Mapping the Posterior Ledge and Optic Foramen in Orbital Floor Blowout Fractures

Abstract

Background: The posterior ledge (PL) is a vital structure that supports the implant posteriorly during orbital floor reconstruction. This study describes a technique for mapping the posterior ledge in relation to the infraorbital margin in patients with orbital floor blowout fractures. The relationship between the optic foramen and posterior ledge was established. Methods: Facial computed tomography (FCT) scans of 67 consecutive patients with isolated orbital floor blow-out fractures were analyzed using Osirix. Planes of Reference for Orbital Fractures (PROF), a standardized technique for performing measurements on FCT, was used. Viewed coronally, the orbit was divided into 7 equal sagittal slices (L1 laterally to L7 medially) with reference to the mid-orbital plane. The distances of PL from infra-orbital margin (IM), and location of optic foramen were determined. Results: The greatest distance to PL is found at slice L5 (Median:30.1mm, Range:13.5–37.1mm). The median and ranges for each slice are as follows: L1 (Median:0.0mm, Range:0.0–19.9mm), L2 (Median:0.0mm, Range:0.0–21.5mm), L3 (Median:15.8mm, Range:0.0–31.7mm), L4 (Median:26.1mm, Range:0.0–34.0mm), L5 (Median:30.1mm, Range:13.5–37.1mm), L6 (Median:29.0mm, Range:0.0–36.3mm), L7 (Median:20.8mm, Range:0.0–39.2mm). The median distance of the optic foramen from IM is 43.7mm (Range:37.0– 49.1mm) at slice L7. Conclusion: Distance to PL from IM increases medially until the slice L5 before decreasing. A reference map of the posterior ledge in relation to the infraorbital margin and optic foramen is generated. The optic foramen is located in close proximity to the posterior ledge at the medial orbital floor. This aids in pre-operative planning and intra-operative dissection.