Background: Oligodactyly of the hand is one of the rarest congenital anomalies of upper extremities and defined as the presence of fewer than five fingers on a hand. Although it usually occurs in association with hypoplasia or absence of ulna, it can occur without abnormality of the forearm bones. The purpose of this study is to present clinical features and radiographic characteristics of hand oligodactyly with thumb. Methods: Five patients of oligodactyly with thumb who showed normal forearm bones, were evaluated. Two patients had threefingered hand with thumb, and three had two-fingered hand with thumb. We analyzed associated abnormalities of carpal and metacarpal bones and measured the lengths of radius and ulna, and width of the wrist on the simple radiographs. We also devised new classification system of oligodactyly based on the thumb deformities and locations of missing digits. Results: Syndactyly among fingers was associated in four patients, clinodactyly caused by delta bone in one, hypoplasia of the thumb in one, camptodactylies in one, symphalangism in one, and radial head dislocation in one. Considering the abnormalities of the carpal bones, the missing digits were presumed to be ulnar-sided digits in two patients, central digits in one patient and both ulnar-sided and central digits in two patients. In patients with missing of central digits, an adjacent metacarpal was hypertrophied. Although the ulnar variances were within normal range, the average lengths of radius and ulna were 6% and 5% shorter than those of contralateral normal side. The average width of the wrist was 9% narrower than that of contralateral normal side. Conclusions: Syndactyly and hypertrophied metacarpal were most commonly observed findings in the oligodactyly with thumb. Although oligodactyly with thumb may be a type of ulnar longitudinal deficiency, however, it can also be a type of central deficiency or combined type of ulnar longitudinal deficiency with central deficiency or radial longitudinal deficiency. We suggest a classification system of oligodactyly with thumb based on locations of missing digits and associated thumb deformities.
