Blow out Fracture

•  Impure blowout fracture: Associated fracture of the orbital rim 

CLINICAL FEATURES:

In children:

• The bones of a child’s orbit are more elastic than adults.
• Thus injury in children causes more anteroposterior buckling creating a fracture with overlapping segments.
• This leads to ‘trapdoor-type’ fracture where prolapsed orbital tissue gets caught in the fracture site leading to severe motility restriction and diplopia in absence of marked congestion or ecchymosis.
• The condition is also called the ‘white-eyed’ blow-out fracture.
• Benign external periocular appearance with a remarkable paucity of eyelid signs but with significant extraocular muscle restriction (usually vertical) on examination ( WEBOF).
• Younger children often do not complain of binocular diplopia, and may simply close one eye.
• severe oculocardiac reflex a vague history and may therefore be misdiagnosed as having an intracranial injury (e.g., concussion).
• Periorbital haematoma: also proptosis of variable degree seen initially due to orbital edema and haemorrhage
• Emphysema: Subcutaneous emphysema with crepitus seen in fractures communicating with air filled sinuses.
•  Paraesthesia over ipsilateral lower lid, cheek and upper lip due to injury to infraorbital nerve.
• Diplopia: Due to restriction of ocular motility. With the entrapment of inferior orbital tissue and inferior rectus muscle, vertical diplopia is more prominent in upgaze. 

In patients with orbital floor fractures

• visual loss can result from globe trauma, injury to the optic nerve, or increased orbital pressure causing a compartment syndrome 
• An orbital hemorrhage should be suspected if loss of vision is associated with proptosis and increased lOP.
• Injuries to the globe and ocular adnexa may also be present.
• 0.8–1 ml increase of bony orbital volume corresponds to 1 mm of enophthalmos on the Hertel exopthalmometer.
• Clinically significant enophthalmos (≥2 mm) occurs with increase in the bony orbital volume of 1.5–2 ml.

DIAGNOSIS:

• Plain X-rays:. Water’s view for detecting an orbital floor fracture .
• X ray shows bony discontinuity in orbital floor with herniation of soft tissue in maxillary antrum seen as ‘tear drop’ sign
• Coronal sections are particularly useful .
• MRI Can be utilized when there is need for greater soft tissue evaluation
• MRI is insufficient in assessing the bony structures and therefore needs to be combined with CT. 

Exam Question

• CT can fairly accurately determine the size of the fracture and its relationship to the orbital soft tissues
• Blow out fracture of the orbit, most commonly leads to fracture of Posteromedial floor of orbit
• Restriction of lateral and upward gaze of eyeball and diplopia with  enophthalmos following history of trauma is suggestive of blow out fracture
• Diplopia, ‘Tear drop” sign , Positive forced duction test & enopthalmous are signs of  blow out fracture