Osteonecrosis

Osteonecrosis (ON), also called Aseptic Necrosis, Avascular Necrosis (AVN), or Ischemic Necrosis, is a result of inadequate or completely absent blood supply to the bone. The term ‘necrosis’ refers to death [Page 1302]of the tissue; ‘osteo’ classifies the death as that of the bone tissue. The name Aseptic refers to the absence of bacteria; in other words, the bone death is not due to a bacterial infection. Avascular means without blood supply; Ischemic refers to a lack of oxygen, which is supplied to the bone by the blood.

To cause ON, an injury or trauma may have cut off the blood supply; the result is a starved bone that may die. Arthritis typically follows. The end of a long bone is the most common site for ON. ON can be debilitat-ing—if the bone at a joint dies or crumbles, the joint itself may cease to function properly; the person may experience mobility issues or severe pain.

There are two major classifications of ON. These types are post-traumatic or non-traumatic. Post-trau-matic ON may occur after a break or other bone trauma. Non-traumatic ON has other, idiopathic causes.

People of all ages are susceptible to ON; however, most often the disorder occurs in a person's thirties to fifties. There is a juvenile form of ON known as Legg-Calvé-Perthes Disease (LCPD or Perthes). This disease is named after the three physicians who first described its symptoms. Perthes affects about one in twelve hundred children, as young as two years old through teenagers. It affects males most of the time, and is usually seen in one hip rather than both. Also known as avascular necrosis of the femoral head, coxa plana, ischemic necrosis of the hip, and osteochondritis, Perthes is the specific death of the ball joint in the juvenile hip. The underlying cause for non-trau-matic Perthes is unknown, but certain populations may have a higher risk of developing it. These populations include Whites, Eskimos, and Asians.

Men and women alike are at risk for ON. The cause of ON is idiopathic, meaning it is unknown. Some risk factors may include alcohol use, arthritis, cancer, or bone injury. People in general good health are at only a low risk of developing ON. Generally, the disorder affects people who have some other health problem involving circulation or blood vessels. For example, someone with impaired blood supply to a region of the body is more likely to develop ON in that region than someone who has proper circulation.

The most common sites on the body for developing ON are the hips, knees, shoulders, and ankles, in descending order. All types of ON are treated by orthopaedic surgeons except for ON of the Jaw; this type of ON is treated by craniofacial surgeons. It is usually associated with tooth extractions or use of bisphos-phonate-containing drugs. Drugs with bisphosphonate are used in the treatment of osteoporosis.

Each year, approximately twenty thousand people are diagnosed with a new case of osteonecrosis in the United States, according to the National Osteonecrosis Foundation and the Center for Osteonecrosis Research and Education.

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