Duplication of the thumb unilateral biphalangeal

Duplication of the Thumb: Unilateral Biphalangeal

Duplication of the thumb, also known as Polydactyly of the thumb or Preaxial Polydactyly, is a congenital anomaly characterized by the presence of an extra thumb. The condition can vary significantly in terms of the size, shape, and functionality of the duplicated thumb. When the duplication occurs on one hand and involves two phalanges (the bones of the fingers and thumbs), it is specifically referred to as unilateral biphalangeal duplication of the thumb.

Etiology

The exact cause of thumb duplication is not fully understood, but it is believed to involve genetic and environmental factors. The condition occurs during the embryonic development of the limbs, specifically during the formation of the Radial Ray. Mutations in certain genes may disrupt the normal patterning of the limbs, leading to duplication.

Classification

Thumb duplications are classified according to the Wassel classification, which is based on the level of duplication. The classification has seven types, ranging from a bifid distal phalanx (Type I) to a complete duplication of the thumb including two separate metacarpal bones (Type VII). Unilateral biphalangeal duplication typically falls under Types II, III, or IV of the Wassel classification.

Symptoms and Diagnosis

Individuals with duplication of the thumb may experience varying degrees of functional impairment, depending on the extent of the duplication. Symptoms can include difficulty with fine motor skills, reduced grip strength, and cosmetic concerns. Diagnosis is typically made through physical examination and may be confirmed with imaging studies such as X-rays to assess the bone structure.

Treatment

Treatment for thumb duplication is surgical and aims to remove the extra thumb and reconstruct the remaining thumb to improve function and appearance. The choice of surgical technique depends on the type of duplication and may involve bone, tendon, and ligament reconstruction. Surgery is usually performed in early childhood to allow for optimal hand function development.

Prognosis

The prognosis for individuals with unilateral biphalangeal duplication of the thumb is generally good, especially with early surgical intervention. Most individuals are able to achieve good hand function and appearance. However, some may require additional surgeries or physical therapy.

Epidemiology

Duplication of the thumb is the most common type of polydactyly affecting the hands. It occurs more frequently in males and can be unilateral (affecting one hand) or bilateral (affecting both hands). The unilateral biphalangeal form is less common than other types of thumb duplication.

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