Polydactyly of the Foot

Polydactyly may be divided into three broad categories as follows:

• Postaxial polydactyly (lateral ray)
• Preaxial polydactyly (medial)
• Central polydactyly ^[16]

Postaxial polydactyly is the most common form,[7] occurring in 80% of cases, followed by preaxial polydactyly (see the image below) and then central polydactyly (~6%[15] ). The duplication may range from a well-formed articulated digit to a rudimentary digit. Abnormalities of the associated metatarsal commonly occur in polydactyly.

Other, more detailed classification systems have also been described (see Presentation).

Polydactyly may occur as an isolated trait or in conjunction with certain syndromes, and there is a positive family history in 30% of cases. The syndromes with which polydactyly has been associated include Ellis-van Creveld syndrome,[17, 18]  trisomy 13, tibial hemimelia, and trisomy 21.

Polydactyly is mostly inherited as an autosomal dominant entity with variable penetrance.[19] At least 10 loci and six genes have been identified as causing nonsyndromic polydactyly in humans, including ZNF141, GLI3,[20] MIPOL1, IQCE, PITX1, and GLI1.[21]  

Adam et al observed clinical findings in 18 cases of diabetic embryopathy and preaxial hallucal polydactyly to identify the features most suggestive of diabetic embryopathy.[22]  They found that proximally placed preaxial hallucal polydactyly, particularly when coupled with segmentation anomalies of the spine and tibial hemimelia, is highly suggestive of diabetic embryopathy. They added that diabetes in the mothers pointed to a possible genetic predisposition interacting with teratogenic effects of poor glycemic control.

The incidence of polydactyly is 1.7 cases per 1000 live births. The frequency is higher in blacks (3.6-13.9 cases per 1000 live births) than in whites (0.3-1.3 cases per 1000 live births). Polydactyly is bilateral in 50% of cases and has a slight male predilection.

According to a multicenter birth defects study, the incidence of isolated postaxial polydactyly has ranged from 6.08 per 10,000 population in Argentinians to 225 per 10,000 in Nigerians.[23]  It affects males more often than females, hands more often than feet, and left limbs more often than right limbs.

Burger et al assessed health-related quality of life (HR-QoL) in children with preaxial polydactyly of the foot, adults with preaxial polydactyly, children with postaxial polydactyly, and healthy control subjects.[24] The primary outcome was difference in the foot-specific quality of life (FS-QoL); the secondary outcome was difference in general HR-QoL according to the Pediatric Quality of Life Inventory (PedsQL). Children and adults with preaxial polydactyly scored the same in all domains. The Oxford Ankle and Foot Questionnaire (OxAFQ-c) and the PedsQL physical domain showed worse outcomes in children with preaxial polydactyly than in healthy controls and those with postaxial polydactyly. 

The patient may present in infancy or at a later date when cosmesis or shoe fit becomes a concern. Obtain a thorough family history, and exclude association with syndromes. Perform a thorough musculoskeletal examination to exclude any other congenital anomalies or signs that occur with known syndromes.

A morphologic classification of polydactyly was described by Venn-Watson (see the image below).[3]

The Venn-Watson classification is based on the configuration of the metatarsal, as follows:

• Normal metatarsal with distal phalanx duplication
• Block metatarsal
• Y-shaped metatarsal
• T-shaped metatarsal
• Normal metatarsal shaft with a wide head
• Duplicated ray

A first metatarsal bracket epiphysis (longitudinal epiphyseal bracket) may occur in preaxial polydactyly.[25]

Several decades later, Seok et al developed a classification system for polydactyly of the foot that was intended to help determine surgical plans and predict outcomes.[26]  This system consists of the following components:

• Three characters (S, indicating syndactylism; A, indicating axis deviation; and M, indicating metatarsal extension
• Three numbers (0, 1, and 2, indicating the degree of complexity of the polydactyly)

For example, the designation S1A1M2 in this system would indicate a case in which syndactylism to the adjacent toe was incomplete with the webbing involving less than half the length of the involved digits, the angulation was 15° or greater but less than 30°, and the metatarsal extension involved the shaft and more.[26]

Burger et al developed a classification system for medial foot polydactyly (the Rotterdam Foot Classification) that was based on the following four categories of anatomic features of the foot[27] :

• Duplication type
• Syndactyly
• Presence of a hypoplastic ray
• Deviation of the hallux

It is imperative that radiographs (see the images below) be obtained before surgical treatment so that the anatomy can be accurately understood and careful preoperative planning can be undertaken.[28] Anteroposterior (AP) and lateral radiographs should provide needed information. More sophisticated imaging studies (eg, magnetic resonance imaging [MRI]) should be reserved for unusual cases.

Surgery is indicated to enhance cosmesis and to improve shoe fit. It is usually performed when the patient is aged approximately 1 year, so that the effect on development and walking is minimal. Generally, surgery should be delayed until skeletal development (ossification) has occurred within the affected rays so that accurate anatomic assessment is possible.

A retrospective comparative study of 24 foot polydactyly patients (30 feet), in which patients were divided into one group that was surgically treated before the age of 5 years (median age, 1 y; range, 9 mo to 4.5 y) and a second group that was surgically treated after the age of 5 years (median age, 8.5 y; range, 6-37 y), found no significant differences between the two groups in terms of results at final follow-up (median follow-up, 16.2 y; range, 7-21 y).[29]

No absolute contraindications for surgical treatment exist. However, parents may choose not to excise the duplicate digit for personal reasons.

