Definition of Osteoporosis
Osteoporosis is a condition of decreased bone mass. This leads to
fragile bones which are at an increased risk for fractures. In fact, it will take much
less stress to an osteoporotic bone to cause it to fracture. The term "porosis"
means spongy, which describes the appearance of osteoporosis bones when they are broken in
half and the inside is examined. Normal bone marrow has small holes within it, but a bone
with osteoporosis will have much larger holes. This picture shows a bone with osteoporosis
on the top with large spongy holes, and a normal bone on the top with normal small
passageways. In severe osteoporosis, this can be exaggerated much more than shown here!
Diagnosing Osteoporosis
There is no method of determining the actual structure of bones
without actually removing a piece during a biopsy (which is not practical or necessary).
Instead, the diagnosis of osteoporosis is based on special x-ray methods called densitometry.
Densitometry will give accurate and precise measurements of the amount of bone (not their
actual quality). This measurement is termed "bone mineral density" or BMD.
The World Health Organization "WHO"
has established criteria for making the diagnosis of osteoporosis, as well as determining
levels which predict higher chances of fractures. These criteria are based on comparing
bone mineral density (BMD) in a particular patient with those of a 25 year old female. BMD
values which fall well below the average for the 25 year old female (stated statistically
as 2.5 standard deviations below the average) are diagnosed as "osteoporotic".
If a patient has a BMD value less than the normal 25 year old female, but not 2.5 standard
deviations below the average, the bone is said to be "osteopenic" (osteopenic
means decreased bone mineral density, but not as sever as osteoporosis).
Interestingly, although these criteria are widely used, they were devised in a Caucasian
female so there will be some differences when these levels are applied to non Caucasian
females or to males in general. Despite this flaw, measurement of BMD is used daily and
has proven to be very helpful in all groups. Some men will be subject to increased
fracture rates when they have significantly less BMD than the predicted fracture level for
women. In other words, some men will be at increased risk for fracture even when
they have osteopenia.
Osteoporosis is different from most other
diseases or common illnesses in that there is no one single cause. The overall health of a
person's bones is a function of many things ranging from how well the bones were formed as
a youth, to the level of exercise the bones have seen over the years. During the first 20
years of life, the formation of bone is the most important factor, but after that point it
is the prevention of bone loss which becomes most important. Anything which leads to
decreased formation of bone early in life, or loss of bone structure later in life will
lead to osteoporosis and fragile bones which are subject to fracture. Several more
pages go into these topics in more detail.
