Dynamic Distraction of the Cervical Facet Joint Produces Higher Mechanical Allodynia than Quasistatic Distraction: Implications of Displacement Thresholds for Pain in Whiplash Loading

Chronic neck pain due to whiplash injury results in 10.2 million visits to ambulatory care settings annually in the United States [1]. During the whiplash kinematic, the cervical facet joint undergoes tensile loading at a strain rate of 500–1000%/s [2,3]. In addition, distraction of the facet joint and its capsule in animal models produces both firing of pain fibers in the capsule and persistent behavioral hypersensitivity (measured by mechanical allodynia) [4,5]. In vivo studies have demonstrated a dependence of pain symptoms on the magnitude of applied joint distraction, with some distraction magnitudes not producing any changes in physiologic outcomes or pain [5]. However, in those studies, joint loading was applied quasistatically, despite the dynamic nature of whiplash. While such work provides insight into mechanisms of facet-mediated neck pain and suggests that the magnitude of joint distraction may affect pain symptoms, those studies did not incorporate the dynamic effects necessary for modeling whiplash. It remains unclear whether dynamic loading of the cervical facet joint can induce behavioral hypersensitivity, and if so, whether the degree of behavioral sensitivity depends on the distraction magnitude. This pilot study compared the effects of dynamically and quasistatically applied facet joint loading on ligament kinematics and corresponding pain symptoms.