Avascular necrosis or osteonecrosis is the cellular death of bone in some part of the body due to obstruction of its blood supply, usually to the growing end (epiphysis) of the bone. It is also called bone infarction or aseptic necrosis of bone. It causes the bone to degenerate and break down, forming tiny cracks, which finally result in the collapse of the bone. It is more common in people between 30 and 60 years of age and both men and women are equally affected. It is most common in the head of the femur.
Avascular Necrosis Illustration. Image Credit: Joshya / Shutterstock
Impairment of blood flow to bone tissue may be caused by:
- Fracture of the bone or dislocation of a joint which damages or kinks blood vessels nearby
- Excessive ingestion of alcohol, which causes increased levels of blood lipids and dyslipidemic changes in blood vessels
- Radiation therapy can cause vascular and osseous damage
- Fatty obstruction of the small blood vessels entering the bone tissue and feeding the bone units
- Obstruction due to diseases, such as sickle cell anemia and Gaucher’s disease
- Other causes include steroid intake at high doses, because it increases levels of lipid levels in the blood and predisposes to poor blood flow
- Bisphosphonate usage can increase osteonecrosis of the jaw as seen in patients who received these drugs for cancers, but not for osteoporosis
- Organ transplantation, especially renal transplants, are linked with osteonecrosis
- Some other conditions associated with a higher risk of avascular necrosis include pancreatitis, diabetes, and systemic lupus erythematosus
However, in a quarter of patients the cause is unknown.
In the initial stages, avascular necrosis is asymptomatic, but pain sets in when the weight is borne by the joint, and in the later stages, joint pain occurs at rest also. Pain is mild or severe, but typically insidious in onset, and localized to the groin, the thigh or the buttock. The pain prevents joint movement in most cases. Other areas include the shoulder joint, knee joint, the spine, the hand and the foot. Bilateral avascular necrosis occurs in about 40-80% of patients, but 10 years later in women on average, than in men.
Avascular necrosis always progresses with time if over 15% of the bone. Once it involves more than 50% of the bone, the bone eventually collapses in on itself. Another sequel is severe osteoarthritis due to erosion of bone contours.
Some tips to prevent avascular necrosis include:
- Avoiding alcohol intake
- Reducing blood cholesterol levels
- Avoiding too high doses of steroids, and especially repeated or high-dose courses
Diagnosis and Treatment
The diagnosis is based on the history and physical examination, complemented by imaging techniques. Avascular necrosis is a condition that should be caught and treated early to prevent collapse of the bone of the joint. In most cases, the joint pain settles with expectant treatment in about 8-12 months and leaves the joint stiff, but with no other functional problems.
The prognosis depends on the part affected, the extent of necrosis and the rate of bone replacement. Treatment may include analgesic and anti-inflammatory medications to control pain and inflammatory reactions, avoiding any activity that loads the affected joint, the use of crutches, and electrical stimulation.
Physical therapy is useful in maintaining and improving joint mobility through the normal range of motion. Precipitating factors such as alcohol consumption and steroid use should be stopped or avoided under supervision. Surgery such as osteotomy, bone grafting, and even joint replacement may be required in very few cases.