Provided
by:
The
National Osteonecrosis Foundation
and
The Center for Osteonecrosis Research and Education
OSTEONECROSIS
INTRODUCTION
Osteonecrosis (ON) affects approximately 20,000
new patients per year in the United States. Although any age group
may develop ON, most patients are between 30 and 50 years old,
with the average age in the late 30's. The diagnosis of ON does
not affect life expectancy, and for this reason several hundred
thousand patients are living with this disease in the U.S. alone.
What is osteonecrosis? First, you should understand that bone
is a living tissue with living cells and a blood supply. Osteonecrosis
means death of bone which can occur from the loss of the blood
supply or by some other means (see ‘What Causes Osteonecrosis?’).
It has been known by a number of other names including ischemic
necrosis of bone, aseptic necrosis or avascular necrosis (AVN).
AVN has been quite popular in its use because it is shorter to
say and write. More recently the term ON (osteonecrosis) has been
adopted.
In the following sections, a review of the factors that play
a role in your individual treatment and results of those treatments
are discussed. It is important to understand that each patient
is unique. Differences in the amount of bone involvement, other
diseases that you may have, your level of activity, and other
factors are extremely important in determining the appropriate
treatment for each individual patient. None of the information
presented here is intended to take the place of the individual
patient-physician encounter. Rather, this brochure is designed
to help you understand more about the disease and will assist
you in discussing specific treatment options with your physician.
Who’s at Risk?
If a person is completely healthy, the risk of getting osteonecrosis
is quite small, probably less than one in
100,000. Another way to understand this is that most of the people
who get ON probably have an underlying health problem. Most patients
are between 30 and 50 years old with an average age of 38. Patients
over the age of 50 are likely to have developed ON either by a
fracture of the hip or more rarely in association with disease
of the major blood vessels to the lower leg.
Legg-Calve-Perthes Disease
Children, ranging in age from 4 to early teenage years, get a
form of osteonecrosis called Legg-Calve-Perthes disease (Perthes
for short) after the three doctors who first described it. Treatment
for Perthes is completely different than for adult ON. A pamphlet
describing this disease is available from the National
Osteonecrosis Foundation.
What Causes Osteonecrosis?
There are two major forms of ON, post-traumatic and non-traumatic.
Examples of post-traumatic ON, a common cause of ON, include displaced
fractures or dislocations. Minor trauma is not believed to cause
ON. Even major injury does not often result in ON. Certain kinds
of fracture, where the blood vessels to part of the bone have
been physically damaged, may result in ON.
Non-traumatic ON occurs when their is no history of trauma. Scientists
have identified a number of risk factors that may be associated
with non-traumatic ON. We do not know how these risk factors may
lead to the development of the disease. There are many different
ideas (also called hypotheses). But these ideas have not been
proven. There are some cases of osteonecrosis that occur in patients
that are otherwise completely healthy with no detectable risk
factors. This catagory is called "idiopathic", a word
meaning "of unknown cause".
What are the Risk Factors?
One of the most common causes of osteonecrosis
of the hip and of other joints is a displaced fracture or a dislocation.
However, this brochure focuses on non-traumatic osteonecrosis.
The risk factors for osteonecrosis can be separated into two catagories:
definite and probable. The most common risk factor is a history
of high dose steroid treatment for some medical condition (e.g.,
Lupus). Low dose steroids (cortisone, prednisone, etc.) commonly
used for bee stings, poison ivy and acute allergies are not thought
to cause osteonecrosis. The next most common associated condition
is a history of high alcohol use. The greater the alcohol consumption,
the higher the risk of osteonecrosis.
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CAUSES OF OSTEONECROSIS
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DEFINITE
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PROBABLE
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First Symptoms
Unfortunately many patients with ON have had the disease for
quite some time before symptoms are present. The initial symptoms
are usually felt during activity and include pain or aching in
the affected joint. Symptoms usually begin slowly and may initially
be sporadic. Sometimes, the pain may begin quite suddenly. As
the disease progresses, the pain increases and is associated with
stiffness and loss of motion of the involved joint. Limping becomes
common. The hip is the most common joint affected, and the pain
is usually felt in the groin.
