Fracture of cuboidal bones in the foot is common in human and other mammalian athletes. Fatigue fracture of these bones, particularly of the central (navicular) tarsal bone, is believed to be caused by repetitive loading, site-specific bone modeling and remodeling, and subsequent fatigue failure.1–3 Racing Greyhounds are excellent subjects by which to study adaptive modeling and fatigue because their right and left limbs are asymmetrically loaded during training and racing counterclockwise on oval tracks. Located on the medial aspect of the outside limb, right CTBs are subjected to substantially greater compressive loads than are left CTBs and consequently sustain as much as 96% of fractures.4 An increase in load on the right CTB causes that bone to increase in size and sustain a greater amount of matrix microdamage than the contralateral bone.1,2
Catastrophic failure of the CTB has been proposed to be due to coalescence of the microcracks, inadequate reparative response, or weakness during bone resorption amid an extensive remodeling process within the bone.1,5–7 However, fractured CTBs from racing Greyhounds have not been rigorously evaluated and the nature of any important differences between fractured and nonfractured right CTBs remains unclear.
The purpose of the study reported here was to evaluate CTBs from skeletally mature racing Greyhounds and determine whether there were site-specific modeling and remodeling responses in naturally occurring fractures in right CTBs, with use of standard and contact radiography, CT, and histologic evaluation. We hypothesized that unique site-specific modeling and remodeling patterns would be detected in fractured bones. Specifically, we hypothesized that the BMD of fractured right CTBs would be greater than that of intact right and left CTBs and that dorsal slab fractures would occur through a transition zone between bone tissues of differing densities.
Bone mineral density
Central tarsal bone
Dipotassium phosphate equivalent density
Region of interest
Picker PQS, Philips Medical Systems NA, Bothell, Wash.
Dipotassium phosphate phantom, model 3T, Mindways Software Inc, San Francisco, Calif.
The Original Super Glue, Super Glue Corp, Rancho Cucamonga, Calif.
Model 340CP, Exakt Technologies Inc, Oklahoma City, Okla.
EXAKT Technologies, Exakt Technologies Inc, Oklahoma City, Okla.
Faxitron, model 43855A, Faxitron X-ray LLC, Lincolnshire, Ill.
SAS, version 9.1.3, SAS Institute Inc, Cary, NC.
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