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Knowledge of the bony anatomy of the orbit is integral to the understanding of
fractures at this site. The superior portion of the orbit is composed of the superior
orbital rim and orbital roof, which is part of the thick frontal bone. The medial
wall is formed by the ethmoid bone, which is adjacent to the nasal bones. The
lateral wall is formed by the greater wing of the sphenoid and the zygoma, which
are also quite thick. The floor and the inferior orbital rim are formed by the
zygoma and the maxilla, which are relatively thin, and are further weakened by
the groove for the infraorbital nerve.
Fractures of the floor of the orbit, sometimes known as “orbital blowout
fractures,” typically occur when a medium-sized, round, hard object, such as a
baseball, strikes the eye ( Fig. 107.3 ). The volume of the globe is fixed; thus,
when an acute increase in orbital space (an opening in the floor of the orbit)
occurs, the globe may be pushed posteriorly in the orbit, producing
enophthalmos, a sunken appearance to the eye. A true orbital blowout fracture
denotes a fracture of the floor of the orbit, with an intact inferior orbital rim.
Although these fractures are quite rare in children, they are often due to direct
trauma to the zygoma rather than a compression of the globe itself. Blood and
orbital fat may sink into the maxillary sinus, clouding the sinus on radiograph (
Fig. 107.4 ). Asymmetry in the horizontal level of the eyes (orbital dystopia) may
also be present. The infraorbital nerve, the terminal branch of the maxillary
division of the trigeminal nerve, exits the maxilla just below the infraorbital rim.
Manifestations of injury to this nerve include decreased sensation to the cheek,
upper lip, and upper gingiva on the affected side. Nausea and vomiting are often
present with orbital blowout fractures and may be mistaken as symptoms of head
injury.