Avascular Necrosis
What is it?
Avascular necrosis ("AVN")
is a disease resulting from the temporary or
permanent loss of the blood supply to the bones.
Without blood, the bone and tissue surrounding it
dies, which causes the bone to deteriorate, often
leading to collapse of a joint. AVN is also known
as osteonecrosis, ischemic necrosis, and aseptic
necrosis, strikes both men and women and affects
people of all ages. It is most common among
people in their thirties and forties.
Who gets it?
There are common causes of AVN,
such as fracture or dislocation of the femur
(thigh bone) which results in injury to the blood
circulation, leading to trauma-related AVN.
Studies suggest that this type of AVN may develop
in more than 20 percent of people who dislocate
their hip joint.
In addition, thrombi or emboli
(blood clots), inflammation, and damage to or
narrowing of the arteries (from fat droplets)
which block the blood supply to the hip joint
cause AVN. Increased pressure within the bone
also is associated with AVN - 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.
Studies now show that there is an
increased incidence of AVN seen in people who
chronically use steroids (such as prednisone)
which are commonly used to treat diseases in
which there is inflammation, such as systemic
lupus erythematosus, rheumatoid arthritis, and
vasculitis. Long-term, systemic (oral or
intravenous) steroid use is associated with 35%
of all cases of non-traumatic avascular necrosis.
However, there is no known risk of AVN associated
with the limited use of steroids. Doctors are not
exactly sure why the use of steroids sometimes
leads to AVN; they may interfere with the
body’s ability to break down fatty substances
which in turn build up and clog the blood
vessels, causing them to narrow, which reduces
the amount of blood that gets to the bone.
Excessive alcohol use and steroid
use are two of the most common causes of
non-traumatic AVN. In people who drink an
excessive amount of alcohol, fatty substances may
block blood vessels causing a decreased blood
supply to the bones, resulting in AVN.
Other risk factors or conditions
associated with non-traumatic AVN include
Gaucher’s disease, pancreatitis, radiation
treatments, chemotherapy, decompression disease,
and blood disorders such as sickle cell disease.
What are the symptoms?
The area most frequently involved
is the femoral head (hip joint); however, the
elbow, knee, shoulder, wrist, and ankle can also
be affected. The amount of disability that
results from AVN depends on what part of the bone
is affected, how large of 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 itself
– old bone is torn away and reabsorbed, and
replaced with new bone. In the course of AVN,
however, bone tissues break down faster than the
body can repair them. In the early stages of AVN,
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. If AVN progresses and the bone
and surrounding joint surface collapse, pain may
increase dramatically and 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.
AVN may be present without any
pain. In most cases, however, pain often develops
dramatically, and increases in severity once the
AVN has progressed. If the patient has hip pain,
it is often due to flattening of the normally
round femoral head, bone fragmentation, and
eventual collapse of the femoral head.
Diagnosis
Your doctor will perform a
complete physical examination and ask about your
past medical history, including your health
problems, and medication history. As with any
other diseases, early diagnosis increases the
chances of treatment success.
Your doctor will obtain an x-ray
to help identify the cause of your joint pain,
such as a fracture or arthritis. In the earliest
stages of AVN, standard x-rays are often normal.
If the x-ray is normal, you will probably have
additional tests. A magnetic resonance image (MRI)
is the most sensitive non-invasive method for
diagnosis of AVN, and will show if there is any
damage to the bone marrow, the bone itself, and
the structures in and around the joint. In
addition, MRI may show diseased areas that are
not yet causing any symptoms.
In addition, your doctor will
evaluate the opposite hip as well, because there
is an 80% chance that the other hip is affected,
even though you may have no symptoms at the time.
Treatment
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. Several
treatments are available that can help prevent
further bone and joint damage and reduce pain. To
determine the most appropriate treatment, your
doctor considers the following:
-
Your age
-
The stage of the disease –
early or late
-
The location and amount of bone
affected – a small or large area
-
The cause of AVN – with an
ongoing cause such as steroid or alcohol use,
treatment may not work unless use of the
substance is stopped
If less than 15% of the femoral
head is involved, AVN may resolve without any
further treatment. Non-operative (conservative)
treatment consists of partial weight bearing with
the use of crutches for six weeks then
re-evaluation by your orthopaedic surgeon.
However, non-surgically managed cases most often
show an 85-92% risk of progression of the
disease, and for this reason, it is usually best
to treat the hip surgically. The shoulder and
knee do better with conservative treatment than
the hip does, and this is usually the treatment
of choice for these joints. If AVN is diagnosed
early, your doctor may treat you by limiting your
activities or recommending that you use crutches.
In some cases, reduced weight bearing can slow
the damage caused by AVN 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,
however, most patients will eventually need
surgery to repair the joint.
On the other hand, if greater
than 50% of the femoral head progresses to
collapse, it will ultimately require surgery.
Surgical treatment involves one or a combination
of four different procedures:
-
Core decompression is a
procedure that involves drilling into the
femoral neck (hip bone), through the necrotic
(dead) area in order to relieve the pressure in
the bone and to allow the bone to regrow in the
area and heal on its own. 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.
Patients are required to use crutches for 6
weeks following this procedure in order to
prevent the risk of fracture.
-
Bone grafting is a procedure
that involves taking a graft (segment of
healthy bone) from the fibula (bone below the
knee), and placing it into the core after core
decompression. Bone grafting can either be non-vascularized
(not using the blood vessels of the hip) or
vascularized (using the blood vessels of the
hip). In a vascularized procedure, the blood
vessels of the graft are saved and are
reattached to the blood vessels of the hip. The
disadvantages of this procedure include a
longer recovery period, less complete relief of
pain than after total hip arthroplasty, and the
potential of nerve injury to the calf in which
the bone graft was taken. There is a lengthy
recovery period after a bone graft, usually
from 6 to 12 months.
-
Osteotomy. There are several
types of osteotomies; however, all of these
procedures attempt to shift the diseased
femoral head by relocating some viable (living)
cartilage in the weight bearing area so that
you will have less pain when walking. After the
procedure, your activities are very limited for
3 to 12 months.
-
Arthroplasty (total hip
replacement) entails replacing the hip joint
with an artificial femoral head and part of the
femur with an artificial stem. The surgeon may,
however, determine that the patient only needs
replacement of the femoral head with an
endoprosthesis (ball). A total hip replacement
appears to provide the best results, and leads
to complete or nearly complete relief of pain
and relatively normal function in 90-95% of
patients. With modern surgical techniques and
devices, these artificial hips should continue
to function for at least ten to fifteen years
in the majority of patients.
In addition to the above surgical
and non-surgical treatments, doctors and
researchers are exploring the use of medications,
electrical stimulation, and various therapies to
increase the growth of new bone and blood
vessels. These treatments are used
experimentally, alone, and in combination with
other treatments, such as osteotomy and core
decompression.
Physicians Who
Treat Avascular Necrosis
This information has been designed as a comprehensive and quick reference
guide written by our health care reviewers. The health information written
by our authors is intended to be a supplement to the care provided by your
physician. It is not intended nor implied to be a substitute for
professional medical advice.
|
