Growth in width of the metacarpals - an investigation in human fetuses

The process of growth in width of the human hand during fetal life has neve r been described. Do metacarpals grow concentrically and separation between the bones occurs through expansion of soft tissues? Or is growth eccentric , a process termed drift by Enlow, a relocation in space of organs? Hands o f 10 spontaneously aborted fetuses (age range: between 14.5 and 24 weeks of gestation) were examined paying special attention to the bone bark. A thic ker bone bark was taken as an indication of growth in that direction. The t hickness of the bone bark was measured at the radial and ulnar sides at the level of the proximal and of the distal physes of the second to fifth meta carpals. A ratio of radial over ulnar bone bark thickness (R/U ratio) was c alculated. The third metacarpal grew almost concentrically (R/U ratio 1.12 +/- 0.06). The second metacarpal grew in a radial direction (R/U ratio 3.29 +/- 0.19) and the fourth and more so the fifth metacarpal grew in an ulnar direction (R/U ratio 0.70 +/- 0.04 and 0.42 +/- 0.02, respectively). The d ifferences in R/U ratios between every metacarpal were statistically signif icant for all comparisons P < 0.001. Fetal growth in width of the human met acarpals is eccentric and not concentric. It is concluded that during growt h in width the metacarpals move away from the midline of the hand and that growth occurs through eccentric bone apposition rather than through soft ti ssue expansion. (C) 2001 Orthopaedic Research Society. Published by Elsevie r Science Ltd. All rights reserved.