Progression of the Disease
In the earliest stage of the disease, x-rays appear normal and
the diagnosis is made using MRI. Once it can be seen on x-ray,
it is not actually the dead bone that can be seen but the healing
response of the living bone to the area of necrosis. The advanced
stages of ON begin when the dead bone starts to fail mechanically
through a process of microfractures of the bone. Eventually, this
will result in damage to the other side of the joint, requiring
major joint reconstruction.
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These x-rays of the hip show the different stages
of the disease. At first (stage I), there are no detectable
changes on x-ray (fig A). In stage II, there are some changes
but the surface is still intact (fig B). As the disease progresses,
the surace begins to collapse (fig C) until, finally, the
integrity of the joint is destroyed (fig D). |
In the more advanced stages of the disease and/or when more of
the joint is diseased, it is less likely that the natural joint
can be preserved. Fortunately, joint replacement procedures today
are highly successful, even in the relatively young patients affected
by ON. It is always the physicians desire to preserve the normal
joint whenever possible. Unfortunately many patients do not visit
the doctor until their joint has an advanced stage of the disease.
Extent of Disease
The femoral head (the ball part of the hip) is the most frequent
bone involved and will be used for this discussion. It is rare
for the entire weight-bearing surface of the femoral head to be
involved. However if more than half of the surface is involved,
treatments designed to preserve the femoral head have a much lower
chance of success.
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MRI's
of Femoral Heads
diagnosed with Osteonecrosis
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Small
Lesion
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Large
Lesion
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How Is Osteonecrosis Diagnosed?
The first, and most important, thing that a physician
can do is to perform a thorough physical examination and to ask
questions about your medical history. Once there is a suspicion
of osteonecrosis, your physician will likely obtain one or more
of the following tests:
- X-ray
- Magnetic Resonance Imaging (MRI)
- Bone Scan
- Computed Tomography (CT)
- Biopsy
The principle diagnostic tool is the x-ray. By the time that
most patients have significant symptoms, the disease is advanced
enough to be seen on standard x-rays. In most cases the x-ray
will show the area of bone that is involved. However, the very
earliest stages of ON cannot be seen on a regular x-ray. A widely
used tool is called an MRI. [This test does not involve x-ray
radiation.] These special images are able to detect tissue changes
that are not seen on a plain x-ray. Occasionally, your doctor
may order a CT scan, which is a special series of x-rays interpreted
by the computer to show the three dimensional structure of the
bone. Any of these tests will help the doctor to determine how
advanced the disease is in your case.
TREATMENT
Introduction
Before entering
into a description of some of the treatments available for ON,
it is important to understand the concept of risk/benefit ratio.
Any surgical procedure has a certain element of risk involved.
Even no treatment at all has the risk that the disease will progress,
so doing nothing is not risk free. Some procedures may have a
lower likelihood of success but have very little risk. Other procedures
may have a higher degree of success, but also have a higher degree
of risk. The physician must work with the patient in assessing
all the factors that evaluate both risk and benefit for the patient
in their particular circumstance. What is right for one patient
may be absolutely wrong for another. This is particularly true
for ON because each patient presents with a unique set of factors
(age, associated disease, specific joint(s) involved, extent and
progression of disease). Any treatment needs to be determined
between you and your treating physician. Ask questions, get answers!
Non-Surgical
Treatment
Protected
weight bearing Canes,
crutches or a walker are useful in alleviating the pain
associated with ON. They can also be useful in protecting the
joint between the time of diagnosis and scheduling of elective
surgery. Limiting weight bearing may also play a role in limiting
progression while associated medical conditions are managed. However,
protected weight bearing alone is never an adequate treatment
for ON nor will it result in cure of the condition, no matter
how long it is maintained. Rarely, an associated medical condition
may result in a patient not being able to have surgery. In this
case, protected weight bearing may be recommended for pain management.
