Knee cartilage

What is knee cartilage?

The cartilage found in a joint is known as articular cartilage and its primary purpose is to act as a buffer to stop bones of the joint rubbing together. Cartilage is very slippery, so the bones can slide against each other without damage. In the knee it takes the form of two C-shaped pieces of material called the meniscus.

The lateral meniscus (on the outer side of the knee) is more commonly damaged than the medial meniscus (on the side nearest to the other knee).

Risk factors

The blood supply to the meniscus is limited to the outer rim – the rest has no blood supply. For that reason, when damaged, the meniscus is unable to undergo the normal healing process that occurs in the rest of the body. In addition, with age, the meniscus begins to deteriorate, becoming more vulnerable to degenerative tears. A partial or total tear of a meniscus may occur when shearing forces are put on the knee as a person quickly twists or rotates the upper leg while the foot stays still.

Typically, when the meniscus is damaged, the torn piece begins to move in an abnormal fashion inside the joint. Cartilage injuries are common in certain sports such as football, netball, tennis and skiing, which immense twisting forces may be placed on the knees.

Symptoms

Because the space between the bones of the joint is very small, the torn fragment may become caught between the bones of the joint. When this happens, the knee becomes painful, swollen, and difficult to move. But many people have tears without symptoms.

Treatment and prevention

Doctors used to routinely remove a torn meniscus but are now aware that this can lead to arthritis in the joint. So if possible the meniscus is repaired or preserved.

The knee will usually be examined using a thin telescopic instrument called an arthroscope to check out the inside of the joint. If the tear is minor and the pain and other symptoms settle (this may take as much as six or more weeks), the doctor may simply recommend a muscle-strengthening programme to try to prevent further damage.

If the tear to a meniscus is more extensive, the doctor may perform keyhole surgery to see the extent of injury and to repair the tear. The doctor can sew the meniscus back in place if the patient is relatively young, the injury is in an area with a good blood supply, and the ligaments are intact. If the patient is elderly or the tear is in an area with a poor blood supply, the doctor may cut off a small portion of the meniscus to even the surface.

Once a meniscal injury has occurred, care should be taken to protect the knee with extra support during sports, to reduce the risk of further injury.