Polydactyly

Etiology

Polydactyly may present as an isolated trait or may occur in conjunction with other syndromes. Some patients may have a family history. Polydactyly may be associated with other diseases or syndromes such as Diamond-Blackfan anemia, Fanconi anemia, Ellis-van Creveld syndrome, VACTERL (vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal anomalies, and limb abnormalities), trisomy 13, and trisomy 21.[2][3][4][5]

Advanced molecular techniques have identified multiple gene loci that are responsible for the development of polydactyly which includes GLI3 which is associated with Greig cephalopolysyndactyly syndrome, the sonic hedgehog gene (SHH), fibroblast growth factor (FGF), homeobox protein aristaless-like 4 (ALX4), homeobox D (5’-HoxD), ZNF141, MIPOL1, IQCE, and PITX1.[1][3][6]

Epidemiology

According to the study by Finley et al. in the USA, polydactyly is 10 times more common in Black versus White males and 22 times more common in Black females than White females. The incidence of polydactyly is 2.3 per 1000 in White males, 13.5 per 1000 in Black males, and 0.6 per 1000 in White females and 11.1 per 1000 in Black females.[7] 

The nature of polydactyly in the world seems to be influenced by genetic and ethnic factors. The incidence of preaxial polydactyly is 0.08 to 1.4 in 1,000 live births. It is more common in Whites and also relatively frequent in Native American and Asian patients.[8][9]

In contrast, postaxial polydactyly is 10 times more frequent in the Black population compared to Whites. Postaxial polydactyly is more common than preaxial polydactyly and is frequently associated with other congenital defects. Its prevalence is 1-2/1000 live births.[1][10]

Pathophysiology

Two theories are responsible for the development of polydactyly. One is a disorder in the programmed cell death during fetal limb development, and another is the genetic mutations of some gene loci. Limb development and growth are controlled by at least two signals, including the zone of polarizing activity (ZPA), where the sonic hedgehog molecule is found to mediate ZPA activity. Another signal is the apical ectodermal ridge (AER) that expresses fibroblast growth factors.[8][11]

Preaxial polydactyly is due to the disturbance of the ectodermal and preaxial mesodermal apoptosis during the early embryologic period, approximately before the eighth week. Abnormal expression of genes such as the sonic hedgehog gene, Hox genes, bone morphogenic proteins, and GLI3 in the zone of polarizing activity is responsible for the development of preaxial polydactyly.[8]

History and Physical

Patients with polydactyly may present in infancy or later and may appear in isolation or with other birth defects. Polydactyly of hand and foot can be classified into 3 main categories: preaxial, central, and postaxial. In 1995, the congenital hand committee of the International Federation of Societies for Surgery of the Hand decided to change the terms preaxial and postaxial polydactyly to radial and ulnar polydactyly. Radial polydactyly involves the thumbs, and ulnar polydactyly involves little fingers. Central polydactyly includes the ring, middle, and index fingers, and is often associated with syndactyly and cleft hand.[3][12] 

The most common form of polydactyly of hand is radial polydactyly, and the prevalence rate is higher in Whites compared to other ethnic populations. Most cases are sporadic and unilateral without any associated systemic problems. In these cases, the extra digits are seen anterior to the thumb. Radial polydactyly was further classified by Wassel in 1969 into seven subtypes, serially from type I to type VII, and it is used by hand surgeons very effectively during the management of the patients.[8]Ulnar polydactyly was classified by Temtamy and Mckusick into two categories, type A and type B. The terms radial, central, and ulnar are used to describe the polydactyly of the upper limb.

