full-muscle transposition

Full-muscle transposition is a strabismus operation that moves the whole tendon of one or more rectus muscles to substitute for the action of an absent or severely deficient muscle.^1,2 The most common indication is severe lateral rectus weakness from an acquired sixth nerve palsy, and the superior and inferior recti are then moved to the insertion of the paretic lateral rectus.^1,2

A recess-resect procedure often succeeds if the paretic lateral rectus keeps some function.² If little or no abducting force remains, the transposed vertical recti supply a new source of abducting force, usually with weakening of a contracted medial rectus.^2,4 Electromyographic studies support the view that the effect of a transposition is purely mechanical, and the operation may restore only some motility in the field of the paralyzed muscle.³

Full-tendon transposition transfers more force than the Hummelsheim procedure, in which only the lateral halves of the vertical recti are moved, but carries a higher risk of anterior segment ischemia.² For that reason the entire tendon is moved only if at least one rectus insertion is intact and has not been operated on, and three rectus muscles are not detached from the globe in one procedure.^3,4