Threshold cervical range-of-motion necessary to detect abnormal intervertebral motion in cervical spine radiographs

Study Design. Whole human cadaver model to assess a common diagnostic test for cervical spine stability. Objective. Determine criteria that can be used to determine if sagittal plane angular motion of the head/neck during a cervical spine flexion/extension study is adequate to reliably assess intervertebral motion (IVM). Summary of Background Data. Flexion/Extension radiographs of the cervical spine are commonly used to help identify specific abnormalities in IVM. Several authors have recognized that inadequate patient effort can make flexion/extension studies unreliable, but validated guidelines for assessing the adequacy of these studies are not available. Methods. Increasingly severe anterior-to-posterior (N = 6), and posterior-to-anterior (N = 6) soft tissue injuries were simulated in the cervical spines of 12 human cadavers. Sagittal plane radiographic images were taken with 4 gradually increasing amounts of overall flexion and extension motion of the head. IVM was measured for each level of sagittal plane rotation of the head/neck using previously validated computer-assisted methods. Results. With less than 60 degrees of sagittal plane rotation of the head/neck, intervertebral rotation or displacement was almost never greater than the 95% confidence interval previously established for asymptomatic people. Even with 60 degrees or more motion, intervertebral rotation and displacement were within normal limits after extensive damage to the soft-tissues. The center- of-rotation was the most sensitive measure for detecting soft tissue damage. Conclusion. The results of this study suggest that clinicians should make sure patients can flex and extend their head/neck to a minimum range of 60 degrees before evaluating them for a dynamic motion study to assess cervical spine stability. Even with adequate motion, interverterbral rotation and translation can remain within normal limits in the presence of extensive soft tissue damage. The most sensitive measure for detecting soft tissue damage was center-of-rotation although it lacks specificity, particularly in the presence of underlying degenerative and is not readily assessed in most clinical situations.