Blow out Fracture

DEFINITIONS:
  • Orbital floor fractures are common, and result from blunt orbital trauma in which force is delivered to the thin bones of the orbital floor, typically along the infraorbital canal. The risk of enophthalmos is greatest when both the floor and the medial wall are fractured
TYPES:
  • Pure blowout fracture: Fracture of the Posteromedial orbital floor with intact orbital rim
  • 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’ f
  • racture 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
  1. visual loss can result from globe trauma, injury to the optic nerve, or increased orbital pressure causing a compartment syndrome 
  2. An orbital hemorrhage should be suspected if loss of vision is associated with proptosis and increased lOP.
  3. Injuries to the globe and ocular adnexa may also be present.
  4. 0.8–1 ml increase of bony orbital volume corresponds to 1 mm of enophthalmos on the Hertel exopthalmometer.
  5. 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

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