The meniscus is a "C"-shaped wedge of cartilage that sits between the two bones that meet in the knee. The knee contains two menisci - one on the inside of the joint (the medial meniscus) and one on the outside (the lateral meniscus). The structures are designed to stabilize the joint as a person glides, turns, jumps or puts weight on the leg. The menisci also cushion the ends of the bones to prevent them from rubbing together during movement.

Trauma or sudden twisting, pivoting or deceleration can cause a tear to form on a meniscus. A very minor tear may go unnoticed. But more serious injuries can cause knee tenderness or pain, stiffness, fluid under the knee and popping or locking of the joint.

Treating a Meniscus Tear

Initially, doctors may try a conservative approach to treating a meniscus tear. Rest of the affected knee, ice, compression and elevation (RICE) are often recommended. Non-steroidal anti-inflammation medications can be used to relieve pain.

If conservative treatment fails to ease the symptoms, or if the tear is severe, doctors may recommend surgery. It's often done through small incisions using a lighted viewing tube and small surgical instruments. The area of damage is located. Tissue may be trimmed or a section of the meniscus may be removed. Any debris inside the joint may also be removed.

Meniscus Transplantation

In cases of severe meniscus injury, surgeons may completely remove the damaged cartilage. However, that means the joint loses its protective cushion, allowing the ends of the bones to rub together during movement. Over time, that damages the bones, causing more inflammation, pain and, later, arthritis. Eventually, patients may require joint replacement.

Brian Gruber, M.D., an Orthopedic Surgeon with The CORE Institute® in Phoenix, AZ, says severe meniscus tears are especially a problem for younger patients who want to remain active. They are too young for joint replacement and face early onset of arthritis. In select cases, he uses a meniscus transplant to treat patients.

In a meniscus transplant, the patient's damaged meniscus is replaced with one from a deceased donor. First, X-rays of the knee joint are taken. The images are sent to a transplant company, where measurements are taken to determine the appropriate size of the donor meniscus. The transplant company also has to match the patient's tissue type. It can take weeks for a suitable match to be found.

Once the donor meniscus is identified, it's shipped to the physician. Even though the meniscus is matched for size, the surgeon still needs to refine the shape to match the recipient's joint anatomy.

After the transplant, the patient needs to keep weight off the joint for several weeks. A rehabilitation program is started about one month after surgery to strengthen the limb and enable it to safely withstand weight. The patient may have certain activity limitations for about six months.

Jeff Lyman, M.D., also an Orthopedic Surgeon at The CORE Institute®, says meniscus transplants are not done very often. They are typically reserved for young patients who don't have any knee alignment problems.

In March, the Meniscus Transplant Study Group presented results on 137 patients who had been followed from three months to 10½ years. About 81 percent of them reported a successful outcome (i.e., reduction of pain and swelling and improved quality of life). Failure rate for the transplant was about 19 percent. Infection and tissue rejection increase the risk of transplant failure.

For information on meniscus transplantation:

http://www.meniscustransplantation.org/studies.htm

For information on the treatment programs at The CORE Institute:

http://www.thecoreinstitute.com

For general information on meniscus injuries and treatment:

American Academy of Orthopaedic Surgeons, public website

The Knee Society

National Institute of Arthritis and Musculoskeletal and Skin Diseases