[The hand: embryology and main malformative mechanisms].

Upper limb bud appears in the cervical region of the embryo during the fifth week of development. It is made of epithelia and underlying mesenchyme. Diffusible growth factors, expressed by the apical ectodermal ridge, direct the proximal-distal growth. Other factors are expressed by zone of polarizing activity and ectoderm. They induce together anterior-posterior growth and dorsal-ventral polarity of the limb bud. The development of axial skeleton pattern is controlled by transcription factors from the HOX family, which are expressed in a stripe along the proximal and distal edges of the limb bud. Embryologic mechanisms of the main hand malformations are described, as well as their known genetic or mechanical aetiologies.