Image analysis of the inferior rectus muscle in orbital floor fracture using cine mode magnetic resonance imaging.

Purpose: The main cause of diplopia induced by orbital floor fracture is strangulation or damage of the extraocular muscles, and the outcome varies depending on the severity of trauma. In this study, we evaluated the dynamics of the eyeball and inferior rectus muscle based on cine magnetic resonance (MR) images acquired before surgery. The preoperative images and outcomes were retrospectively investigated.

Material And Methods: The subjects were 20 patients with orbital floor fracture. The patients repeated upgaze and downgaze, and images of these were acquired using cine mode magnetic resonance imaging (MRI). Image series were obtained in the sagittal direction including the eyeball and long axis of the optic nerve. The eyeball rotation angle, strangulation, and morphology of the inferior rectus muscle were evaluated in each phase.

Results: On cine mode MRI, the outcome was poor in cases with a maximal inferior rectus muscle thickness of 5 mm or greater on extension (two or more times thicker than on the healthy side).

Conclusions: Our results suggest that the development of sequelae can be predicted by preoperative image analysis using cine MRI, which may be beneficial to help surgeons understand the mechanism of contracture.