Densitometric properties of long bones in dogs, as determined by use of dual-energy x-ray absorptiometry.

We performed dual-energy x-ray absorptiometry (craniocaudal and lateromedial views) on 10 pairs of humeruses, radiuses, femurs, and tibias from dogs, using an alignment jig, to determine the homotypic bone mineral density variations of long bones. The bones were divided into 3 regions: proximal, middle, and distal parts of the diaphysis. The bone mineral density of cortical bone, medullary bone, and total bone was determined. Of 160 homotypic comparisons, 21 indicated significant (P < or = 0.05) differences between right and left bones at either a region or location. These differences were observed most frequently in the craniocaudal view and were probably secondary to positioning errors. Evaluation of elliptical bones, such as the radius, also indicated that, when the thicker dimension, such as the lateromedial view of the radius was measured, the bone mineral density of regions-of-interest in that view was greater than that in the opposite view (ie, craniocaudal view of the radius). This study validates the concept of using the contralateral limb as the control condition in orthopedic studies of dogs, particularly when evaluating the densitometric properties of long bones. This study also emphasizes the importance of accurate positioning to prevent inadvertent alteration of bone mineral density results when using dual-energy x-ray absorptiometry. Dual-energy x-ray absorptiometry is particularly susceptible to positioning errors, because it converts a 3-dimensional structure into a 2-dimensional image.