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AVASCULAR
NECROSIS
What
Is Avascular Necrosis?
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. 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.
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 torn away and 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 by
certain risk factors (non-traumatic avascular necrosis), such
as some medications (steroids) 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.
Injury
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.
Steroid Medications
Corticosteroids such
as prednisone are commonly used to treat diseases in which there
is inflammation, such as systemic lupus erythematosus, rheumatoid
arthritis, and vasculitis. Studies suggest that long-term, systemic
(oral or intravenous) corticosteroid use is associated with
35 percent of all cases of non-traumatic 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 lead 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.
Alcohol Use
Excessive alcohol
use and corticosteroid use are two of the most common causes
of non- traumatic 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 avascular necrosis.
Other Risk Factors
Other risk factors
or conditions associated with non-traumatic 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
strikes 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 collapses, pain may
develop or increase dramatically. Pain may be severe enough
to limit the patient’s range of motion in the affected joint.
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
success.
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.
X Ray
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 i ts 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.
Bone Scan
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.
Computed/Computerized
Tomography
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 damage.
Biopsy
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 requires surgery.
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 suffer 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 patient’s disease:
- The age of the
patient.
- The stage of the
disease—early or late.
- The location and
amount of bone affected—a small or large area.
- 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:
- 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 some patients. Most patients eventually
will need surgery, however, 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 patients.
- 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. 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 doctor.
In addition to the
above treatments, doctors are exploring the use of medications,
electrical stimulation, and combination therapies to increase
the growth of new bone and blood vessels. These treatments have
been used experimentally alone and in combination with other
treatments, such as osteotomy and core decompression.
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 doctors
to ensure that appropriate treatments are used.
What
Research Is Being Done To Help People With Avascular Necrosis?
With proper treatment,
most people with avascular necrosis can lead normal lives. But
there is still a lot to learn about prevention, diagnosis, and
treatment. For example, researchers are studying:
- New ways to diagnose
avascular necrosis in its earliest stages, when non- surgical
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 life.
Where
Can People Find More Information About Avascular Necrosis?
Arthritis
Foundation
1330 West
Peachtree Street
Atlanta,
GA 30309
404/872-7100
800/283-7800
or call your local chapter (listed in the telephone directory)
World Wide
Web address: http://www.arthritis.org
The Hip Society
c/o Richard
B. Welch, M.D.
One Shrader
Street, Suite 650
San Francisco,
CA 94117
415/221-0665
Fax: 415/221-4023
The Society maintains
a list of physicians who are specialists in problems of the
hip and provides physician referrals by geographic area.
Acknowledgments
The NIAMS gratefully
acknowledges the assistance of Thomas D. Brown, Ph.D., of the
University of Iowa; James Panagis, M.D., M.P.H., of the National
Institutes of Health; and Harry E. Rubash, M.D., of the University
of Pittsburgh Medical Center, in the preparation and review
of this fact sheet.
The National Arthritis
and Musculoskeletal and Skin Diseases Information Clearinghouse
(NAMSIC) is a public service sponsored by the NIAMS that provides
health information and information sources. The NIAMS, a part
of the National Institutes of Health (NIH), leads the Federal
medical research effort in arthritis and musculoskeletal and
skin diseases. The NIAMS sponsors research and research training
throughout the United States as well as on the NIH campus in
Bethesda, MD, and disseminates health and research information.
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