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The CoULD Ulnar Polydactyly Classification: Multicenter Analysis
Holly Cordray, BS
1; Apurva S Shah, MD MBA
2; Suzanne Steinman, MD
3; Douglas Hutchinson, MD
4; Donald S. Bae, MD
5; Shaun D. Mendenhall, MD
41Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA; 2The Children's Hospital of Philadelphia, Philadelphia, PA; 3Division of Plastic Surgery, Seattle Children's Hospital, Seattle, WA; 4University of Utah, Salt Lake City, UT; 5Department of Orthopedic Surgery, Boston Children's Hospital, Harvard Medical School, Boston, MA
Introduction: The Temtamy-McKusick classification defines ulnar/postaxial polydactyly with a well-developed accessory digit as type A and cases with a rudimentary pedunculated digit as type B. Surgeons widely agree on type B treatment, but type A cases present more diverse phenotypic presentations and reconstructive challenges. No system for further classification has gained broad clinical acceptance. We developed a classification based on radiographic morphology that also helps guide surgical treatment.Materials & Methods: All ulnar polydactyly type A cases at a major pediatric hospital from 2012-2022 were reviewed and combined with a multicenter cohort from the Congenital Upper Limb Differences (CoULD) Registry. Preoperative radiographs were reviewed to determine morphologic themes and propose subtypes. Clinical relevance was evaluated by discussion and analysis of operative notes to confirm that each subtype corresponds to a distinct reconstructive plan. Four attending pediatric hand surgeons classified all radiographs; inter-rater and intra-rater reliability were determined by Cohen's ?. Results: The cohort included 125 type A hands from 84 patients (48.8% bilateral). Fifteen cases (17.9%) were syndromic and 37 (44.0%) reported a family history. Six subtypes emerged from radiographic analysis, described in Table 1. Our classification is based upon the proximal extent of the skeletal "duplication,” comprising A1-Hypoplastic, A2-Phalangeal, A3-Divergent Metacarpophalangeal, A4-Bifid Metacarpal, A5-Duplicated Metacarpal, and A6-Complex types (Figure 1). We propose a reconstructive plan for each subtype to assist with surgical decision-making, outlined in Table 2. Inter-rater reliability was almost perfect (? = 0.96).
Raters agreed that all cases were classifiable, achieving 96.8% initial agreement. Intra-rater reliability after a two-week interval was likewise almost perfect (? = 0.89).
Conclusions: The CoULD Ulnar Polydactyly (CUP) Classification is feasible, comprehensive, and relevant to operative management. Its ability to describe all cases in a national sample endorses suitability for widespread use, covering more phenotypic variation than the only previously proposed system. The CUP Classification received approval from all CoULD Registry sites, with potential to frame the care pathway and standardize outcomes for this congenital hand difference.
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