In older people, the meniscus grows weaker with age. The tissue that makes up the meniscus becomes degenerative and much easier to tear. Meniscal injuries in older people occur as a result of a fairly minor injury, even from the up and down motion of squatting. Degenerative tears of the meniscus are commonly seen as a part of the overall condition of osteoarthritis of the knee in the older population. In many cases, there is no one associated injury to the knee that leads to meniscal tears (Sutton, 1999).
In order to understand how the menisci can be injured, you must understand the basic anatomy of the menisci and why they are important. The menisci are two oval (semilunar) fibrocartilages that deepen the articular facets of the tibia and cushion any stresses placed on the knee joint. They enhance the total stability of the knee, assist in the control of normal knee motion, and provide shock absorption against compression forces between the tibia and the femur (Booher, 2000). Articular cartilage covers the ends of the bones that make up the joint. The articular cartilage surface is a tough, very slick material that allows the surfaces to slide against one another without damage to either surface. This ability of the meniscus to spread out the force on the joint surfaces as we walk is important because it protects the articular cartilage from excessive forces occurring in any one area on the joint surface, leading to degeneration over time (Sutton, 1999).
Blood is supplied to each meniscus by the medial genicular artery. Each meniscus can be divided into three circumferential zones: the red-red zone is the outer or peripheral one third and has a good vascular supply; the red-white zone is the middle one third and has a minimal blood supply; and the white-white zone on the inner one third is avascular (Arnheim,1997).
The medial meniscus is larger and more oval or C-shaped in the outline than the lateral meniscus. The medial cartilage is also more firmly fixed to the tibia and the capsule than the lateral meniscus; as a result, it is much more frequently injured than the lateral cartilage. Because of its attachments to the medial collateral ligament, the medial meniscus may also be injured in conjunction with a sprain of this ligament (Arnheim, 1997).
The lateral meniscus is smaller and more round or O-shaped. It is not as firmly attached to the tibia and it is not attached to the lateral collateral ligament. Therefore, the lateral meniscus has greater freedom of movement, and it is not injured nearly as often as the medial meniscus (Booher, 2000). The lateral meniscus also attaches loosely to the lateral articular capsule and the popliteal tendon. The Wrisberg ligament is the part of the lateral meniscus that projects upward, close to the attachment of the posterior cruciate ligament. Then the transverse ligament joins the anterior portions of the lateral and medial menisci (Arnheim, 1997).
Meniscal tears are among the most common of all knee injuries. The menisci are frequently injured or torn as they become displaced, trapped, pinched, or crushed between the femoral condyles and tibial plateaus. The damaged sustained by the menisci varies, ranging from a very small tear along the periphery of the cartilage to a large longitudinal tear which is generally referred to as a "bucket-handle tear". The menisci are often injured by twisting activities during weight bearing, but also can be direct blows to the knee or chronic trauma (Booher, 2000).
Acute injuries to the...