44 Facet Block
Perspective
Facet blocks are used to diagnose and treat subsets of patients with chronic low-back and neck pain. Difficulties may arise in interpreting the results of facet blocks because the innervation of facet joints is diffuse, and radiographic changes in facet joints may or may not be linked to a specific patient’s pain. Despite the caveats, the pain relief attained with facet injection seems convincing, although in contrast to many other pain management techniques, extra care must be taken in balancing the patient, the pain syndrome, and the treatment regimen with the individual clinical setting.
Patient Selection
Facet-related pain remains a diagnosis of exclusion, supported by reproduction of the pain during arthrography and relief of pain after diagnostic facet injection. In patients with lumbar pain syndromes, facet-related pain is often located in the low back and is described as a deep, dull ache that is difficult to localize. It may be referred to the buttocks or to the posterior leg, and infrequently it extends more distally into the lower leg. The pain is often made worse by lumbar extension, especially with lateral flexion to the affected side because this maneuver opposes the facet joints more forcefully. In cervical facet pain syndromes, the pain remains deep and aching, and the level of the facet involvement dictates the referral pattern of the pain. There are distinct upper, lower, and pancervical neck facet pain syndromes.
Pharmacologic Choice
Diagnostic blocks are most often performed with 1 to 2 mL of local anesthetic, either 1% to 1.5% lidocaine, 0.25% to 0.5% bupivacaine, or 0.2% to 0.5% ropivacaine. Lidocaine is chosen if immediate interpretation is sought, whereas bupivacaine or ropivacaine is used if diagnostic information is sought over a longer interval. For therapeutic injection, the total volume of solution is kept at 1.5 to 2.0 mL, although 20 mg of methylprednisolone is added to the local anesthetic (most often a longer-acting agent for a therapeutic injection). For either diagnostic or therapeutic injection, the needle position is confirmed with 0.25 to 0.5 mL of a radiocontrast agent, Hypaque-M 60% (Sanofi Winthrop, Irving, Tex).
Placement
Anatomy
The 33 vertebrae that make up the spinal column are linked by intervertebral disks and longitudinal ligaments anteriorly and through facet joints posteriorly. The posterior facet joints allow flexion, extension, and rotation of the vertebral column while providing a means for the axial nerves to exit the vertebral column on their way to becoming peripheral nerves. The facet joints are synovial joints formed by the inferior articular processes of one vertebra and the superior articular processes of the adjacent caudad vertebra. These articular processes are projections, two superior and two inferior, from the junction of the pedicles and the laminae. In the cervical and lumbar portions of the vertebral column, the facet joints are posterior to the transverse processes, whereas in the thoracic region the facet joints are anterior to the transverse processes (Fig. 44-1). In the cervical vertebrae, the joint surfaces are midway between a coronal and an axial plane, whereas in the lumbar region, the joints (at least the posterior portion) assume an orientation approximately 30 degrees oblique to the sagittal plane (Fig. 44-2).
Figure 44-1. Superior and lateral views of cervical (A), thoracic (B), and lumbar (C) facet joints. Angle of the facet joints in the sagittal plane is indicated in the insets. Transverse processes are highlighted in purple in each image.
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