Thumb Duplication

Triphalangia

20%

Thumb polydactyly is classified by the Wassel classification (Table 82—1). The Wassel type IV is the most common followed by type VII and type II. Clinical appearance varies from a mild widening thumb to a complete duplication of the entire thumb. The radial half of the thumb is often more hypoplastic. There may be fibrous connections between the two thumbs. The nail may be one large nail, a conjoined nail, or a completely duplicated nail. The adductor pollicis and deep head of the flexor pollicis brevis typically insert on the ulnarmost thumb, and the abductor pol-licis, the superficial head of the flexor pollicis brevis, and the opponens pollicis insert on the radial most thumb. The joints are stiff and the collateral ligaments are shared.

If surgical reconstruction is to be performed, the optimal age is between 1 and 2 years. At 6 months, gross grasp and grip are seen. At 1 year of age thumb and index function is seen, with voluntary release seen at 18 months. If surgical intervention is put on hold until 2 years, the neurovascular and tendinous structures are larger and complications may be fewer.

Nonoperative Treatment

Certain systemic abnormalities make surgical reconstruction contraindicated. These include Holt-Oram and Diamond-Blackfan syndromes and Fanconi's anemia, which can be associated with duplicate thumb. In certain cultures, surgical reconstruction is also contraindicated. In the Asian culture, it is unethical to remove a body part. In these cases, adequate therapy must be provided to the child to allow for adequate hand function.

Surgical Treatment

An initial skin incision is made in a zigzag fashion beginning just distal to the carpometacarpal joint, based on the radial aspect of the hand (Fig. 82—4). The radial hypoplastic thumb is encircled and the incision is continued distally to joint the ulnar thumb. Anomalous tendons and neurovascular structures innervating the duplicate thumb should be identified. The neurovascular structures are ligated if the determination is made to ligate the hypoplastic thumb. The tendons are dissected back to their bifurcation.

Duplicate Thumb
Figure 82—4. An initial skin incision is made in a zigzag fashion beginning just distal to the carpometacarpal joint, based on the radial aspect of the hand. (A) Dorsal view. (B) Volar view.
Figure 82—5. The extensor pollicis longus and flexor pol-licis longus tendons are then decentralized.

The thenar muscles are dissected from surrounding tissue and released from their insertion into the more radial hypoplastic thumb. These muscles will be readvanced later to the remaining ulnar thumb.

To reconstruct the radial collateral ligament to the metacarpophalangeal (MP) joint, a strip of tissue, which includes periosteum from the proximal phalanx and proximally based periosteum of the metacarpal, is tagged for lateral advancement. This allows access to the MP joint and the widened metacarpal head with a dual-facet structure. The extra facet is shaved down. If the metacarpal is angulated ulnarly, a closing wedge osteotomy is necessary. When the osteotomy is aligned and fixed with Kirschner wires, the radial collateral ligament of the MP joint, which was reconstructed, is sutured distal to volar. The dissected thenar muscles are advanced and attached to the periosteum at the base of the proximal phalanx. The extensor pollicis longus and flexor pollicis longus tendons are then decentralized (Fig. 82—5). The incision is closed with attention to the zigzag to avoid development of a contracted scar (Fig. 82—6).

The thumb is immobilized for 3 to 4 weeks. At this time the wire is removed if the osteotomy is healed. A protective splint is recommended for an additional 3 to 4 weeks.

Complications

Decreased range of motion Instability at the reconstructed MP joint

Figure 82—6. The incision is closed with attention to the zigzag to avoid development of a contracted scar.

Preaxial Polydactyly

Development of a longitudinal scar

Incomplete correction along with a characteristic angular deformity, the zigzag deformity

Suggested Readings

Cheng JCY, Chan KN, Ma YFY. Polydactyly of the thumb: a surgical plan based on 95 cases. J Hand Surg [Am] 1984;9A:155-165.

Cohen MS. Thumb duplication. Hand Clin 1998;14:17-27.

Dobyns JH, Lipscomb PR, Cooney WP. Management of thumb duplication. Clin Orthop 1985;195:26-44.

Graham TJ, Ress AM. Finger polydactyly. Hand Clin 1998;14:49-64.

Heras L, Barco J, Cohen A. Unusual complication of ligation of rudimentary ulnar digit. J Hand Surg [Br] 1999;24B:750-751.

Huffstadt AJ. Polydactyly—bifid thumb. Hand 1981;13:81-84.

Hung L, Cheng JC, Bundoc R, Leung P. Thumb duplication at the metacarpopha-langeal joint. Management and a new classification. Clin Orthop 1996;323:31-41.

Lourie GM, Costas BL, Bayne LG. The zig-zag deformity in pre-axial polydactyly. A new cause and its treatment. J Hand Surg [Br] 1995;20B:561-564.

Wassel HD. The results of surgery for polydactyly of the thumb. Clin Orthop 1969; 64:175-193.

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