Duplication of the metacarpal

Partial or complete duplication of the duplicated thumb metacarpal and all distal bones encompasses groups 5 and 6 in the Wassel classification. At this level, a number of considerations are relevant:

• the ulnar metacarpal is usually dominant but C-shaped (a delta bone); this may require a corrective osteotomy
• thenar muscles need to be transferred from the discarded digit to the remaining digit
• the first web may be tight and require release
• if the ulnar digit is too ulnar on the trapezium, it can be translocated to the retained base of the radial thumb metacarpal to give a better axis for function