Surgical treatment consists of excision of the duplicated digit and reconstruction of any associated abnormalities in the remaining rays (eg, longitudinal epiphyseal bracket).[5, 12, 13, 14] A thorough preoperative examination should be undertaken, including evaluation of radiographs, to formulate an operative plan. Most patients have good-to-excellent results after surgery (see the images below). Careful surgery helps to ensure better cosmetic and functional outcomes.

Operative details

Most medial digits in preaxial polydactyly and most lateral digits in postaxial polydactyly are usually resected. This allows the foot to be narrow, with a straight medial or lateral border.

Postaxial polydactyly

In postaxial polydactyly, a racquet-shaped or oval incision is made at the base of the most lateral digit and carried through skin and fascia. Tendons are divided as distally as possible. The capsule of the metatarsophalangeal (MTP) joint is divided, and the digit is disarticulated. Care is taken to remove T or Y extensions of the metatarsal head or to reshape an expanded metatarsal head. The capsule is repaired, the skin closed, and a bandage or cast applied.

Park et al conducted a retrospective study to evaluate the operative treatment of postaxial polydactyly in 27 patients.[30] For excision of the medial toe, dorsal rectangular flap and full-thickness inguinal skin grafting were used; for excision of the lateral toe, a racket-shape incision was used. The investigators concluded that satisfactory functional and cosmetic results were obtained with dorsal rectangular flap and full-thickness inguinal skin grafting for medial toe excision and with the toe selection algorithm that was employed.

The so-called on-top plasty has been described by several authors as a successful treat,emt for certain types of postaxial polydactyly.[31, 32]

Preaxial polydactyly

In preaxial polydactyly, the medial toe is usually excised. The toe is again removed through disarticulation. Care must be taken to appropriately balance the abductor and adductor hallucis muscles and to minimize hallux varus. Correction of an associated longitudinal bracket epiphysis helps to prevent the development of hallux varus and an excessive short first metatarsal. The capsule is repaired as accurately as possible.

If the more lateral toe is hypoplastic and is excised, the intermetatarsal ligament must be reapproximated. A Kirschner wire (K-wire), left in place for 4-6 weeks, may be helpful in maintaining position and avoiding varus deformity. A soft dressing or cast may be used.

In a study of children who had preaxial polydactyly of the foot with type IV (proximal phalangeal) or type VI (metatarsal) duplication, Burger et al compared the outcomes of medial hallux excision with those of lateral hallux excision.[33] They found that foot function by virtue of plantar pressure was better after lateral hallux excision in type IV duplication and after medial hallux excision in type VI duplication. Surgeons and laypersons perceived the foot as more normal after lateral excision in type VI, whereas children reported no differences.

Berman et al described two cases of tarsal-type preaxial polydactyly (a true prehallux), a rare variant.[34] Two newborns presented with similar polydactylies in the context of multiple congenital anomalies: one with an accessory digit arising medially from the right foot at the medial malleolus and the other with an accessory digit arising medially from the right foot at the talus. Both patients underwent resection of the extra digit and reconstruction, including transfer of the accessory anterior tibial tendon arising from the preaxial extra digit to the remaining first ray. At 2 years after surgery, both patients were walking well. Transfer of the tendon prevented loss of dorsiflexion strength and foot drop postoperatively.

Central polydactyly

In central polydactyly, a dorsal racquet-shaped incision is made at the base of the duplication. The extra digit is excised through disarticulation. The intermetatarsal ligament is reapproximated before closure. A cast or orthosis may be useful postoperatively to minimize a residual widened forefoot. A careful plastic skin closure is used in all patients; cosmesis is a concern.

Osborn et al conducted a retrospective case series review of 22 patients (27 feet) who underwent surgical treatment of central polydactyly using the dorsal and plantar advancement flap technique.[35] Significant narrowing of the forefoot was achieved after surgery. This radiographic narrowing was maintained with growth after a mean follow-up of 8 years. However, persistent clinical widening of the forefoot after surgery was reported in the majority of cases (82%).

The researchers concluded that the dorsal and plantar advancement flap technique provides excellent radiographic and functional outcomes in the treatment of central polydactyly: It successfully narrows the forefoot on radiographs, and this narrowing is maintained with growth over time.[35] They advised that families be made aware that it is common for patients to experience persistent widening of the forefoot relative to normal, despite successful radiographic narrowing after surgery.

A cast or soft dressing is used. If a K-wire is used, it is usually left in place for 4-6 weeks. A walking cast allows the small child to be active and at the same time protects the surgical incision.

The patient must be monitored and evaluated for residual or future deformity.

The most common complication in preaxial polydactyly is hallux varus. This may cause pain and difficulty with shoe wearing, warranting subsequent surgical correction.

Failure to correct a longitudinal bracket epiphysis that may be associated with a duplicate great toe can result in the development of hallux varus. The deformity should be addressed when noted. The bracket can be resected to allow for untethered growth, and the varus can be corrected with capsulorrhaphy and K-wire fixation at the MTP joint. Resection and metatarsal osteotomy may occasionally be needed in the older child.[36]

Patients with postaxial polydactyly may have residual angular deformity, including angulation at the MTP joint and bowing of the metatarsal. This usually is not clinically significant.

In patients with central polydactyly, a widened forefoot is a common complication.

All patients are at risk for developing MTP joint subluxation or angular deformity and residual deformities of the metatarsal head. Incomplete excision of elements that are not yet ossified may also lead to future problems or deformity.