Modified radiographic classification for postaxial polydactyly of the foot: An analysis of 121 digits in 98 children.

OBJECTIVE

To evaluate the imaging features of congenital postaxial polydactyly (CPP) and introduce a modified radiographic classification based on radiographic pathoanatomy of CPP.

METHOD: We retrospectively analyzed the data of 98 cases (121 digits) of CPP treated in our hospital from August 2014 to April 2023. Watanabe et al. classified polydactyly of the foot into fifth-ray duplication and sixth-ray duplication, further categorizing them by their anatomical origin into distal phalangeal, middle phalangeal, proximal phalangeal, and tarsal types. Lee subsequently refined the Watanabe classification into middle phalangeal, medial proximal phalangeal, lateral proximal phalangeal, proximal phalangeal head, floating, fourth metatarsal, and fifth metatarsal types. The modified classification is classified into four groups based on the pathoanatomy of the polydactyly: A (joint), B (epiphysis), C (bone) and D (soft tissues). Each group includes 4 subtypes according to the level of the CPP, with subtypes 1 through 4 extending from the distal phalanx to metatarsal or inter-phalangeal to tarso-metatarsal joints. The combined subtypes complete the modified classification. The modified classification includes specific subtypes from the Watanabe classification and the Lee classification.

RESULT: A total of 98 cases (121 digits) were included in the study. Among them, 13 (10.74%) and 8 (6.61%) CPPs could not be classified according to the Watanabe and Lee system. Only 3 digits (2.48%) could not be classified according to the modified classification. According to the modified classification, the most common types of CPP were C4 (44/121; 36.4%), D2 (19/121; 15.7%) and A3 (15/121; 12.4%). Additionally, 6 digits (4.96%) were classified as combine type, including B3+D3 and B3+D4 types. The modified classification showed excellent intra- (0.875) and interrater reliability (0.851) relative to the Watanabe (0.863 and 0.820) and Lee (0.793 and 0.822).

CONCLUSION

The modified classification with excellent inter- and intra-rater reliability is more comprehensive and practical compared to the Watanabe and Lee classification and convenient for clinical communication and guiding treatment choices.