Objective—To quantify geometric, inertial, and histomorphometric
properties at the mid-diaphyseal level
of left and right metacarpal bones (MCB) of racing
Sample Population—MCB from 7 racing Greyhounds
euthanatized for reasons unrelated to MCB
Procedures—Mid-diaphyseal transverse sections of
left and right MCB were stained with H&E or microradiographed.
Images of stained sections were digitized,
and cross-sectional area, cortical area, and maximum
and minimum area moments of inertia of each
bone were determined. Histomorphometric data
(osteonal density, osteonal birefringence, and
endosteal new lamellar bone thickness) were collected
in 4 quadrants (dorsal, palmar, lateral, medial).
Values were compared between limbs and among
bones and quadrants.
Results—Cross-sectional area, cortical area, and
maximum and minimum moments of inertia of left
MCB-IV and -V were significantly greater, compared
with contralateral bones. Overall osteonal densities in
the dorsal quadrants of left MCB were greater, compared
with lateral and medial quadrants. Also, percentage
of birefringent osteons was significantly
greater in the dorsal quadrant of left MCB-III, -IV, and
-V, compared with the palmar quadrant. Thickness of
new endosteal lamellar bone was not significantly
influenced by limb, bone, or quadrant.
Conclusions and Clinical Relevance—Increased
cortical thickness and geometric properties of left
MCB-IV and -V of Greyhounds, together with altered
turnover and orientation of osteons in the dorsal
quadrants of left MCB, are site-specific adaptive
responses associated with asymmetric cyclic loading
as a result of racing on circular tracks. Site-specific
adaptive remodeling may be important in the
etiopathogenesis of fatigue fractures in racing Greyhounds.
(Am J Vet Res 2001;62:787–793)