Surgical
Treatment
Core
Decompression
This
is a surgical procedure that involves taking a plug of bone out
of the involved area. It is applicable for mild to moderate degree
of involvement that has not yet progressed to collapse. Because
this involves creating a 
hole
in the bone, six weeks of protected weight bearing is necessary
to avoid fracture through the hole. Pain relief from this procedure
has been excellent, but it has not been as effective at delaying
the progression of the disease in the long term. In centers that
do this procedure frequently, most studies have reported good
results in the appropriate cases. However, there is some controversy
about this procedure with a few studies that have been reported
showing generally poor results.
Bone
Grafting When a section
of the bone has died, as is the case in ON, it doesn’t spontaneously
heal. One approach to this problem is to surgically remove the
dead bone and fill the empty space with bone graft that is either
taken from the patient or from the bone bank. The success of this
approach depends upon the quantity of bone that has died.
Vascularized
Bone Grafting
Regular
bone graft, whether from the bone bank or from the patient, is
itself dead bone. It serves as a scaffold for the body to build
new bone around, but the body also has to grow a new blood supply.
For this procedure, a bone with its blood vessels is taken from
the patient and hooked up to blood vessels near the hip. The dead
bone is removed from the femoral head and replaced with the grafted
bone that carries with it its own blood supply. The advantage
of this approach is that the body doesn't have to rebuild a new
blood supply and the bone graft keeps its physical and mechanical
properties. This is most appropriate prior to the collapse of
the joint, but is sometimes used in cases with early (limited)
collapse.
Healing and
complete filling of the defect still has to take place, during
which time crutches or a walker has to be used. The disadvantage
of this procedure is that a substantial piece of bone has to be
taken from the lower leg (the fibula, the smaller bone of the
lower leg below the knee). Some patients may develop pain in the
area from which the bone graft is taken. The operation also takes
several hours and requires a team experienced in these techniques.
The patient is also required to be on crutches for several months.
If both hips are involved, it may be necessary to delay treating
one hip for quite some time during which period the femoral head
may undergo collapse.
Osteotomy
(Cutting the Bone) Usually
the location of the ON is in the area of the bone that bears weight.
In some cases the bone can be cut below the area of involvement
and rotated or turned so that another portion of the bone, that
is not involved in the ON, can become the new weight-bearing area.
These operations are not very common anymore, but may apply to
special cases with smaller lesions.
Femoral
Head Resurfacing [FHR]
Initially
only the femoral head is involved, not the socket of the hip joint.
FHR involves implanting a metal hemisphere over the femoral head,
which exactly matches the size of the original femoral head. This
is similar to capping a tooth when the root is still good, as
opposed to pulling the tooth and putting in a false tooth. It
is known that over a period of many years, the metal head will
gradually wear out the socket and will need to be converted to
a total hip replacement. This procedure is designed to "buy time"
for the younger individual 
whose
extent of disease or degree of progression is such that one of
the preservative procedures listed above cannot be performed.
Most patients with ON are under 50. It is generally believed that
total hip replacement (THR) today will not last the 30+ years
most of these patients will require. Therefore, it is possible
that at least two procedures will be necessary for the treatment
of this disease during a patient’s lifetime. If the 2 procedures
are a femoral head resurfacing followed later by a primary total
hip replacement, this is preferable to a primary THR followed
by a revision THR. However, although the early results have been
favorable, FHR is still a relatively new procedure which is currently
being evaluated.
Femoral
Head Replacement
This
is basically half a total hip replacement. All comments about
femoral head resurfacing apply to femoral head replacement. However,
because a femoral head replacement also puts a stem inside the
femoral bone (the femoral shaft) it is a little more extensive
than the resurfacing procedure. If it needs to be revised, it
is a little more difficult to convert to a total hip replacement
than the resurfacing procedure. There is also no evidence that
a femoral head replacement is more successful than a femoral head
resurfacing.
