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Dec.
2 , 2002 |
Why Some Old Bones Break So Easily
 We
know a fall is far more serious for Grandma than for a 3-year-old.
Scientists have thought the increased risk of fracture in old
age was largely due to loss of bone mass, but Rensselaer researcher
Deepak Vashishth says this can't be the only reason. He is now
examining bone quality and the differing shapes of microscopic
cracks that develop in bones in the course of daily living. His
research may increase a doctor's ability to predict — and
even reduce fracture — risks for older people.
"Because we find significant overlap in
bone density within a group of older individuals who have and
have not sustained hip fractures, there must be something more
than bone mass loss that contributes to fragility," says
Vashishth, assistant professor of biomedical engineering.
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"Because we find significant overlap
in bone density within a group of older individuals who have
and have not sustained hip fractures, there must be something
more than bone mass loss that contributes to fragility."
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That "something more" seems to be a
function of bone quality that varies from individual to individual.
As bone quality deteriorates, day-to-day loading results in an
accumulation of microscopic cracks. Vashishth has found that these
cracks differ, depending on where they are located, and the resulting
damage may change with age.
Tension (on the outside of a bend) produces thousands
of diffused, submicroscopic cracks that don't seriously affect
fragility. Whereas compression (on the inside of a bend) produces
cracks that can be 50 to 80 microns in length (the diameter of
a human hair).
Compression damage is a more serious factor in
fragility, says Vashishth. He has discovered that compression
damage propagates faster and draws osteoclasts (bone-absorbing
cells) up along the cement lines that bond bone together. This
creates a weakening in the bone structure that extends a considerable
distance along the bone interior. That increases fragility and
fracture risk.
Believing that Vashishth and his colleagues are
onto something, the National Institute of Arthritis and Musculoskeletal
Research, a division of NIH, has granted $1.4 million to support
the research for five years. Vashishth is working with Rena Bizios
of Rensselaer, David Fyhrie of Henry Ford Hospital, Jae Rho of
the University of Memphis, and David Burr of Indiana University-Purdue
University Indianapolis.
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