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Because triphalangeal thumbs cannot easily oppose and do not possess many of the optimal qualities found in most opposable thumbs, they tend to cause the hand to be less effective in use and, therefore, prove to be more problematic in daily life. Cause
Malformations of the upper extremities can occur in the third to seventh embryonic week. In some cases the TPT is hereditary. In these cases, there is a mutation on chromosome 7q36. If the TPT is hereditary, it is mostly inherited as an autosomal dominant trait, non-opposable and bilateral. The sporadic cases are mostly opposable and unilateral. Syndromes
Triphalangeal thumb can occur in syndromes but it can also be isolated. The triphalangeal thumb can appear in combination with other malformations or syndromes.Syndromes include:

Holt-Oram syndrome
Aase syndrome
Diamond-Blackfan anemia
Townes-Brocks syndromeMalformations include:
Radial polydactyly
Syndactyly
Claw-like hand or foot

Diagnosis
Classifications
There are multiple classifications for the triphalangeal thumb. The reason for these different classifications is the heterogeneity in appearance of the TPT. The classification according to Wood  describes the shape of the extra phalanx: delta (Fig. 4), rectangular or full phalanx (Table 1). With the classification made by Buck-Gramcko a surgical treatment can be chosen (Table 1). Buck-Gramcko differentiates between six different shapes of the extra phalanx and associated malformations.Table 1: Classifications of Wood  and Buck-Gramcko

Treatment
The goals of surgical treatment are: reducing length of the thumb, creating a good functioning, a stable and non-deviated joint and improving the position of the thumb if necessary. Hereby improving function of the hand and thumb.