MCL Injuries

The medial collateral ligament is a strong band of connective tissue that runs along the inner side of the knee, connecting the femur, or thighbone, to the tibia, or shinbone.

Its primary function is to resist forces that push the knee inward and to help control side-to-side movement. The MCL contributes to stability during walking, running, pivoting, jumping, and other activities that place stress on the knee. It works with the other ligaments and surrounding muscles and tendons to maintain proper alignment and stability as the knee moves.

An MCL injury occurs when the ligament is overstretched or torn. These injuries are classified according to their severity.

• A grade 1 MCL injury is a mild sprain in which the ligament has been stretched but remains intact. Tenderness and discomfort may develop along the inside of the knee, although the joint generally remains stable.
• A grade 2 injury involves a partial tear. Pain and swelling may be more noticeable, and some looseness or instability can occur.
• A grade 3 injury is a complete tear of the ligament. Because the MCL can no longer provide its normal degree of support, the knee may feel unstable, particularly during movements that place stress on the inner side of the joint.

MCL injuries can occur alone or together with damage to other structures in the knee. More significant twisting injuries or high-energy impacts may involve additional ligaments, cartilage, or other tissues.

A direct blow to the outside of the knee is one of the most common causes of an MCL injury. The impact forces the knee inward, placing excessive tension on the ligament along the inside of the joint.

This mechanism is frequently seen in contact sports such as football, soccer, hockey, and basketball. A collision, tackle, or fall can force the knee into an abnormal position and injure the ligament.

MCL injuries can also occur without direct contact. Planting the foot and suddenly changing direction may cause the knee to collapse inward, particularly when the knee is partially bent. An awkward landing after a jump can produce a similar force.

Skiing is another activity associated with MCL injuries. A fall in which the skis move apart or the lower leg is forced outward can place substantial stress on the inner knee.

Outside of athletics, MCL injuries may result from falls, workplace accidents, motor vehicle collisions, or other incidents that cause the knee to twist or move beyond its normal range.

Pain along the inside of the knee is one of the most common symptoms. The discomfort may be concentrated directly over the ligament or extend across the inner portion of the joint.

Tenderness is also common, particularly when pressure is applied over the injured ligament. Swelling may develop soon after the injury, although the amount can vary considerably depending on its severity.

Bruising may occur following a more substantial injury, particularly when the ligament has been partially or completely torn or the injury resulted from a direct impact.

More significant MCL injuries can cause instability. The knee may feel loose or unreliable when standing, walking, changing direction, or placing weight on the affected leg. Some people describe a sensation that the knee may buckle or give way.

Stiffness and reduced range of motion may also occur, making it difficult or uncomfortable to fully bend or straighten the knee.

Because MCL injuries can occur together with injuries to other knee structures, symptoms alone may not indicate the full extent of the damage.

Diagnosing an MCL injury typically begins with a discussion of how the injury occurred and the symptoms that developed afterward.

During a physical examination, your physician will evaluate the location of tenderness and swelling, knee range of motion, and overall joint stability. The opposite knee may also be examined for comparison, since the normal amount of ligament movement can vary between individuals.

X-rays do not show the MCL itself, but they may be used to rule out fractures or other bone injuries that can occur during the same event.

Magnetic resonance imaging, or MRI, provides detailed images of the ligaments and other soft tissues within the knee. An MRI may be recommended when the severity of the MCL injury is uncertain or when damage to additional ligaments, cartilage, or other structures is suspected.

An accurate diagnosis helps determine the grade of the MCL injury and whether other parts of the knee have also been affected.