Thumb duplication at the metacarpophalangeal joint. Management and a new classification.

Duplication at the metacarpophalangeal joint level (Wassel Type IV) is the most common type thumb duplication (polydactyly), accounting for 50%. It can be subdivided into 4 types: (A) hypoplastic (12%), (B) ulnar deviated (64%), (C) divergent (15%), and (D) convergent (complex) (9%). Type D has the most complex bone and soft tissue anomalies and is most likely to have residual deformities. A surgical protocol emphasizing early operation within 1 year of age, 1 stage osteotomy, meticulous collateral ligament repair, and abductor pollicis brevis tendon reattachment is presented. Twenty-one cases with an average followup of 5.25 years were reviewed. The cosmetic and functional results were satisfactory. Of a score system of 20 points, the mean score was 17.9. All except 1 patient had a stable metacarpophalangeal joint. Fifteen patients had a good range of movement, and 17 patients are satisfied with the outcome of surgery. Scar hypertrophy occurred in 2 patients.