Needle Entry Angle to Prevent Carotid Sheath Injury for Fluoroscopy-Guided Cervical Transforaminal Epidural Steroid Injection

OBJECTIVE: To suggest rotation angles of fluoroscopy that can bypass the carotid sheath according to vertebral levels for cervical transforaminal epidural steroid injection (TFESI). METHODS: Patients who underwent cervical spine magnetic resonance imaging (MRI) from January 2009 to October 2017 were analyzed. In axial sections of cervical spine MRI, three angles to the vertical line (α, angle not to insult carotid sheath; β, angle for the conventional TFESI; γ, angle not to penetrate carotid artery) were measured. RESULTS: Alpha (α) angles tended to increase for upper cervical levels (53.3° in C6-7, 65.2° in C5-6, 75.3° in C4-5, 82.3° in C3-4). Beta (β) angles for conventional TFESI showed a constant value of 45° to 47° (47.5° in C6-7, 47.4° in C5-6, 45.7° in C4-5, 45.0° in C3-4). Gamma (γ) angles increased at higher cervical levels as did α angles (25.2° in C6-7, 33.6° in C5-6, 43.0° in C4-5, 56.2° in C3-4). CONCLUSION: The risk of causing injury by penetrating major vessels in the carotid sheath tends to increase at upper cervical levels. Therefore, prior to cervical TFESI, measuring the angle is necessary to avoid carotid vessels in the axial section of CT or MRI, thus contributing to a safer procedure.