Metacarpal Index by Digital X-ray Radiogrammetry

Abstract

Metacarpal index (MCI), the combined cortical midmetacarpal thickness divided by the outer midmetacarpal diameter, fell into oblivion when dual photon absorptiometry was introduced a quarter of a century ago. Modern PC-based digital X-ray radiogrammetry (DXR) with multiple, automated thickness and diameter measurements offers a unique opportunity for precise and accurate measurements of MCI (DXR-MCI). We hypothesize that DXR-MCI in contrast to projected areal bone mineral density (DXA-BMD) is independent of bone size and studied 384 normal women by measuring DXR-MCI and DXA-BMD of the lumbar spine, hip, and distal radius. A normative MCI database for women is presented. It has its maximum in the third decade, and a moderate biologic variation that seems to decline with age. It was found that DXR-MCI was independent of body weight and body surface area, whereas all DXA-BMD values were significantly dependent on them. Body height was significantly correlated with DXA-BMD at all sites, but less so with DXR-MCI. The latter was correlated with metacarpal bone length. It is suggested that the moderate correlation between MCI and body height would be abolished if the region of interest used for calculation of MCI be adjusted according to individual metacarpal bone length. DXR-MCI correlated significantly with DXA-BMD at the sites measured, and particularly well with that of the distal radius (r = 0.67; p < 0.0001).