Arthrography in thumb polydactyly with bifurcation at the interphalangeal or metacarpophalangeal joints provides practical information at surgery.

We carried out arthrography in 19 thumbs of 18 patients in whom duplication was observed at the interphalangeal (Wassel type II) or metacarpophalangeal (Wassel type IV) joints on radiographs. The average age at surgery was 12.3 months and average duration of post-surgical follow-up was 21.3 months. Based on the arthrographic findings, the types of cartilaginous connections were subdivided into five groups. In group 1, there was a cartilaginous connection at the base of duplicated phalanges. In group 2, there was a cartilaginous connection of the radial digit between the distal and proximal phalanges, or between the proximal phalanx and metacarpal. In group 3, the phalanges separated at a common joint without any cartilaginous connection. In group 4, the radial digit demonstrated fibrous attachment to the capsule without any joint formation. In group 5, each joint was completely separated without any cartilaginous connection. These arthrographic findings could not be detected on radiographs. Different surgical procedures were carried out according to the form of cartilaginous connection.