Multiple classification systems resulted from these predecessors; however, none were universally adopted. These systems did not include all congenital anomalies, and terminology varied greatly between hand surgeons from Europe and the United States. Most hand surgeons adopted the classification system proposed by Swanson in 1964. This system was based on the assumption that anomalies should be grouped by the anatomic part of the limb affected during development. He created six basic categories in his initial system: failure of differentiation of parts, arrest of development, duplications, overgrowth, congenital circular constriction band syndrome, and generalized skeletal defects. His system introduced the concept of embryologic failure and allowed a large group of conditions to be included in the failure of differentiation group. Swanson’s classification system also provided a comprehensive but simple system, which classified both complex and simple diagnoses, using straightforward language (Chung 2011; Entin et al. 1972; Kelikian 1974; Knight and Kay 2000; Manske and Oberg 2009; Sammer and Chung 2009; Swanson 1976; Swanson et al. 1983).

This classification system was reviewed by the American Society for Surgery of the Hand (ASSH), the International Federation of Societies for Surgery of the Hand (IFSSH), and the International Society for Prosthetics and Orthotics (ISPO) and modified to include a seventh category, undergrowth. The resulting classification system was published in 1974 in the orthotics and prosthetics literature and as the inaugural issue of the American volume of the Journal of Hand Surgery in 1976 (Manske and Oberg 2009; Swanson 1976). This was subsequently referred to as the IFSSH classification system and included the seven major categories, with subcategories, subclassifications, and anatomic levels of anomalies and diagnoses (Table 5) (Knight and Kay 2000; Manske and Oberg 2009; Swanson 1976; Swanson et al. 1983).

Authors who have found it difficult to classify complex cases, particularly with respect to cleft hand and symbrachydactyly, have criticized the IFSSH classification system. Knight and Kay published a more detailed version of the classification system in 2000, which attempted to include all congenital anomalies within the seven categories. The authors remarked that the IFSSH system was artificial and that a distinction between failure of formation and differentiation does not truly exist. They felt these two categories overlapped and represented a spectrum of deformity. In addition, the authors noted that complex deformities might have combinations of malformations, which do not belong to any one category. It is truly a morphological classification system without considering etiology (Buck-Gramcko and Ogino 1996; Chung 2011; De Smet et al. 1997; Knight and Kay 2000; Lamb 1990; Manske and Oberg 2009; Ogino et al. 1986; Sammer and Chung 2009).

The Japanese Society for Surgery of the Hand also published a modification of the IFSSH classification system, with the addition of two new categories: abnormal induction of rays and unclassifiable cases (Table 6) (Sammer and Chung 2009). This system attempted to include the concept of causation into the abnormal induction group as was recently suggested in experimental studies. This category included simple and complex syndactyly, central polydactyly-cleft hand-osseous syndactyly complex, and triphalangeal thumb. The authors had previously noted that typical cleft hand often involves absence of the central rays, polydactyly and syndactyly, which were classified under three different groups in the IFSSH system. Their new group attempted to include all components after embryologic studies supported the common etiology. However, the revised classification system was not universally accepted, as differences between abnormal induction and abnormal formation were not thought to be significant (Chung 2011; Manske and Oberg 2009; Naruse et al. 2007; Sammer and Chung 2009).

As knowledge was gained in the field of Genetics , increasing information became available which gave insight into some of the mechanisms of congenital anomalies. This caused many authors to reexamine the current IFSSH classification system and attempt to apply it to this new knowledge. Tonkin, in 2006, recognized the problems that arose when attempting to classify deformities in a morphologically based system, given our increasing understanding of genetic causation (Manske and Oberg 2009; Tonkin 2006). This was clearly apparent when examining “typical cleft hand” and “atypical cleft hand.” Considering the JSSH recommendations regarding a new group, “abnormal induction of rays,” Tonkin recognized that syndactyly, central polydactyly, and clefting should be grouped together; however, the genetic etiology behind the phenotype was extremely varied with a complex pathway rather than one specific gene abnormality. Because of this complex interaction in hand development, he found that simply moving these diagnoses from one group to another within the IFSSH classification system in order to attempt to introduce some understanding of etiology would not suffice, and a major reassessment was needed. Alternatively, he proposed a new classification with a descriptive focus, which identified the location of deformity with an additional subclassification based upon the tissue involved and its specific features (Manske and Oberg 2009; Tonkin 2006). He suggested that a descriptive classification system could provide a “universal language” for discussion, which would not attempt to explain causation for the deformity (Table 7) (Tonkin 2006, 489 and 495).