A patient sustains orbital blowout fracture. On examination there is enophthalmos, restricted upgaze, and diplopia on upward gaze. CT scan shows herniation of inferior rectus and orbital fat into the maxillary sinus. The MECHANISM causing restricted upgaze is:
- A Entrapment of the inferior rectus or surrounding perimuscular connective tissue system in the fractured floor ✓
- B Direct contusion injury to the superior rectus muscle
- C Haematoma in the superior rectus sheath
- D Fourth nerve palsy from intracranial injury
Correct answer: A. Entrapment of the inferior rectus or surrounding perimuscular connective tissue system in the fractured floor
Explanation
In orbital floor blowout fractures, the inferior rectus muscle or (more precisely) the Lockwood's ligament and perimuscular connective tissue system becomes entrapped in the fracture, mechanically restricting elevation of the globe (upgaze). Forced duction test confirms restriction. Surgery to release the entrapped tissue should be done within 1–2 weeks to prevent fibrosis. The mechanism is pure mechanical tethering, not a nerve palsy. Enophthalmos results from increased orbital volume when fat herniates into the sinus.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.