Early “90/90 deformity” of the thumb: pathogenesis and surgical correction

Early 90/90 deformity of the thumb is not only present in cases of chronic polyarthritis. In order to avoid pathological hyperextension in the distal joint, active stabilization of the metacarpophalangeal joint of the thumb can be restored by transposing and inserting the extensor indicis tendon in the proximal phalanx, at the same time maintaining the agonistic-antagonistic play of tendons. The different pathogenic forms and the surgical technique for correction of the deformity are demonstrated in this paper.