Isolated Type II Preaxial Polydactyly

A boy with intrauterine growth restriction was born by spontaneous vaginal delivery at 38 weeks of gestation to a 22-year-old gravida 1, para 1 mother. The pregnancy had been uneventful, with no evidence of congenital malformations on prenatal ultrasonograms. The boy’s birth weight was 2,344 g, and there were no complications at birth. 

On physical examination, the newborn’s left thumb was split in 2 on the distal aspect, with two fully formed nails (Figure A). The mother denied having taken any medications during pregnancy other than prenatal vitamins. She had no family history of supernumerary digits. 

A radiograph of the affected thumb revealed duplication of the distal phalanx and the soft tissues of the thumb (Figure B). Findings of a thorough examination for identifiable dysmorphic features were negative. Karyotyping and centromeric gene hybridization tests both reported normal results with no genetic abnormalities.

Although polydactyly is not rare, isolated type 2 preaxial polydactyly of the thumb is relatively less common compared with other types. Polydactyly is defined as postaxial (occurring on the ulnar border), preaxial (occurring on the radial border of the hand), or central (occurring between adjacent fingers). The incidence of preaxial polydactyly is reported to be as high as 1 in 3,000 births.¹ More commonly seen in the white population compared with the African American population, preaxial polydactyly also has a high incidence in the American Indian and Asian populations.²

Preaxial polydactyly has been classified into 7 types according to the level of bifurcation and the extent of the deformation³: type I, bifid distal phalanx; type II, duplicated distal phalanx; type III, bifid proximal phalanx; type IV, duplicated proximal phalanx; type V, bifid metacarpal; type VI, duplicated metacarpal; and type VII, triphalangism. Of the 7 types, type IV seems to be most common. The inheritance pattern of preaxial polydactyly usually is sporadic, except for type VII thumb polydactyly, which is associated with several syndromes including Holt-Oram syndrome, Fanconi anemia, Townes-Brocks syndrome, congenital hypoplastic anemia, and Aase syndrome.

Radiographs of the affected limb are useful to assess whether the rudimentary digit contains any skeletal elements. Surgical correction of the preaxial polydactyly is necessary in order to create a functioning thumb. Surgery is recommended in the first year of life, generally between 9 and 15 months of age. Surgical options include ablation of the digit with collateral ligament reconstruction, central resection from each of the duplicated thumbs to recreate a single digit (Bilhaut-Cloquet procedure), and the rarely indicated on-top plasty.⁴

REFERENCES 

1. Jobe MT. Congenital anomalies of the hand. In: Canale ST, Beaty JH, eds. Campbell’s Operative Orthopedics. Vol 1. 11th ed. Philadelphia, PA: Mosby Elsevier; 2008:4367-4449.
2. Leung PC, Chan KM, Cheng JC. Congenital anomalies of the upper limb among the Chinese population in Hong Kong. J Hand Surg Am. 1982;7(6):563-565.
3. Wassel HD. The results of surgery for polydactyly of the thumb: a review. Clin Orthop Relat Res. 1969;64:175-193.
4. Guo B, Lee SK, Paksima N. Polydactyly: a review. Bull Hosp Jt Dis. 2013;71(1):17-23.