Duplication of the thumb. A 20-year retrospective review.

Thumb duplication is a common congenital abnormality accounting for 6.6% of all hand deformities. The object of the primary surgery is to achieve a thumb with aligned joint surfaces and epiphyses perpendicular to the long axis, central flexor and extensor tendons, and adequate collateral ligaments. Experienced surgeons with an understanding of the abnormal anatomy and knowledge of the numerous refinements in technique cannot guarantee a flawless result. Of 43 cases treated in this Unit during the period 1970-1989 49% were noted to have secondary deformities. Angulation at the IP and/or MP joints were the most commonly observed problems. Unsatisfactory results were seen with a greater frequency following correction of the more complex deformities.