Radiographic study of homotypic variation of long bones in dogs

Dogs have been used extensively as an experimental model for studying musculoskeletal disorders. Many of these studies incorporated sequential radiography to quantitate a particular treatment's effect, using the contralateral bone as the control condition. The contralateral bone can be used as a control only if there is bilateral symmetry between right and left limbs. We performed radiography (craniocaudal and lateromedial views) on 10 pairs of humeri, radii, femora, and tibiae from dogs, using an alignment jig, to radiographically determine homotypic geometric variations of long bones. The bones were divided into 5 regions: proximal epiphysis, proximal metaphysis, diaphysis, distal metaphysis, and distal epiphysis. The total bone diameter, medullary diameter, and cortical width (total of medial + lateral cortex or total of cranial + caudal cortex) were measured at specified slices throughout each of these regions. Fourteen of 540 homotypic comparisons revealed significant differences between right and left bones at either a slice or region. Although there were only 14 significant differences between right and left bones at any region or slice, measurements were more precise with lower coefficients of variation in the diaphyseal and epiphyseal regions. Homotypic differences in diaphyseal and epiphyseal regions were < 5.3 and 7.5%, respectively (power = 0.8). In metaphyseal regions, however, homotypic differences were larger; these differences could have been as large as 11.5% for total bone diameter, 15.6% for medullary diameter, and 80.0% for cortical width without achieving significant differences between populations (power = 0.8). This study validated the concept of using the contralateral limb as the control condition in orthopedic studies using dogs, particularly when evaluating the geometric properties of long bones radiographically.