The medical collateral ligament, or MCL, is the piece of connective tissue that joins the femur (thigh bone) to the tibia (shin bone). It is one of four ligaments that stabilize the knee, and is prone to injury especially for those who engage in impact sports. Injury to the MCL includes strain, sprain, tear or rupture.

Knee Pain

One of the first signs of injury to the medical collateral ligament of the knee is persistent knee pain. According to the National Institutes of Health, this pain or tenderness is usually located on the inside of the knee, around the ligament itself 1. However, pain may also be spread throughout the entire knee joint. MCL pain is often worse when standing, or when moving the knee (bending or straightening it). The severity of the injury, such as a strain versus a complete MCL tear, is often directly related to the severity of knee pain.

Knee Instability

Because the MCL is one of four main ligaments that stabilize the knee, an MCL injury often results in a feeling of knee instability. According to the Mayo Clinic, someone with an MCL injury may feel as though their leg will buckle when they stand or walk, and may find it difficult to put weight on the knee. In addition, the knee may make a popping sound when moving or when bearing weight. The degree of knee instability relates to the degree of injury. For instance, someone with an MCL strain may find bearing weight uncomfortable, while someone with a complete tear may not be able to stand upright on their affected leg.

Knee Swelling

Most knee injuries cause some degree of swelling. Swelling caused by an injury to the medial collateral ligament of the knee may be spread throughout the entire knee joint, though it may be most noticeable on the inner surface of the knee. This swelling may become worse after moving or attempting to bear weight on the injured leg. The swollen knee is also usually sensitive to touch after an MCL injury.

Positive MCL Test

If a doctor suspects an MCL injury, he will usually perform a routine test called an “MCL test.” According to the National Institutes of Health, this test is designed to reveal a loose MCL caused by injury 1. The MCL tests is performed by positioning the knee at a 25 degree angle, and applying pressure to the outer side of the knee. This test is performed when a person is lying on their back. A person with an MCL injury will experience pain when pressure is applies to the knee in this position.

Postitive Scan

The final way to detect an injury to the medial collateral ligament of the knee is to perform a diagnostic scan. An X-ray or MRI can reveal damage to the MCL as small as a micro-tear. A positive X-ray or MRI can also be helpful to check for other knee injuries, as MCL injuries are often accompanied by injuries to one of the other three knee ligaments.