triphalangealthumbpolydactyly

Triphalangeal refers to a digit that has three phalanges instead of the usual two. The term most commonly describes the thumb (triphalangeal thumb) but can apply to other fingers. Triphalangeal presentation can be isolated or part of a broader limb-anomaly pattern, such as triphalangeal thumb–polydactyly syndrome, or occur within conditions like Holt-Oram syndrome.

Genetics and etiology are diverse. In many familial cases, the trait shows autosomal dominant inheritance with variable expressivity. Mutations in HOXA13 are strongly associated with triphalangeal thumb–polydactyly syndrome. Less commonly, mutations linked to Holt-Oram syndrome, such as TBX5, can include triphalangeal thumbs among radial ray abnormalities. The underlying mechanism involves disturbance of limb bud patterning and segmentation during development, resulting in an extra phalanx within the digit.

Clinical features vary from mild to pronounced. Affected infants may present with a thumb that is broad or angled, sometimes with altered opposition, grip, or range of motion. Additional anomalies of the hand or other limbs may occur in syndromic cases.

Diagnosis is based on physical examination and radiographic confirmation of three phalanges and the bone arrangement. Prenatal ultrasound can detect limb anomalies in some cases.

Management is tailored to severity and functional impact. Mild, nonfunctional differences may be observed. Surgical options aim to improve function and appearance and can include excision of the extra phalanx, osteotomies to realign the thumb, and tendon balancing or joint reconstruction. In syndromic forms, treatment also addresses associated anomalies. Prognosis is variable and depends on the presence and severity of accompanying conditions.