The atlanto-occipital joint is an often overlooked source of upper posterior neck pain and suboccipital headache. 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 nature, involving the upper neck and occipital region (Fig. 1.1). Pain emanating from the atlanto-occipital joint is exacerbated with lateral range of motion and flexion and extension of the upper cervical spine. It frequently coexists with pain from the atlantoaxial joint. The patient suffering from pain from the atlanto-occipital joint will frequently complain of neck pain, occipital and suboccipital headaches, preauricular pain, and limited range of motion. The patient may experience an exacerbation of pain at extremes of range of motion as well as sleep disturbance, nausea, and difficulty in concentrating.

The atlanto-occipital joint serves as the articulation between the occiput of the skull and atlas (Fig. 1.2). The atlanto-occipital joint possesses a well-developed joint capsule, cartilage, and synovium. This modified V-shaped joint has a limited range of motion of 35 degrees and functions to aid in the positioning of the sense organs by allowing the head to nod forward and backward. It differs from the true facet joints of the lower cervical spine in that it lacks a true posterior articulation. The atlantooccipital joint also lacks classic intervertebral foramina. The joint lies anterior to the posterolateral columns of the spinal cord (Fig. 1.3). The vertebral artery ascends within the cervical spine via the transverse foramen and then 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, which enters the foramen magnum in the midline (Fig. 1.4). The diagonal course of the vertebral artery provides an important landmark when performing ultrasound-guided atlanto-occipital nerve block (Fig. 1.5). The C1 nerve root, which is also known as the suboccipital nerve, exits between the skull and C1 vertebra and lacks the characteristic dorsal sensory root seen with other spinal nerves in most patients. It provides motor innervation to the suboccipital muscles and interconnects with fibers of the C2 and C3 nerves, which may explain the overlapping pain symptomatology when any of these nerves are traumatized or inflamed.