Effects of Cervical Extension on Deformation of Intervertebral Disk and Migration of Nucleus Pulposus

Abstract

BackgroundWe theorized that active cervical extension should influence the position of the nucleus pulposus (NP) within the intervertebral disk (IVD) in the sagittal plane. Although several studies on the lumbar IVD have been conducted, there are no quantitative data for in vivo positional changes of the NP in the cervical IVD. ObjectiveTo evaluate the influence and mechanism of cervical extension on the deformation and migration of IVD and NP in the sagittal plane and understand underlying mechanisms of the extension maneuver. DesignAsymptomatic subjects underwent magnetic resonance imaging while supine with their cervical spines in neutral and extended positions. SettingAcademic medical center. ParticipantsTen young, healthy male participants (age range 19-30 years; mean 22.4 ± 1.64 years). MethodsT2-weighted sagittal images from C3-C4 to C6-C7 of subjects in both neutral and extension positions were analyzed. Main Outcome MeasurementsDeformation of IVD and positional change of NP were quantified and compared between neutral and extension positions. Intersegmental angles between vertebrae, horizontal positions of anterior and posterior IVD and NP margins, IVD outer and inner heights, and sagittal morphology of NP were quantified and compared between the neutral and extension positions. Correlations between the measured parameters and segmental extension angle were also investigated. ResultsAnterior and posterior IVD margins moved posteriorly with respect to the vertebral body in extension. Both NP margins remained unchanged relative to the vertebral body but moved anteriorly with respect to the IVD. IVD outer and inner heights in the anterior region increased in extension, and morphological changes of the NP were less noticeable when compared with its relative migration within the IVD. Most of the intradiskal changes were linearly correlated with the segmental extension angle. ConclusionsCervical extension induces anterior migration of the NP away from the posterior disk margin and may have a clinical effect on diskogenic neck pain resulting from internal disk disruption. Level of EvidenceNot applicable.