What is the pathophysiology of facet joint pain in low back pain (LBP)?

Updated: Aug 22, 2018
  • Author: Jasvinder Chawla, MD, MBA; Chief Editor: Stephen A Berman, MD, PhD, MBA  more...
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Answer

Answer

The superior and inferior articular processes of adjacent vertebral laminae form the facet or zygapophyseal joints, which are paired diarthrodial synovial articulations that share compressive loads and other biomechanical forces with the intervertebral disk. Like other synovial joints, the facets react to trauma and inflammation by manifesting pain, stiffness, and dysfunction with secondary muscle spasm leading to joint stiffness and degeneration. This process is borne out, as previously described, through the degenerative cascade of the trijoint complex. Numerous radiological and histological studies have shown that diskal and facet degeneration are linked and that, over time, degeneration of the segment leads to osteoarthritis of the facets.

Studies of provocative intra-articular injection techniques demonstrated local and referred pain into the head and upper extremities from cervical facets, into the upper midback and chest wall from thoracic facets, and into the lower extremity from the lumbar facets. The fibrous capsule of the facet joint contains encapsulated, unencapsulated, and free nerve endings.

Immunohistochemical studies have demonstrated nerve fibers containing neuropeptides that mediate and modulate nociception (eg, SP, CGRP, VIP). SP-filled nerve fibers have been found in subchondral bone and degenerative lumbar facets subjected to aging and cumulative biomechanical loading. In fact, SP levels are correlated with the severity of joint arthritis. The infusion of SP into joints with mild disease reportedly accelerates the degenerative process. Furthermore, these chemicals and inflammatory mediators have been linked to proteolytic and collagenolytic enzymes that cause osteoarthritis and degradation of the cartilaginous matrix. Therefore, evidence of nociceptive afferents and the presence of algogenic neuropeptides, such as SP and CGRP, in facets and periarticular tissues support a role for these structures as spinal pain generators. Clinical research has demonstrated facet pain in 54-67% of patients with neck pain, 48% of patients with thoracic pain, and 15-45% of patients with LBP.


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