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Ligaments are tough bands of tissue that connect the ends of bones together. The collateral ligaments, located on either side of the knee, limit side to side motion of the knee. The medial collateral ligament (MCL) is found on the side of the knee closest to the other knee. The lateral collateral ligament (LCL) is found on the opposite side of the knee.

Collateral Ligament Injuries

If an injury causes these ligaments to stretch too far, they may tear. The tear may occur in the middle of the ligament, or where the collateral ligament attaches to the bone. If the force from the injury is great enough, other ligaments may also be torn. The most common combination is a tear of the MCL and a tear of the anterior cruciate ligament (ACL). The ACL runs through the center of the knee and controls how far forward the shinbone moves in relation to the thighbone.

While MCL tears are more common, a torn LCL has a higher chance of causing knee instability. One reason for this is that the top of the shinbone forms a deeper socket on the side nearest the MCL. On the other side, near the LCL, the surface of the tibia is flatter, and the end of the shinbone can potentially slide around more. This difference means that the side of the knee joint where the LCL is found is more likely to become unstable as a result of a collateral ligament injury.


The collateral ligaments can be torn in sporting activities, such as skiing or football. This usually occurs when the lower leg is forced sideways–either toward the other knee (medially) or away from the other knee (laterally). A blow to the outside of the knee while the foot is planted can stress the MCL and result in a tear of the ligament. Slipping on ice can cause the foot to move outward, taking the lower leg with it. The body weight pushing down causes an awkward and unnatural force on the whole leg. As a result, the MCL may be torn because the force hinges the knee open, putting stress on the MCL.

The LCL is most often injured when the knee is forced to hinge outward away from the body. It can also be torn if the knee gets snapped backward too far (hyper extended).


An injury severe enough to actually tear one of the collateral ligaments causes significant damage to the soft tissues around the knee. There is usually bleeding into the tissues around the knee, swelling of the tissues, and perhaps bleeding into the knee joint itself. As the initial stiffness and pain subsides the knee joint may feel unstable, and the knee may give way and not support your body weight.

Collateral Ligament Injuries

Chronic, or long-term, instability due to an old injury to the collateral ligaments is a common problem. If a 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.


History and Physical Exam

The initial physical examination usually gives a very good indication of which ligaments have been torn in and around the knee. In some cases, there is too much pain and muscle spasm to completely tell what is damaged in your knee. Your physician may suggest a period of rest with a knee splint and then reexamine the knee in five to seven days.

Radiological Tests

X-rays may be required to rule out the possibility that any bones have been damaged. Stress X-rays may be useful to confirm that one of the collateral ligaments has been torn. Stress X-rays are plain X-rays taken with someone attempting to open the side of the joint that is suspected of being unstable. The X-rays will show a widening of the joint space on that side if instability is present.

Magnetic resonance imaging (MRI) may be ordered if there is evidence that multiple injuries have occurred, including injury to the ACL or cartilage in the knee joint (also called the meniscus). The MRI machine uses magnetic waves rather than X-rays to create pictures that look like slices of the knee. Usually this test is done to look for injuries, such as tears in the meniscus or ligaments of the knee.

Collateral Ligament Injuries

This test does not require any needles or special dye and is painless. If there is uncertainty in the diagnosis following the history and physical examination, or if other injuries in addition to the collateral ligament tear are suspected, an MRI scan may be suggested.


Non-Surgical Treatment

An isolated injury to the LCL or MCL rarely requires surgery. Significant tears to the LCL are usually treated by holding the knee straight in a cast or brace for three weeks. Most doctors opt not to immobilize the knee in a cast when the MCL is torn. Some doctors prefer to issue their patients a knee brace after the injury if there is significant pain and instability.

Initial treatments for a collateral ligament injury focus on decreasing pain and swelling in the knee. Rest and anti-inflammatory medications, such as aspirin, can help decrease these symptoms. You may need to use crutches until you can walk without a limp.

Physical therapy treatments are common for collateral ligament injuries. Therapists may treat swelling and pain with the use of ice, electrical stimulation, and rest periods with your leg supported in elevation.

