Triangulating the ledge: radiographic study of the floor of orbit and derivation of a novel template

In orbital floor reconstruction, the need for the orbital implant to reach the exact position of the posteromedial ledge is essential, but owing to the complex anatomy of the region, visualisation of the ledge may be difficult. Several morphometric studies, both radiographic and cadaveric, have calculated a mean length from the orbital rim to the ledge. However, those linear measurements are unreliable and possess a higher margin of error for intraoperative guidance. This study attempts to triangulate the position of the posterior ledge from three easily accessible and reproducible points on the orbit and tries to provide a better guideline. A total of 50 patients (25 male and 25 female) with no history of orbital trauma or orbital surgery were selected randomly for this study. Computed tomography (CT) of both orbits, was done from three anatomically consistent and reproducible points: the infraorbital rim just above the infraorbital foramen (point A), hamulus lacrimalis (point B), and the most anterior point of the inferior orbital fissure (point C). The distance from these landmarks to the posterior ledge was measured using DICOM imaging software. A polygonal template was fabricated using the data obtained, which was used for intraoperative guidance. The mean (SD) distance to the posterior ledge from point A was 32.99 (1.35) mm, from point B was 31.36 (1.31) mm, and from point C was 20.19 (1.40) mm. There were no significant differences between left and right orbit or between male and female subjects. The template guides the shape, size, and direction of the orbital implant, reducing the risk of undersized or misplaced implants.