The third occipital nerve (TON) and cervical facet joints are common sources of cervicalgia and headache. These conditions can arise sponTaneously or secondary to trauma or to surgery. Given the complex innervation of the head and neck, diagnostic blocks are the only reliable way to precisely identify the source of pain arising from the TON or cervical zygapophyseal joints. If two separate blinded diagnostic blocks on separate days are positive in a concordant fashion, the patient may be a candidate for neurotomy or radiofrequency ablation.

The TON supplies the C2-C3 facet joints and also a small area of skin inferior to the occiput. The lower cervical medial branches innervate the facet joints and the cervical multifidus muscles. Specific pain referral patterns have been identified for each level of facet joint, but there is considerable variation between patients.

Radiofrequency neurotomy has been an evidence-based treatment of choice for chronic pain related to whiplash syndrome, although it is more widely used for the management of neck pain attributed to degenerative changes. Isolated cervical facet joint arthropathy may also be treated with intra-articular injections of local anesthetic and corticosteroid to treat acute inflammation. Medial branch analgesic injections should be performed to confirm the pain generator and exclude other conditions.

The cervical zygapophyseal joints have uniquely variable innervation.

The C2-C3 joint is exclusively innervated by TON, which is essentially the posterior ramus of the C3 root, much thicker than the ventral ramus. TON crosses the C2-C3 facet joint, and its course can vary from the apex of the C3 superior articular process (SAP) to adjacent to the C2-C3 intervertebral foramen. The most common location is the lower half of the convexity of the C2-C3 facet joint. Care must be taken to avoid confusing this nerve with the C3 medial branch. The nerve is usually elevated over the surface of the bone by 1 to 2 mm.

Each cervical facet joint below the C2-C3 level is innervated by articular branches of the medial branch nerves from the levels above and below that joint. These medial branches arise from the cervical dorsal rami, which come off the spinal nerve and pass over the base
of the transverse process. The medial branches come off these dorsal rami and wrap medially around the articular pillars, held in place by fascia and by the semispinalis capita tendon. This fixed location allows the medial nerves to be targeted in an area with clear bony landmarks that is not adjacent to the spinal nerve or vertebral artery. The medial branch of the C7 dorsal ramus is slightly cephalad in its course compared to the other cervical levels, and crosses over the SAP of that vertebra.

The zygapophyseal joints themselves are formed by the articulation of the superior and inferior articular processes of adjacent cervical vertebrae. The orientation of the facet joints changes from being 45 degrees superior to the transverse plane at the C2-C3 level to nearly vertical at the cervicothoracic junction.

Patient Position: Lateral decubitus position with head on a pad to keep neck in a neutral position.

Transducer: A broadband high-frequency linear array transducer.

Transducer Position: Transverse, just caudal to mastoid process on either side. The vertebral artery is identified just caudal to this and is followed further caudally to the C2 transverse process, and further caudally to C2-C3 facet joint. The apex of this joint is identified and used as a target for needle insertion. Then the transducer is rotated 90 degrees to a longitudinal position. Gentle adjustment of the transducer is typically required to obtain a clear “wave-shaped” line of the articular processes and joints. The “valleys” represent center of articular pillars, and the “peaks” correspond to the joints themselves (Fig 51.1). The most cranial “peak” that found is the C2-C3 joint. Cranially to it, the cHaracteristic image will reflect descending C2 lamina and the C1-C2 interspinous space. The cross section of the TON may be visible crossing the C2-C3 joint in this plane (Fig. 51.2). This area is marked on the skin.

Needle: 2- to 3.5-inch, 22G needle.