[Polydactyly of the hands. Recommendation for expanded classification]

The few anatomical findings summarized in the literature have now been expanded by our own anatomical dissections on four hands of still-born infants with postaxial polydactyly, and by intra-operative microsurgical investigations of 25 polydactylous hands. New experimentally-based knowledge of embryology helps interpret the morphogenesis and specific anatomy of polydactyly. It can be postulated that both the location and definite form of polydactyly are a function of the location and extent of initial excessive cell proliferation and disturbance of cell necrosis in the hand blastema. The conclusive discussion of special findings regarding anatomical structures shows regular pattern formations which lend themselves to a broader classification. The classification of malformations of the hand by Temtamy and McKusick was used as a framework for the classification of polydactyly, whether it was existing as an isolated form or as part of a syndrome. The osteological types I to VI found by Wassel in thumb duplication are confirmed by our anatomical findings. Special coding of anatomical findings enabled us to identify four variants and three forms, depending on the development of the digital palmar arteries and nerves. For the triphalangeal pre-axial fingers and the post-axial fifth finger, the five osteological types described by Müller and those described by Duhamel are increased to ten. Comparison with our anatomical findings shows four variants of these osteological types. For post-axial polydactyly, types XI through XIV, existing in three variants, have been defined.