Hereditary Multiple Exostoses (HME) is a rare skeletal disorder
that is inherited in an autosomal dominant fashion. As the name
suggests, this disorder is characterized by multiple bony growths or
tumors (exostoses), often on the growing end (epiphysis) of the long
bones of the legs, arms, and digits. These bony growths are covered
by cartilage and usually continue to grow until shortly after
puberty. They may cause deformities, especially of the ankle, knee,
Although any bone can be affected, the long bones (legs,
arms, fingers, toes), pelvis and shoulder blades are the most
common, while the face and skull are generally unaffected. Boys and
girls can both be affected. Older literature claimed that boys were
more severely troubled by MHE, but bigger series of patients studied
recently do not support this theory
MHE can be troublesome. Because the exostoses grow near the
growth centers of the bone, they can make the growth center grow
poorly, or only part of it grow poorly. This makes a lot of people
with MHE somewhat shorter than average or have bowed arms or legs.
Often, the forearm will bow out toward the lime finger, or the legs
can become knock kneed. This is frequently concerning, but function
is often normal though cosmetically, the bowing can be very
troubling. Sometimes folks with MHE get stiff, especially in the
elbows and hips, usually because their exostoses block some of their
motion. While children are growing, exostoses can be painful. They
seem to be very sensitive to getting bumped. Kids often develop
exostoses on the inside of their knees and these can hit together
when they run, which hurts!
Sometimes exostoses grow near nerves or tendons and press on
them. In these cases, they often need to be removed so they won't
damage the structure laying over them.
The most frightening complication of MHE is also one of the most
uncommon. Rarely (less than 1% of the time), the benign exostoses of
MHE can become a malignant tumor called chondrosarcoma. This happens
almost always after adulthood when skeletal growth has ceased.
Usually, patients who develop chondrosarcoma are in their 20's to
50's. If a person with MHE notices that an exostoses is getting
bigger or painful after they have stopped growing they should get to
their doctor! Growth and pain are two important warning signs that a
benign tumor has become malignant. Chondrosarcoma is very rare, but
it is something MHE families must know about
Some people with MHE never require any treatment. They learn to
compensate for deformity or decreased range of motion so they
function normally. When deformity does occur, it often happens so
slowly that the patient can compensate for it well, while others may
require surgery to help them.
If an exostoses is painful, pressing on an important structure,
cosmetically unattractive or if easily bumped, it can be surgically
removed. Once removed, exostoses can reoccur (about 20 - 50% of the
time), but may not regrow to a size large enough to be symptomatic.
Removal itself is usually a fairly small procedure; some are removed
without ever staying overnight in the hospital.
If an exostoses causes a growth abnormality, like bowing, sometimes
just removing the exostoses early enough will allow the bone to
straighten itself out and remodel as the child grows. Some bowing is
so severe that not only must the exostoses be removed, but also the
bone must be straightened. This can be done by either cutting the
bone, straightening it and then holding it in place while it heals
or if the child is still growing by changing the rate of growth on
one side of the growth plate. Currently there are several options
and your doctor should be able to explain them to you.
If an exostoses does become malignant and turn into a chondrosarcoma
then it must be removed. A specialist in orthopedics and bone tumors
would be required to help with this.