Avascular necrosis is a disease resulting from the
temporary or permanent loss of the blood supply to the bones. Without
blood, the bone tissue dies and causes the bone to collapse. If the
process involves the bones near a joint, it often leads to collapse of
the joint surface. This disease also is known as osteonecrosis, aseptic
necrosis, and ischemic bone necrosis.
Although it can happen in any bone, avascular necrosis
most commonly affects the ends (epiphysis) of long bones such as 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. Avascular necrosis
usually affects people between 30 and 50 years of age; about 10,000 to
20,000 people develop avascular necrosis each year. Orthopaedic doctors
most often diagnose the disease.
The amount of disability that results from avascular
necrosis depends on what part of the bone is affected, how large an area
is involved, and how effectively the bone rebuilds itself. The process
of bone rebuilding takes place after an injury as well as during normal
growth. Normally, bone continuously breaks down and rebuilds--old bone
is reabsorbed and replaced with new bone. The process keeps the skeleton
strong and helps it to maintain a balance of minerals. In the course of
avascular necrosis, 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.
What Causes Avascular Necrosis?
Avascular necrosis has several causes. Loss of blood
supply to the bone can be caused by an injury (trauma-related avascular
necrosis or joint dislocation) or by certain risk factors (nontraumatic
avascular necrosis), such as some medications (steroids), blood
coagulation disorders, or excessive alcohol use. Increased pressure
within the bone also is associated with avascular necrosis. The pressure
within the bone causes the blood vessels to narrow, making it hard for
the vessels to deliver enough blood to the bone cells.
When a joint is injured, as in a fracture or dislocation,
the blood vessels may be damaged. This can interfere with the blood
circulation to the bone and lead to trauma-related avascular necrosis.
Studies suggest that this type of avascular necrosis may develop in more
than 20 percent of people who dislocate their hip joint.
Corticosteroids such as prednisone are commonly used to
treat diseases in which there is inflammation, such as systemic lupus
erythematosus, rheumatoid arthritis, inflammatory bowel disease, and
vasculitis. Studies suggest that long-term, systemic (oral or
intravenous) corticosteroid use is associated with 35 percent of all
cases of nontraumatic avascular necrosis. However, there is no known
risk of avascular necrosis associated with the limited use of steroids.
Patients should discuss concerns about steroid use with their doctor.
Doctors aren't sure exactly why the use of corticosteroids
sometimes leads to avascular necrosis. They may interfere with the
body's ability to break down fatty substances. These substances then
build up in and clog the blood vessels, causing them to narrow. This
reduces the amount of blood that gets to the bone. Some studies suggest
that corticosteroid-related avascular necrosis is more severe and more
likely to affect both hips (when occurring in the hip) than avascular
necrosis resulting from other causes.
Excessive alcohol use and corticosteroid use are two of
the most common causes of nontraumatic avascular necrosis. In people who
drink an excessive amount of alcohol, fatty substances may block blood
vessels, causing a decreased blood supply to the bones that results in
Other Risk Factors
Other risk factors or conditions associated with
nontraumatic avascular necrosis include Gaucher's disease, pancreatitis,
radiation treatments and chemotherapy, decompression disease, and blood
disorders such as sickle cell disease.
Who Is Likely To Develop Avascular Necrosis?
Avascular necrosis affects both men and women and affects
people of all ages. It is most common among people in their thirties and
forties. Depending on a person's risk factors and whether the underlying
cause is trauma, it also can affect younger or older people.
What Are the Symptoms?
In the early stages of avascular necrosis, patients may
not have any symptoms. As the disease progresses, however, most patients
experience joint pain--at first, only when putting weight on the
affected joint, and then even when resting. Pain usually develops
gradually and may be mild or severe. If avascular necrosis progresses
and the bone and surrounding joint surface collapse, pain may develop or
increase dramatically. Pain may be severe enough to limit the patient's
range of motion in the affected joint. In some cases, particularly those
involving the hip, disabling osteoarthritis may develop. The period of
time between the first symptoms and loss of joint function is different
for each patient, ranging from several months to more than a year.
How Is Avascular Necrosis Diagnosed?
After performing a complete physical examination and
asking about the patient's medical history (for example, what health
problems the patient has had and for how long), the doctor may use one
or more imaging techniques to diagnose avascular necrosis. As with many
other diseases, early diagnosis increases the chances of treatment
It is likely that the doctor first will recommend a
radiograph, commonly called an x ray. X rays can help identify many
causes of joint pain, such as a fracture or arthritis. If the x ray is
normal, the patient may need to have more tests. Research studies have
shown that magnetic resonance imaging, or MRI, is the most sensitive
method for diagnosing avascular necrosis in the early stages. The tests
described below may be used to determine the amount of bone affected and
how far the disease has progressed.
An x ray is a common tool that the doctor may use to help
diagnose the cause of joint pain. It is a simple way to produce pictures
of bones. The x ray of a person with early avascular necrosis is likely
to be normal because x rays are not sensitive enough to detect the bone
changes in the early stages of the disease. X rays can show bone damage
in the later stages, and once the diagnosis is made, they are often used
to monitor the course of the condition.
Magnetic Resonance Imaging (MRI)
MRI is quickly becoming a common method for diagnosing
avascular necrosis. Unlike x rays, bone scans, and CT
(computed/computerized tomography) scans, MRI detects chemical changes
in the bone marrow and can show avascular necrosis in its earliest
stages. MRI provides the doctor with a picture of the area affected and
the bone rebuilding process. In addition, MRI may show diseased areas
that are not yet causing any symptoms.
