Subclassification and surgical algorithm for Wassel type III thumb polydactyly: a retrospective analysis of 94 cases

INTRODUCTION: Wassel type III thumb polydactyly is characterized by a bifid proximal phalanx. Although a relatively rare subtype, it is considered one of the most challenging types to reconstruct as often the distal duplication requires some form of combination procedure for optimal aesthetic outcomes. METHODS: A retrospective review of 94 patients with Wassel type III thumb duplication analysed patient characteristics, radiographic features, surgical techniques, and outcomes. A modified classification was designed based on the osseous morphological patterns and interphalangeal (IP) joint stability. Subtype III-A showed similar combined proximal phalangeal and metacarpal head widths with narrow inter-duplication distance; subtype III-B showed a wider proximal phalanx with unstable IP joint; subtype III-C showed a wider proximal phalanx (A > B) with a stable IP joint; and subtype III-D showed divergent alignment at the metacarpophalangeal joints and convergence at the IP joints. RESULTS: The median age at surgery was 15 months with a median follow-up of 36.5 months. Optimal results were observed with these surgical techniques: a modified Bilhaut-Cloquet (BC) procedure for the distal and distal-proximal phalanges in subtype III-A and III-B, respectively; minor thumb resection with reattachment of the abductor pollicis brevis and collateral ligament for subtype III-C; and reconstruction similar to Wassel type IV-D for subtype III-D. Postoperative thumb deviation correlated with mismatched surgical techniques. Minor nail ridging after the modified BC procedure diminished over time. CONCLUSION: This study proposes a subtype classification and surgical algorithm to guide management of Wassel type III thumb polydactyly to produce optimal aesthetic and functional results. Future prospective multicenter studies with standardized outcome measures are needed to validate these findings and optimize surgical protocols. LEVEL OF EVIDENCE: IV.