Definition of Osteoporosis
“Osteoporosis is a systemic skeletal
disease, characterized by low bone
and micro architectural
deterioration of bone tissue with a
increase in bone fragility
and susceptibility to fracture.”
Decreased bone mineral density is a result of a
combination of genetic and environmental factors that
affect both peak bone mass and the rate of bone loss
These factors include medications, diet, race, sex,
lifestyle, and physical activity
HOW IS BONE DENSITY USEFUL?
Bone Density Is Essential for Diagnosis of
Low bone mass defines osteoporosis
We have to measure it for a direct diagnosis of osteoporosis
Poor architecture would also suffice for diagnosis but we
have no diagnostic tool available to accurately assess it in
It is important to look for the etiology of the disease
Approximately 10 million people have osteoporosis.
Another 14-18 million have osteopenia (low bone
Approximately 1.5 million fractures per year attributed
to osteoporosis, and more than 37,000 deaths from
subsequent fracture-related complications
women older than 65
women younger than 65
years who have 1 or more
women who present
with fragility fractures
•Women who are
considering therapy in
which BMD will affect
Women who have
been on hormone
(HRT) for prolonged
Men who experience fractures after minimal
People with evidence of osteopenia on radiographs
or a disease known to place them at risk for
Levels of serum calcium, phosphate, and alkaline
phosphatase are usually normal in persons with
primary osteoporosis, although alkaline phosphatase
levels may be elevated for several months after a
It is important to also check thyroid function, and
testosterone levels in men
First, obtain plain radiographs if a decrease in bone
mineral density is suspected
Osteopenia may be apparent as radiographic lucency
but is not always noticeable until 30% of bone mineral
Plain radiography is not as accurate as BMD testing
BMD tests are usually done on bones that are likely to
break as a result of osteoporosis like the lower spine
Can also be done on the wrist or heel
Devices that measure BMD include:
Quantitative computed tomography
Dual-energy x-ray absorptiometry (DEXA)
tomography measures BMD as a
true volume density in g/cm3,
which is not influenced by bone
This technique can be used for
both adults and children.
Disadvantages in that (1) it only
determines bone density at the
spine, (2) osteophytes can
interfere with measurement,
and (3) it is associated with
significant radiation exposure
and high cost
Quantitative ultrasonography of the calcaneus can be
used for general screening
However, this is not as accurate as other methods and
thus is less useful in following response to treatment
Its advantages include low cost, portability, and lack of
Radiogrammetry, used to
measure cortical dimensions, is
usually performed on the hand,
specifically the second
It is useful in assessing BMD in
children and is the simplest and
least expensive method
Disadvantages are that it is not
as precise as DEXA and,
therefore, is less sensitive for
detecting changes over time
Dual-energy x-ray absorptiometry requires less radiation, is
less expensive, and has better reproducibility than
quantitative computed tomography
Can also measure bone density at the spine and the hip. It
has become the standard method for determining bone
This method can be used in both adults and children
Confounding factors in DEXA results interpretation
(falsely high bone density) include spinal fractures,
osteophytosis, and extraspinal (eg, vascular) calcification
Peripheral DEXA can be used to measure BMD in the wrist
How DXA Works
DXA uses 2 levels of x-ray photon energy to measure
the amount of minerals in bone. The difference in
attenuation of the x-rays by bone generates 2-D
measurements of bone mineral content in grams and
areal BMD. DXA x-rays are produced with a fan beam
or a pencil beam. Pencil-beam equipment uses small,
angled x-ray beams that move across the patient in a
linear direction. The fan-beam generators use a wider
beam that reduces scan times but increases radiation
dose to patients.
On the day of the exam eat normally. Should not take calcium supplements for
at least 24 hours before your exam.
Should wear loose, comfortable clothing, avoiding garments that have zippers,
belts or buttons made of metal. Objects such as keys or wallets that would be in
the area being scanned should be removed.
Should remove some or all of your clothes and to wear a gown during the exam.
Remove jewelry, removable dental appliances, eye glasses and any metal objects
or clothing that might interfere with the x-ray images.
Inform physician if recently had a barium examination or have been injected
with a contrast material for a computed tomography (CT) scan or radioisotope
scan. If so, may have to wait 10 to 14 days before undergoing a DXA test.
