CONGENITAL DEFORMITIES OF THE EXTREMITIES According to Geoffroy Saint-Hilaire the following classes should be made of deformities of the four extremities having the same pathogenesis and etiology: 1. Ectromelia, where one or more of the extremities are entirely missing.
2. Hemimelia, where only the proximal part of an extremity is developed, the organ becoming more rudimentary as it proceeds toward the periphery.
3. Phocomelia, where the upper segments are missing, the distal segments—hand or foot—protruding direct from the body.
The pathogenesis of these deformities, as well as of partial defects of the various extremities, is explained by the failure of the extremities or their parts to connect.
The etiology consists in a disturbance in the course of development, caused either by degeneration or accidental strangulation and adhesions owing to interference by bands and folds. The latter may be normally present in the neighborhood of the embryo, or they may have developed through pathological processes (strangulation by the umbilical cord, amniotic bands). Deep constrictions are sometimes present after birth
as evidence of such strangulations which, by growing deeper into the tissues, may lead to congenital amputation (Figs. 41 and 42). Pi(ichaud has published illustrations of phoconielia in brother and sister.
Both the biological and traumatic etiological factors may occur combined, as the solitary or continuous effect of a trauma may give a pathological direction to the course of development. Fig. 41, for in stance, illustrates a combination of strangulation and polydactylism. Fig. 42 shows mantis vara caused by the twisting of the umbilical cord. In this way it is possible to explain easily on a biologico-degenerative basis the occurrence of amputations and other deformities of the extremities.