Introduction

Greyhounds race anti-clockwise around an ovoid track with relatively tight bends. This is believed to inflict asymmetric limb stresses leading to asymmetric adaptive remodelling. This involves bone resorption followed by new bone formation; indicated by increases in bone mineral density (BMD). During remodelling, bone is mechanically weaker and more susceptible to damage if subjected to further loading. Further understanding of this process is required if injury prevention strategies are to be developed.

Aim

To determine the extent of left-to-right differences in BMD in the distal thoracic limb bones of racing Greyhounds.

Materials and Methods

Thoracic limbs were collected from 15 racing Greyhounds, euthanatized due to injury or when behavioural problems prevented re-homing. All limb specimens were disarticulated at the elbow and stored at -20°C prior to further processing.

Computed tomography (Siemens Somatom Helical Scanner) was used to generate detailed, cross-sectional images of the limbs allowing injury status to be determined.

Dual-energy x-ray absorptiometry (DXA) (Lunar Prodigy Bone Densitometer) of the distal aspect of each limb was used to determine the bone mineral density (BMD) of the entire carpal and metacarpal areas. The carpal and metacarpal bones were then excised, DXA scanned and total BMD determined. Mean and standard deviation BMD were calculated for each region of interest (ROI). The effect of side (left versus right) on BMD was examined using a paired t-test (significance set at P<0.05).

Results

The BMD for measured ROI were determined for entire limbs and isolated bones. No significant left-to-right differences were seen in the total BMD of the entire carpal and metacarpal regions. However, the BMD of the third carpal bone was significantly higher in the right limb and the BMD of the fourth carpal bone was significantly higher in the left. Significant differences were also seen in the second, third, fourth and fifth metacarpal bones, with BMD being higher in the right limb for the second and third, and higher in the left limb for the fourth and fifth metacarpal bones.

Discussion

Significant left-to-right differences in BMD were seen in carpal bones III to IV and metacarpal bones II to V. Further work will evaluate whether these differences are within normal limits for racing Greyhounds or if they are due to the cyclic stresses of training and racing leading to adaptive remodelling of the distal limb bones.