A boxer is struck under the left eye. He now has numbness of the left cheek and upper lip, double vision on looking up, and CT shows a defect in the thinnest wall of the orbit with herniation of orbital fat into the maxillary sinus. Which structure is most likely entrapped at the fracture site?
- A Superior oblique muscle
- B Inferior rectus muscle ✓
- C Medial rectus muscle
- D Levator palpebrae superioris
Correct answer: B. Inferior rectus muscle
Explanation
Blowout fractures typically involve the orbital floor, the thinnest orbital wall, at the roof of the maxillary sinus. Herniation or entrapment of the inferior rectus (and inferior oblique with surrounding fat) limits elevation, producing vertical diplopia worst on upgaze. Infraorbital nerve injury in the floor explains cheek and upper lip anesthesia. Medial rectus relates to lamina papyracea fractures of the ethmoid, and levator and superior oblique occupy the roof and superomedial angle respectively.
Reference: Bailey and Love Short Practice of Surgery, 28th ed.
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Written and medically reviewed by the StethoPrep medical team.