Triphalangeal

Triphalangeal is a term used in human anatomy to describe a digit that has three phalanges instead of the usual number for that digit. The most common context is the thumb, where an extra middle phalanx yields a triphalangeal thumb. Triphalangism can occur as an isolated hand anomaly or as part of a broader condition known as triphalangeal-thumb-polydactyly syndrome (TPTPS).

Anatomy and forms vary. In isolated triphalangism, the thumb may have a complete extra phalanx or only a partially formed one, which can affect joint alignment and tendon mechanics. When triphalangism is part of TPTPS, it often accompanies extra digits or other limb malformations, reflecting a developmental disturbance during limb formation.

Genetics and development are central to understanding triphalangeal thumb presentations. Many cases of TPTPS are inherited in an autosomal dominant pattern and have been linked to mutations in HOXA13, a gene in the HOX cluster that guides limb development. Isolated triphalangism may occur sporadically without a familial history.

Diagnosis typically relies on clinical examination and radiographic imaging, which reveal the number and arrangement of phalanges and help assess joint integrity and tendon function. Evaluation for associated anomalies may be warranted when triphalangism is part of a broader syndrome.

Management is individualizedbased on severity and functional impact. Some individuals require no intervention, while others benefit from surgical correction. Procedures may include removal or reshaping of the extra phalanx, reconstruction or realignment of joints and tendons, and postoperative rehabilitation to improve thumb function and grip. Prognosis is generally favorable with appropriate treatment, though some cases may necessitate additional procedures for recurrent deformity or functional issues.