Avascular Necrosis (Osteonecrosis) (Aseptic Bone Necrosis) (Ischemic Bone Necrosis)
Avascular necrosis is a disease caused by the temporary or permanent loss of the blood supply to the bones. If the process involves the bones near a joint it can lead to collapse of the joint surface. It is also known as osteonecrosis, aseptic bone necrosis, and ischemic bone necrosis. In avascular necrosis 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 painful arthritis and immobility.
There are many possible causes of avascular necrosis, for example excessive steroid use, alcoholism, trauma, decompression sickness, hypertension, vasculitis, rheumatoid arthritis, lupus, thrombosis, radiation, and sickle cell anaemia. In some cases thre is no identifiable cause.
This disease primarily affects the joints at the shoulder, knee, and hip. Although it can happen in any bone, avascular necrosis most commonly affects the ends (epiphysis) of long bones. It usually affects people between 30 and 50 years of age and about 15,000 people develop avascular necrosis of the head of the femur in the US each year. When it occurs in children at the femoral head, it is known as Legg-Calvé-Perthes syndrome.
Early x-rays are usually normal in the early stage of the disease, therefore bone scintigraphy and MRI are the diagnostic modalities of choice since both can detect minimal changes at early stages of the disease.
Avascular necrosis is especially common in the hip joint. A variety of methods are now used to treat avascular necrosis. The most common method is total hip replacement (THR). Doctors tend not to use total hip replacement in younger patients due to the short life-span of the procedure. A new treatment is metal on metal resurfacing in which only the head of the femur is removed as opposed to THR in which the entire neck is removed. Some doctors also prescribe bisphosphonates (e.g. alendronate) which reduces the rate of bone breakdown by osteoclasts, thus preventing collapse. This is espedically a problem with THR. Another treatment is the Free Vascular Fibular Graft (FVFG); a portion of the fibula, along with its blood supply, is removed and transplanted into the femural head.