Treatment of residual instability and extensor lag in polydactyly of the thumb.

Extensor indicis tendon transfers were used in six cases with residual deformity of the thumb in polydactyly. The indication was extensor lag and instability of the interphalangeal joint. At mean follow-up of three and a half years, normal stability was improved. Full extension was achieved in three cases and two cases also derived some benefits from this operation. Alignment was improved in five cases.