Magnetic resonance imaging after surgical transposition defines the anteroposterior location of the rectus muscle pulleys

Introduction: Connective tissue pulleys serve as the functional origins of the rectus extraocular muscles (EOMs) and constrain the sideslip of the pos terior EOM bellies after transposition surgery. Anterior to the pulleys, EO M paths appreciably displace to reach their transposed insertions. The infl ection points in the EOM paths from minimal posterior displacement to maxim al anterior displacement should define the anteroposterior location of the EOM pulleys after transposition. Methods: Contiguous cross-sectional magnet ic resonance images were obtained in planes perpendicular to the long axis of the orbit over its entire anteroposterior extent before and after operat ion in 6 patients who underwent rectus muscle transposition surgery. Four p atients underwent full tendon width transposition of the vertical rectus mu scles laterally for lateral rectus palsy. Two of these patients had augment ation of the transposition with sutures that fixated the temporal margins o f the transposed muscles posteriorly to the-sclera adjacent to the borders of the lateral rectus muscle. One patient underwent full tendon width trans position of the horizontal rectus muscles superiorly for superior rectus pa lsy. One patient underwent full tendon width transposition of both lateral rectus muscles inferiorly for "A" pattern esotropia. Paths of EOMs were def ined relative to the area centroid of the orbit. Pulley locations were infe rred from EOM paths. The postoperative change in EOM pulley location was ob tained by subtracting the preoperative pulley location from the postoperati ve pulley location for each image plane. Results: For all patients, th post operative change in EOM belly location was relatively small posterior to th e globe-optic nerve junction. The 2 patients with abducens palsy who underw ent placement of posterior augmentation sutures, however, demonstrated a si gnificantly larger displacement of the posterior vertical rectus paths comp ared with similar patients who did not receive augmentation sutures. For a II horizontally transposed vertical rectus muscles and inferiorly transpose d lateral rectus muscles, the inflection of the EOM path began 3 mm anterio r to the globe-optic nerve junction. For the superiorly transposed medial r ectus muscle and lateral rectus muscle, the inflection began 6 mm anterior to the globe-optic nerve junction. Conclusions: The anteroposterior locatio ns of the EOM pulleys can be defined by analysis of EOM displacement after transposition surgery. Augmentation of transpositions by posterior suturing displaces the EOM pulleys substantially more than nonaugmented transpositi ons.