Detection of altered collagen fiber alignment in the cervical facet capsule after whiplash-like joint retraction.

The cervical facet joint has been identified as the source of pain in patients with whiplash-associated disorders, but most clinical studies report no radiographic evidence of tissue injury in these disorders. The goal of this study was to utilize quantitative polarized light imaging to assess the potential for altered collagen fiber alignment in human cadaveric cervical facet capsule specimens (n = 8) during and after a joint retraction simulating whiplash exposure. Although no evidence of ligament damage was detected during whiplash-like retraction, mechanical and microstructural changes were identified after loading. Retraction produced significant decreases in ligament stiffness (p = 0.0186) and increases in laxity (p = 0.0065). In addition, image analysis indicated that 21.1 ± 17.1% of the capsule sustained principal strains that were unrecovered immediately after retraction. Altered collagen fiber alignment was detected in 32.7 ± 22.9% of the capsule after retraction. The capsule regions with unrecovered strain and altered fiber alignment after retraction were significantly co-localized with each other (p < 0.0001), suggesting the altered mechanical function may relate to a change in the tissue's fiber organization. The identification of altered fiber alignment in this ligament following retraction without any tears implicates the whiplash kinematic as a potential cause of microstructural damage that is not detectable using standard clinical imaging techniques.