Osteoarthritis: X-ray of a hip joint showing osteoarthritis. The bone in the lower right is the femur (thigh bone). This is connected to the pelvis by a ball-and-socket joint. Osteoarthritis is a disease of the joint cartilage that is associated with changes in the underlying bone. It is recognized on X-rays by a reduction in the joint space (due to loss of cartilage), by the presence of osteophytes (bony projections), and by a ragged, irregular appearance of the remaining joint. Osteoarthritis is associated with mechanical wear and most commonly affects the elderly. Deterioration of the joint causes pain, stiffness and lack of mobility.