Avascular necrosis, also called osteonecrosis, is a condition in which bone death occurs because of inadequate blood supply to it. Lack of blood flow may occur when there is a fracture in the bone or a joint dislocation that may damage nearby blood vessels. Hip joint is most commonly affected; however, the knee and shoulder may also be involved.
Osteoarthritis, also called degenerative joint disease, is the most common form of arthritis. It occurs most often in the elderly. This disease affects the tissue covering the ends of bones in a joint called cartilage. In osteoarthritis, the cartilage becomes damaged and worn out, causing pain, swelling, stiffness and restricted movement in the affected joint. Although osteoarthritis may affect various joints including the hips, knees, hands, and spine, the hip joint is most commonly affected. Rarely, the disease may affect the shoulders, wrists, and feet.
Hip osteonecrosis occurs due to disruption of the blood supply to the highest part of the thigh bone (femoral head). Due to lack of nourishment, the bone tissue of the femoral head dies and gradually collapses, which may further lead to degeneration of the underlying cartilage.