Osteoarthritis. Light micrograph of a section through the cartilage of a joint in the early stages of osteoarthritis. The damaged cartilage (purple) has lost its smooth appearance. The surface (top) has become flaky. As the disease progresses the cartilage continues to be eroded until the underlying bone (pink and white, bottom) is exposed. The bone then becomes thickened, hard and dense, a process known as eburnation. These changes lead to joint pain and limited movement of the joint. The hips and knees are most commonly and most severely affected. Osteoarthritis may result from overuse of a joint and is most common in the elderly.