Meniscal Injuries

The meniscus is one of the most commonly injured structures in the knee. Meniscal injuries can occur in any age group, but causes are somewhat different for each age group. In younger people, the meniscus is fairly tough and rubbery, and tears usually occur as a result of a fairly forceful twisting injury. In the younger age group, meniscal tears are more likely to be caused by athletic activity (Sutton, 1999).

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.