The reduced blood flow to the bone may be the result of blockage by a blood clot, medication, or the deliberate stoppage of flow during surgery or because of measures taken to control a hemorrhage (major bleed). The most commonly affected sites are the proximal and distal femoral heads, the upper part of the leg bone that attaches into your hip. Other commonly affected sites include the ankle, shoulder and elbow.

Causes

There are many causes of avascular necrosis such as alcoholism, excessive steroid use, post trauma, caisson disease (decompression sickness), vascular compression, hypertension, vasculitis, thrombosis, damage from radiation, bisphosphonates (particularly the mandible) and sickle cell anaemia. In some cases it is idiopathic (no cause is found). Rheumatoid arthritis and lupus are also common causes of AVN.

Avascular necrosis is caused by impaired blood supply to the bone, but it is not always clear what causes that impairment. Osteonecrosis often occurs in people with certain risk factors (such as high-dose corticosteroid use and excessive alcohol intake) and medical conditions. However, it also affects people with no health problems and for no known reason. Following are some potential causes of osteonecrosis and other health conditions associated with its development.

Symptoms

In avascular necrosis of the hip, groin pain may extend down the front and inner portions of the thigh or be felt in the buttocks. The person limps, trying to minimize all hip movements. As the disorder progresses, more and more tiny fractures of the hip occur, and the bone eventually collapses. The pain also increases, and the hip joint feels stiff and loses some of its range of motion.

Although pain may develop insidiously, many patients remember the hour when they first felt incapacitating pain. As the bone progressively collapses, almost all patients develop pain aggravated by mechanical stresses (eg, in the hip; standing, moving, walking) and eased by rest. Eventually, 67% of patients have pain at rest and 40% have pain at night, which may be accompanied by prolonged morning pain and stiffness.

Avascular necrosis begins as a painless bone abnormality. It can remain painless. The involved bone often later develops pain, especially with use. For example, if a hip joint develops avascular necrosis in the ball of the hip joint, pain can be noted - especially with weight-bearing. As the ball of the hip joint collapses from the degeneration of the bone from aseptic necrosis, pain in the groin can be felt with hip rotation and pain can sometimes be noted with rest after weight-bearing.

Treatment

Although rest and the exercises can sometimes heal the affected portion of bone, surgery is usually needed. In as many as 80 percent of patients with early disease, an operation called core decompression can spark regeneration of the bone. In this procedure, the surgeon drills out the damaged section of bone up to the head of the femur. This opens up channels for blood vessels to reach the diseased area and foster the production of new bone. Hip pain is relieved, and as many as 75 percent of patients avoid joint replacement later on.

Bisphosphonate medications, such as alendronate (Fosamax), also may play a role in the treatment of this disease. In some studies of people with avascular necrosis affecting the ball portion of the hip joint (femoral head), bisphosphonates appeared to slow the progression of the disease and reduce pain. More research is needed before doctors can make a strong recommendation about the use of bisphosphonates in the treatment of avascular necrosis.