Focal (restricted to a limited area) injury to the articular cartilage of joint can occur following an injury. Articular cartilage is a durable, but complex, structure that covers the ends of the bones at a joint and allows the joint surfaces to slide and roll smoothly back and forth without pain during movement. Injury can result in a focal tear, split, or separation of the articular cartilage from the underlying bone. Cartilage injury can occur in any joint, although it occurs most
commonly in the knee, followed by the ankle, elbow, and shoulder. Cartilage has no blood supply and therefore, no potential to heal, making articular cartilage injuries difficult to treat. The natural history of focal articular cartilage injury is to progressively get worse until arthritis occurs. Arthritis describes the condition when the articular cartilage covering the ends of the bones has worn out diffusely (over a broad area) on both sides of the joint and the ends of the bone are exposed and rubbing, producing in inflammation and pain.