What are the signs of entrapment in a blowout fracture?

Signs of Entrapment in Blowout Fracture

The key signs of entrapment in a blowout fracture include restricted ocular motility with positive forced duction testing, diplopia, oculocardiac reflex (bradycardia, nausea, vomiting, dizziness), and CT evidence of muscle or periorbital tissue herniation through the fracture site. 1

Clinical Signs and Symptoms

Ocular Motility Disturbances

• Restricted eye movement, particularly in the direction opposite to the entrapped muscle
• Positive forced duction test (resistance when attempting to move the eye in certain directions)
• Limited ductions and versions, especially in upward or downward gaze for floor fractures
• Diplopia (double vision), particularly in primary position or downgaze 1

Oculocardiac Reflex Manifestations

• Bradycardia or heart block
• Nausea and vomiting
• Dizziness
• Loss of consciousness in severe cases
• These symptoms can mimic increased intracranial pressure, especially in pediatric patients 2

"White-eyed Blowout Fracture" Presentation

• Minimal external signs of trauma despite significant internal injury
• Particularly common in children and adolescents
• Severe nausea, vomiting, headache that can be mistaken for head injury
• Marked restriction of ocular movement 3

Imaging Findings

CT Scan Findings

• Evidence of muscle or periorbital tissue herniation through fracture site
• "Missing muscle sign" - absence of the entrapped muscle in multiple contiguous CT cuts 4
• Small trap-door type fracture with soft tissue herniation
• CT is preferred over MRI when metallic foreign bodies are suspected 1

MRI Findings (when appropriate)

• Provides more precise imaging of extraocular muscles
• Can show edema and inflammation in entrapped muscles
• May be performed dynamically to assess muscle function 1

Special Considerations

Pediatric Patients

• Higher risk of trap-door type fractures with muscle entrapment
• May present with "white-eyed" appearance (minimal external signs)
• Can be misdiagnosed as increased intracranial pressure due to similar symptoms
• Requires more urgent intervention to prevent muscle necrosis 2, 5

Medial Wall Fractures

• Medial rectus entrapment may occur with medial wall fractures
• Similar presentation to floor fractures but with horizontal rather than vertical gaze restriction
• Early recognition and treatment is critical for good outcomes 5

Clinical Pitfalls to Avoid

• Misdiagnosing oculocardiac reflex symptoms as head injury or increased intracranial pressure 2
• Failing to perform forced duction testing in cases of limited ocular movement
• Relying solely on imaging without clinical correlation (some entrapments may not be obvious on initial imaging) 6
• Delaying treatment in cases with positive signs of entrapment, which can lead to permanent diplopia, muscle necrosis, and vision loss 7

Remember that entrapment requiring immediate surgical intervention is indicated by CT evidence of entrapped muscle or periorbital tissue with a nonresolving oculocardiac reflex, particularly in "white-eyed" blowout fractures seen in children 1.