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Avascular
Necrosis (AVN)--Causes,
symptoms, treatment options
AVN--also
called osteonecrosis--is a progressive bone disorder
that can require potentially significant surgical treatment.
For anyone at risk of developing AVN, awareness is the best
defense.
AVN
is a well-named condition. "Avascular necrosis" literally
means cell death resulting from the loss of blood supply.
The disease is also referred to as "osteonecrosis", which
literally means that bone tissue cells are dying ("osteo-"
means bone).
As
these names imply, AVN can develop following a reduction in
blood supply to an area of bone. Bone is living tissue, and
requires good blood circulation just like any other tissue.
As the affected region of bone dies, it becomes brittle, and
susceptible to breakage. Usually long bones (such as the thighbone)
are affected, and the dying area is typically at the end of
the bone, near the joint.
In
its early stages, AVN sufferers may or may not experience
joint pain. Joint pain can certainly have many causes, many
of which are not serious. To diagnose AVN, an MRI (magnetic
resonance imaging) scan is usually performed, because X-rays
will only detect the late stages of AVN.
The
time from the onset of symptoms until the function of the
joint is irrevocably lost can be as short as several months,
or well over a year, in the absence of interventions to slow
the progression of AVN (see below). This time course is probably
as short as it is in part because symptoms may not be present
during the very early stages of AVN; in these cases, symptoms
(i.e., joint pain) fails to appear until the bone loss has
already progressed somewhat.
Late
stage AVN can only be described as debilitating. In most cases,
late stage AVN also involves arthritis in the affected areas.
Causes
and risk factors
In
the U.S., approximately 10,000 to 20,000 new cases of AVN
are diagnosed each year, commonly in people between 30 and
50 years of age (more frequently in men than women). Given
that approximately 84 million people in that age range live
in the U.S., the overall prevalence in the general population
can be estimated at no more than 0.02%.
Known
risk factors for AVN
The
following have been associated with an increased risk of developing
AVN in the general population:
- Bone fractures
- Corticosteroid
use
- Alcohol use
- Elevated cholesterol/triglycerides
- Sickle cell
anemia
- Dysbaric conditions
(the "bends", decompression disease)
- Gaucher's disease
- Pancreatitis
- Lupus
Because
AVN develops following the reduction of the blood supply to
the bone, risk factors for AVN generally include conditions
that reduce the blood supply. Alcohol dependency and the use
of corticosteroids are thought to cause this by leading to
the formation of fat deposits in the end region of arteries
in the bone. Elevated cholesterol and triglycerides, as well
as Gaucher's disease (a chemical defect that leads to the
abnormal accumulation of fatty substances) probably also increase
the risk of AVN in a similar fashion. AVN is actually the
third most common complication of long bone fractures, because
the fracture itself can lead to mechanical disruptions of
the blood flow to bone. Sickle cell anemia is thought to predispose
people to AVN because the blood becomes more viscous.
The "bends"
have been implicated in the development of AVN in scuba divers,
but the mechanism remains unclear.
Managing
AVN
The best
way of approaching AVN clinically is to prevent its occurrence
in the first place--anyone with the above-mentioned risk factors
should take measures to reduce them. AVN is a progressive
disorder, and once it has developed to the latter stages,
joint replacement surgery becomes necessary. This is a fairly
significant procedure, so managing AVN before reaching late
stages is best.
For patients
with early stage AVN, several options are available. Mechanical
approaches to reducing the stress on the affected bone can
sometimes both provide pain relief and slow the progression
of AVN.
Surgery
(less radical than joint-replacement) during early-stage AVN
can also stave off the progression of the disorder. Specifically,
three types of procedures may be performed:
- Core
Decompression: As the name implies, this procedure aims
to relieve pressure on the interior of the bone, which in
turn encourages improved blood flow to affected areas. This
is accomplished by drilling into the bone and removing the
dead and dying bone.
- Osteotomy:
The affected bone is cut and realigned in such a way as
to relieve stress to the bone.
- Bone
graft: Healthy bone is grafted onto a joint following
core decompression surgery.
These
procedures unfortunately do not cure AVN.
AVN
risk factors and HIV
Before
1996, there were only 38 case reports of AVN in HIV+ people
that were published in the medical literature. This does not
mean that there were only 38 diagnosed cases, only that these
were all the cases that were described in the literature.
However, the fact that AVN had not received much attention
from HIV clinicians is indicative of its rarity in this population.
A group
at Georgetown University Medical Center reported at the 6th
Conference on Retroviruses and Opportunistic Infections (Feb.
1999, Chicago, IL) that 8 of their HIV+ patients had AVN--since
they had only about 600 patients, this represented a prevalence
rate of over 1%! Of course, there is no way to know how representative
this patient group is of the HIV-infected population at large.
However, this rate is over 50-fold higher than that for the
general population.
If the
incidence of AVN is truly increasing among the HIV infected,
what could be the culprit? Given the small population of HIV+
AVN sufferers discussed in published reports, it is very difficult
to discern clearly what had predisposed these patients to
AVN. One possibility is that AVN could be a direct or indirect
consequence of recently-developed treatment options that are
now routinely prescribed for HIV+ individuals. Alternatively,
the reduction in HIV mortality that has resulted from the
widespread use of cocktail therapies in this country could
be unmasking AVN as a complication of long-term HIV infection.
Furthermore,
some conventionally-accepted risk factors probably apply to
a fair number of HIV-infected people, particularly those on
treatment for HIV infection. In recent years, it has become
clear that antiretroviral therapy can cause elevated triglycerides
and cholesterol, and some specific medications (e.g., ddI)
are associated with pancreatitis. Additionally, many HIV+
individuals receive steroid treatments in addition to their
antiretroviral drugs. It remains to be determined whether
the side effects of HIV therapies predispose patients to AVN.
A final
word of caution
No one
should consider stopping any of their medications on their
own; anyone with concerns about the treatments they are receiving
should discuss these concerns with their physician. Anyone
who stops or reduces his/her medication on his/her own runs
the serious risk of developing viral drug resistance and other
health problems.
For more
information on AVN, you may call the Arthritis Foundation
at 800/283.7800. The National Institute of Arthritis and
Musculoskeletal and Skin Diseases has an informative article
on their website at www.nih.gov/niams/healthinfo/avnecqa.htm.
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