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The Menisci
(singular form = meniscus) of the knee are crescent-shaped pads of tough, rubbery fibrocartilage, which is a tissue commonly referred to as "gristle" in the table meat processing industry. The paired menisci of the human knee are often simply referred to as the knee's "cartilages". They exist between the femur (thigh bone) and tibia ("shin bone") to cushion the knee joint during day-to-day use (see FIGURES 1a-1c). Their specific job is to spread out the joint's bone-to-bone contact pressure (caused by carrying your body weight) over a broad area. This avoids concentrated stress in any one spot, which can cause breakdown and deterioration (arthritis) of the articular (gliding surface) cartilage covering the ends of the femur and tibia. Several forms of meniscus damage and deterioration are known to occur, which for general convenience have traditionally been lumped together under the umbrella terms "meniscus tear" or "torn cartilage".

Basic knee anatomy, demonstrating the location of the medial (inner) meniscus and lateral (outer) meniscus.
FIGURE 1b - This photograph demonstrates a cross-section of the medial half of a normal human knee specimen. Above, you see the rounded contour of the femoral condyle. Below, you see the flatter, upper surface of the tibia. These two bones have been drawn apart here to better demonstrate the meniscus (see arrows), which lies between them. You can see that the meniscus is a wedge-shaped structure when viewed in cross-section. It is held in place here by its attachment to the knee's capsular ligament on the left-hand side.

FIGURE 1c - In this picture, the same knee anatomy specimen seen in Figure 1-b is shown, but in a more normal anatomic configuration, with the femur (above) resting upon the tibia (below). Here you can easily see how the meniscus serves as a natural cushion or pad, interposed between the femur and tibia. The arrows demonstrate the direction of joint loading forces while standing. This specimen also demonstrates nicely how the bones of the knee are lined with articular (joint surface) cartilage (the white, border tissue coating the spongy-appearing, dark red bone). Articular cartilage adds to the shock-absorbing capability of the knee and provides the joint with smooth, low-friction gliding surfaces.

Just like the rest of our body parts, our menisci do age and ultimately degenerate. While they can be suddenly torn apart by a violent injury at any age, they typically become gradually weakened, worn and broken down by natural processes as we get older, at times causing symptoms while at other times not. The rearward (posterior) portions of the menisci seem to receive the great majority of stress, both in day-to-day life and in traumatic knee sprains, thus almost all surgical work ends up being done on the posterior two thirds of these structures. Tears of the frontal (anterior) portions of the menisci occur only with relative rarity. Because healthy menisci perform a useful function in the knee, when injured they should be repaired and preserved whenever possible and practical. Meniscus lesions are typically classified by orthopedic surgeons as being either "traumatic" or "degenerative" tears.


® 2007. The Knee and Shoulder Centers of New Jersey and Pennsylvania.