Tensile stretching of cervical facet joint capsule and related axonal changes

Abstract

This study examines axonal changes in goat cervical facet joint capsules (FJC) subjected to low rate loading. Left C5-C6 FJC was subjected to a series of tensile tests from 2 mm to failure using a computer-controlled actuator. The FJC strain on the dorsal aspect was monitored by a stereo-imaging system. Stretched (n = 10) and unstretched (n = 7) capsules were harvested and serial sections were processed by a silver impregnation method. The mean peak actuator displacement was 21.3 mm (range: 12-30 mm). The average peak strain encompassing various regions of the capsule was 72.9 ± 7.1%. Complete failure of the capsule was observed in 70% of the stretched capsules. Silver impregnation of the sections revealed nerve fibers and bundles in all the regions of the capsule. A blinded analysis of digital photomicrographs of axons revealed a statistically significant number of swollen axons with non-uniform caliber in stretched FJCs. Axons with terminal retraction balls, with occasional beaded appearance or with vacuolations were also observed. Stretching the FJC beyond physiological range could result in altered axonal morphology that may be related to secondary or delayed axotomy changes similar to those seen in central nervous system injuries where axons are subjected to stretching and shearing. These may contribute to neuropathic pain and are potentially related to neck pain after whiplash events.

Ketorolac Reduces Spinal Astrocytic Activation and PAR1 Expression Associated with Attenuation of Pain after Facet Joint Injury

“…Color image is available online at www.liebertpub.com/neu injury. [5][6][7]43 Injured afferents release excitatory neuropeptides, such as substance P, glutamate, and calcitonin gene-related peptide, at their terminals that directly activate astrocytes and other glial cells in the spinal cord that can amplify neuronal excitability via the release of pro-inflammatory cytokines and prostaglandins. [25][26][27] Glial activation was observed here at 7 days after painful facet joint distraction (Fig.…”

“…1,2 The cervical facet joint is a common source of neck pain identified in clinical studies, 3,4 with mechanical reports also documenting nociceptor innervation of the capsule and its mechanical vulnerability for injury from non-physiologic joint and spine motions. [5][6][7] Despite reports suggesting that injury to the cervical facets is a major contributor to persistent neck pain, 8 the cellular mechanisms by which pain is initiated and maintained after joint injury have yet to be defined.…”

The Physiological Basis of Cervical Facet-Mediated Persistent Pain: Basic Science and Clinical Challenges

“…12,17,27,41,43,55,57,71 Mechanical stretch of the facet to failure (mean ± SD, 72.9% ± 7.1% strain) produces morphological abnormalities (ie, focal swelling, vacuolations, and terminal retraction balls) in the axons innervating the facet capsule in the goat. 43 However, as described above, subfailure stretch of the facet capsule exceeding physiologic strains is sufficient to damage the ligament's microstructure and induce pain. 27,76 As such, characterizing the functional changes of neurons and understanding their relationships to the local injury mechanisms during loading below the tissue failure threshold are important, and many studies have initiated these investigations using both in vivo and in vitro models.…”

“…67,80,85 Because the facet joints are innervated by mechanoreceptive and nociceptive afferent fibers, 5,14,42 any abnormal loading of the facet joint can also generate forces that mechanically load those afferents and initiate a host of pathophysiological responses that can lead to pain. 43,53,54,57 In particular, injury of the innervated ligament tissue that encapsulates the synovial joint has the potential to generate pain (FIGURE 1). 53,54 As such, this commentary focuses on the physiological mechanisms by which biomechanical loading of the facet capsule can lead to pain, and the challenges in defining relevant thresholds for pain, biomechanical tissue injury, and neuronal responses, by integrating findings from basic science studies to inform the clinical management and/or diagnosis of whiplash-mediated facet pain.…”

Stretch-induced network reconfiguration of collagen fibres in the human facet capsular ligament

“…The cervical facet capsular ligament (FCL) is a quintessential example material in which the subfailure tissue responses have an important physiological impact, even in the absence of macrostructural failure. The FCL is innervated by nociceptive neurons that are responsible for pain sensation [1][2][3]. Excessive FCL stretch, which can occur during neck trauma, can activate the nociceptive pain fibres embedded in the collagen matrix of the FCL [1,3,4].…”