Classification of Orbital Floor Fracture Patterns Associated With Inferior Rectus Muscle Entrapment

Certain orbital floor fracture types have been associated with orbital soft tissue entrapment leading to irreversible inferior rectus muscle injury and permanent diplopia. This "trapdoor" fracture occurs more frequently in the pediatric population since the facial skeleton is elastic. Literature on adult entrapment is scarce. We discuss the spectrum of clinical and radiologic presentations of inferior rectus muscle entrapment in the adult population and propose a novel classification based on bone and soft tissue interactions seen on imaging.

Three adult patients with isolated orbital floor fractures and inferior rectus muscle entrapment were identified from 2015 to 2017. These patients led to a systematic review of the literature on inferior rectus entrapment. Based on the review and case series, a classification system was developed for orbital floor fracture patterns associated with entrapment observed on CT imaging.

Comminuted orbital floor fractures with clinical and radiographic evidence of entrapment were demonstrated in 3 adult patients. Surgery was performed within 24 hours of admission and resulted in restored baseline gaze in all patients. The literature review and patient cases suggested 3 types of orbital floor fracture patterns associated with inferior rectus muscle entrapment.

We propose a classification system consisting of 3 patterns of orbital floor fractures associated with inferior rectus entrapment. Entrapment in adult patients most commonly occurs in the setting of comminuted floor fractures. Ischemia of the inferior rectus muscle leading to permanent injury of the muscle is unlikely in adults as opposed to pediatric patients, who sustain different fracture patterns.