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Facial nerve
2%
49/2017
Supraorbital nerve
84%
1689/2017
Abducens nerve
8%
165/2017
Zygomaticotemporal nerve
3%
53/2017
Zygomaticofacial nerve
48/2017
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The supraorbital nerve is at risk if the anterior pin is placed too medially. When placing pins during halo immobilization a relative safe zone for anterior pin placement is located 1 cm above the orbital rim and superior to the lateral two thirds of the orbit. This prevents injury to both the supraorbital and supratrochlear nerve which are both located medially (supratrochlear nerve more medial than supraorbital nerve). Posterior pin-site locations are less critical and can be positioned on the posterolateral aspect of the skull, diagonal to the contralateral anterior pins. Pins should enter the skull perpendicular to the cortex, with the ring or crown sitting below the widest portion of the skull and passing about 1 cm above the helix of the ear. Garfin et al. review complications associated with halo immobilization. They found pin-loosening in 36% of the patients, pin-site infection in 20%, pressure sores under either a plastic vest or a plaster cast in 11%, nerve injury in 2%, dural penetration in 1%, dysphagia in 2%, cosmetically disfiguring scars in 9%, and severe pin discomfort in 18%. Botte at al. report superficially infected pins are managed with local pin care and oral antibiotics. Persistent or severe infections require pin replacement to a nearby site, parenteral antibiotic therapy, and incision and drainage as needed. Illustration A shows the region of the safe zone in relation to the supraorbital nerve and supratrochlear nerve. Illustration B shows a surgical image of the supraorbital nerve. Illustration C shows the branches of the Trigeminal nerve (CN V) which include the supraorbital nerve and supratrochlear nerve. Incorrect Answers: Answer 2: The facial nerve (CN VII) controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity. It is not at risk with anterior pin placement. Answer 3: The abducens nerve (CNVI) is an intracranial nerve that is not at risk from direct damage with pin placement. Abducens nerve palsy, leading to absence of lateral gaze, is one complication of halo placement but is thought to be related to a traction injury on the nerve. Answer 4 and 5: The zygomaticotemporal nerve and zygomaticofacial nerve are both branches of the Trigeminal nerve, but are not in the region of the medial-superior orbit.
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