The meniscus is a special structure in the knee that spans and cushions the space between the joint surfaces of the thigh bone (or femur) and the shin bone (or tibia). There are two menisci in each knee – one on the inside (medial meniscus) and one on the outside (lateral meniscus). They are made of strong fibrocartilage and are shaped like the letter “C.” These menisci look like suction cups that are carefully molded to the shape of the joint surfaces of the thigh and shin bones.
The specific shape and size of the meniscus allows it to serve several functions. When you stand up, your weight is borne evenly through your legs and, as a result, your knees. The stress is even higher during walking, running, and jumping. As a result, the body needs a cushion to keep the bones from grinding against each other and causing harm. The meniscus helps to cushion this weight and transmits the load across the knee joint.
Also, because the meniscus is carefully molded to the shape of the joint surfaces of the thigh and shin bones, it helps to evenly distribute the load throughout the knee. This load-sharing also helps to avoid knee injury and is extremely important to the function and health of the knee. An injury to the meniscus can affect its ability to function normally.
Another important characteristic of the meniscus tissue is its ability to get oxygen from its blood supply and heal. Small blood vessels are only present in the outer one-third of the meniscus (known as the “red zone”); the inner two-thirds (also known as the “white zone”) are “avascular” - without a blood supply. Thus, most meniscus injuries affecting the inner, avascular, two-thirds will not heal, as oxygen is required in the area of injury for proper healing.
The most common meniscus injury is a meniscal tear, which most often happens when an athlete quickly turns the body, pivoting on the knee while the foot is held in place. This motion results in a twisting within the knee that can tear the meniscus. This may occur in sporting events including football, basketball, and soccer, but can happen in any activity where this twisting motion takes place.
If a meniscus is torn, the knee usually becomes painful and swollen after the injury occurs. Ascending or descending stairs may become particularly painful and cause increased swelling of the knee. Locking or catching sensations can be experienced following a meniscal tear as well. The leg may feel some weakness and cause a sense of buckling or “giving way,” since the displaced torn fragment and swelling in the knee can affect the thigh muscles that support knee function.
There are many options that are available for treatment of a torn meniscus. These options range from anti-inflammatory medications and rehabilitation with a physical therapist to surgery. The treating orthopedic surgeon will discuss these options and help decide the ideal option based on the patient history, physical examination and the type of tear seen on imaging studies including plain x-ray and magnetic resonance imaging (MRI).
A non-operative physical therapy treatment program will often focus first on reducing pain and maintaining the full motion of the knee. Oral non-steroidal anti-inflammatory medications (such as Ibuprofen) may also be prescribed. After the initial injury pain has decreased and the knee motion is restored, treatment may move to muscle strengthening.
If surgery is required for treatment of the meniscal tear, this will likely be performed arthroscopically through small incisions, using a fiber-optic camera and small specialized instruments. These instruments allow careful removal of the torn sections or repair of the meniscal tear with sutures or “tacks.”
Since the meniscus has an important role in the long term health and function of the knee, the surgeon will always attempt to keep or repair any part of the meniscus that has the blood supply and potential to heal. Some meniscal tears occur in the “avascular” part of the meniscus and cannot be repaired. In this case, the torn portion of the meniscus is removed. If the tear is large and occurs in a part of the meniscus with a good blood supply, then a repair may be performed.
In addition, the patient age is important for healing, as patients in their 40s to 50s will often have a complex degenerative tear with poor quality tissue that cannot be repaired.
The post-operative recovery from repair of a meniscal tear is extremely important and will change according to the type of meniscal surgery that is required.
If a meniscus tear is repaired, then limited weight bearing with crutches may be required for approximately 4-6 weeks. On the other hand, if the torn portion of the meniscus is removed, then protected weight bearing may only be required for a few days.
The early rehabilitation will focus on achieving full knee motion and reducing the swelling from surgery. After this has been achieved, the primary focus will be on restoring muscle strength.
The time that may be required to achieve a complete recovery after surgery will depend on the injury and the extent of meniscal surgery necessary for repair. The treating physician and physical therapist or athletic trainer will carefully guide the rehabilitation after surgery. A well-directed rehabilitation plan is important to achieve an excellent result.