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Avascular necrosis (osteonecrosis)
What is avascular necrosis?
Avascular necrosis, or osteonecrosis, is the name given to bone death, a condition that occurs when the blood supply to an area of the bone is cut off either temporarily or permanently.
Bone is living tissue, which is supplied by many blood vessels. Bone that does not have a supply of blood (avascular) for an extended period of time becomes brittle and eventually collapses. This can lead to severe cases of arthritis and dysfunction in the affected joint.
The thighbone (femur) is the most commonly affected bone, followed by the shoulder. Other large joints, including the knee, ankle and wrist, can also be affected.
This condition is also known as ischaemic bone necrosis, aseptic necrosis and bone infarction.
The inside of the bones consists of a strong, honeycomb-like structural tissue, called trabecular tissue. This tissue forms a lattice pattern along the bone stress lines next to bone marrow cavities. Without a fresh blood supply, the trabecular tissue ceases to provide structure or strength to the bone, which often causes the bone to collapse. Certain bones are more at risk, as they rely only on one or very few blood vessels for their blood supply. The ball-shaped end of the femur, which forms part of the hip joint, relies on blood vessels that pass through the thinner shaft of the femur, which can be broken during a fall.
The most common causes of avascular necrosis are as follows:
- Corticosteroid medications - when taken in high dosages or long-term, these medications have been found to cause avascular necrosis, but the exact reasons why have not been identified;
- Chemotherapy or radiotherapy treatment - these can damage blood vessels as a side effect of treatment, and;
- Long-term and excessive alcohol consumption - the exact effect of alcohol on bones has not been determined.
There are several risk factors that can result in avascular necrosis:
- Corticosteroid medication that is used in high doses or long-term;
- Chemotherapy or radiotherapy;
- Organ transplants;
- HIV, Gaucher disease and cancer;
- Lupus, gout and decompression sickness ('the bends') and blood-clotting illnesses such as sickle-cell anaemia;
- Osteoarthritis, osteoporosis and vasculitis (inflamed blood vessels);
- Bisphosphonates - medication given to prevent bone disorders;
- Previous dislocation or bone fracture, and;
- Cigarette smoking, asthma and pancreatitis.
Osteonecrosis of the jaw
Osteonecrosis of the jaw is a rare and serious condition, in which the cells of the jawbone begin to die. This can sometimes develop following radiotherapy to the head and neck area, bisphosphonates treatment, or after a tooth extraction while having either of the two treatments. The symptoms of osteonecrosis of the jaw include severe pain and development of an infection or pus in the exposed area.
Spontaneous osteonecrosis of the knee
Spontaneous osteonecrosis of the knee is when a section of the knee bone dies. It is more common in women and has been linked to osteoporosis. The symptoms usually start in the inner knee, and include localised swelling and tenderness.
Perthes' disease, also known as coxa plana or Legg-Calve-Perthes disease, is a type of avascular necrosis that affects the hip joints of children - most often boys - aged between 3-11 years, for reasons that are currently unknown. During this condition, there is a reduced supply of blood to the round head of the thighbone, known as the femoral head, which fits into the hip socket. This causes loss of bone cells and softening and collapse of the hip joint, which results in pain, limping and reduced movement.
However, most children will recover fully and without complications, using treatments such as braces, pain-relief medications and rest from high-impact activities.
Signs and symptoms
During the first stages of avascular necrosis, there are often no signs or symptoms. Once the bone damage worsens, however, the following symptoms may develop:
Methods for diagnosis
A doctor can suspect avascular necrosis based on a person's medical history and a physical examination. To help confirm the diagnosis, the following tests may also be carried out.
An X-ray is usually the first recommended imaging test for any bone condition. However, as X-rays are not always useful for detecting avascular necrosis in its early stages, they are used more often to track the condition's progression.
Magnetic resonance imaging
Magnetic resonance imaging (MRI) creates an image that can detect changes in the density and structure of your bones. MRI is considered the best option for diagnosing avascular necrosis, as the scans can reveal any chemical changes in the bone marrow, as well as the presence of abnormal tissue, prior to development of any symptoms.
Computerised tomography scan
A computerised tomography (CT) scan can provide detailed imaging of the interior bone structure, revealing any areas of avascular necrosis.
In a bone scan a radioactive substance is injected into the bloodstream. Its circulation is detected by a gamma camera, revealing any problem with blood flow to the bones.
A bone biopsy can provide supportive evidence of avascular necrosis, but as it requires surgery, non-invasive tests such as MRI are usually preferred.
Types of treatment
The type of treatment offered will depend on the level of damage in the bones, age, activity levels, life expectancy and presence of other health conditions. If avascular necrosis is in its early stages, more treatment options are available than in cases of severe avascular necrosis. Treatment options will typically be decided by a specialist and can include the following options:
Protected weight-bearing involves taking weight off the affected joint by using supportive aids such as crutches. This treatment can help with pain relief, but will not cure the condition.
Currently, there is no medication that directly stops the progress of or cures avascular necrosis. However, some medications may be beneficial early in the condition. These include:
- Lipid-lowering medications - these break down the fatty (lipid) deposits in the blood vessels, which otherwise can reduce blood flow;
- Anticoagulants - these prevent formation of blood clots that can reduce blood flow to the bones;
- Hypertension medication - lowers blood pressure and improves blood circulation;
- Non-steroidal anti-inflammatory medication (NSAIDs) - to reduce inflammation in the affected area, and;
- Bisphosphonates - used to treat osteoporosis with favourable outcomes observed in cases of avascular necrosis. 
Pulsed electrical stimulation has been used to encourage bone growth, and some evidence has suggested that it is effective in the treatment of early-stage avascular necrosis.
Hyperbaric oxygen treatment involves entering a pressurised chamber where the lungs can absorb up to three times more oxygen than normal. The treatment has been shown to provide significant improvements in pain, range of mobility and bone healing in some cases of early-stage avascular necrosis. 
Working with a physiotherapist to design and use strengthening exercises may be helpful with increasing flexibility and range of movement.
Surgery is not typically recommended, except in cases of bone damage or collapse. Surgical procedures include:
This procedure involves taking healthy bone from another part of the body and implanting it into the area affected by avascular necrosis. This can be done together with a core decompression procedure.
Bone core decompression
This procedure involves replacing a section of dead bone with a bone graft. Historically, bone core decompression was used as a diagnostic procedure to test bone marrow density, but as patients reported pain relief after the procedure, it became a therapy. It has been shown to regenerate bone growth and prevent the exterior of the bone from collapsing, eliminating the need for a joint replacement.
This less common procedure involves cutting away the dead bone from a weight-bearing area and reshaping the bone to allow healthy bone and cartilage to bear the weight instead.
If the avascular necrosis is in its later stages and the bone has collapsed, a complete joint replacement may be required. The surgeon will replace damaged bone with a prosthetic joint. Both the ball and socket of the hip may be replaced.
If left untreated, avascular necrosis can lead to bone collapse, arthritis and physical disability.
Avascular necrosis is a condition that requires medical treatment in its early stages, to try and reduce the chances of bone collapse or surgery. Though it cannot be cured, if detected early on, the symptoms can be managed and bone damage minimised.
In many cases, avascular necrosis cannot be prevented, but you can lower your risk by avoiding long-term use of corticosteroids, if you can, and avoiding excessive alcohol consumption.