Posterior fixation sutures: A revised mechanical explanation for the fadenoperation based on rectus extraocular muscle pulleys

PURPOSE: To determine the effect of the rectus extraocular muscle pulleys o n the fadenoperation, an operation designed to fixate the posterior muscle belly to the underlying retroequatorial sclera, METHODS: First, duction into the field of action of the operated-on muscle was quantified retrospectively after fadenoperation, Magnetic resonance ima ging was then performed prospectively after surgery to verify anatomic chan ges. Forced duction testing was performed prospectively during surgery befo re and after faden placement. Finally, computed tomography in a cadaver con taining radiographic markers was performed prospectively to determine the e ffect of fadenoperation on the position of the medial rectus insertion rela tive to its pulley, RESULTS: Mean maximum adduction after medial rectus fadenoperation was 18 d egrees (range, 10 to 25 degrees; 13 eyes). Fadenoperations combined with la rge medial rectus recessions restricted adduction more than fadenoperations combined with smaller recessions (P = .019), but even fadenoperations with out recessions substantially restricted adduction, Mean maximum abduction a fter lateral rectus fadenoperation was 40 degrees (range, 25 to 45 degrees; four eyes), Axial magnetic resonance imaging in two eyes demonstrated a sm aller loss of muscle tangency to the globe during contraction than predicte d by geometric models. Forced ductions in nine patients performed immediate ly after faden placement demonstrated a new mechanical restriction to ducti on toward the operated on muscle. Cadaveric computed tomographic scans demo nstrated posterior displacement of the medial rectus pulley during adductio n after fadenoperation. CONCLUSIONS: Posterior fixation sutures do not significantly decrease muscl e torque during contraction. Because posterior fixation sutures posteriorly displace the pulley sleeve during duction toward the operated on muscle, t he mechanical restriction after surgery probably represents the force defor ming the pulley. This mechanical restriction may account for the limitation in duction seen after fadenoperation, (C) 1999 by Elsevier Science Inc. Al l rights reserved.