Augmented vertical rectus transpositions: Intraoperative measurement of torsion following sequential muscle detachment.

After vertical recti transposition surgery, a torsional change may occur. We hypothesized that step-by-step monitoring of the intraoperative torsional position of the eye can avoid any unexpected complications and identify critical moments of surgery that may have adverse effects. Nine patients with sixth nerve palsy that underwent complete transposition of the superior (SR) and inferior rectus (IR) muscles to the lateral rectus muscle by means of the technique of augmented vertical recti transposition were prospectively included. The torsional position of the eye was recorded at eight stages of the procedure. We observed two distinct patterns of induced torsional deviation during partial disinsertion of a vertical rectus muscle depending on whether disinsertion began medially or laterally, after cutting about 3/4 of the muscle fibers: ¾ nasal disinsertion of the SR and ¾ temporal disinserton of the IR caused intorsion, ¾ temporal disinsertion of the SR and ¾ nasal disinsertion of the IR caused extorsion. Torsion improved after the vertical rectus was attached temporally to the sclera along the spiral of Tillaux with tying of the augmentation suture to the LR. The greatest change in torsion was from ¾ temporal disinsertion of the SR (5°extorsion), to reattachment along the spiral of Tillaux temporally (5°intorsion). The SR and IR have different torsional effects, which only appears when more than half of the fibers are detached. Augmented transposition does not cause any additional torsional effects. This intraoperative monitoring system can be used to detect unintended torsional complications, especially during transposition surgery.