Avascular Necrosis
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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.
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.
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, 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.
Alcohol Use
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 avascular
necrosis.
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.
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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.
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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.
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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 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.
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.
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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 patient's disease:
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The age of the patient
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The stage of the disease--early or late
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The location and amount of bone affected--a small or large
area
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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.
Conservative Treatment
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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 pain.
-
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.
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Range-of-motion exercises--may be prescribed to
maintain or improve joint range of motion.
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Electrical stimulation--to induce bone growth.
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.
Surgical Treatment
-
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.
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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.
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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.
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.
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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 studying:
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New ways to diagnose avascular necrosis in its earliest
stages, when nonsurgical treatment is most likely to help.
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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.
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Improvements to the various types of hip replacements,
to prevent younger patients from needing more than one hip replacement
during their lives.
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National
Institute of Arthritis and Musculoskeletal and Skin Diseases Information
Clearinghouse
American Academy of
Orthopaedic Surgeons
Arthritis Foundation
The Hip Society
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