Reference data for assessing widening between spinous processes in the cervical spine and the responsiveness of these measures to detecting abnormalities.

Background Context: Traumatic injury to the spine is evaluated and treated based on the perceived stability of the spine. Recent classification schemes have established the importance of evaluating the discoligamentous complex to fully comprehend stability. There are a variety of techniques to evaluate the discoligamentous complex, including assessment of interspinous distance. However, there currently are no clinically validated methods to define and assess abnormal interspinous widening.

Purpose: The purpose of the study was to provide reference data and evidence to support the objective use of spinous process widening in the diagnosis of cervical spine injury and instability.

Study Design: The study was designed to be biomechanical and observational.

Methods: Distances between spinous processes were measured from lateral flexion-extension X-rays of 156 skeletally mature asymptomatic subjects who reported never having had neck symptoms as well as 12 whole human cadavers before and after creating increasingly severe damage to posterior structures. Cervical interspinous distances were measured and then normalized to the width of the C4 vertebral end plate. The change in the distance from flexion to extension was also calculated.

Results: Descriptive statistics, including the 95% confidence intervals for each cervical level were tabulated for 863 levels in 149 analyzable asymptomatic volunteers. In the simulated cadaver model, interspinous widening was highly specific and mildly sensitive for detecting damage to the posterior structures of the cervical spine.

Conclusions: This study provides reference data that can be used to quantitatively assess interspinous process widening in the cervical spine. Application of the reference data to a cadaver model of cervical trauma suggests that although objective evidence of abnormal widening may be uncommon, when present, it is suggestive of extensive damage to the cervical spine. Derived from this data were two "rule of thumb" criteria to identify abnormal interspinous widening in flexion X-rays; when greater than 30% relative to an adjacent level (40% between C1-C2 and C2-C3) or greater than 50% of the anterior-posterior width of the C4 vertebral body (30% for C2-C3).