A Boon for Bone Research
Astronauts operating in a weightless environment for long
periods are subject to a form of bone deterioration known as
disuse osteoporosis, which can pose a serious hazard for crews
on future space missions that might run two years or more. After
long exposure to microgravity, weight bearing bones lose calcium
and density, become very brittle and are easily fractured.
For two decades, NASA has been engaged in study and experimentation
toward developing countermeasures-special nutritional/exercise
programs, for example-to microgravity-induced bone deterioration.
A particular need of this research was a way of making direct
measurements of bone stiffness and mass; while there were available
instruments for determining the mineral density of bone, an indirect
indicator of bone strength, researchers became increasingly aware
of the limitations of such systems in predicting fracture risk.
At Louisiana's Ochsner Bone Clinic, a technician is measuring
the stiffness of a young patient's ulna in a research project
aimed at developing advanced methods of treating bone disorders.
They turned their attention toward developing a practical,
inexpensive, non-invasive way of making strength measurements,
a system sensitive enough to monitor and evaluate small changes.
The need for such an instrument went way beyond space flight.
Since bone deterioration affects a substantial portion of the
U.S. population, such an instrument offered broad utility as
a research tool for studying bone abnormalities caused by disease,
aging and disuse, and as a means of evaluating fracture healing.
Now, for the first time, there exists a commercially available
instrument to serve those needs. Called the Mechanical Response
Tissue Analyzer (MRTA), it is the result of a three-way collaboration
among Ames Research Center; Stanford University, Palo Alto, California;
and Gait Scan, Inc., Ridgewood, New Jersey, a small business.
Beginning in 1977, NASA Ames and Stanford University teamed on
a research program aimed at developing impedance devices capable
of measuring the mechanical stiffness of human bones. Bending
stiffness is a property of the bone that reflects the materials
in the bone and its shape; stiffness can be correlated to bone
density and calcium content, thereby providing useful information
for research on astronaut disuse osteoporosis and related bone
disorders among the general population.
After more than a decade of effort, the team came up with
a workable device and conducted clinical testing at Stanford
University Orthopedic Hospital. In 1989, Ames and Stanford were
joined by Gait Scan, which invested its own funds in refining
the technology, developing a practical and affordable instrument,
and bringing it to the commercial market.
Shown here is the spinoff Mechanical Response Tissue Analyzer
that makes possible, for the first time, direct measurements
of bone flexibility.
The resulting MRTA is a portable device that detects the bone's
response to a brief vibratory stimulus and produces a measurement
of the bending stiffness of the ulna (arm) and the tibia (lower
leg), the parts of the human body directly involved in weight
lifting and weight bearing activities. A technician places a
small probe on the skin surface of the limb to be tested and
a five-second electrically-induced vibration is applied. The
frequencies from the resonating bone are detected at the same
site as the stimulator and analyzed by the system's computer,
which produces an accurate reading of the bone's bending stiffness.
"The major attraction of the technology," says Dr.
Sara Arnaud of Ames Research Center's Life Sciences Division,
"is the speed and simplicity with which the measurement
gives a complete picture of bone strength." Among other
advantages are its safety-MRTA uses no radiation as do some other
methods of examining bone-and its cost, about $20,000, which
makes it relatively inexpensive as medical systems go.
The MRTA has a wide range of potential applications. It will
be used for the original purpose: astronaut postflight monitoring.
Dr. Arnaud is using the device to measure tibia strength among
working women at Ames. Gait Scan is pursuing applications in
monitoring the effects of exercise and rehabilitation on bone
stiffness and in osteoporosis, the underlying cause of some 1,300,000
bone fractures each year that involve treatment costs estimated
at close to $4 billion.
An application of particular interest is MRTA's use by the
Ochsner Bone Clinic, New Orleans, Louisiana, a facility dedicated
to research and treatment of patients with osteoporosis and metabolic
bone disorders. In a project headed by clinic co-director Dr.
Alan Burshell and Dr. Steven Smith, the MRTA is being used in
a study of osteogenesis imperfecta, or O.I., a disease
characterized by brittle bones and increased risk of fracture.
The project involves the cooperation of six generations of
a large Louisiana family, the Heberts, who have a history of
hereditary O.I. More than 50 members of the family have O.I.,
although others are not afflicted. One single household has sustained
more than 80 fractures; an individual in another family has broken
more than 50 bones.
The Ochsner team uses the MRTA to measure bone flexibility,
then it compares results among family members with O.I. and those
without it. MRTA measurements are further compared with data
from CT scans, bone density readings by other instruments, and
biochemical/genetic information from blood, urine and skin analysis.
Dr. Burshell hopes that this mass of information will lead to
advanced treatments for O.I., osteoporosis and other bone disorders.
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