Objective: Presence of a supernumerary digit that is not a thumbComments:
Although it is appealing to believe in many cases that the supernumerary (non-thumb) digit is the most ulnar, there may be no evidence for this. When the digit is de minimus, this seems reasonable by parsimony. When it is fully formed with a supernumerary metacarpal and functional, it may be impossible to determine which of the fingers is supernumerary. Nevertheless, the designation as postaxial is reasonable given the tradition of this designation. Postaxial polydactyly has been divided into two types: A (a fully formed digit) and B (digitus minimus, or a pedunculated, non-articulating, non-functional appendage). We recognize these subtypes but note that post-axial polydactyly actually represents a spectrum from type A to type B. When the type is indeterminate, no subtype is specified.