The authors present a new classification of polydactyly based on radiomorphological alterations. The malformations are defined in two directions, as in a system of coordinates. The longitudinal arrangement is based on the pathogenetic principle of bifurcation of a finger or a toe ray from distal to proximal. We accordingly divided polydactylies into five types: distal phalanx, middle phalanx, proximal phalanx, metacarpal or metatarsal, carpal or tarsal. The transverse arrangement indicates which rays are involved. All polydactylies, including the special forms such as rudimentary manifestations, triphalangism, and multiple duplications, can be incorporated into this simple basic scheme. Depending on their characteristics, the special forms are further subdivided, e.g., into a distal or proximal phalanx type with simple or double triphalangism, or a tarsal type with third-degree duplication and first-degree aplasia. Numerous radiological examples and schematic drawings illustrate the classification. The advantage of the classification is that it depends exclusively upon the skeletal finding and all manifestations are registered according to a simple scheme longitudinally and transversely. This makes them codifiable for the computer and suitable for multicenter studies. The special forms, the rudiment, triphalangism, and multiple duplication, can easily be further subclassified. Moreover, the nomenclature is simple and is oriented to anatomical terminology.

The authors report on experience gained in the surgical treatment of eight patients with congenital hallux varus associated with polydactyly of the big toe. Aside from a description of the "radiological anatomy", the paper focuses in particular on the intraoperative soft tissue findings. In addition to the supernumerary bone structures, muscle and tendon anomalies were found in all the patients. In four patients the cause of the varus malposition was found to be fibrous stands extending from the rudimentary big toe to the tarsus. In five patients the abductor hallucis muscle was found to be shortened. An analysis of the surgical results shows that these soft tissue changes must be taken into account during surgery. In addition to complete removal of the polydactylic supernumerary, fibrous strands must be resected and shortened muscles severed or elongated. In many cases, operations on the basal joint capsule and plastic surgery are also necessary.

Congenital triangular deformity of the foot bones may occur in phalanges and metatarsals. As it resembles the Greek letter delta it is called "delta phalanx" and "delta metatarsal". We report on 19 delta formations in ten patients with foot polydactyly. Our long-term follow-up of these patients indicates four stages in the ossification process: no ossification of the epiphysis; appearance of single or multiple ossification centers; unification of the ossification centers with nonosseous tissue between the diaphysis and the epiphysis; and, finally, complete ossification. Pathogenetically, the delta formation may represent an intermediate stage in the bifurcation process of a polydactylic ray. Splitting longitudinally in a direction from distal to proximal, it is the root of the bifurcated toe ray.