Blowout fracture

Blowout fracture
An orbital blowout fracture of the floor of the left orbit.
Classification and external resources
Specialty	emergency medicine
ICD-10	S02.3
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An orbital blowout fracture is a traumatic deformity of the orbital floor or medial wall, typically resulting from impact of a blunt object larger than the orbital aperture, or eye socket. There are two broad categories of blowout fractures: open door, which are large, displaced and comminuted, and trapdoor, which are linear, hinged, and minimally displaced. They are characterized by double vision, sunken ocular globes, and loss of sensation of the cheek and upper gums due to infraorbital nerve injury.

In pure orbital blowout fractures, the orbital rim (the most anterior bony margin of the orbit) is preserved, while with impure fractures, the orbital rim is also injured. With the trapdoor variant, there is a high frequency of extra-ocular muscle entrapment, despite minimal signs of external trauma, a phenomenon referred to as a 'white-eyed' orbital blowout fracture. They can occur with other injuries such as transfacial Le Fort fractures or zygomaticomaxillary complex fractures. The most common causes are assault and motor vehicle accidents. In children, the trapdoor subtype are more common.

Surgical intervention may be required to prevent diplopia and exophthalmos. Patients that are not experiencing enophthalmos or diplopia, and that have good extraocular mobility can be closely followed by ophthalmology without surgery.

Orbital floor fractures were investigated and described by MacKenzie in Paris in 1844 and the term blow out fracture was coined in 1957 by Smith & Regan, who were investigating injuries to the orbit and resultant inferior rectus entrapment, by placing a hurling ball on cadaverous orbits and striking it with a mallet.

The force of a blow to the orbit is dissipated by a fracture of the surrounding bone, usually the orbital floor and/or the medial orbital wall. In blowout fractures, the medial wall is fractured indirectly. When an external force is applied to the orbital cavity from an object whose diameter is larger than that of the orbit, the orbital contents are retropulsed and compressed. The consequent sudden rise in intraorbital pressure is transmitted to the walls of the orbit, which ultimately leads to fractures of the thin medial wall and/or orbital floor. Theoretically, this mechanism should lead to more fractures of the medial wall than the floor, since the medial wall is slightly thinner (0.25 mm vs 0.50 mm). However, it is known that pure blowout fractures most frequently involve the orbital floor. This may be attributed to the honeycomb structure of the numerous bony septa of the ethmoid sinuses, which support the lamina papyracea, thus allowing it to withstand the sudden rise in intraorbital hydraulic pressure better than the orbital floor.

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