Neural Response of Cervical Facet Joint Capsule to Stretch: A Study of Whiplash Pain Mechanism

Anomalous fiber realignment during tensile loading of the rat facet capsular ligament identifies mechanically induced damage and physiological dysfunction

“…The current study detected anomalous realignment in that aspect of the joint at displacements (0.6270.32 mm; Table 1) near the 0.7 mm that produces collagen fiber disorganization in the lateral capsule, increased expression of pain-related neuromodulators in the peripheral and central nervous system, and significant behavioral hypersensitivity (Lee and Winkelstein, 2009;. Electrophysiological studies have also provided evidence of facet-mediated pain through the identification of nociceptor activation and mechanoreceptor saturation at loading magnitudes below gross tissue rupture (Lu et al, 2005a;Lu et al, 2005b). However, in all of those studies, the threshold for subfailure injury was inferred using peak strain in the facet capsule due to a lack of any visual evidence of damage.…”

“…Additionally, decreased tissue stiffness and altered viscoelastic properties have been identified (Panjabi and Courtney, 2001;Panjabi et al, 1999), but no study has been able to identify a specific point during loading when the tissue structure changes during assumed injurious loading. In addition to the potential for generating pain (Cavanaugh et al, 2006;Lee et al, 2004b;Lee and Winkelstein, 2009;Lu et al, 2005a;Lu et al, 2005b), subfailure loading produces an increase in fibroblast-mediated remodeling (Provenzano et al, 2005), further suggesting the occurrence of structural damage prior to tissue failure. These studies attributed an array of mechanical and cellular responses to tissue damage from subfailure loading, but required multiple specimens to identify an injury threshold.…”

Detection of Altered Collagen Fiber Alignment in the Cervical Facet Capsule After Whiplash-Like Joint Retraction

“…The magnitude of the maximum unrecovered e 1 in over half of the specimens (Table 3) exceeded the strain threshold reported to activate nociceptor firing defined in a goat model of facet capsule stretch. 18 In addition, previous work with a rat model has demonstrated that facet joint displacements that produce persistent pain symptoms also induce laxity in the capsular ligament and collagen fiber disorganization. 15,16,22 When placed in the context of these other in vivo studies, the detection of altered fiber alignment and unrecovered strain observed after facet retraction in the current study would suggest that whiplash-like loading may be sufficient to generate facet-mediated pain.…”

“…In vivo models of facet joint injury indicate that altered collagen fiber organization and facet capsular ligament laxity may be produced following joint loading that produces persistent pain. 16,18,22 Furthermore, these in vivo studies demonstrate that neither partial failure nor capsule rupture is required to initiate facet-mediated pain, 22 suggesting painful facet joint injuries cannot be identified through traditional load-based or medical imaging techniques. Therefore, mechanistic studies are needed to understand the microstructural origins of facet capsular ligament damage and determine the potential for altered microstructural organization and laxity in the human facet capsule following whiplashlike facet retraction.…”

The failure response of the human cervical facet capsular ligament during facet joint retraction

“…Mechanical trauma to ligament tissue can cause microstructural damage that may not be visually detected (Lu et al, 2005;Petterson et al, 1997;Quinn and Winkelstein, 2008;Voyvodic et al, 1997). Because of this, common macroscale indicators of tissue damage, such as a visible tissue rupture or partial failure during mechanical loading, may not fully characterize the threshold for injury to ligament tissue.…”