In contrast, the terms tibial, central, and fibular are used to describe polydactyly of the lower limb. Polydactyly of the lower limb was classified by Swanson based on the presentation of the extra digit on the foot. If extra digit affects the great toe, it is called tibial polydactyly, and when it affects the little toe, it is called fibular polydactyly. When the central three digits are affected, then it is called central polydactyly.[13]

Evaluation

At 9 weeks of intrauterine life, fetal finger buds can be seen through transvaginal sonography. Once polydactyly is detected, the clinician should be alert to evaluate for further anomaly screening. A thorough ultrasound evaluation should be done to image the heart, kidneys, nervous system, and limbs for identification of syndromes such as trisomy 13, Meckel-Gruber syndrome, Diamond-Blackfan anemia, Fanconi anemia, etc. For the diagnosis of isolated polydactyly, a follow-up ultrasound between 17 and 34 weeks should be done with a biometric profile.[3][14][15]

After birth, radiographic investigations should be carried out once the infant is confirmed to have polydactyly to evaluate for bony elements in the extra digit. Before surgery, radiologic findings are needed to see the accurate anatomy of the extra digits and what type of surgery is required. Anteroposterior (AP) and lateral radiographs should provide adequate information for treatment purposes.[3][16]

Treatment / Management

Treatment of Polydactyly of the Hand

The treatment of polydactyly depends on the complexity and location of the deformity. If it is a simple surgery, an outpatient surgical procedure may be enough. If it is more complex, then the surgery can involve the bones, ligaments, and tendons. Minor cases can be treated by tying off the base of extra digits, which interrupts blood flow and causes the digit to fall off.[17][18] 

In the early postnatal period, type A ulnar or postaxial polydactyly can be corrected by suture ligation or excision in the office under local anesthesia. After the suture ligation, there is an increased risk of painful neuroma formation. Sharp excision is another alternative for ulnar polydactyly to avoid neuroma formation. Type B ulnar polydactyly is also corrected by suture ligation that induces necrosis of the distal segment, which causes the autoamputation of extra digits approximately 10-20 days later.

If preaxial or radial polydactyly involves the radial hand and thumb, the functional and stable thumb should be ensured by using reconstructive techniques. Due to the functional importance, consultation with a surgeon who is expert in hand surgery is typically needed.[3][19][20][21](B3)

Treatment of Polydactyly of the Foot

Surgical therapy is indicated to enhance cosmesis and to improve quality of life. In order to minimize the effect on development and walking, surgery should be done at the age of approximately 1 year. Management of polydactyly of the foot seems to be simple at first glance, but careful consideration is needed before and during the surgical correction due to the multiformity of its configuration. But as a whole, treatment should be individualized.

Most medial and lateral digits of tibial and fibular polydactyly are usually resected. Care must be taken to minimize hallux varus in the case of tibial polydactyly. Because of its rare presentation, the treatment of central polydactyly of the foot is not well described. But in most of the cases, a racquet-shaped incision can be used to excise supernumerary central digits.[6](B3)

Differential Diagnosis

Polydactyly may be present in isolation or may be associated with the components of some syndromes including the following: 

• Trisomy 13
• Meckel syndrome
• Down syndrome
• Acrocallosal syndrome
• Basal cell nevus syndrome
• Diamond-Blackfan anemia
• Bardet-Biedl syndrome
• Biemond syndrome
• Fanconi anemia
• Ellis van Creveld syndrome
• McKusick-Kaufman syndrome
• Mirror hand deformity (ulnar dimelia)
• Mohr syndrome
• Oral-facial-digital syndrome
• Pallister-Hall syndrome
• Rubinstein-Taybi syndrome
• Short rib polydactyly
• VACTERL (vertebral defects, anal atresia, cardiac defects, trachea esophageal fistula, renal anomalies, and limb abnormalities) association

Prognosis

For children with isolated polydactyly, the prognosis is excellent. Most children can use their fingers and toes after surgery with a full range of motion. If polydactyly presents as a part of the syndrome, the prognosis may be poor due to the presence of other birth defects rather than the effect of polydactyly.

Complications

In polydactyly of the hand, bleeding and anesthetic complications may occur during the perioperative period. Functionality can be decreased later due to the contracture or ligamentous laxity. A painful neuroma is another complication, especially when using suture ligation, and it occurs at the treatment site. Beneath the suture ligation site, a painful neuroma forms because the digital nerves of the extra digit are cut off at the skin level, so it cannot retract in the soft tissues. As a result, the children are prone to injury to the skin tag resulting in skin breakdown.[3]

In polydactyly of the foot, hallux varus is the most common complication of tibial polydactyly that may lead to subsequent surgical correction. Fibular polydactyly may have a residual angular deformity.