Joint Distractions Sufficient to Produce Pain Increase Collagen Fiber Undulation in the Cervical Facet Capsular Ligament in the Rat

Whiplash and its associated disorders are significant societal and health problems with half of affected patients reporting neck pain at one year after injury [1]. The cervical facet joint and its capsule have been identified in both biomechanical and clinical studies as a common site of painful injury during whiplash [2]. Also, in vivo joint distractions, which mimic the facet capsule loading reported in human cadaveric whiplash simulations, can produce behavioral hypersensitivity suggestive of chronic pain symptoms in the rat [3]. Increased laxity and decreased stiffness in the capsule are also produced after both painful joint distractions in the rat [4] and whiplash loading of the neck using cadaveric spines [5]. Together, these findings suggest that subfailure loading of the joint and its capsule produces both mechanical changes and pain. Yet, identifying the mechanical response associated with pathophysiological conditions in the capsular ligament requires an understanding of if, and how, its load-bearing microstructure is altered following painful loading.