Surgical treatment is usually performed to improve appearance. Early amputation is indicated when the polydactylous finger is a flail, poorly attached appendage. When the attachment of the extra digit is more complex, the digit to be sacrificed should be selected carefully. Bony architecture and tendon function and distribution must be considered. The marginal digit or the one that appears most normal is not necessarily the most functional one. In some patients, usable structures from the amputated digit should be preserved for transfer to the digit to be preserved. For example, if one of the two adjoining digits has greater flexor power while the other has greater extensor power, the latter is amputated and its extensor mechanism is transferred.

Duplication of the thumb can be partial or complete; partial forms include the bifid and bifurcated thumb. The thumb may be split at the interphalangeal or metacarpophalangeal joint, or the split may stem from the metacarpal diaphysis. When a polydactylous thumb is amputated, tendons should be regrouped to reinforce the power of the thumb or the part to be spared. Treatment of duplication distal to the interphalangeal joint consists of resection of a V-shaped segment of skin, nail, and bone. This principle can be adapted to the treatment of duplications proximal to the interphalangeal joint, although in children, the final correction may be delayed to avoid injury to the growth plates. When a twin digit is divided, the collateral ligaments must be reconstructed at the amputation site.

A triphalangeal thumb is another expression of thumb duplication and is often associated with serious cardiac anomalies or hematopoietic disorders. If the thumb can be positioned in opposition, treatment is optional. There may be a progressive recurvatum deformity caused by a wedge-shaped ossicle interposed between the distal and proximal phalanges; this ossicle can be removed in childhood. If the thumb cannot be opposed and resembles an index finger, surgical treatment may include creation of a first web space, rotational osteotomy, and tendon transfer. In complex preaxial (radial) polydactyly, the thumb is duplicated with triphalangism of one or both of the extra digits.

IV. Overgrowth

The terms overgrowth and gigantism describe conditions in which either part or all of the limb is disproportionately large. This may occur in the digit (macrodactyly), hand, forearm, or entire limb; similar defects may occur in the lower limb. The condition is seldom bilateral and usually not hereditary.

Macrodactyly. Four types of macrodactyly have been described. In the first type, the most common type, the enlarged portion is in the distribution of a major nerve and is associated with abnormally large nerves infiltrated with large amounts of fat. It most often occurs in the distribution of the median nerve in the hand and the medial plantar nerve in the foot. The second type is associated with neurofibromatosis. The third type is very rare and associated with unusual hyperostosis without enchondroma. The fourth type occurs with hemihypertrophy of the ipsilateral upper and lower limb and is associated with adrenal, renal, and brain tumors.