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Triphalangeal thumb
First described by Columbi in 1559,〔H. Kelikian, Hyperphalangism, congenital deformities of the hand and forearm, 1974〕 triphalangeal thumb (TPT) is a congenital malformation where the thumb has three phalanges instead of two. The extra phalangeal bone can vary in size from that of a small pebble to a size comparable to the phalanges in non-thumb digits. The true incidence of the condition is unknown, but is estimated at 1:25,000 live births.〔Lapidus PW, Guidotti FP, Coletti CJ, Triphalageal thumb. Surg Gynecol Obstet, 1943〕 In about two-thirds of the patients with triphalangeal thumbs, there is a hereditary component.〔Temtamy SA, McKusick VA, the genetics of hand malformations, Birth defects Orig Artic Ser, 1978〕 Besides the three phalanges, there can also be other malformations.
==Appearance==
The triphalangeal thumb has a different appearance than normal thumbs. The appearance can differ widely; the thumb can be a longer thumb, it can be deviated in the radio-ulnar plane (clinodactyly), thumb strength can be diminished. In the case of a five fingered-hand it has a finger-like appearance, with the position in the plane of the four fingers, thenar muscle deficiency, and additional length. There is often a combination with radial polydactyly.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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