There are two menisci in the knee; each rests between the thigh bone (femur) and shin bone (tibia). The menisci are made of tough cartilage and conform to the surfaces of the bones upon which they rest. The menisci function to distribute a person’s body weight across the knee joint and to improve the shape of the join between the 2 bones, contributing to the stability of the knee joint.
Without the meniscus present, the weight of your body would be unevenly applied to the bones in your legs (the femur and tibia). The function of the meniscus is critical to the health of the knee
Pain and Symptoms
- Pain. The degree of this will vary according to the site and extent of the injury and the type of activity being performed. There may be severe pain if a torn fragment of meniscus catches between the tibia and femur. Sometimes, a past injury causes pain months or years later, particularly if the affected knee is injured again.
- Swelling. The knee may swell immediately if blood vessels are damaged with the injury, or swell more slowly as part of the inflammatory process that occurs following injury. Swelling is sometimes difficult to see.
- Knee function. You maybe unable to straighten or bend the knee fully. In severe cases, no walking is possible due to the intensity of the pain. The knee may click, or may ‘lock’ from time to time if the torn fragment interferes with normal knee movement. A locked knee means that it gets stuck when it is bent and cannot be straightened without manually moving or manipulating the leg).
Causes of Injury
The two most common causes of a meniscal tear are due to traumatic injury (often seen in athletes) and degenerative processes (seen in older patients who have more brittle cartilage). The most common mechanism of a traumatic meniscus tear occurs when the knee joint is bent and the knee is then twisted. The meniscus may tear fully or partially. The seriousness of the injury depends on its size, and the exact site and shape of the tear.
In severe injuries, other parts of the knee may also be damaged in addition to a meniscal tear. For example, a person may also sprain or tear a ligament or have problems, with the joint surface.
Meniscal cartilage does not repair very well once it is torn since it does not have a good blood supply, except in children where some repair is possible. In the adult the outer edge of each meniscus has some blood vessels, but the
area in the centre has no direct blood supply (it is ‘avascular’). So, some small outer tears may heal in time, but larger tears, or a tear in the middle of a meniscus, tend not to heal. However many meniscal tears, even if they do not repair can settle sufficiently to avoid surgery.
In some cases the symptoms of meniscus injury go away on its own after a few weeks. However, in many cases the symptoms persist for longer.