The medial collateral ligament is a strong band of connective tissue located along the inner side of the knee. It extends from the thighbone to the shinbone.

The primary function of the MCL is to help keep the knee stable by resisting forces that push the knee inward. It also contributes to overall knee control during walking, running, pivoting, jumping, and other activities that place stress on the joint.

The MCL works together with other important knee ligaments, including the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), and lateral collateral ligament (LCL). Together, these structures help maintain proper alignment and stability while allowing the knee to move normally.

Because the MCL is located along the inner side of the knee, it can become stretched or torn when excessive force pushes the knee toward the body’s midline.

An MCL tear occurs when the ligament is stretched beyond its normal capacity and some or all of its fibers are damaged.

MCL injuries are typically classified according to their severity.

A Grade 1 MCL injury is a mild sprain in which the ligament has been stretched but remains largely intact. Patients may experience tenderness and discomfort while maintaining relatively good knee stability.

A Grade 2 injury involves a partial tear of the ligament. Pain and swelling may be more noticeable, and the knee may feel somewhat loose or unstable.

A Grade 3 MCL injury is a complete or nearly complete tear. The ligament can no longer provide normal support, which may result in significant instability along the inner side of the knee.

Some MCL tears occur by themselves, while more severe knee injuries may involve damage to additional structures such as the ACL, meniscus, or other ligaments. Identifying associated injuries is an important part of determining the appropriate treatment plan.

One of the most common causes of an MCL tear is a direct blow to the outside of the knee. When force strikes the outer portion of the knee, the joint can be pushed inward, placing excessive tension on the MCL.

This mechanism frequently occurs during contact sports such as football, soccer, hockey, rugby, and basketball.

MCL tears can also occur without direct contact. A sudden twisting movement, awkward landing, rapid change in direction, or loss of balance can place enough stress on the ligament to cause an injury.

Skiing is another activity associated with MCL injuries because the knee can become twisted or forced inward while the foot remains secured inside the ski boot.

The severity of an MCL injury depends on the amount and direction of force placed on the knee. A relatively minor force may stretch the ligament, while a more significant impact can cause a partial or complete tear.

Symptoms can vary depending on the severity of the injury. One of the most characteristic symptoms is pain along the inner side of the knee where the MCL is located.

Patients may also experience tenderness when pressure is applied over the ligament. Swelling can develop shortly after the injury, although the amount of swelling varies.

Other symptoms may include stiffness, difficulty bending or straightening the knee, discomfort while walking, and pain when changing direction.

With more significant tears, the knee may feel unstable or as though it could give way. Activities involving pivoting or side-to-side movements can be particularly difficult because these movements place additional stress on the damaged ligament.

Some people report feeling or hearing a popping sensation when the injury occurs. However, a pop does not necessarily indicate the severity of the tear and can also occur with injuries involving other structures inside the knee.

Diagnosis typically begins with a discussion of how the injury occurred and the symptoms the patient has experienced. Understanding whether the knee was struck from the outside, twisted, or injured during a particular activity can provide important information about which structures may have been damaged.

During the physical examination, Dr. Gazzaniga evaluates the location of tenderness, swelling, knee movement, and overall stability. Specific stress tests can be used to determine whether the MCL is functioning normally and whether excessive movement is present along the inner side of the knee.

X-rays may be obtained to evaluate the bones and rule out fractures or other abnormalities. Although an MCL tear itself does not appear on a standard X-ray, imaging can help identify injuries that may have occurred at the same time.

An MRI may be recommended when additional information is needed. MRI provides detailed images of the soft tissues and can help determine the location and severity of an MCL tear while also evaluating the ACL, meniscus, cartilage, and other structures within the knee.

An accurate diagnosis allows the orthopedic specialist to determine the severity of the MCL injury and whether additional knee injuries need to be addressed.