Comparing the injectate spread and nerve involvement between different injectate volumes for ultrasound-guided greater occipital nerve block at the C2 level: a cadaveric evaluation.

The clinical efficacy of this technique using the 5-mL injectate seems unlikely to arise from the blockade of GON alone. Instead, its efficacy likely arises from the blockade of most nerves originating from the dorsal ramus of the upper cervical spinal nerve at the suboccipital area. Even using 1 mL of injectate may not guarantee blockade of the GON alone.