Anatomy and Purpose of the Meniscus
The meniscus is a very important shock absorber of the knee made of a very strong substance called fibrocartilage. It protects the cartilage of the joint, keeping it from wearing out and causing early arthritis. A large percentage of our body weight is distributed through the meniscus as we walk, run, and jump. The meniscus adds to the stability of the knee joint by helping the shape of the femur or thigh bone conform to the tibia or leg bone. The meniscus also plays a role in the nourishment of the joint cartilage that covers the bones in the joint.
Causes for Meniscus Tears
Several events can cause the meniscus to become damaged. It can tear or rip from force, pinching it between the femur and the tibia. Most frequently this is a twisting-type force and is relatively common in sports-related knee injuries. Occasionally it is associated with a ligament rupture. It does not always require a major fall or twist to cause a meniscal tear. Some occur with nothing more than getting up from a squatting position. Certain meniscal tears occur gradually over a long period of time. In older patients these may represent so-called degenerative meniscal tears and may not be symptomatic. The location of the tear within the meniscus may determine the type of treatment which is most appropriate.
Symptoms of Meniscus Tear
An acute meniscal tear may be heard as a "pop" and felt as a tear or rip in the knee. Many are followed within a few minutes to hours by swelling of the knee as a result of blood accumulation. Some do not result in much swelling and some present themselves in a less acute fashion. Patients with meniscal tears often describe a popping or catching in their knee. Some actually can feel something out of place. In the most dramatic situations the knee will actually lock, preventing the patient from fully extending or straightening the knee -- or occasionally from flexing or bending it. The pain or discomfort is usually along the joint line or where the femur and tibia bone come together. It often starts out relatively painful; then with time, much (if not all) of the pain disappears except with certain activities. Some patients will have the tear become asymptomatic (no symptoms) for a time, especially if their activity level decreases significantly.
Tenderness is elicited by deep palpation (examination using the hands) along the joint line. Twisting the knee while flexing it will occasionally cause or reproduce the patient's symptoms.
Testing for Diagnosis of Meniscal Tears
Meniscal tears do not show up on plain x-rays because the meniscus does not contain calcium the way bones do. There are some specialized tests such as the MRI scan which are helpful in further evaluating the meniscus, although like most medical tests, they cannot be relied upon with 100%. In fact, several recent studies have revealed that the MRI scan is not as accurate as a good clinical history and physical exam by a specialist.
Treatment for Meniscal Tears
Some meniscal tears, especially in relatively inactive people, will go on to become asymptomatic. This is particularly true in older patients. Unfortunately, for many people the symptoms do not go away completely and may actually worsen over time. This may actually be due to a worsening of the tear. The knee can occasionally lock up on the patient, preventing them from bending or straightening the knee. Few meniscal tears will heal on their own in the way that an ankle sprain, for instance, will. Only very small tears that are in the periphery of the meniscal tissue, and usually only in young patients, will heal on their own. Those tears associated with an unstable knee, such as when a ligament injury occurs, have a poorer prognosis due to their risk of re-injury.
Treatment must be individualized according to the symptoms and the patient's activity level. Some patients can live with a meniscal tear without significant worsening over time and need have nothing done after the initial recovery phase. Others will not be able to function at their pre-injury level without treatment.
There is no known medicine or therapy that will heal or fix a torn meniscus. It is a mechanical problem that often requires a mechanical solution. This usually means either partial excision or repair of the tear. Excision versus repair is often decided at the time of arthroscopic surgery and will depend upon several factors. The patient's age, the age of the tear, the size and location, as well as the patient's activity level all play a role in deciding whether a tear can be repaired or must be excised. In general, due to the essential role of the meniscus in protecting the knee from early arthritis, repair is always preferable to removal.
Once it has been decided by the patient that the best option is a surgical one, the procedure is scheduled. It is performed on an outpatient basis (meaning no overnight hospital stay), and it is performed arthroscopically. The knee is systematically evaluated using the arthroscope and the nature of the problem is clarified. Treatment for the problem is then accomplished at that time. If the meniscal tear can be repaired, small stitches are placed from inside the knee out and then a small incision is made at the joint line to allow tying the knots. If the tear is not repairable, the minimal amount of meniscus possible is removed so that a smooth, stable surface remains. Occasionally other types of problems are found at the time of arthroscopy such as cartilage damage or fragments of bone or cartilage. These can also be treated at that time. The patient does not feel any pain during the surgery. Photographs are often taken of the inside of the knee during the procedure, and a copy is made for the patient for subsequent review. The procedure usually takes about 45 minutes, although this varies with the complexity of the procedure.
Most clinical studies indicate that even in the best of circumstances there is still up to a 20% failure rate of the meniscus healing. This might mean a second arthroscopy many months later to remove the unhealed meniscal tear. Despite this potential failure rate, it is best, when possible, to try to repair all meniscal tears that are reasonable candidates for healing. Some meniscal repairs involve passing sutures from inside the knee out with a potential risk for nerve or blood vessel damage. Great care is taken to avoid this and thankfully, it is a very rare occurrence.
If a meniscal repair has been performed, a knee brace is worn for six weeks after surgery while walking. The knee is carefully rehabilitated in therapy with a progressive program of exercises so that the patient can return as quickly as possible to activities and sports. If no meniscal repair was performed, no knee brace is necessary and the recovery period is shortened. If a large amount of meniscal tissue is lost, there is a significant potential for the development of arthritis in the knee due to increased wear of the cartilage. This can take many years to develop but unfortunately, is inevitable in many patients. It is for this reason that it is so important to repair the meniscal tear if possible. The long-term outcome of meniscal repair and/or partial meniscal excision is quite good. Most patients have few limitations and return to participation in most, if not all, of their pre-injury activities.