The atlantoaxial joint is an often overlooked source of upper posterior neck and suboccipital headache pain. The joint is susceptible to arthritis and is frequently traumatized during acceleration/deceleration injuries. The pain following such injuries is often initially attributed to soft tissue injury such as muscle strain and/or bruising. The pain is ill defined and dull in character involving the upper neck and occipital region (Fig. 2.1). Pain emanating from the atlantoaxial joint is exacerbated with lateral rotation and flexion and extension of the joint and surrounding upper cervical spine. It frequently coexists with pain from the atlanto-occipital joint and the C2/C3 facet joints due to convergence of fibers from these anatomic structures with trigeminal afferent fibers via the trigeminocervical nucleus.

The patient suffering from pain from the atlantoaxial joint will frequently complain of neck pain, occipital and suboccipital headaches, preauricular pain, as well as a limited range of motion with exacerbation of pain at the extremes of range of motion. Sleep disturbance is common as is nausea and difficulty in concentrating. The unique anatomic structure of the atlantoaxial joint also makes it susceptible to instability, which may be exacerbated when the joint is subjected to trauma. A number of diseases are associated with atlantoaxial instability, and they are listed in Table 2.1. The clinician should look carefully for atlantoaxial joint abnormalities and/or instability in patients who have sustained trauma to the joint or who are suffering from the diseases listed in Table 2.1 as failure to identify fractures of the odontoid process and C2 vertebral body and/or disruption of the transverse ligaments with resultant joint instability can have disastrous consequences should the joint sublux (Figs. 2.2 and 2.3).

The atlantoaxial joint serves as the articulation between the C1 and C2 vertebra. The atlantoaxial joint possesses a welldeveloped capsule, cartilage, and synovium and, like the atlanto-occipital joint, does not possess classic intervertebral foramina seen in the lower cervical vertebrae. The joint allows lateral rotation of the skull of 72 degrees in either direction from the midline and functions to aid in the positioning of the sense organs. It also allows a limited degree of flexion and extension independent of the atlanto-occipital joint and other facet joints of the cervical spine. The vertebral artery ascends via the transverse foramen of the cervical spine, traveling across the lateral one-third of the atlantoaxial joint. The artery ultimately exits the C1 transverse foramen and turns medially to course diagonally across the posteromedial aspect of the atlanto-occipital joint to join with the contralateral vertebral artery at the level of the medulla to form the basilar artery. The basilar artery then ascends to enter the foramen magnum in the midline (Fig. 2.4). The course of the vertebral artery provides an important landmark when performing ultrasoundguided atlantoaxial nerve block (Fig. 2.5). The C2 nerve root exits above the C2 vertebra and provides some motor innervation to the suboccipital muscles. The fibers of the medial branch of the C2 nerve root dorsal primary ramus form the greater occipital nerve. Fibers from the C2 nerve root interconnect with fibers of the C1 and C3 nerves, which may help explain the overlapping pain symptomatology when any of these nerves are traumatized or inflamed.

The patient is placed in prone position with patient’s cervical spine slightly flexed and the skin prepped with antiseptic solution. A total of 3 mL of preservative-free dilute local anesthetic
is drawn up in a separate 5-mL sterile syringe. When the pain being treated is thought to be secondary to an inflammatory process, a total of 2.5 mg of nonparticulate dexamethasone is added to the local anesthetic with the first block, and 1.5 mg of nonparticulate dexamethasone is added with subsequent blocks. A high-frequency linear transducer is placed in the transverse orientation in the midline at the level of the occiput (Fig. 2.6). The transducer is then slowly moved caudally to identify first the C1 and then the C2 vertebral bodies. The C1 vertebral body has only a vestigial spinous process, and the C2 vertebral body is the first cervical vertebral body with a bifid spinous process making its identification easier (Figs. 2.7 and 2.8). When the C2 vertebra is identified, the transducer is then moved laterally until the exiting C2 nerve root is identified (Figs. 2.9 and 2.10). The transducer is then moved slightly more laterally until the vertebral artery is identified. Color Doppler may be used if the vertebral artery is not readily apparent (Fig. 2.11). The atlantoaxial joint should then be easily identified in between the exiting C2 root and the vertebral artery. A 22-gauge, 3½-inch styletted spinal needle is then advanced into the atlantoaxial joint using an out-of-plane approach under real-time ultrasonography, while constant attention is paid to the location of the vertebral artery laterally and the C2 nerve root medially.