Chapter 24

### INDICATIONS

The indications for injections of the facet joint include:

• Facet-mediated low back pain

• Diagnostic blocks of facet-mediated low back pain

• Paravertebral spasm

• Facet joint arthritis

• Facet joint effusions

• Facet-mediated pain in rheumatoid arthritis

• Facet-mediated pain in ankylosing spondylitis

• Patients with relief from anesthetic blocks of the facet joint

• Facet joint cysts

Facet joint cysts are associated with facet joint arthropathy, degenerative disc disease, and degenerative spondylolisthesis and cause lower back pain, unilateral radicular pain, neurogenic claudication, and cauda equina syndrome. Most patients with lumbar cysts are in their sixties with a slight female predominance.

### RELEVANT ANATOMY

• Each spinal segment is a “three-joint complex” comprised of an interveterbral disc anteriorly and paired posterior synovial facet joints.

• On axial imaging, the facet joints approximate a C or J shape.

• Each joint influences the other two, with degenerative changes in one, affecting the entire complex.

As the intervertebral discs degenerate and the outer annular fibers begin to fragment, the posterior load increases and allows excessive facet joint motion to occur. This abnormal motion accounts for excessive shear forces in the facet joint, resulting in degradation of the cartilage and joint effusion formation. The facet capsule helps limit axial rotation.

• An intact capsule holds 1 to 2 mL of joint fluid with larger effusions implying a loss of capsular integrity and abnormal joint motion (Figure 24-1).

• The facet joint cysts are intraspinal extradural masses, located lateral to the thecal sac and adjacent to the arthritic facet joint ((36)) (Figure 24-2).

• They are most commonly found at the L4-L5 segment, followed by L5-S1, L3-L4, and L2-L3. ((37)).

• The cysts represent synovial exvaginations that arise secondary to recurrent joint effusions and may be considered similar to Baker cysts in the popliteal fossa.

Facet effusions.

###### Figure 24-2.

Facet joint cysts.

### BASIC CONCERNS AND CONSIDERATIONS

The initial radiographic assessment of patients presenting with lumbar facet-mediated pain begins with standard radiographs including AP, lateral, and oblique views. The curved configuration and sagittal orientation of the lumbar facet joint generally limits the utility of frontal and lateral views.

• CT scan more accurately determines the extent of the degenerative changes, but it is poor for evaluation of the presence of facet fluid or cystic formation.

• MRI scanning underestimates the extent of the severity of the osteoarthritic changes, but it is highly sensitive to facet joint fluid and the assessment of the facet cyst.

• The classification of the facet arthropathy by CT scan or MRI can be performed using the Pathria or Fujiwara classifications, respectively.

• Higher grades of facet joint osteoarthritis are more likely to have larger ...

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