Women should always inform their physician and x-ray technologist if there is
any possibility that they are pregnant. Many imaging tests are not performed
during pregnancy so as not to expose the fetus to radiation. If an x-ray is
necessary, precautions will be taken to minimize radiation exposure to the
How does the procedure work?
The DXA machine sends a thin, invisible beam of low-
dose x-rays with two distinct energy peaks through the
bones being examined. One peak is absorbed mainly
by soft tissue and the other by bone. The soft tissue
amount can be subtracted from the total and what
remains is a patient's bone mineral density.
DXA machines feature special software that compute
and display the bone density measurements on a
How is the procedure performed?
This examination is usually done on an outpatient basis.
In the Central DXA examination, which measures bone density in the hip and
spine, the patient lies on a padded table. An x-ray generator is located below
the patient and an imaging device, or detector, is positioned above.
To assess the spine, the patient's legs are supported on a padded box to flatten
the pelvis and lower (lumbar) spine. To assess the hip, the patient's foot is
placed in a brace that rotates the hip inward. In both cases, the detector is
slowly passed over the area, generating images on a computer monitor.
You must hold very still and may be asked to keep from breathing for a few
seconds while the x-ray picture is taken to reduce the possibility of a blurred
image. The technologist will walk behind a wall or into the next room to
activate the x-ray machine.
The peripheral tests are simpler. The finger, hand, forearm or foot is placed in a
small device that obtains a bone density reading within a few minutes.
An additional procedure called Lateral Vertebral Assessment (LVA) is now
being done at many centers. LVA is a low-dose x-ray examination of the spine
to screen for vertebral fractures that is performed on the DXA machine.
•Clinically most valuable sampling
–PA Lumbar spine (compression
–Proximal femur (hip fracture)
•Use total regions of spine and hip
•Use lowest T-score of these two
•In elderly patient, due to
deformity and degenerative
changes, difficult to interpret
spine scan; then consider hip or
What Are The Results?
Results are reported as two values, T and Z scores
T scores are the number of standard deviations
above or below what is normally expected in a
healthy young adult of the same sex
Z score is the number of standard deviations above
or below what is normally expected for someone of
the same age, sex, weight, and ethinic origin
The Z score is helpful because it may suggest that the
patient may have a secondary form of osteoporosis
unrelated to normal aging which is causing decreased
A score less than -1.5 should make you investigate the
cause of decreased BMD
Another Report Card
For example, if the T-score is -2.0, the BMD is lower than
average by two standard deviations. If the Z-score is -0.5,
your bone density is less than the norm for people your age
by one-half of a standard deviation
Relation of BMD to Fracture Risk
How important is change in BMD
•In untreated patients, Low BMD=high
•Treatments for osteoporosis increase
BMD & reduce risk
•Is the reduction in fracture risk with
treatment due to the increase in BMD?
DXA bone densitometry is a simple, quick and noninvasive procedure.
No anesthesia is required.
The amount of radiation used is extremely small—less than one-tenth
the dose of a standard chest x-ray, and less than a day's exposure to
natural radiation. (0.3micro sv)
DXA bone density testing is the most accurate method available for the
diagnosis of osteoporosis and is also considered an accurate estimator
of fracture risk.
DXA equipment is widely available making DXA bone densitometry
testing convenient for patients and physicians alike.
No radiation remains in a patient's body after an x-ray examination.
X-rays usually have no side effects in the typical diagnostic range for
There is always a slight chance of cancer from excessive
exposure to radiation. However, the benefit of an
accurate diagnosis far outweighs the risk.
Women should always inform their physician or x-ray
technologist if there is any possibility that they are
The effective radiation dose for this procedure varies.
No complications are expected with the DXA
Bone Scans for Osteoporosis: How
Bone scan every two years in women with
osteoporosis or who are at high risk.
Because the response to treatment occurs
slowly, this is usually an acceptable time
In cases with high bone turnover rates, like
women taking high-dose steroids," checking
bone density as often as every six months
may be necessary,
OTHER USES OF DEXA SCAN
A. Total Body BMC versus Age and Total Body BMD
versus Age reference databases.
Metabolic bone diseases and conditions.
Glucocorticoid-treated patients with congenital
adrenal hyperplasia ,total Body BMD Is significantly
Postmenopausal women with type 1 diabetes.
