FACET SYNDROME AND THE RELIEF OF LOW BACK PAIN

Introduction

The lumbar facet joints were first suggested to be a major source of
back pain and sciatica in 1911. The role of the lumbar facet joints is
now well described in the literature and has an estimated incidence of
between 15-21% of nonspecific low back pain. It's interest as a site
of pain has waxed and waned over the last 40 years for two reasons. The
first has been the preoccupation of surgeons since 1934 with the lumbar
disc as the primary determinant of low back pain. The second has been
the lack of correlation between symptoms and X-ray imaging. It has only
been after the realization that lumbar disc surgery has only limited
success and is not a comprehensive treatment for all back pain that the
lumbar facets have seen a resurgence as a significant treatable cause of
low back pain and disability. However, it wasn't until 1971, when Rees
proposed surgical denervation of the facet joint by percutaneous
rhizotomy, that interest in "facet syndrome" was peaked. This interest
was further bolstered in 1976 when Mooney and Robertson confirmed the
entity by intra-articular injections of hypertonic saline in volunteers
to reproduce the symptoms felt by many chronic back pain sufferers.

Clinical Presentation

• Unfortunately there are no clinical or laboratory test to definitively
  diagnose facet syndrome. The mere presence of morphological changes in
  the joints on imaging studies does not necessarily implicate the joint
  as the cause for pain. Therefore, the diagnosis of facet syndrome
  relies exclusively on the results of radiographically confirmed
  diagnostic anesthetic blocks. Studies have confirmed that the pattern
  of pain is unreliable in the diagnosis of facet syndrome , , however,
  below is a typical pain drawing for patients with pain of facet origin.
  This pain drawing could be easily misinterpreted as typical sciatica or
  other known causes of low back
  There is considerable variation in symptoms between patients, however
  the features most commonly associated with the syndrome include:
  
• Tenderness localized over one or more facet joints,
• Diffuse referred pain over the buttock and sometimes posterolateral thigh,
• Exacerbation of pain with any sustained posture,
• Loss of lumbar lordosis, or paraspinous muscle spasm
• Exacerbation of pain with hyperextension.
  

Anatomy & Pathophysiology

The normal function of the vertebral facet joints is to resist axial
rotation or torsion of the intervertebral joint and protect the disc
from annular tears. The articular facets, upon lumbar flexion, resist
saggital translation (forward shear) by direct impaction of the
articular surfaces. Normally the facet joints do not have a weight
bearing function, but with disc space narrowing, as with aging and disc
disease, the joint may be required to bear as much as 70% of the axial
compressive forces. Facet joint pain is believed to emanate from the
synovial membrane in the joint capsule resulting from repeated
stretching, strain or subluxation of the joints with impingement of
nonarticular bony surfaces around the joint.

Nerve supply to the facet joints has been a matter of controversy and
the source of much of the disagreement regarding the techniques for
definitive treatment. The nerve supply originates from the medial
branches of the posterior primary rami of the spinal nerves. The nerve
curves around the medial end of the transverse process in a groove
formed by the junction of the transverse with the root of the superior
articular facet. Articular branches are given off to the zygoapophysial
joints both above and below the nerve. The anatomy differs at the L5
level in that the L5 dorsal ramus itself, rather than its medial branch
crosses the ala of the sacrum at its junction with the superior
articular process of the sacrum.

Diagnosis & Treatment

As stated previously, the diagnosis of lumbar facet syndrome is
entirely dependent upon the results of radiographically guided lumbar
facet blocks. This procedure can be performed by either 1)
Intra-articular local anesthetic infiltration or, 2) Medial nerve branch
blocks. The specificity of both procedures is entirely dependent upon
the experience of the operator and the incidence of false positive
results is not known. Several studies bear out the predictive value of
diagnostic facet blocks and advocate its use prior to radiofrequency
facet denervations.

Intra-articular blocks have the advantage of adding corticosteroids
which may reduce or abolish the inflammatory response. Medial nerve
blocks have the advantage of being prognostic of the results attainable
with radiofrequency denervation.

Conservative treatment consists of physical therapy to "unload" the
facet joints and other physical modalities for pain relief, however the
response to treatment is limited or inconsistent, several studies have
confirmed the benefit of radiofrequency lumbar facet denervations.
Several advancements have been made in the technique which have
increased its' safety and effectiveness. New 22 gauge disposable
electrodes have been developed which have greatly enhanced patient
comfort by allowing the physician to anesthetize and ablate the nerve
through a single needle. In addition the targeting approach for
lesioning has recently been modified to take into account the physical
spread of the current to maximize the "burn" area. These modification
have increased the likelihood of a successful denervation with confirmed
long term success rates between 35-76% in patients treated with this
procedure.