Duplicated thumb bifurcation at the metacarpophalangeal joint level: factors affecting surgical outcome.

In order that the factors causing poor surgical outcome might be clarified, 175 duplicated thumbs bifurcating at the metacarpophalangeal joint level were analyzed. Cases were further divided into types A-D, based upon the details of the bifurcation form; that is, based on the connection of the radial digit to the ulnar components by either cartilage, joint, or fibrous tissue. The incidence of each type was 16% for type A (wide cartilaginous connection between phalanges), 68% for type B (2 separate phalanges), 6% for type C (cartilaginous connection to metacarpal), and 10% for type D (fibrous connection to joint capsule). Triphalangeal types and the relative size of the excised digit were determined by the preoperative radiograph. One hundred six cases were available for evaluation with a minimum of 3 years' follow-up. Good results were obtained in 50% of types A and C and in 80% of types B and D. Three phalanges in the preserve digits were observed in 10 cases and surgery on all but 1 resulted in a fair outcome. In cases where the size of the excised digit was more than 75% of the preserved digit, the results were fair or pool in 93%. The presence of subdivisions of types A and C, of 3 phalanges in the preserved digit, and of a relatively bigger excised digit were factors causing poor results, despite intensive reconstructive surgery.