Modified Wassel-Flatt Type III Radial Polydactyly: Subtypes and Their Outcomes

Purpose: We aimed to subdivide modified type III radial polydactyly and evaluate the applied surgical procedures and outcomes according to the subtypes.

Methods: This study included 32 thumbs of 32 patients treated for modified Wassel-Flatt type III radial polydactyly from March 2008 to December 2018. Each patient was subclassified into parallel, divergent, and convergent types according to the alignment of the duplicated digit. The parallel type was further divided according to the treatment method applied. The parallel A group comprised patients treated with reconstructing the radial collateral ligament of the interphalangeal (IP) joint after removing only the distal phalanx and preserving the proximal phalanx of the extra digit, and the parallel B group comprised patients treated with excision of the extra digit at the bifurcation site of the proximal phalanx. We evaluated the Japanese Society for Surgery of the Hand scores and radiographic angulation of the IP and metacarpophalangeal joints at a mean follow-up of 38 months.

Results: Fourteen cases were parallel type (6 and 8 in the parallel A and B groups, respectively), 14 were divergent type, and 4 were convergent type. Patients in the parallel A group had significantly better IP and metacarpophalangeal joint angulation and Japanese Society for Surgery of the Hand scores than those in the parallel B group. Patients in the parallel A group had significantly better Japanese Society for Surgery of the Hand scores than those in the divergent and convergent groups.

Conclusions: Reconstructing the radial collateral ligament of the IP joint after removing only the distal phalanx and preserving the proximal phalanx of the extra digit was associated with better outcomes than the excision of the extra digit at the bifurcation site in the parallel type cases. The parallel type treated with proximal phalanx preservation and ligament reconstruction had better clinical outcomes than other types of modified Wassel-Flatt type III radial polydactyly.

Type of study/level of evidence: Prognostic IV.