 or 3) can take six to 10 weeks to improve before return to competitive athletics. At the end of rehabilitation, if there is a continued sense of instability, then surgery may be an option to restore that stability and reduce symptoms. In this situation, the MCL usually needs to be reconstructed or replaced. If surgery is done early, in light of associated injuries, then sometimes a direct repair of the torn MCL can be done to restore stability.

You should contact your doctor if there is an obvious deformity of the knee, knee joint swelling or if the pain is not improving after two weeks of rest.

Dr. Eric W. Edmonds is a pediatric and adolescent orthopedic sports medicine specialist at Rady Children’s Hospital-San Diego and an assistant professor of orthopedics at UC San Diego. He can be reached at