Fluoroscopy-Guided Blockade of the Greater Occipital Nerve in Cadavers: A Comparison of Spread and Nerve Involvement for Different Injectate Volumes

BACKGROUND: Fluoroscopy-guided blockade of the greater occipital nerve (GON) is an accepted method for treating the symptoms of cervicogenic headaches (CGHs). However, the spread patterns among different injectate volumes of fluoroscopy-guided GON blocks are not well defined. OBJECTIVE: A cadaveric study was established to determine the spread patterns of different volumes of dye injectate within a fluoroscopic GON block. Study Design. Cadaveric study. Setting. Xingtai Institute of Orthopaedics; Orthopaedic Hospital of Xingtai. METHODS: 15 formalin-fixed cadavers with intact cervical spines were randomized in a 1 : 1 : 1 ratio to receive a fluoroscopy-guided GON injection of a 2, 3.5, or 5 ml volume of methylene blue. The suboccipital regions were dissected to investigate nerve involvement. RESULTS: The suboccipital triangle regions, including the suboccipital nerves and GONs, were deeply stained in all cadavers. The third occipital nerve (TON) was stained in 7 of 10 administered 2 ml injections and in all the 3.5 ml and 5 ml injections. Compared to the 3 ml injectate group, the 5 mL cohort consistently saw injectate spreading to both superficial and distant muscles. Limitations. Given that cadavers were used in this study, cadaveric soft tissue composition and architecture can potentially become distorted and consequently affect injectate diffusion. CONCLUSIONS: A 3.5 or 5 mL fluoroscopy-guided GON injection of methylene blue successfully stains the GON, TON, and suboccipital nerves. This suggests that such an injection would generate blockade of all three nerve groups, which may contribute to the efficacy of the block for CGH. A volume of 3.5 ml may be enough for the performance of a fluoroscopy-guided GON block for therapeutic purposes.