Cervical Facet Joint Mechanics: Its Application to Whiplash Injury

Epidemiological and clinical studies have identified the cervical facet capsule as a potential site of whiplash injury and prerotation of the head and neck as a risk factor for whiplash injury. However, biomechanical data related to the cervical facet capsule and its role in whiplash injury remain limited in the literature. In this study, cervical spine motion segments were tested in a pure moment test frame and the full field strains were determined throughout the facet capsule. Motion segments were tested with and without a pretorque in pure bending. Bending tests were followed by isolated facet elongation tests to failure. Maximum principal strains during bending were compared to failure strains.

Statistically significant increases in principal capsular strains were observed in the facet which was contralateral to the pretorque. In contrast, no significant differences were present in the ipsilateral facet when large flexion-extension moments were applied. Capsular strains during bending were significantly less than strains at catastrophic joint failure. The same was true for subcatastrophic failures, except in the presence of a contralateral pretorque. The results of this study indicate that pretorque of the head and neck increases facet capsular strains, supporting the role of this joint in the whiplash injury mechanism. The facet capsule does not appear to be at risk for gross injury during pure bending through an angular range of motion similar to the range of motion experienced in experimental studies of whiplash. However, the findings of this study indicate that a small portion of the population may be at risk for subcatastrophic injury when exposed to these loads.