Asymmetric densitometric and mechanical adaptation of the left fifth metacarpal bone in racing greyhounds

The densitometric and mechanical structural properties of the left and right fifth metacarpal bones of 10 racing greyhounds with a fracture of the central tarsal bone and 10 without a fracture were investigated by dual energy x-ray absorptiometry and a servo-hydraulic materials testing machine. In all the greyhounds the bone mineral density of the left fifth metacarpal bone was significantly greater than that of the right (P<0.001), but there was no significant difference between the degree of asymmetry in bone mineral density in the two groups. The ultimate torque and energy-to-failure of the left fifth metacarpal bone of the greyhounds with a fracture of the right central tarsal bone were significantly higher than in the right fifth metacarpal bone and higher than in both the left and right fifth metacarpal bones of the greyhounds with no fracture (P<0.05). The ultimate torque and energy-to-failure were significantly related to bone mineral density (P<0.005), and 22 per cent of the variation in these structural properties could be explained by variations in bone mineral density. Fifth metacarpal remodelling in response to asymmetric cyclic loading is bone-specific, and structural properties are enhanced in the left fifth metacarpal of greyhounds with a fracture of the right central tarsal bone.