Poterior fixation uture: a revied mechanical explanation for the fadenoperation baed on rectu extraocular mucle pulley

PURPOE: To determine the effect of the rectu extraocular mucle pulley on the fadenoperation, an operation deigned to fixate the poterior mucle belly to the underlying retroequatorial clera. METHOD: Firt, duction into the field of action of the operated-on mucle wa quantified retropectively after fadenoperation. Magnetic reonance imaging wa then performed propectively after urgery to verify anatomic change. Forced duction teting wa performed propectively during urgery before and after faden placement. Finally, computed tomography in a cadaver containing radiographic marker wa performed propectively to determine the effect of fadenoperation on the poition of the medial rectu inertion relative to it pulley. REULT: Mean maximum adduction after medial rectu fadenoperation wa 18 degree (range, 10 to 25 degree; 13 eye). Fadenoperation combined with large medial rectu receion retricted adduction more than fadenoperation combined with maller receion (P = .019), but even fadenoperation without receion ubtantially retricted adduction. Mean maximum abduction after lateral rectu fadenoperation wa 40 degree (range, 25 to 45 degree; four eye). Axial magnetic reonance imaging in two eye demontrated a maller lo of mucle tangency to the globe during contraction than predicted by geometric model. Forced duction in nine patient performed immediately after faden placement demontrated a new mechanical retriction to duction toward the operated-on mucle. Cadaveric computed tomographic can demontrated poterior diplacement of the medial rectu pulley during adduction after fadenoperation. CONCLUION: Poterior fixation uture do not ignificantly decreae mucle torque during contraction. Becaue poterior fixation uture poteriorly diplace the pulley leeve during duction toward the operated-on mucle, the mechanical retriction after urgery probably repreent the force deforming the pulley. Thi mechanical retriction may account for the limitation in duction een after fadenoperation.