The patient was a 1-year-old girl with ipsilateral polydactyly of the thumb, and hypoplasia of the thumb and thenar muscle. The radial thumb had no nail, and radiography revealed a proximal phalanx and metacarpal, but no distal phalanx. The ulnar thumb was a floating thumb, and a distal phalanx and an incomplete proximal phalanx were noted on radiography. On-top plasty was performed to reconstruct the morphology of the thumb and to preserve sensation. We transposed the ulnar floating thumb to the top of the radial thumb as a pedicle flap with the digital nerve and artery of the floating ulnar thumb. As angiospasm occurred during surgery, the operation was changed to a two-stage procedure. The postoperative course was uneventful, and function and morphology of the reconstructed thumb remain improved as of 2 years postoperatively. Radiography revealed bone union at the level of osteosynthesis. In such cases, hypoplasia of the vessels may warrant a two-stage procedure to reduce the risk of angiospasm and congestion.
