Polydactyly Reconstruction

Synopsis

Polydactyly of the hand refers to the presence of an extra digit or part of a digit. It can be defined as radial, central, or ulnar, referring to the region of the extra digit. The condition can occur in isolation or as part of a syndrome. Radial polydactyly, or thumb duplication, is classified by the Wassel classification. Ulnar polydactyly is classified into two or three types.

Introduction

Polydactyly (poly = more; dactylos = finger) refers to the presence of more than five digits on at least one extremity. It is one of the most common congenital upper extremity differences, together with camptodactyly and syndactyly. The disorder is easily detected at birth, and cosmetic concerns usually lead the parents to seek surgical intervention at an early age. Depending on the type and severity of duplication, there may also be functional impairment.

The classification of polydactyly of the hand can be divided into radial, central, and ulnar polydactyly, referring to the anatomical location of the extra digit or part of a digit. The incidence of polydactyly varies depending on the type of polydactyly and the studied population. Ulnar polydactyly is 10 times more common in those of African descent and twice as common in males, whereas radial polydactyly is more common in Asians. Central polydactyly is extremely rare in all published studies.

A separate entity is the mirror hand or ulnar dimelia. In the forearm, two ulna bones may exist without a radius. Because the medial side is a mirror image of the lateral side, the term mirror hand became popular. It is extremely rare. The classic mirror hand is unilateral, usually with 7 to 8 fingers without a thumb, and is not combined with other anomalies. The etiology is unknown. An inheritance pattern has not been described. Geneticists believe it is due to a spontaneous mutation.

The incidence of radial polydactyly is 0.08 to 1.4 per 1000 live births, and 20% of cases are bilateral. With respect to ulnar polydactyly, in a prospective screening study of 11,161 newborns, the prevalence rate of type B ulnar polydactyly was 1 in 143 live births of African American infants and 1 in 1339 live births of Caucasian infants. Bilateral involvement was present in 76% of patients, and 86% had a positive family history. Central polydactyly is less common than radial and ulnar polydactyly. In a review of 144 cases of polydactyly at the University of Iowa, 22 cases of central polydactyly were reported. Central polydactyly is often seen with associated syndactyly and cleft hand. It can occur in isolation or as part of a syndrome, such as Grebes' chondrodysplasia. The incidence of mirror hand is very rare, with only approximately 70 cases reported since its original description in the sixteenth century.

Radial polydactyly occurs most commonly as an isolated problem, whereas ulnar polydactyly is more commonly associated with a systemic syndrome.

Radial Polydactyly

Clinical Presentation

Radial polydactyly, also referred to as thumb duplication, is usually classified according to the Wassel system ( Fig. 5.2.1 ). It is based on radiographs and refers to the skeletal level of thumb duplication : type I at the distal phalanx; type II at the interphalangeal (IP) joint ( Fig. 5.2.2A and B ); type III at the proximal phalanx; type IV at the metacarpophalangeal (MP) joint ( Fig. 5.2.3A and B ); type V at the metacarpal; and type VI at the carpometacarpal (CMC) joint. When one of the thumbs is triphalangeal, it is classified as type VII. The most common Wassel types are type IV (50%), type II (20%), and type VII (12%). Wassel type I thumb duplication is the least common type. Some types of radial polydactyly are not accounted for by the Wassel classification. These include the triplicated thumb, the pedunculated type or a duplicated thumb with no bony attachment to the main thumb, the radially deviated type, and the radial polydactyly associated with thenar muscle hypoplasia.

Several authors do not agree with the term “duplicated thumb” since both thumbs are usually smaller than a normal thumb and have less mobility. For this reason, the term “split thumb” can be encountered instead.

Radial polydactyly usually occurs sporadically. Genetic counseling is therefore not necessary. An exception to this includes cases of radial polydactyly where one thumb is triphalangeal (Wassel type VII). This phenotype has been linked to a mutation on chromosome 7q36, and it demonstrates an autosomal dominant inheritance pattern. The affected gene is involved in the regulation of the sonic hedgehog protein. Radial polydactyly can occur in the setting of a syndrome, such as Holt-Oram syndrome, Fanconi's anemia, and Rubinstein-Taybi syndrome.

In the absence of surgical intervention, most children with radial polydactyly can function without any serious functional limitation. However, some patients have an associated pollex abductus that restricts normal flexion and extension of the associated joints. Additionally, patients with uncorrected deformity may face the stigma associated with abnormal thumb appearance as they integrate into society.

