Role of Negative Vector Orbit in Orbital Blow-Out Fractures.

Background: Negative vector orbit is defined as the most anterior globe portion protrudes past the malar eminence. The aim of the study was to evaluate the relationship between negative vector orbit and blow-out fracture location analyzing the distance between the anterior corneal surface and orbital bone with facial soft tissue in medial and orbital floor blow out fractures using orbital computed tomography (CT). Methods: Seventy-seven patients diagnosed with blow-out fractures involving the medial or orbital floor were included. Distances from the anterior cornea to lower lid fat, inferior orbital wall, inferior orbital rim, and anterior cheek mass were measured using orbital CT scans. The proportion of negative vector orbit and measured distanced were compared between medial wall fracture and orbital floor fracture. Medical records including age, sex, concomitant ophthalmic diagnosis, and nature of injury were retrospectively reviewed. Results: Forty-three eyes from 43 patients diagnosed with medial wall fracture and 34 eyes from 34 patients diagnosed with orbital floor fracture were included. There was no significant difference in the distance from the anterior cornea to lower lid fat (P = 0.574), inferior orbital wall (P = 0.494), or orbital rim (P = 0.685). The distance from anterior cornea to anterior cheek mass was significantly different in medial wall fracture (-0.19 +/- 3.49 mm) compared with orbital floor fracture (-1.69 +/- 3.70 mm), P = 0.05. Negative vector orbit was significantly higher in orbital floor fracture patients (24 among 34 patients, 70.6%) compared with those with medial wall fractures (19 among 43 patients, 44.2%) (P = 0.04). Conclusions: Patients presenting with a negative vector orbit relationship when the most anterior portion of globe protruded past the anterior cheek mass and malar eminence were more likely to develop orbital floor fracture than medial wall fracture. (C) 2017 by Mutaz B. Habal, MD.

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