There are essentially four separate ligaments that stabilize the knee joint. Two of the four ligaments are the medial collateral ligament (MCL) on the inside of the knee and the lateral collateral ligament (LCL) on the outside of the knee. Ligaments connect bone to bone. The collateral ligaments of the knee connect the femur (thigh bone) on the top to the tibia (shin bone) on the bottom. These ligaments help to limit side to side movements of the knee.

If these ligaments are stretched too far, they may tear. The tear may occur in the middle of the ligament or it may occur where the collateral ligament attaches to the bone on either end. If the force is great enough other ligaments may be torn as well. The most common combination is a tear of the medial collateral ligament (MCL) and the anterior cruciate ligament (ACL).

Injuring a collateral ligament usually involves a significant force, such as a fall or a direct force to the side of the leg. The medical collateral ligament (MCL) is the most injured ligament in the knee but fortunately it is usually only a Grade I or II sprain (see grading chart). Collateral ligaments can be torn in sporting activities, such as skiing, football or rugby. This usually occurs when the lower leg is forced sideways. A blow to the outside of the knee while the foot is planted can put stress on the medial collateral ligament (MCL) and result in a tear. Swelling occurs but it is typically just on the medial (inside) of the joint rather than the whole joint. The lateral collateral ligament (LCL) outside of the knee can also be torn but it is less common. Slipping on ice can cause the foot to slip outwards taking the lower leg with it.

Mechanisms of Injury

• Blow to the side of the knee
• Fall to the side while foot is planted
• Knee giving way

Signs and Symptoms
An injury violent enough to actually tear one of the collateral ligaments causes significant damage to the soft tissues around the knee. At the time of injury a popping sensation may be felt or heard in the knee. There is usually bleeding into the tissue around the knee, and swelling of tissues. The knee is stiff and painful. As the initial stiffness and pain recedes there may be a feeling of instability in the knee and the knee may give way and not support your body weight.

Chronic instability due to an old injury to the collateral ligaments may also occur. If the torn ligament heals but is not tight enough to support the knee, a feeling of instability will persist. The knee will give way at times, and may be painful with heavy use.

Ligament injuries are usually graded in terms of their severity:

Grade I - mild sprain that does not limit function, motion or strength to any noticeable degree. Some micro tearing or slight stretching occurs; however the overall integrity of the ligament is preserved. The ligament hurts if stressed but is stable. Tenderness and swelling may be present.

Grade II - a moderate sprain characterized by greater swelling and tenderness. The signs include partial disruption of the ligament which is painful to stress. There is detectable laxity but the ligament has an eventual endpoint.

Grade III - complete ligament tear and laxity with no endpoint or stability to testing. Abnormal motion and significant loss of strength and function.

Risk Factors

• Impact sports such as, Skiing, football, Rugby, Soccer, Hockey
• Previous ligament injuries
• Increased joint laxity

Diagnosis
When an injury to the knee occurs the initial examination by the physician usually gives a good indication of which ligaments have been injured in and around the knee. The doctor will exert pressure on the side of the knee to determine the degree of pain and looseness of the joint. In some cases there is too much pain and muscle guarding to completely tell what is damaged in the knee. Your physician may suggest a period of rest and physical therapy and then re-examine the knee in 5-10 days. This will allow some of the initial pain and spasm to decrease and the exam may be more reliable. The swelling will also get better during this time allowing for a better examination of the knee.

X-rays may be required to rule out the possibility that damage has occurred to the bone as well. Stress X-rays may be beneficial to confirm that one of the collateral ligaments has been torn. Stress X-rays are simply plain X-rays taken with stress being applied by an examiner to open that side of the joint that is suspected to be unstable. The X-rays will show a widening of the joint space on that side if instability is present.

An MRI scan may be ordered if there is evidence that multiple injuries have occurred, including injury to the meniscus or anterior cruciate ligament.

Treatment
An isolated injury to the LCL or MCL seldom requires surgical repair or reconstruction. Most injuries to the collateral ligaments will heal with bracing in about 4-6 weeks. The initial treatment for a collateral ligament injury focuses on decreasing pain and inflammation in the knee. Physical therapy treatment is beneficial to aid in decreasing pain and inflammation, improving motion, and regaining strength. Rehabilitative exercises should be given to help regain normal range of motion and strengthen the muscles around the knee. Exercises should be designed to allow the muscles around the knee to be exercised while limiting the stress on the ligaments.

Surgical intervention
Immediate repair of an acutely torn collateral ligament is usually not needed. Once surgery is indicated an incision through the skin allows access to the tear in the ligament is required. The most common indication for surgical repair is usually in combination with surgical repair of other damaged knee structures. If the ligament has been pulled from its attachment on the bone it is reattached to the bone with either large sutures or a special metal bone staple. Tears of the middle of the ligament are usually repaired by sewing the ends together.

Chronic instability caused by a collateral ligament injury and subsequent laxity may require a surgical reconstruction. A reconstruction differs from a repair of the ligament. A reconstruction operation usually works by either tightening up the loose ligament or replacing the loose ligament with a tendon graft. If a tendon graft is needed, it is usually taken from somewhere else in the same knee or tissue from anther person (Allograft). A common graft that is used is the semitendinosis tendon (in the hamstring). Studies have shown that this tendon can be removed without a major affect on the strength of the leg. There are other, much bigger and stronger hamstring muscles that can take over the function of the tendon once it is removed. There are numerous different ways to perform a surgical reconstruction of either the lateral collateral ligament or the medial collateral ligament depending on which has torn.

After surgery for either repair or reconstruction of the collateral ligament, physical therapy should be resumed to enhance rehabilitation and assure the best outcome.