Type I (Distal Phalanx) and Type II (Distal Interphalangeal Joint)

Treatment of these less severe forms of thumb duplication depends on the extent of the duplication and on whether the duplication is symmetrical or asymmetrical. When the duplicated thumbs share a nail and are well aligned, surgical correction is optional.

In the case of an asymmetrical duplication, the smaller thumb is ablated, its collateral ligament is transferred to the dominant thumb, and the tendons are centralized. The skin incision must be planned to allow sufficient coverage of the retained dominant thumb. It can be placed dorsally or, less conspicuously, laterally. Proximal exposure follows a zig-zag pattern. First, the nail and nail bed of the lesser thumb are excised, and the skin is dissected superficial to the extensor tendon. The collateral ligament of the minor thumb is elevated distally with an osteoperiosteal sleeve ( Fig. 5.2.2C ). If the IP joint has a separate facet for the minor thumb, the collateral ligament is also detached from its proximal insertion in continuity with the periosteum, which is raised as a longitudinal flap. This forms a proximally based ligament-periosteal sleeve. Chondroplasty is then performed, and the extra articular facet is trimmed with a scalpel blade. If malalignment of the retained thumb persists, a closing wedge osteotomy can be performed in the future. The slips of extensor and flexor tendons to the lesser thumb may be used to augment their counterparts on the retained/dominant thumb. The collateral ligament is sutured to the periosteum of the base of the retained distal phalanx using a nonabsorbable braided suture. A percutaneous 0.045-inch Kirschner wire (K-wire) may be driven from the thumb tip across the IP joint to maintain proper alignment. The skin incision is closed with absorbable sutures ( Fig. 5.2.2D ), and the upper limb is placed in a long arm thumb spica cast.

In patients with nearly symmetrical thumb duplication, the Bilhaut-Cloquet procedure may be considered. This procedure involves resection of central portions of bone and nail of the duplicated segments longitudinally and reapproximation of the remaining structures with either sutures or a transverse K-wire. This procedure, however, has been criticized for resulting in post-operative nail deformity, physeal growth disturbance, and IP joint stiffness. Baek et al. have proposed a modified extra-articular technique in which the IP joint is reconstructed with one thumb and the second thumb is used to reconstruct the distal phalanx. Nonetheless, results in both cases seem to demonstrate obvious nail deformity, and it is the authors' preference to avoid these techniques.

Type III (Proximal Phalanx) and Type IV (Metacarpophalangeal Joint)

Type III and IV thumb duplications are usually managed in a similar fashion: The dominant thumb is retained, and the minor thumb is ablated. In a patient that presents thumbs that are equal in size, the ulnar thumb is preferentially retained because of the importance of the MP joint ulnar collateral ligament, which is essential for pinch. The skin incision is planned as described for types I and II ( Fig. 5.2.3C ). The MP joint radial collateral ligament is detached distally from the minor/deleted thumb with an osteoperiosteal sleeve. The abductor pollicis brevis, which inserts on the radial thumb, is also raised with an osteoperiosteal sleeve together with the radial collateral ligament. If the metacarpal has a separate articular facet for the minor thumb, the radial collateral ligament is also carefully dissected off of its proximal attachment in continuity with the periosteum and thenar musculature. The extra articular facet is excised ( Fig. 5.2.3D ), and the radial collateral ligament, together with the abductor pollicis brevis, is reattached to the periosteum at the base of the proximal phalanx of the retained thumb.

Extraarticular misalignment may be further corrected with a closing wedge osteotomy of the proximal phalanx if necessary. Tendons are realigned on the ulnar thumb as described previously ( Fig. 5.2.3E ).

Of note, it is not uncommon for patients to demonstrate elements of thumb hypoplasia, with the presence of a pollex abductus, which is an abnormal connection between the extensor and the flexor tendons to the thumb , as well as a tight first web space. These elements should be treated with tenolysis and first web space reconstruction.

A percutaneous K-wire is driven across the MP joint. The patient is placed in a long arm thumb spica cast.

Type V (Metacarpal) and Type VI (Carpometacarpal Joint)

Reconstruction follows the same principles described for types III and IV reconstruction. The thenar muscles that are attached to the deleted thumb should be transferred to the retained thumb. Additionally, the first web space may be deficient, necessitating simultaneous deepening with a simple or four-flap Z-plasty or a dorsal advancement flap.