Exercises are used to help you regain normal movement of joints and muscles. Range of motion exercises should be started right away to help you regain full movement of your knee. This includes the use of a stationary bike, gentle stretching, and careful pressure applied to the joint by the therapist.

When you regain full knee movement and improved strength, gradually you’ll be able to return to work and activities. Some doctors prescribe the use of a functional brace for athletes who intend to return quickly to their sport. These braces give support and help the knee work better after an injury.


If other structures in the knee are injured, surgery may be required. Some surgeons feel that a combination of an ACL tear and an MCL tear should be treated surgically. Others disagree and feel that the MCL tear should be treated conservatively first and the ACL reconstructed later.

Collateral Ligament Injuries

Repair of a recently torn collateral ligament usually requires the surgeon to make an incision through the skin over the area where the tear in the ligament has occurred. If the ligament has been pulled from its attachment on the bone, the ligament is reattached to the bone with either large sutures (strong stitches) or a special metal bone staple. Tears to the middle areas of the ligament are usually repaired by sewing the ends together.

Chronic swelling or instability caused by a collateral ligament injury may require a surgical reconstruction. Reconstruction differs from repair of the ligaments, described earlier. A reconstruction operation usually works by either tightening up the loose ligaments or replacing the loose ligament with a tendon graft.

In the tightening procedure, your doctor will use the remaining ligament tissue and take up the slack. This is usually done by detaching one end of the ligament from its place on the bone and moving it so that it becomes tighter. The ligament is then reattached to the bone in the new place and held with metal staples or sutures.

If a tendon graft is needed to replace the loose ligament, it is usually taken from somewhere else in the same knee. Taking tissue from your own body is called an autograft. A common autograft that is used is one of the hamstring tendons called the semitendinosus tendon. Studies have shown that this tendon can be removed without affecting the strength of the leg. In this operation, your doctor will use the tendon graft to replace the damaged ligament. The ends of the tendon graft are attached to the bone using large sutures or metal staples.

Another way to replace a badly torn collateral ligament is with an allograft. For this procedure, the surgeon gets graft tissue from a tissue bank. This tissue is usually removed from an organ donor at the time of death and sent to a tissue bank. There the tissue is checked for infection, sterilized, and stored in a freezer. When needed, the tissue is ordered by the physician and used to replace the torn ligament.


Minor sprains of either the MCL or LCL should heal within four to six weeks. Moderate tears should rehabilitate within two months and severe MCL tears require up to three months. If patients are still having problems after three months, they will likely need surgery. Treatment for severe tears or ruptures of the LCL are the challenging, because they tend to leave the knee joint unstable, and patients with this condition typically don’t do well with non-surgical care.

Rehabilitation proceeds cautiously after surgery of the collateral ligaments, and treatments will vary depending on the type of surgical procedure that was used. Some doctors have their patients use a continuous passive motion (CPM) machine after surgery to help the knee begin to move and to alleviate joint stiffness. Most patients are prescribed a hinged knee brace to wear when they are up and about. Doctors occasionally cast the leg after reconstruction surgery of the LCL.

You are strongly advised to follow the recommendations about how much weight your knee can bear while standing or walking. After a ligament repair, you will be instructed to put little or no weight on their foot when standing or walking for up to six weeks. Weight bearing may be restricted for up to twelve weeks after a ligament reconstruction.

You usually take part in formal physical therapy after collateral ligament surgery. The first few physical therapy treatments are designed to help control the pain and swelling from the surgery. The goal is to help you regain full knee motion as soon as possible. Physical therapists will also work with you to make sure you are using crutches safely and only bearing the recommended amount of weight while standing or walking.

As the rehabilitation program evolves, more challenging exercises are chosen to safely advance the knee’s strength and function. Ideally, you will be able to resume their previous lifestyle activities. You may be encouraged to modify their activity choices, especially if an allograft procedure was used.

The physical therapist’s goal is to help you keep your pain under control, ensure only a safe amount of weight is placed on the knee, and improve their range of motion and strength. When patients are well underway, regular visits to the therapist’s office will end. The therapist will continue to be a resource, but you will be in charge of doing your exercises as part of an ongoing home program.

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