Medial Rectus Muscle Incarceration in Orbital Trapdoor Fractures, an Uncommon Yet Treatable Cause of Diplopia

Abstract

Abstract: : Purpose: Our purpose is to describe the phenomenon of medial rectus muscle incarceration in orbital medial wall trapdoor fractures occuring in a pediatric population. Most case series of acute post traumatic diplopia occuring in children deal with incarceration of the inferior rectus muscle within trapdoor fractures. We describe the entity of acute post traumatic diplopia, occuring with little clinical or radiographic evidence of injury, secondary to medial rectus incarceration. Methods: Interventional case series Results: Two previously healthy males, ages 11 and 14, were referred for evaluation of horizontal diplopia immediately following blunt trauma to the left orbit. External examination in both cases demonstrated minimal to no left upper eyelid ecchymosis and a notable absence of additional signs of injury including no chemosis or subconjunctival hemorrhage. In both cases the left eye was limited moderately in abduction and minimally in adduction: ocular motility was otherwise normal. Exophthalmometry measurements were normal. The remainder of the examinations was unremarkable. On computed tomography (CT) there was no apparent displacement of the medial walls, however, in the first case the left medial rectus muscle was located within the ethmoid sinus and in the second the left medial rectus had an abnormal shape. The shape of the muscle in the latter case was circumferentially smaller than the contralateral muscle and was in physical contact with its associated orbital wall, suggesting partial incarceration. Both cases were managed with emergent surgical repair. Intraoperatively in each case linear fractures were found on the orbital wall with minimal bone displacement, yet there was evidence of incarcerated soft tissue including the medial rectus muscle. The soft tissue was gently released during each procedure and the medial rectus muscle was returned to its normal postion. In each of the cases ocular motility was returned to normal by the third post-operative month, with symmetric globe postions. Conclusions: When evaluating pediatric patients with horizontal diplopia following blunt orbital trauma, medial rectus incarceration should be considered, as early intervention appears to result in a favorable outcome.

Keywords: strabismus: etiology • orbit • imaging methods (CT, FA, ICG, MRI, OCT, RTA, S