Total Body BMC and Total Body BMD measurements
and z-scores are useful in the management of OI in
Total Body %Fat vs. Age reference
Traditional anthropomorphic measures of obesity like BMI
and waist circumference quantify excess weight or size, not
excess fat, and misclassify patients by failing to assess
pathogenic visceral fat depots.
DXA visceral fat measurements may be superior to
traditional measures for evaluating obesity-related disease
The available literature supports visceral fat thresholds of
100 cm2 for increased risk and 160cm2 for high risk and
suggests this classification scheme may identify patients
most likely to benefit from preventive interventions.
What is visceral fat?
Visceral fat occurs within the envelope formed by the
abdominal muscles, principally within the greater and
lesser omentum that connects the abdominal organs, and
in mesenteric fat. A small amount is also found
Visceral fat is more dangerous than subcutaneous fat
because visceral fat cells release proteins that contribute to
inflammation, atherosclerosis, dyslipidemia, and
Visceral fat is associated with metabolic risk factors and
all-cause mortality in men, and is therefore considered a
pathogenic fat depot
Y is visceral fat estimation
It is important to recognize that even subjects who are
normal weight and have a Body Mass Index (BMI) < 25 can
have a significant accumulation of visceral fat, increasing
their risk for cardiovascular disease, diabetes, and other
obesity-related health risks.
Likewise, some overweight or obese patients may have
relatively low levels of visceral fat, normal metabolic
profiles, and few or no additional risk factors.
A DXA visceral fat measurement may distinguish
apparently normal weight subjects with high visceral fat
levels and high disease risk from metabolically normal
subjects with BMIs in the overweight or obese category.
Computed tomography image of the abdomen at the level of the fourth
lumbar vertebrae with visceral cavity outlined in white (right) and visceral fat filled
In black on left.
Discussions regarding bone density typically focus on
postmenopausal women, osteoporosis, and fracture risk.
Although these are the most common reasons patients
have skeletal strength assessments, the use of bone
densitometry and bone mineral density measurement in
pediatric patients is becoming increasingly valuable to
assess children with diseases that cause inadequate bone
Pediatric patients’ bone density most often is measured
using DXA and expressed by Z-score, which measures
standard deviations from norms for peer based
Abnormal Skeletal Development
Treatmenting adolescents at risk of decreased BMD
presents many difficulties for clinicians. Current
research indicates that many factors eg, chronic
illness, poor diet, illnesses or injuries that cause
immobilization, and certain genetic or hormonal
disorders, place adolescents at risk for skeletal
Interpretation of Pediatric Skeletal Measurement
DXA scans are recommended for
measurement of BMD in pediatric patients
who have a condition that increases risk of
skeletal weakness, along with a secondary
condition such as recurrent fractures,
lowimpact trauma fractures, back pain,
spinal deformity, height loss, change in
ability to ambulate, or diagnosed
When a pediatric patient’s measurements are less than
2 standard deviations from the standard mean, the
report should indicate that the patient’s skeletal
strength is “low for age.” Terminology such as
osteopenia and osteoporosis that is used for adult DXA
interpretation should not be used in pediatric DXA
reports unless certain criteria is met. The ISCD
guidelines state that a diagnosis of osteoporosis be
made when the a pediatric patient has a DXA diagnosis
of “low for age "in addition to a significant fracture
Benefits of Pediatric DXA
If the ordering clinician, technologist, and interpreting
radiologist ensure that the pediatric DXA examination is
performed correctly and provides accurate results, the
examination can provide great benefit to the patient. In
cases of “low for age” BMD and childhood predictors of
adult osteoporosis, there are many interventions available
that can improve the patient’s skeletal health and return
bone mass to normal levels.
Current recommendations for pediatric patients include
appropriate nutrition such as calcium and vitamin D,
encouragement of weight-bearing activity, and physical
Other uses of DEXA!!
%Fat Trunk/%Fat Legs vs. Age and Trunk/Limb Fat
Mass Ratio vs. Age reference databases.
Many antiretroviral agents cause a redistribution of fat
mass termed lipodystrophy. Lipodystrophy
assessment is often made by physical assessment and
is passively reported in trials of antiretroviral agents.
Although DXA has some limitations, it is currently the
recommended method of measurement of BMD and,
in conjunction with a detailed clinical assessment, can
be used for diagnosis of osteoporosis, in adults as well
as in children
It also has a wide avenue to be exploited in other
diseases like obesity, lipodystrophy and others.
ITS TIME TO
RID OF THE