The Wassel classification is commonly used to describe congenital thumb polydactyly. This was first described in 19691, and separates duplicate thumbs into 7 distinct types by the level of duplication. We report a thumb duplication that does not fit the Wassel classification and propose a new addition to the classification based on this case.
The patient was noted to have a complete duplicate distal and proximal phalanx. The metacarpal was neither bifid nor duplicated. The radial sided metacarpal was complete, however the ulnar sided metacarpal was a metacarpal head only, with no metacarpal shaft or base associated with this digit. The metacarpals were radiologically and clinically separate.
The radial sided digit had both an FPL and EPL, however it lacked an ulnar collateral ligament and adductor insertion. The ulnar sided digit lacked a FPL and EPL, however had an intact UCL and the insertion of the adductor pollicis brevis (APB).
Our patient underwent excision of the ulnar sided digit with preservation of the UCL and APB. These were then used to reconstruct the UCL for the ulnar thumb MCPJ and the APB was reattached. The patient was reviewed three months post operatively with clinical and radiological follow up, with good functional outcome and Kapandji score of 9.
We propose that this thumb would be best classified a Wassel classification Vb. We review the literature around radial polydactyly and propose an amendment to the Wassel classification to include this Vb subtype.