SP17. Classification of Orbital Floor Fracture Patterns Associated With Inferior Rectus Muscle Entrapment

PURPOSE: Orbital floor fractures can involve herniation of orbital contents into the maxillary sinus. In rare cases, the orbital contents can become trapped between minimally displaced linear fragments of fractured bone. The incarcerated tissue may include the inferior rectus muscle, which may ultimately result in ischemia of the muscle. Inferior rectus muscle entrapment in the setting of orbital floor fractures - particularly trapdoor fractures - is most commonly seen in children. In adults, muscle entrapment is not as common because the orbital floor is not as elastic and fractures are often comminuted. Based on a systematic review of the literature and case series of adult patients with entrapment, we developed a novel classification of inferior rectus entrapment in orbital floor fractures. METHODS: A systematic review of literature was performed using the following search terms: orbital fracture, orbital floor, inferior rectus muscle AND (herniation or entrapment), entrapment. Clinical descriptions and radiologic patterns of orbital floor fractures and the inferior rectus muscle were analyzed in the included studies. A retrospective case series consisting of three adult patients with inferior rectus muscle entrapment in traumatic isolated orbital floor fractures was performed. RESULTS: Twenty-nine studies with a total of 275 adult and pediatric patients who had inferior rectus muscle entrapment were included our systematic review. The three patients included in our case series had comminuted orbital floor fractures with clinical and radiographical evidence of entrapment. Surgical release of the entrapped inferior rectus muscle was performed within 24 hours of presentation and resulted in restored baseline gaze in all patients at 2-months follow-up. Based on our review and case series, we developed a classification system for orbital floor fractures associated with entrapment based on the fracture pattern and/or comminution seen on CT imaging. Type I is a linear type fracture and consists of a true trapdoor pattern with minimal or no displacement of the orbital floor. On CT, this type is characterized by the absence of orbital floor displacement. This type can be further sub-divided based on the location of the inferior rectus - in the internal orbit (Type Ia) or in the maxillary sinus (Type Ib). The hinged type (Type II) occurs when a piece of orbital floor fractures in a swinging door fashion and orbital soft tissue herniates into the maxillary sinus. Our three patients sustained comminuted orbital floor fractures, which we designated as Type III, where the inferior rectus muscle and perimuscular soft tissue are displaced into the maxillary sinus and the muscle is incarcerated within the bony fragments. CONCLUSION: We propose a classification system consisting of three main types of orbital floor fractures associated with inferior rectus entrapment. Entrapment in adult patients appears to occur in the setting of comminuted floor fractures. This classification system can serve as a groundwork for future studies addressing treatment in adult patients with orbital floor fractures.