Also known as bone scintigraphy, bone scans are used most
commonly in patients who have normal x rays. A harmless radioactive dye
is injected into the affected bone and a picture of the bone is taken
with a special camera. The picture shows how the dye travels through the
bone and where normal bone formation is occurring. A single bone scan
finds all areas in the body that are affected, thus reducing the need to
expose the patient to more radiation. Bone scans do not detect avascular
necrosis at the earliest stages.
A CT scan is an imaging technique that provides the doctor
with a three-dimensional picture of the bone. It also shows "slices" of
the bone, making the picture much clearer than x rays and bone scans.
Some doctors disagree about the usefulness of this test to diagnose
avascular necrosis. Although a diagnosis usually can be made without a
CT scan, the technique may be useful in determining the extent of bone
A biopsy is a surgical procedure in which tissue from the
affected bone is removed and studied. Although a biopsy is a conclusive
way to diagnose avascular necrosis, it is rarely used because it
Functional Evaluation of Bone
Tests to measure the pressure inside a bone may be used
when the doctor strongly suspects that a patient has avascular necrosis,
despite normal results of x rays, bone scans, and MRIs. These tests are
very sensitive for detecting increased pressure within the bone, but
they require surgery.
What Treatments Are Available?
Appropriate treatment for avascular necrosis is necessary
to keep joints from breaking down. If untreated, most patients will
experience severe pain and limitation in movement within 2 years.
Several treatments are available that can help prevent
further bone and joint damage and reduce pain. To determine the most
appropriate treatment, the doctor considers the following aspects of a
The age of the patient
The stage of the disease--early or late
The location and amount of bone affected--a small or
The underlying cause of avascular necrosis--with an
ongoing cause such as corticosteroid or alcohol use, treatment may not
work unless use of the substance is stopped.
The goal in treating avascular necrosis is to improve the
patient's use of the affected joint, stop further damage to the bone,
and ensure bone and joint survival. To reach these goals, the doctor may
use one or more of the following treatments.
Medicines--to reduce fatty substances (lipids)
that increase with corticosteroid treatment or to reduce blood
clotting in the presence of clotting disorders. Nonsteroidal
anti-inflammatory drugs may also be prescribed to reduce
Reduced weight bearing--If avascular necrosis is
diagnosed early, the doctor may begin treatment by having the patient
remove weight from the affected joint. The doctor may recommend
limiting activities or using crutches. In some cases, reduced weight
bearing can slow the damage caused by avascular necrosis and permit
natural healing. When combined with medication to reduce pain, reduced
weight bearing can be an effective way to avoid or delay surgery for
Range-of-motion exercises--may be prescribed to
maintain or improve joint range of motion.
Electrical stimulation--to induce bone
Conservative treatments have been used experimentally
alone or in combination. However, these treatments rarely provide
lasting improvement. Therefore, most patients will eventually need
surgery to repair the joint permanently.
Core decompression--This surgical procedure
removes the inner layer of bone, which reduces pressure within the
bone, increases blood flow to the bone, and allows more blood vessels
to form. Core decompression works best in people who are in the
earliest stages of avascular necrosis, often before the collapse of
the joint. This procedure sometimes can reduce pain and slow the
progression of bone and joint destruction in these
Osteotomy--This surgical procedure reshapes the
bone to reduce stress on the affected area. There is a lengthy
recovery period, and the patient's activities are very limited for 3
to 12 months after an osteotomy. This procedure is most effective for
patients with advanced avascular necrosis and those with a large area
of affected bone.
Bone graft--A bone graft may be used to support a
joint after core decompression. Bone grafting is surgery that
transplants healthy bone from one part of the patient, such as the
leg, to the diseased area. Commonly, grafts (called vascular grafts)
that include an artery and veins are used to increase the blood supply
to the affected area. There is a lengthy recovery period after a bone
graft, usually from 6 to 12 months. This procedure is complex and its
effectiveness is not yet proven. Clinical studies are under way to
determine its effectiveness.
Arthroplasty/total joint replacement--Total joint
replacement is the treatment of choice in late-stage avascular
necrosis and when the joint is destroyed. In this surgery, the
diseased joint is replaced with artificial parts. It may be
recommended for people who are not good candidates for other
treatments, such as patients who do not do well with repeated attempts
to preserve the joint. Various types of replacements are available,
and people should discuss specific needs with their
For most people with avascular necrosis, treatment is an
ongoing process. Doctors may first recommend the least complex and
invasive procedure, such as protecting the joint by limiting movement,
and watch the effect on the patient's condition. Other treatments then
may be used to prevent further bone destruction and reduce pain. It is
important that patients carefully follow instructions about activity
limitations and work closely with their doctor to ensure that
appropriate treatments are used.
What Research Is Being Done to Help People With
With proper treatment, most people with avascular necrosis
can lead productive lives. But there is still a lot to learn about
prevention, diagnosis, and treatment. For example, researchers are
New ways to diagnose avascular necrosis in its earliest
stages, when nonsurgical treatment is most likely to help.
The various causes of avascular necrosis so that,
someday, it may be possible to prevent the disease.
New treatments and improvement of the treatments that
are available. In the future, medication may be an effective treatment
for avascular necrosis.
Improvements to the various types of hip replacements,
to prevent younger patients from needing more than one hip replacement
during their lives.
Keeping on Top of Your Condition
Keeping in tune with your disease or condition not only makes treatment less intimidating but also increases its chance of success, and has been shown to lower a patients risk of complications. As well, as an informed patient, you are better able to discuss your condition and treatment options with your physician.
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Where Can People Find More Information About
American Academy of Orthopaedic Surgeons
Des Plaines, IL 60017
Phone: 800-824-BONE (2663) (free
1330 West Peachtree
Atlanta, GA 30309
Phone: 404-872-7100 or 800-283-7800 (free
or call your local chapter (listed in the telephone
The Hip Society
951 Old County Road,
Belmont, CA 94002