Metal-on-Metal
Resurfacing The
original concept of replacing the surface of the femoral head
with metal and the acetabulum with a plastic liner had a high
failure rate due to failure on the acetabular side. The concept
has reappeared with a metal liner on the socket side. Experience
is limited but the procedure shows promise.
Total
Hip Replacement [THR]
When
the ON is advanced to the point that there is involvement of the
socket as well, then the only thing that will be effective is
either
a hip fusion (making the hip completely stiff) or a total hip
replacement (THR). THR is one of the most successful surgical
procedures ever devised. Success rates are usually above 95%!
The problem with total hip replacements for patients with ON is
that it is not uncommon for the patient to have a life expectancy
of more than 40 or even 50 years. With current technology we don't
think that it is likely that a THR will last that long. For this
reason, many physicians will want to try some procedure to put
off THR for a few years even when it is known that that procedure
will not in itself be successful forever. If your disease is advanced,
and/or extensive, then THR may be the only thing that makes sense.
Work is currently in progress to develop and evaluate newer total
hip replacements, such as ceramic-on-ceramic devices, which may
be much more durable than present components, and which theoretically
might last a lifetime even in younger patients with ON.
Can
It Be Prevented?
At
present, there is no known prevention. However, it is reasonable
to believe that if some of the risk factors are treated or eliminated,
you would decrease your risk for getting the disease. For this
reason, steroids should only be taken as necessary and alcohol
consumption should always be in moderation. Some experimental
drug protocols are being evaluated which may have a place in treatment
or prevention in the future.
Early
Recognition and Intervention
An important
message has been learned over the past few years in the treatment
of osteonecrosis. Early diagnosis and early intervention provides
the best opportunity for alleviating the collapse of the joint
surface and delaying the need for hip replacement surgery. The
only other treatment option is hip arthrodesis - surgical fusion.
Since this condition commonly occurs in both hips, it’s important
that both hips be thoroughly assessed at each evaluation. Furthermore,
if osteonecrosis is first diagnosed in a joint other than the
hip, the hip should also be evaluated.
THE
FUTURE
Currently,
there are several studies being conducted to evaluate drugs that
may lead to the prevention of this disease. The effectiveness
of these drugs has not been proven in scientifically controlled
studies in large numbers of patients. But they do offer hope for
the future.
Other
treatments are being evaluated to improve the results of the current
surgical treatments. Bone graft substitutes and electrical stimulation
are being studied in select centers throughout the country.
The
future is dependent on a better understanding of why some people
get the disease and some do not even when they have the same underlying
conditions (steroids, alcohol, etc.) Because the disease does
not affect large numbers and because most physicians do not see
a lot of patients with osteonecrosis, it is important that an
organization like the National Osteonecrosis
Foundation brings together
patients, their families, and physicians to promote increased
awareness of this disease and to support large scale research
efforts.
The
National Osteonecrosis Foundation
The National
Osteonecrosis Foundation is made up of a group of patients, their
families, physicians, and other caring individulas who are interested
in finding a cure for osteonecrosis. It is the mission of this
foundation to provide support for medical research and for the
education of patients, physicians, and other health professionals.
If you are interested in more information, please contact us:
The
National Osteonecrosis Foundation, Inc.
Suite 201
5601 Loch Raven Blvd.
Baltimore, MD 21239
PHONE: (410) 532-5985
FAX: (410) 532-5908
Websites:
NONF
Website
http://www.osteonecrosis.org
Support
Group for Patients with ON
http://members.aol.com/MarieS1520/2bkn.html
Support
Group for Patients with Perthes
http://maxpages.com/lpsupportgroup
National
Osteonecrosis Foundation, Inc.
Membership Enrollment Card
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