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A medial collateral ligament (MCL) tear is an injury to one of the major ligaments stabilizing the knee. It occurs when the biomechanical limits of the medial collateral ligament have been exceeded. The injury is associated with pressure or stress from the outside of the knee. A medial collateral ligament injury most often happens when the knee is hit directly on its outer side. It can also occur as a result of repeated stress on the ligament.

The knee joint is a complex hinge joint connecting the thigh bone (femur), which is the longest bone in the body, to the second longest bone in the body, the shin bone (tibia). It is protected in the front by the patella (kneecap), a small flat triangular bone that also plays a role in knee extension. The knee is the largest joint in the body and acts in coordination with the pelvis, hip, upper leg, lower leg, ankle and foot to facilitate a complete range of lower body movements. It is a strong weight-bearing joint that allows the leg to flex, extend, and twist slightly from side to side.

There are four major ligaments in the knee. With help from the quadriceps muscles in the front of the thighs and the hamstrings in the back of the thighs, these ligaments act to stabilize the knee and keep it moving in the proper direction. Two of these ligaments, referred to as the collateral ligaments, are located on the sides of the knee. They function to control the lateral motions of the knee and help to brace the joint against unusual movement. The collateral ligament that is located on the inner part of the knee is known as the medial collateral ligament. This wide thick band of tissue connects the thigh bone (femur) to the shin bone (tibia) helps to prevent the leg from over-extending in an inward direction.

An injury to the MCL can occur as the result of a blow to the outside of the knee, as frequently seen in several sports that include elements of tackling or blocking, as well as from sports that involve quick stops and turns. In addition medial collateral ligament injuries may be the result of an accident in which the lower leg has splayed outward, or in cases of repeated stress to the ligament. MCL injuries are sometimes accompanied by damage to the other ligaments.

The symptoms of a medial collateral ligament injury may include:

  • Pain or tenderness
  • Swelling
  • Stiffness
  • Instability/Unsteadiness)

Evaluating for possible MCL damage begins with a thorough history of the injury and the performance of a physical exam. During the clinical examination the doctor will check for pain and tenderness along the inside of the knee as well as gently apply pressure to the knee in a variety of leg positions. Imaging tests may be ordered to assess the tear in detail, to check for associated damage, and to rule out other disorders.

A torn medial collateral ligament often responds to conservative therapy. Initial non-surgical treatment involves reducing pain and inflammation while restricting any side-to-side movement of the knee. Exercises and physical therapy are helpful to regain knee and leg strength. Surgical options are reserved cases where the torn MCL cannot heal, or if it is associated with other ligament injuries.