Dual energy X ray absorptiometry of ex vivo HcB/Dem mouse long bones: left are denser than right

Dual energy X ray absorptiometry (DXA) has become a popular analytical technique in mice and other small animals. Comparative study of bone properties at different anatomical sites is an active area of study in model organisms. Such investigations require that site-specific data be generated and interpreted. There are no published data addressing the degree to which contralateral mouse bones resemble each other in the absence of an experimental intervention, nor are there data addressing the correlation of bone densitometry measurements between anatomically distant sites. To address these gaps in our knowledge, we used DXA to compare excised mouse femora and humeri. At the population level, left bones were slightly but significantly denser than right bones, with an overall adjusted bone mineral density (BMD) difference of 0.7 +/- 0.3 and 0.5 +/- 0.2 mg/cm2 at the femur and humerus, respectively. At the level of bone pairs from a single animal, absolute adjusted BMD disparities between the right and left sides were 2.3 +/- 1.9 mg/cm2 at the femur and 1.7 +/- 1.4 mg/cm2 at the humerus. Correlation coefficients between left and right sides were 0.78 for adjusted BMD at both sites. The correlation coefficient between side-averaged femoral and humeral BMD was 0.81, but ranged between 0.70 and 0.75 when limited to ipsilateral or contralateral femur-humerus pairs. Our findings suggest the desirability of randomizing limbs for treatment in studies using contralateral limb controls. These observations may represent the densitometric manifestation of behavioral and neuroanatomical lateralization in laboratory mice.