ABSTRACT
During the early stages of development, the embryo has a laminar structure consisting of three different germ cell layers, from which specific systems will develop. The limb buds first appear at the end of the fourth week of development, with the forelimbs preceding the hindlimbs by 1-2 days. The anteroposterior axis (thumb to little finger) is regulated by the zone of polarizing activity (ZPA), a mass of cells within the posterior aspect of the limb bud. Amniotic band syndrome (ABS) is a congenital disorder believed to result from the entrapment of fetal limbs or organs within intrauterine fibrous amniotic bands, produced by partial rupture of the amniotic sac. The physis is a structure consisting of chondrocytes arranged in a highly ordered, layered fashion within an extracellular matrix in line with the longitudinal axis of the bone. Altering the forces acting upon the physis affects its activity, with compression retarding growth (Hueter-Volkmann principle).
