label: Aplasia/Hypoplasia of the proximal phalanx of the thumb
label_lc: aplasia/hypoplasia of the proximal phalanx of the thumb
description: "This term applies if the proximal phalanx of the thumb is either small/hypoplastic or absent. In contrast to the proximal phalanges of the digits 2-5, the proximal phalanx of the thumb is embryologically equivalent to the middle phalanges of the other digits, whereas the first metacarpal is embryologically of phalangeal origin and as such equivalent to the proximal phalanges of the other digits."