DUPLICATED THUMB BIFURCATION AT THE METACARPOPHALANGEAL JOINT LEVEL -FACTORS AFFECTING SURGICAL OUTCOME

In order that the factors causing poor surgical outcome might be clari fied, 175 duplicated thumbs bifurcating al the metacarpophalangeal joi nt level were analyzed. Cases were further divided into types A-D, bas ed upon the details of the bifurcation form, that is, based on the con nection of the radial digit to the ulnar components by either cartilag e, joint, or fibrous tissue. The incidence of each type was 16% for ty pe A (wide cartilaginous connection between phalanges), 68% for type B (2 separate phalanges), 6% for type C (cartilaginous connection to me tacarpal), and 10% for type D (fibrous connection to joint capsule). T riphalangeal types and the relative size of the excised digit were det ermined by the preoperative radiograph. One hundred six cases were ava ilable for evaluation with a minimum of 3 years' follow-up. Good resul ts 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 si ze of the excised digit was more than 75% of the preserved digit, the results were fair or poor in 93%. The presence of subdivisions of type s A and C, of 3 phalanges in the preserved digit, and of a relatively bigger excised digit were factors causing poor results, despite intens ive reconstructive surgery.