What Is Osteonecrosis?
Osteonecrosis is a disease resulting from the temporary or permanent loss of blood supply to the bones. Without blood, the bone tissue dies, and ultimately the bone may collapse. If the process involves the bones near a joint, it often leads to collapse of the joint surface. Osteonecrosis is also known as avascular necrosis, aseptic necrosis, and ischemic necrosis.
Although it can happen in any bone, osteonecrosis most commonly affects the ends (epiphysis) of the femur, the bone extending from the knee joint to the hip joint. Other common sites include the upper arm bone, knees, shoulders, and ankles. The disease may affect just one bone, more than one bone at the same time, or more than one bone at different times.
According to the American Academy of Orthopaedic Surgeons, 10,000 to 20,000 people develop osteonecrosis each year, and most of them are between 20 and 50 years of age. Osteonecrosis is the underlying diagnosis in approximately 10 percent of hip replacements. Orthopaedists – doctors who specialize in the diagnosis and treatment of injuries and diseases of the musculoskeletal system – most often diagnose this disease. The amount of disability that results from osteonecrosis depends on what part of the bone is affected, how large an area is involved, and how effectively the bone rebuilds itself.
Normally, bone continuously breaks down and rebuilds – old bone is replaced with new bone. This process – which takes place after an injury as well as during normal growth – keeps the skeleton strong and helps it to maintain a balance of minerals. In the course of osteonecrosis, however, the healing process is usually ineffective and the bone tissues break down faster than the body can repair them. If left untreated, the disease progresses, the bone collapses, and the joint surface breaks down, leading to pain and arthritis.
Avascular Necrosis of Bilateral Femoral Heads (Coronal T1) showing bilateral avascular necrosis of differing age