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Synpolydactyly of the Hand: An Updated Classification System
Apurva S. Shah, MD MBA1, Emily M Graham, MD1, Andrea S Bauer, MD2, Suzanne Steinman, MD3, Shaun D. Mendenhall, MD1 and Lindley B Wall, MD4, (1)The Children's Hospital of Philadelphia, Philadelphia, PA, (2)Department of Orthopedic Surgery, Boston Children's Hospital, Harvard Medical School, Boston, MA, (3)Division of Plastic Surgery, Seattle Children's Hospital, Seattle, WA, (4)Washington University School of Medicine, St. Louis, MO

Synpolydactyly is a rare congenital hand difference characterized by central polydactyly and syndactyly. In 2016, Wall et al. developed radiographic classification criteria for synpolydactyly based on five common polydactyly patterns; 25% of reported cases were unclassifiable using this system. This study determined if a modified Wall classification would better capture the range of osseous and soft tissue phenotypes with acceptable inter- and intra-rater reliability.
A multicenter pediatric hand surgery team developed a modified classification system describing the location and morphology of the polydactylous portions and the complexity of the syndactylous component of synpolydactyly (Table 1). Subsequently, three hand surgeons independently reviewed radiographs and clinical photographs of synpolydactyly from the Congenital Upper Limb Differences (CoULD) registry. Each rater was asked to apply the modified classification to each hand. More than 2 weeks later, the cases were distributed again for reassessment. Radiographic inter- and intra-rater reliability were assessed using percent exact agreement and Fleiss kappa scores, with scores >0.80 deemed as substantial agreement.
Thirty-three hands from 21 patients were included in this investigation. All 33 cases were classifiable with the updated classification schema, whereas only 25/33 (76%) were classifiable by the original system proposed by Wall et al (p=0.003). Most cases presented with extranumerary bones starting at the metacarpals (42%), followed by the proximal phalanges (27%), middle phalanges (24%), and distal phalanges (6%). Morphology of the most proximal polydactylous bone was predominantly bifid/synostotic (54.5%) or rudimentary (36.4%). Polydactylous bones immediately distal were commonly bifid/synostotic (45.5%) or of normal morphology (36.4%). Across all cases, simple incomplete and complex syndactyly were more common than simple complete syndactyly (36.4% and 36.4% vs. 27.3%, respectively) (Figure 1). Inter-rater and intra-rater reliabilities were substantial with Fleiss kappa scores of k=0.83 and k=0.89, respectively, and an overall percent exact agreement of 87.5%.
This modified Wall classification system allows increased capture of the bony and soft tissue differences seen in synpolydactyly and is readily adoptable across users. Using the proposed classification system will permit more accurate scientific reporting and may contribute to how synpolydactyly is categorized and managed.

CoULD Synpoly Figure 1 AAHS_10July23.png
CoULD Synpoly Table 1 AAHS_10July23.jpg
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