though may occur in conditions such as OSTEOPET-
ROSIS.
Bone Density TestingA number of tests can measure bone density.
Among them are
- dual energy X-RAYabsorptiometry (DEXA or
DXA), which uses low-DOSEX-ray to measure
the bone mass in the spine and hip - peripheral dual energy X-ray absorptiometry
(pDEXA or pDXA), which uses low-dose X-ray
to measure the bone mass in the wrist or heel - single-energy X-ray absorptiometry (SXA),
which uses low-dose X-ray to measure the
bone mass in the wrist or heel - quantitative ULTRASOUND, which uses sound
waves to measure the bone mass in the heel,
patella (kneecap), and tibia (long bone in the
lower leg) - quantitative computed tomography (QCT),
which uses X-ray to measure the bone mass in
the spine - peripheral quantitative computed tomography
(pQCT), which uses X-ray to measure the bone
mass in the wrist
DEXA provides the most detailed information
and is simple to perform. QCT and pQCT are varia-
tions of COMPUTED TOMOGRAPHY(CT) SCANthat use
somewhat higher doses of X-ray and are more com-
plex to perform but can be more reliable in people
who have already had fractures of the spine or hip.
Mobile clinics and even some pharmacies use
peripheral methods for screening. All testing meth-
ods to measure bone density are painless, noninva-
sive, and take 20 minutes or less to complete.
Bone density tests report two scores:
- The T-score compares an individual’s bone den-
sity to a figure that represents the bone density
of a healthy adult in his or her mid-20s, the
period when bone density is at its highest. The
comparison is gender specific. - The Z-score compares an individual’s bone den-
sity to a figure that represents other adults of
the same age. The Z-score comparison is also
gender specific.
Because older adults have lower bone mass, the
Z-score is less significant than the T-score for
assessing the presence of osteopenia and osteo-
porosis. Generally the T-score and the Z-score cor-
relate; a person who has a low T-score also has a
low Z-score.
The difference between an individual’s bone
density score and the representative standard
score is the standard deviation (SD), reported as a
positive (+) or negative (–) figure. Each full SD
represents about 10 percent of normal bone mass.
The lower the T-score, the greater the percentage
of bone loss. A T-score that is 2.5 SDs or more
below the norm (–2.5) is the diagnostic marker for
osteoporosis.BONE DENSITY SCORES
Diagnostic Category T-Score Z-Score
healthy –1 or higher –1 or higher
OSTEOPENIA(increased –1 to –2.5 –1 to –2.5
risk for fracture)
OSTEOPOROSIS(significant below –2.5 below –2.5
risk for fracture)See also ESTROGENS; HORMONE; OSTEOMALACIA.bone spur An extension of BONE tissue, also
called an osteophyte, that commonly develops
near a JOINT. A bone spur has a jagged, pointed
appearance. Doctors believe bone spurs develop as
a means of protecting a joint exposed to excessive
stress or disease process. Most bone spurs do not
cause symptoms, though may be apparent as
bumps in the MUSCLEor other soft tissue. Bone
spurs cause PAINwhen they irritate surrounding
tissues such as MUSCLEand CARTILAGE. Bone spurs
are especially common in the heels, hands, shoul-
ders, and spine.
NONSTEROIDAL ANTI-INFLAMMATORY DRUGS(NSAIDS)
often succeed in relieving the INFLAMMATIONand
pain. For bone spurs that cause substantial pain,
the doctor may inject the site with cortisone and a
topical anesthetic agent to reduce inflammation
and relieve pain.
See also ACHILLES TENDON INJURY; REPETITIVE
MOTION INJURIES.bursa A fluid-filled sac between layers of MUSCLE
that buffers the movement of muscles against eachbursa 311