Brief communication: non-circular geometry and radiogrammetry of the second metacarpal

Traditional radiogrammetry of the second metacarpal midshaft reconstructs cortical cross-sectional geometry from mediolateral (ML) linear dimensions based on circular model. However, comparison of anteroposterior (AP) versus mediolateral radiographic dimensions in a sample of paired metacarpals shows that AP total and medullary widths typically exceed ML widths by 5% to 10%. As well, in 13% of males and 25% of females, the two metacarpals are dissimilarly shaped, i.e., the AP/ML ratio is > 1.0 for one side and < 1.0 for the other. This situation exaggerates the differences in geometric properties between sides and constitutes a potentially significant source of bias for analyses of bilateral asymmetry. These results suggest that the circular model is inappropriate for estimation of cross-sectional geometry at this anatomical location.