The cervical facet capsule and its role in whiplash injury - A biomechanical investigation

Study Design. Cervical facet capsular strains were determined during bendin g and at failure in the human cadaver. Objective. To determine the effect of an axial pretorque on facet capsular strains and estimate the risk for subcatastrophic capsular injury during no rmal bending motions. Summary of Background Data. Epidemiologic and clinical studies have identif ied the facet capsule as a potential site of injury and prerotation as a ri sk factor for whiplash injury. Unfortunately, biomechanical date on the cer vical facet capsule and its role in whiplash injury are not available. Methods. Cervical spine motion segments were tested in a pure-moment test f rame and the full-field strains determined throughout the facet capsule. Mo tion segments were tested with and without a pretorque in pure bending. The isolated facet was then elongated to failure. Maximum principal strains du ring bending were compared with failure strains, by paired t test. Results. Statistically significant increases in principal capsular strains during flexion-extension loading were observed when a pretorque was applied . All measured strains during bending were significantly less than strains at catastrophic joint failure. The same was true for subcatastrophic ligame nt failure strains, except in the presence of a pretorque. Conclusions. Pretorque of the heed and neck increases facet capsular strain s, supporting its role in the whiplash mechanism. Although the facet capsul e does not appear to be at risk for gross injury during normal bending moti ons, a small portion of the population may be at risk for subcatastrophic i njury.