Blow-Out Fracture

Basics

Description

Defined as an orbital floor fracture that results from sudden blunt trauma to the globe:
- Typically caused by the force of a projectile > half the size of the fist
- Force transmitted through the noncompressible structures of the glove to the weakest structural point, the orbital floor, causing it to “blow out”
Orbital floor serves as roof to air-filled maxillary and ethmoid sinuses:
- Communication between the spaces results in orbital emphysema
Orbit contains fat, which holds the globe in place:
- Orbital floor fracture may result in herniation of the fat on the inferior orbital surface into the maxillary or ethmoid sinuses
- Leads to enophthalmos owing to orbital volume loss and sinus congestion; fluid collection may occur secondary to edema and bleeding
Infraorbital nerve runs through the bony canal 3 mm below the orbital floor:
- Injury may result in hypoesthesia of the ipsilateral cheek and upper lip
- To distinguish facial hypoesthesia related to local swelling from nerve injury: Test for sensation on the ipsilateral gingiva, which is within the infraorbital nerve distribution
Inferior rectus and the inferior oblique muscle run along the orbital floor:
- Restriction of these extraocular muscles may occur because of entrapment within the fracture, contusion, or cranial nerve dysfunction
- Typically manifests as diplopia on upward gaze
- Inability to elevate the affected eye normally on exam
Medial rectus located above the ethmoid sinus:
- Less commonly entrapped
- Diplopia on ipsilateral lateral gaze

Etiology

Caused by a projectile that strikes the globe. The force is transmitted through the noncompressible structures of the globe to the weakest structural point, the orbital floor resulting in a blow-out fracture
Pediatric Considerations

Orbital roof fractures with associated CNS injuries more common in children
Orbital floor fractures: Unlikely before 7 yr of age:
- Orbital floor is not as weak a point in the orbit due to lack of pneumatization of the paranasal sinuses
Unfortunately fractures can occur in children and may result in unrecognized entrapment of the rectus muscle labeled the “white-eyed” fracture:
- Findings are subtle and there may be little associated soft tissue injury
- These children may present with marked nausea, vomiting, bradycardia, headache, and irritability suggestive of a head injury that commonly distracts from the true diagnosis

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