Classification of Middle Phalangeal Postaxial Polysyndactyly Based on Intraoperative Arthrography Is Useful for Surgical Decision-making in Children Younger Than 2 Years.

BACKGROUND The middle phalangeal type of postaxial polysyndactyly (MPPP) of the foot is a common congenital limb anomaly and is usually treated surgically at a young age. Owing to the insufficiency of radiologic evaluation due to largely cartilaginous portions of the pediatric foot, we performed intraoperative arthrography (IOA) for MPPP. This study was aimed at presenting a new classification system for foot MPPP in young children based on IOA findings and investigating its intraoperative decision-making. METHODS Thirty-seven patients aged below 2 years who underwent IOA and surgical treatment of foot MPPP in our institute between January 2018 and April 2020 were retrospectively reviewed. The mean patient age at operation was 1.31 years (range, 0.91 to 1.99 y). IOA was performed in the common proximal interphalangeal (PIP) joint. The excisional level and side were determined on the basis of the IOA findings and bony alignment between the proximal and distal phalanges for functional and cosmetic purposes. Arthrographic findings and surgical procedures were recorded. RESULTS A new classification divided MPPP into 2 major types according to the presence (type A) or absence (type B) of longitudinal contrast filling between the fifth and sixth middle phalanges. These 2 major types were further divided into 4 subtypes according to the shape of the PIP joint by contrast filling. There were 19, 15, and 3 cases of type A, B, and indeterminate IOA. Fifth and sixth ray excisions were performed in 26 and 11 cases, respectively. Interobserver reliability of the classification represented excellent agreement (Cohen κ coefficient=0.823). CONCLUSIONS Our new classification based on IOA helped determine the articular dominance and its detailed morphology, which can help predict postoperative stability and mobility of the remaining toe. IOA is a simple, safe, and useful imaging tool for the surgical treatment of foot MPPP in patients aged below 2 years. LEVEL OF EVIDENCE Level III.