Three cases of syndactyly, polydactyly, and hypoplastic triphalangeal thumb: (Haas's malformation).

Three cases of a complex malformation of the hand involving syndactyly, polydactyly, and hypoplastic triphalangeal thumb are presented. In all three patients, six metacarpal bones and hypoplasticity of the thenar muscles were present. In one patient, both hands, except the most radial digits of the left hand, were completely fused by soft webs as reported by Haas and Ofodile. In two other patients, the extent of the webs differed from Haas's case, but one of them was similar to Ofodile's first case. In all instances the supernumerary digit had a triphalangeal configuration and the thenar muscles were hypoplastic, often associated with some degree of webbing.