Chapter 14

### INTRODUCTION

The atlanto-occipital (AO) and atlanto-axial (AA) joints are unique joints in the spine, connecting the cervical region to the base of the skull. The AA and AO joints are an often under-appreciated cause of pain, and should be part of the differential diagnosis of cervical spine pain and occipital headaches.

### INDICATIONS

AO joint injections are indicated for:

• The diagnosis and treatment of AO joint pathology, which presents as deep pain in the suboccipital region, often unilateral

• Especially after flexion/extension injuries

• Particularly when movement in flexion and extension causes pain

• Cervicogenic headaches that are impairing functional life indices (restorative sleep capacity, endurance, and quality of life)

• Persistent upper cervical pain that is leading to escalating opioids to control symptoms

• Persistent occipital neuralgia poorly responsive to occipital nerve blocks

The AO joint primarily refers to the ipsilateral suboccipital and retromastoid region, although pain may also refer to the paracervical, suprascapular, and levator scapular regions.1 The normal AO joint is ellipsoid, and permits passive flexion and extension of about 10 degrees as well as 10 degrees rotation and side bending of about 10 degrees.2 There may be decreased range of motion, crepitance, and abnormal head position. When there is pain with side bending during protraction or retraction, the most likely joint affected is the AO joint. Pain or decreased range of motion when nodding from a full rotation is usually related to the AO joint. Unfortunately, the radiologic diagnosis of AO joint pathology has a high false-negative result, since onset of pain precedes any observable structural abnormalities. Characteristic referred pain patterns from AA and AO joint pathology overlap those patterns from the greater and lesser occipital nerves as well as the pain from the C2/3 facet joint,1 making clinical diagnosis difficult. See Figure 14-1.

### CONTRAINDICATIONS

• Infection at the injection site

• Coagulopathy

• Cervical spine instability

• Previous cervical fusion at that level

### RELEVANT ANATOMY

The first two bones of the cervical spine are unique in their shape and function (Figure 14-2). The C1, or atlas, vertebra is unique in that it does not have a ventral vertebral body, but rather functions as a relay between the occiput and C2. The AO joint is the articulation of the superior articular facet of C1 (the atlas) and the occiput. The AO joint articulates the atlas (C1) with the occiput (C0) and constitutes the C0-1 joint. The AO joint straddles the spinal cord with the foramen magnum on either side and is V-shaped, slanting caudally and medially (Figure 14-3); it holds a volume of 1.0 cc.3

###### Figure 14-1.

Patterns of occipital pain. (Used with permission from Andrea Trescot, MD.)

###### Figure 14-2.

Lateral view of AA and ...

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