Chondromalacia patella occurs when the articular cartilage that typically sits behind the kneecap to protect the knee bones softens and becomes worn. Without the cartilage to protect them, the bones rub against one another, causing friction and pain. While this condition typically starts as a small soft spot behind the cap, it gradually worsens so that more of the cartilage softens. Some cartilage can even crack or shred into a fibrous mass or float around the knee joint, irritating the joint lining and causing the cells in the lining to produce fluid, which is known as joint effusion. In really bad cases, the damaged cartilage can wear off, completely exposing the undersurface of the knee cap, which can grind painfully against the other knee bones. Many conditions and circumstances can contribute to the development of chondromalacia patella, including a kneecap fracture or dislocation, a muscle imbalance, a meniscus injury, poor alignment, overuse, an infection in the joint, repeated episodes of bleeding, and repeated steroid injections. Chondromalacia patella most often affects young adults and is especially common in athletes who put repeated stress on their knees (runners, joggers, skiers, cyclists, etc.) Most people experience chondromalacia patella as an achy pain in the front of the knee, just behind the cap of the knee.