I am frequently asked questions about meniscus problems in the knee. The meniscus is a cartilage washer situated between the femur (thigh bone) and tibia (large shin bone); a meniscus is located on the inside (medial) and outside (lateral) aspects of each knee. The meniscus distributes the weight-bearing stress placed on the other type of cartilage in the knee (and in all joints), articular cartilage, which lines the end of each bone (think of the shiny material at the end of a chicken bone). The menisci (plural) also provide some stability within the knee, acting like bumpers. When you hear about a professional athlete having surgery for a cartilage tear in his knee, this usually refers to a meniscus injury. Significant bending and twisting of the knee may cause the meniscus to tear; injury occurs more easily with age. Think of the meniscus like a sponge — thick and pliable when it is new; thinner and friable as it ages. Less stress is required to damage a meniscus in an older athlete, known as a degenerative tear.
A torn meniscus usually causes swelling in the knee; this develops over a day or two and typically is not extremely large. Pain is present with bending and twisting of the joint. The history of an injury and the typical findings on exam raise suspicion for a meniscus tear; MRI can confirm the diagnosis. Treatment is dependent on a number of factors. The blood supply to the meniscus is limited to the outer edge; when a tear occurs in the outer aspect of the meniscus, it may heal without further intervention. Unfortunately, the majority of tears occur in other areas. If symptoms persist for longer than a couple of weeks, surgery is recommended; the exception to this is a locked knee. In this case, the meniscus tears in such a way that a flap becomes wedged in the joint, preventing the knee from fully extending (straightening). It may be possible for a physician to manipulate the knee to “unlock it”; otherwise surgery should be performed expeditiously.
Surgery is performed arthroscopically — a fiber optic camera is inserted into the joint through a small incision. Fluid continuously flows into the joint through another incision; the fluid keeps the structures in the knee separated and flushes the joint. The joint is thoroughly inspected. The meniscus injury is then addressed.
Partial meniscectomy is the most common surgical treatment for meniscus injuries. Using the arthroscope, the torn portion of the meniscus is removed (resected), with the goal of leaving behind as much healthy cartilage as possible. Crutches are used for a day or so until walking is comfortable. Activities are increased over a few weeks; full activities may be resumed within two to four weeks for most people.
If the tear is in the outer edge and has relatively good blood flow, the tear may be repaired; the torn edges are held together with special sutures. The recovery process is slower; the patient remains on crutches for about a month (surgeons have different protocols, so the length of recovery will vary) before being allowed to start weight bearing. Activities are re-introduced gradually over several months. Although this process is prolonged if a repair is performed, the meniscus is intact, which is better in the long run. Ideally, all meniscus tears would be repaired, but unfortunately, tears of the inner aspect of the structure do not heal even when sutured. A surgeon may attempt to repair a tear in a somewhat vascular region of the meniscus, especially in a young patient. Unfortunately, if this does not heal, a second surgery is required to resect the torn area.
Degenerative meniscus tears
A degenerative meniscus tear is a different phenomenon. There often is no known injury; because the meniscus is more friable, it tears more easily. Degenerative (arthritic) changes are often present in the articular cartilage in conjunction with the meniscus tear; these changes are manifested as potholes or ruts in the cartilage, ranging from a small scuff in the cartilage to a lesion that extends the depth of the cartilage. Treatment of articular cartilage injuries is a topic for a future article, but ranges from drilling holes that cause bleeding and scar tissue to form in the lesion to joint replacement surgery.
Symptoms related to degenerative meniscus tears often resolve without surgical intervention. Medications such as ibuprofen often provide pain relief; a cortisone injection may also provide pain relief and the ability to resume activities without surgery. What activities can be resumed following a partial meniscectomy? Is there an increased risk of developing arthritis following a meniscus tear? Is my running career over? These and many other questions arise in the face of a meniscus tear.
If I can tolerate the pain, wouldn’t it be better to avoid surgery? Prior to the development of arthroscopy, the answer would have been yes; the entire meniscus was removed during a surgery in which the knee was opened through a very large incision. Surgeons did not realize the importance of the meniscus at that time. As the importance of the meniscus has been learned, conservation of the structure has become a priority. Unfortunately, the meniscus does not function well at the site of the tear, so avoiding surgery will probably not protect the articular cartilage at that site. If pain resolves, surgery is usually not performed. There is concern that a small meniscus tear can become larger if left untreated; this would be dependent on the nature of the tear. Typically a torn edge that becomes caught, causing extension of the tear, is painful, resulting in self-induced activity restrictions.
There is increased risk of developing arthritis in a knee following injury to a meniscus. This is a double-edged sword. Injury to the articular cartilage may occur at the time of the meniscus injury. This is manifested as a bone bruise on MRI. The articular cartilage covers the end of the bruised bone and therefore has been injured; the more severe the initial injury, the greater the likelihood of developing degenerative changes. The loss of part of the meniscus increases the stress load in that portion of the knee and may further increase the likelihood of developing arthritis in the joint. The larger the tear (and amount of meniscus resected) the greater the stress. Other contributing factors to the development of arthritis are the age of the person, the presence of pre-existing damage, and obesity. The increased stress due to meniscal injury will be present over a longer period of time for most young athletes.
The majority of people can resume most activities following meniscus surgery. If a large portion of the meniscus was removed (greater than 50–60 percent), impact activities may needed to be limited, especially in a younger athlete.
To protect the knees, maximizing core and lower extremity strength is essential. Running on softer surfaces may decrease impact forces. Barefoot running techniques also seem to decrease the impact forces on the knees, though the jury is still out on the overall incidence of running related injuries compared with heel strikers. There is no supplement that will re-grow cartilage; glucosamine may provide some benefit in protecting the articular cartilage (mixed results in the medical literature). You may read about meniscus transplants. In younger people with severe articular cartilage and meniscal injury, meniscus transplant is sometimes performed in conjunction with other procedures to preserve the joint. Meniscus transplant is not performed for routine meniscus tears.
In summary, the menisci are important cartilage structures within the knee that reduce stress and provide some stability. Injury to the meniscus is often treated surgically, with the goal of conserving as much of the structure as possible. The surgeon should provide information regarding the status of the articular cartilage in the knee following surgery and give activity recommendations. Maximizing strength and decreasing impact forces may improve the longevity of the joint.
Cathy Fieseler, M.D., is the chairperson of the Road Runners Club of America Sports Medicine Committee and is on the board of directors of the American Medical Athletic Association.
