Polydactyly (Preaxial and Postaxial)
Pertinent Anatomy and Classifications
Polydactyly can be divided based on the region of the hand involved into preaxial (radial), central, and postaxial (ulnar)—with variants on these categories (i.e., ulnar dimelia and mirror hand). However, discussion within this chapter will be limited to preaxial and postaxial polydactyly. According to the Oberg, Manske and Tonkin (OMT) classification, polydactyly falls into Group 1 or “malformations” and into the subtype “failure of hand plate formation/differentiation.” Morphologically polydactyly types can be described based on the duplicated digits’ location, size, individual component development, mobility, and joint stability.
Preaxial polydactyly—also called thumb duplication, thumb polydactyly, radial polydactyly, split thumb—occurs in 1 per 3000–10,000 live births, most commonly in males, and is more common in children of Asian and Native American descent. An ethnic predilection between Caucasians and African Americans is controversial with some sources citing a higher occurrence in Caucasians, while others report equal representation. The etiology is commonly attributed to delayed involution of the apical ectodermal ridge on the radial side of the hand. It is often unilateral and from sporadic mutations. Triphalangism is an exception that is more likely to be hereditary, associated with autosomal dominant inheritance, and associated with systemic syndromes that benefit from referral to a geneticist—including Blackfan–Diamond anemia, Holt–Oram syndrome, Bloom syndrome, Carpenter syndrome, and Ullrich-Feichtiger syndrome. Although many classification systems have been described, the most common clinically utilized system was described by Wassel and is based on the level of the duplication. Starting at the tip of the digit and moving from distal to proximal, Type I involves a split in the midportion of the distal phalanx, Type II involves a split at the distal interphalangeal joint, and so on ( Fig. 8.1 ). Odd classification numbers involve bifurcation of the duplicated thumbs within the phalanx or metacarpal, while even numbers bifurcate at a joint. Triphalangism, or Type VII, usually bifurcates the metacarpophalangeal (MCP) joint (similar to Type IV) but one of the duplicated thumbs has three phalanges rather than two ( Fig. 8.2 ). Type IV is the most common, making up 33%–46% of cases, followed by Type VII (20%–30%) and Type II (9%–28%). Type V (5%–10%), Type III (6%–14%), Type VI (3%–14%), and Type 1 (0%–3%) are less common. Of note, Wassel did not include a category for thumb triplication or for a rudimentary preaxial thumb or “nubbin” attached only by skin and neurovascular pedicle ( Fig. 8.3 ).
Postaxial polydactyly occurs more often (10:1) in African Americans (1 per 139–300 live births) and is less common in Caucasians (1 per 1340–3000 live births). It is more commonly hereditary, inherited in an autosomal dominant pattern with incomplete penetrance, with one of the child’s parents noting a history of similar features as a child, especially in African American children. When the child is Caucasian, it is more likely to be associated with various syndromes with systemic malformations such as Trisomy 13, Ellis-van Creveld syndrome, Laurence–Moon–Bardet–Biedl syndrome, and Meckel syndrome. When it is syndromic, the inheritance pattern is often autosomal recessive, and these patients should be referred for a genetics workup, an echocardiogram, and a renal ultrasound. Temtamy and McKusik described a classification system for postaxial polydactyly where Type A is a partially developed extra digit that articulates with either the fifth metacarpal or its own additional metacarpal, while Type B is a rudimentary digit connected only by a skin bridge and a neurovascular pedicle. Although postaxial polydactyly is more common in African Americans, this is only true for Type B postaxial polydactyly while Type A does not have racial predilection. Stelling and Turek proposed a modification of this classification with Type B being reclassified as Type 1, and Type A being divided into Type 2 (if the extra digit articulates with the fifth metacarpal) and Type 3 (if the extra digit contains its own metacarpal).
Preoperative Evaluation
Genetic counseling should be sought for all cases of syndromic involvement. Preoperative consultation with a hand therapist can be beneficial for children with polydactyly who have substantial functional deficits. By observing the child’s extra digit in resting stance and during play or object manipulation, one can notice preferential use of one of the duplicated digits (usually the ulnar-most thumb in preaxial polydactyly) that is the most functional portion that should be maintained during surgery. If there is unilateral involvement, the therapist observes the noninvolved side to assess the baby or child’s “normal” grasp and pinch. Lack of functional pinch and grip patterns can be a sign of substantial joint instability, which should be documented and communicated to the surgeon. Both passive and active ROM can be measured, documented, and compared to the contralateral side, which can assist in preoperative counseling, as a joint (i.e., interphalangeal joint in a Type IV preaxial polydactyly) that does not bend preoperatively will likely not bend postoperatively. Use of developmental assessment tools such as the HELP and PDMS scales can provide an overview of function in various areas of development including fine and gross motor skills and adaptive/self-help areas, while the Pediatric Outcomes Data Collection Instrument (PODCI) can provide a measure of surgical outcomes (see Tables 8.1–8.3 ). The Hawaii Early Learning Profile (HELP) provides an overview of function in various areas of development including fine and gross motor skills and adaptive/self-help areas (see Table 8.1 ). For a more thorough assessment of fine motor abilities, the Peabody Developmental Motor Scales (PDMS) is recommended (see Table 8.2 ). According to the PDMS, a baby begins to grasp placed toys in the hand at 3–6 months and uses fingers and thumbs to grasp at 6–9 months. The ability to use tip-to-tip pinch of a small object occurs around 9 months. The PODCI questionnaire is a patient-based instrument for monitoring surgical outcomes in pediatric patients across a wide range of ages (see Table 8.3 ).
Age range
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Age range
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