Cartilage is a specialized type of connective tissue with a number of uses throughout the body. There are three main types of cartilage: hyaline (articular, joint) cartilage, fibrocartilage, and elastic cartilage.
Hyaline (articular) cartilage provides a smooth, white, glistening layer that covers the end of the bones at joints. In the knee the end of the femur, the end of the tibia, and the undersurface of the patella are all lined with hyaline cartilage (Fig 1). The main functions of hyaline cartilage are to provide shock-absorbing properties and to allow for a smooth, frictionless gliding surface at the joint. There are no nerve endings in cartilage so there is no discomfort with motion. If the hyaline cartilage layer is injured, however, and the nerve endings of the bone are exposed, the joint begins to hurt.
Articular cartilage lacks blood supply and therefore has a limited capacity for healing. It may be injured by trauma or repetitive injury (Fig 2). Cartilage injuries may present with pain, swelling, and/or locking if a fragment has separated in the joint. The surgical treatment options for cartilage damage are simple debridement (cleanup), microfracture to promote fibrocartilage formation, and any of a number of cartilage transplant procedures. These procedures can often be done utilizing minimally invasive arthroscopic techniques.