Fractographic examination of racing greyhound central (navicular) tarsal bone failure surfaces using scanning electron microscopy

The greyhound is a fatigue fracture model of a short distance running athle te. Greyhounds have a high incidence of central (navicular) tarsal bone (CT B) fractures, which are not associated with overt trauma. We wished to dete rmine whether these fractures occur because of accumulation of fatigue micr odamage. We hypothesized that bone from racing dogs would show site-specifi c microdamage accumulation, causing predisposition to structural failure. W e performed a fractographic examination of failure surfaces from fractured bones using scanning electron microscopy and assessed microcracking observe d at the failure surface using a visual analog scale. Branching arrays of m icrocracks were seen in failure surfaces of CTB and adjacent tarsal bones, suggestive of compressive fatigue failure. Branching arrays of microcracks were particularly prevalent in remodeled trabecular bone that had become co mpact. CTB fractures showed increased microdamage when compared with other in vivo fractures (adjacent tarsal bone and long bone fractures), and ex. v ivo tarsal fractures induced by monotonic loading (P < 0.02). It was conclu ded that greyhound racing and training often results in CTB structural fail ure, because of accumulation and coalescence of branching arrays of fatigue microcracks, the formation of which appears to be predisposed to adapted b one.