Polydactyly

Annette D. Filiatrault

Polydactyly is a common congenital deformity defined as an excess of five digits in humans. It has racial and geographic predilections and may occur as an isolated deformity or, less commonly, in association with certain congenitally inherited syndromes (1,2,3,4,5,6 and 7). Syndactyly, brachydactylia, or an accessory metatarsal may coincide with the supernumerary digit as well as a variety of other associated congenital anomalies (5,7,8). Postaxial polydactyly is the most common hyperdactyly variant and denotes lateral digital duplication, whereas preaxial is applied to medial digital duplication. Central polydactyly is the least common and involves duplication of the innermost digits, most often the second toe (7,8,9 and 10).

CLASSIFICATIONS

Temtamy and McKusick (7) developed a classification scheme based on pedigree analysis to divide polydactyly of the hand into those associated with a syndrome and those that are nonsyndromatic (adapted here for the foot). Under those categories, preaxial and postaxial groups were further separated. Postaxial subtype A was described as an extra digit that is “rather well formed and articulates with the fifth or extra metacarpal (metatarsal)” (7). Conversely, postaxial type B involves an extra digit that “is not wellformed and is frequently in the form of a skin tag” (7). Preaxial polydactyly was subtyped into type 1, first digit polydactyly; type 2, triphalangeal first digit; type 3, triphalangeal first digit with tibial defect; type 4, second digit polydactyly; and type 5, polysyndactyly (4,8,11). Polymetatarsia associated with postaxial polydactyly was classified by Venn-Watson into four anatomical types based on the degree of duplication: wide metatarsal head, Y-shaped metatarsal, T-shaped metatarsal, and metatarsal duplication (5). Preaxial polymetatarsia was anatomically noted to be of a short block or wide first metatarsal type (5,10). Currently, many authors reference Bauth and Olason’s classification method as the most inclusive and reproducible as it denotes the type of duplication in both the longitudinal and transverse skeletal axis (11,12,13,14 and 15).

EVALUATION/SURGICAL CONSIDERATIONS

The indications for polydactyly repair may include psychological or mechanical pain, functional difficulties, and shoe gear irritation. There has also been one reported case of impending pathologic fracture (16). Typically, clinical and radiographic evaluation of the supernumerary ray is sufficient for surgical planning. Rarely would magnetic resonance imaging or computerized tomography be necessary, unless there was a complicated soft tissue or osseous component to the deformity (10). A preoperative angiogram may be considered in the atypical severely deformed lower extremity to determine vascular supply (4). Further medical workup may be necessary prior to surgical reconstruction if the patient’s polydactyly is felt to be part of an inherited syndrome.

The skin tag type (postaxial type B) of polydactyly may be treated after birth with a simple suture ligature with reported good success; however, care must be taken to not perform this if a deformed or duplicated metatarsal is present as this will lead to residual deformity and possibly additional surgery (5,17). For all other forms of polydactyly, there is some debate as to the best age for surgical reconstruction, although the age at clinical presentation will often play a large role in this determination. In most cases, it is preferred to delay surgery until the patient can tolerate anesthesia and is at least 1 year old for better osseous and soft tissue visualization (18). Surgery may be even further delayed if a metatarsal osteotomy is required or if there is any uncertainty as to which digit functions best and should therefore be retained (18,19).

The choice of surgical procedure, as a general rule, “is the one that will give the most normal shape (and function) to the forefoot” (5,20). Given a similar appearance and function of the digits, excision should involve the lateralmost digit in postaxial polydactyly repair and the medialmost toe in preaxial polydactyly for a straight anatomic contour of the foot. The internal digit or metatarsal may be the appropriate digit to resect if the external digit is much superior in form, function, or metatarsophalangeal joint articulation (5,20,21). However, excising the innermost digit will likely result in a wider forefoot with larger spaces between the toes and may require repair of the intermetatarsal ligament or an osteotomy to redirect the appropriate metatarsal segment (10). Duplication of the phalanges without metatarsal involvement may be performed through a double semielliptical incision over the duplication, with removal of the accessory phalanges and soft tissue remodeling (9). Metatarsal involvement often includes a racquet-type incision with more extensive soft tissue rebalancing. Overall, each case should be planned individually based on the anatomy and goals of surgery.

Postaxial polydactyly correction tends to be more straightforward than preaxial polydactyly, which can be complicated with such problems as hallux varus, a short first metatarsal, or a longitudinal epiphyseal bracket (LEB) (12,22). The associated hallux varus has been reported to be caused by adductor hallucis insufficiency and the presence of medial hallux fibrous band contracture, and therefore, each should be addressed surgically if present (12,18). LEB, originally described as a “delta phalanx or metatarsal,” is a rare deformity in which there is an arcuate secondary longitudinal growth plate bracketing the diaphysis and metaphysis of small long bones that restricts normal longitudinal growth. This results in a triangular-shaped shortened and widened bone and may equate to Venn-Watson’s observed “short block first metatarsal” (12,23). LEB can particularly complicate surgical repair of preaxial polydactyly when present in the first metatarsal and often requires resection prior to growth plate closure (24).

TECHNIQUES

GENERAL POLYDACTYLY/POLYMETATARSIA SURGICAL PLAN

The patient is laid supine and after local and general anesthesia, the patient’s foot and leg are prepped and draped in the usual sterile fashion. After exsanguination of the foot, a pneumatic tourniquet is utilized. Skin incision placement involves typically a racquet-type incision. Medial and lateral incisions should avoid scar formation over pressure areas with placement dorsal to the metatarsal head and shaft. Care is taken to ensure coverage of the metatarsal by protecting it with the thicker dermal tissue originating from the plantar aspect of the accessory metatarsal head (10,25). The neurovascularity and musculotendinous insertions to the ray are preserved through anatomic dissection and atraumatic technique (25,26). If the neurovascular structures are duplicated, they may be excised; if misdirected, they will require repositioning (26). Any accessory tendons should be split distally and may be tenodesed to the preserved tendons (27). If an accessory ray is present, it is excised or transected at its junction with the retained metatarsal to avoid cortical splitting (5,10,25). The remaining metatarsal remodels over time and maintains its new shape without regression after resection (5). Disruption of the growth plates should be avoided and if a wide metatarsal head is prominent, it should be trimmed flush to the metatarsal shaft at right angles to the physis so as to not impede growth (5,20,25). A metatarsal osteotomy may be performed to redirect the remaining metatarsal as needed. Periosteal tissues over the remaining ray are to be maintained or repaired. Insertional attachments about the toe should be preserved or reattached, particularly the intermetatarsal ligament and abductor or adductor hallucis tendons if they are disrupted. Any excessive or redundant soft tissue is remodeled for forefoot contouring, and anatomic closure is performed with plastic-type reapproximation of tissues (25,26).

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