Real-time monitoring of stresses and displacements in cervical nuclei pulposi during cervical spine manipulation: a finite element model analysis.

OBJECTIVE: The objective of this study was to research the distribution of stresses and displacements in cervical nuclei pulposi during simulated cervical spine manipulation (CSM). METHODS: A 3-dimensional finite element model of C3/4~C6/7 was established. The detailed mechanical parameters of CSM were analyzed and simulated. During the process, the changes in stresses and displacements of cervical nuclei pulposi within the model were displayed simultaneously and dynamically. RESULTS: Cervical spine manipulation with right rotation was targeted at the C4 spinous process of the model. During traction, levels of stresses and displacements of the nuclei pulposi exhibited an initial decrease followed by an increase. The major stresses and displacements affected the C3/4 nucleus pulposus during rotation in CSM, when its morphology gradually changed from circular to elliptical. The highest stress (48.53 kPa) occurred at its right superior edge, on rotating 40° to the right. It protruded toward the right superior, creating a gap in its left inferior aspect. The highest displacement, also at 40° right, occurred at its left superior edge and measured 0.7966 mm. Dimensions of stresses and displacements reduced quickly on rapid return to neutral position. CONCLUSION: The morphology of the C3/4 nucleus pulposus changed during CSM with right rotation, and it created a gap in its left inferior aspect. Biomechanically, it is more safe and rational to rotate toward the healthy side than the prolapsed side of the intervertebral disk during CSM. Upon ensuring due safety, the closer the application force is to the diseased intervertebral disk, the better is the effect of CSM.

Influence of cervical spine position, turning time, and cervical segment on cadaver intradiscal pressure during cervical spinal manipulative therapy.

OBJECTIVE: The purpose of this study was to determine influences of cervical spine positions, turning times, and cervical segments on cadaver intradiscal pressure (IDP) during cervical spinal manipulative therapy (SMT). METHODS: We simulated cervical SMT with stretching and rotation on 7 fresh adult cadaver specimens in the material test system machine. The changes in IDP for cervical intervertebral disks (C3/4, C4/5, and C5/6) during 4 different stages of cervical SMT (physiologic state, end of the traction stage, turning stage, and finish time) were monitored. Five different cervical positions (extension 20°, extension 10°, neutral position, flexion 10°, flexion 20°) and 3 different turning times (0.06, 0.11, 0.16 second) of IDP were monitored, using micropressure sensors. RESULTS: The variable tendency of cervical IDP presents a "V"-shaped curve during SMT. The 4 stages of SMT had significantly different IDP (F=5498.956; P<.001). There were also significant differences in IDP between 5 cervical positions ([F=1371.216; P<.001], [flexion 20°>flexion 10°>neutral position>extension 10°>extension 20°]), 3 turning times ([F=419.530; P<.001], [0.06>0.11>0.16 seconds]), and 3 cervical segments ([F=84.282; P<.001], [C3/4

Morphological asymmetry of the atlas and its clinical implications.

OBJECTIVE: The aim of this study was to investigate the asymmetry of the adult atlas by deviation frequencies using 3-dimensional (3D) computer models based on the computed tomographic (CT) spine data from healthy patients. METHODS: Sixty adult atlas computer models were reconstructed from CT data of the cervical spine. The morphological asymmetries were investigated and measured with 3D software. Asymmetry in the morphology of the vertebral artery groove was observed, and the angles between the lines connecting the apices of transverse processes and the apices of anterior and posterior tubercles were measured. The lengths of the left and right posterior arches were measured, and the differences in values were categorized. RESULTS: We observed 7 cases (11.67%) with asymmetrical vertebral artery groove forms. There were 4 different categories: foramen-shaped, semi-foramen-shaped, deep, and superficial grooves. The asymmetry was of different shapes on both sides. Relative to the lines connecting the apices of anterior and posterior tubercles, the asymmetry frequency of the transverse processes and the posterior arch length was 6.67% and 16.67%, respectively. CONCLUSIONS: For the specimens in this study, variation in morphology of the atlas was common. Asymmetry of apices of transverse processes, posterior arches, and vertebral artery grooves should be taken into account during clinical palpation, diagnostic imaging, and treatment including spinal manipulation.