A thumb with three phalanges in a single, proximo-distal axis. Thus, this term applies if the thumb has an accessory phalanx, leading to a digit like appearance of the thumb.
Comment:
The requirement for a single PD axis relates to the issue that partial forms of Preaxial polydactyly may comprise a partially duplicated thumb with two distal phalanges and a single proximal phalanx. That finding is instead coded as a mild form of thumb polydactyly. Note that this finding can be readily assessed by examination and/or physical manipulation of the thumb.
Synonyms:
exact_synonym:
Accessory phalanx of the thumb; Digitalized thumb; Finger-like thumb; Triphalangeal thumbs; Triphalangy of thumb