Osteonecrosis answers

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INDEX

What is Osteonecrosis?

Who's at risk?

First Symptoms

Diagnosis

Prevention

Treatment

The concept of Risk/Benefit Ratio

Extent of disease

Progression of the disease

Non-Surgical Treatment

Protected weight bearing

Surgical Treatment

Core Decompression

Bone Grafting

Vascularized Bone Grafting

Osteotomy

Femoral Head Resurfacing

Femoral Head Replacement

Total Hip Replacement

Future Directions

WHAT IS OSTEONECROSIS?

You have been given this brochure either because you or some member

of your family has been diagnosed with osteonecrosis (ON). ON is not

particularly common, afflicting approximately 20,000 new patients per

year in the U.S. However, patients are relatively young, with an

average age of 38 (although any age can be affected). Since the

diagnosis does not affect longevity there are several hundred

thousand patients in the U.S. alone who are living with the disease.

The purpose of this pamphlet is to provide you with information to

help you understand the condition and some of the important issues

with treatment.

What is osteonecrosis? The term literally means death of bone (osteo

= bone, necrosis = death). It has been known by a number of other

names including ischemic necrosis of bone, aseptic necrosis and AVN

(standing for avascular necrosis). AVN has been quite popular in its

use because it is shorter to say and write. More recently the term

ON has been adopted.

ON can affect virtually any bone, but for practical purposes most

cases involve only the hip, knee shoulder or ankle joints in

decreasing order of frequency. In fact, ON of the hip accounts for

more than 90% of the cases.

There are two major forms of ON, post-traumatic and non-traumatic.

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 has been associated with a wide variety of diseases

including gout, lupus, sickle cell disease, kidney or liver disease,

and clotting disorders. In addition, high dosage steroid (cortisone)

use is sometimes associated with ON, as well as high alcohol

consumpution. Finally, as many as 30% of all patients with

osteonecrosis are otherwise completely healthy with no associated

risk factor. This is called " idiopathic, " a medical term meaning " of

unknown cause. "

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. Children, as young as 4 and extending

to the teens, get a form of ON which is called Legg-Calve-Perthe's

disease (Perthe's for short) after the doctors who first described

it. Most patients are between 30 and 50 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. Although the specific

cause of the bone death is not precisely known except in the case of

fracture, a number of conditions have been associated with ON. The

most common includes a history of high dose steroid treatment for

some medical condition (including Lupus, Chronic lung disease, an

organ transplant, etc). Low dose steroids (cortisone, prednisone,

etc) commonly used for bee stings, poison ivy and acute allergies are

not thought to cause ON. The next most common associated condition

is a history of alcohol intake. The higher the intake the higher the

risk.

The mechanisms by which these two risk factors (alcohol and steroids)

cause ON are not well understood. The third most common group, are

those patients who have no risk factors at all, and these patients

are a true medical mystery. No matter what the cause, the symptoms

and course of the disorder are remarkably similar.

FIRST SYMPTOMS

Unfortunately many patients with ON have had the disease for quite

some time before symptoms are present. The initial symptoms are

usually pain or aching in the affected joint with activity, which

subsides after the activity has stopped. Symptoms usually begin

slowly and may initially be intermittent. As the disease progresses,

the pain increases and is associated with stiffness. Limping becomes

common. In the hip, the most common joint affected, the pain is

usually felt in the groin.

DIAGNOSIS

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

the ON cannot be seen on a regular x-ray. A widely used and

relatively new tool is called an MRI which stands for Magnetic

Resonance Imaging. These special images are able to detect tissue

changes that are seen on a plain x-ray. Occasionally, your doctor may

order a CAT 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.

PREVENTION

There are no known effective prevention measures. However 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.

TREATMENT

The concept of Risk/Benefit Ratio Before entering into a description

of some of the treatments available for ON, it is important that this

concept be understood. 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 by have very little

downside 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.

Extent of disease The femoral head 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.

Progression of the disease In the earliest stage of the disease. It

cannot be seen by a normal x-ray. Diagnosis is by MRI. Once it can be

seen on x-ray, it is not actually the dead bone that can be seen but

the response of the living bone to the area of necrosis. The advanced

stages 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, and need for a total joint

replacement.

The greater the extent of the disease and the more advanced the

progression, the less likely that the joint can be saved.

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 present with advanced,

extensive disease.

Non-Surgical Treatment

Protected weight bearing Crutches or a walker are very 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. They may also play a role in limiting progression

while associated medical conditions aare managed. However, protected

weight bearing alone is never adequate treatment for ON and will not

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 an effective long-term solution for pain control.

Surgical Treatment

Core Decompression This is a simple surgical procedure, which

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, one of the complications of the procedure.

There is some controversy about this procedure with a few series that

have been reported showing generally poor results. However, in

centers that do this procedure frequently, most series have reported

good results in the appropriate cases.

Bone Grafting When a section of the bone has died, as is the case in

ON, for some reason it doesn't seem to heal. One of the ways that can

cause the bone to heal 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. Another problem is that during the

healing process, which can be very long (6-12 months) the patient

must be on weight-bearing restriction.

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 retains its physical and

mechanical properties.

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 also 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 will develop symptoms in the area from

which the bone graft is taken. The operation also takes several hours

and requires a team experienced in these techniques.

Osteotomy Usually it is the main weight-bearing area of the bone that

is involved with ON. In some cases the bone can be cut below the area

of involvement and rotated or turned so that another portion tion of

the bone that is not involved in the ON can become the new weight-

bearing area (fig. ). These operations are not very common anymore,

but may apply to special cases.

Femoral Head Resurfacing 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 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 today will not

last the 30+ most of these patients will require. Therefore, if 2

procedures are likely to be necessary, it is important that the first

procedure does not make the second procedure more difficult or less

likely to succeed. A THR following a failed femoral head resurfacing

is more likely to be successful than revision THR that follows a

failed primary THR.

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.

Total Hip Replacement 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. Total hip replacement 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 at total hip

replacement will last that long. For this reason, many physicians

will want to try some procedure to put off total hip replacement for

a few years even when it is known that that proceudre 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.

Future Directions

Although there are several hundred thousand patients alive in the US

with ON, this is largely due to the fact that the average patient

will live 30-40 years. With only 15-20,000 new cases each year (this

is about the same as the number of practicing orthopedic surgeons in

the US).