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.

Variable morphology of the axis vertebrae in 100 specimens: implications for clinical palpation and diagnostic imaging.

OBJECTIVE: The purpose of this study was to investigate and measure the variable morphologies of axis vertebrae and explore the clinical significance of variations as it may pertain to clinical palpation and diagnostic imaging. METHODS: The common variable morphologies in 100 specimens of intact dry adult axis vertebrae (Chinese) were investigated and measured. The frequencies in deviation of odontoid processes, deviation of spinous processes, and presence of bifid spinous processes were observed. The distances between the apices of transverse processes and inferior articular facets were also measured. RESULTS: Variable morphologies of C2 that we observed were deviation of odontoid processes (14 cases, 14.0%), deviation of spinous processes (3 cases, 3.0%), and bifid spinous processes (95 cases, 95.0%). Of the bifid spinous processes, 56 had a process on the left side equal to the right side, 21 were longer on the left, and 18 were longer on the right. The distances between apices of transverse processes and inferior articular facets in the left side of C2 were 17.67 +/- 2.47 mm, and that of the right side were 17.81 +/- 2.55 mm. CONCLUSIONS: Because variable morphology of the axis is common, congenital deviation of the odontoid process, deviation of the spinous process, and asymmetrical bifid spinous processes should be taken into account during clinical palpation and diagnostic imaging.

Morphological changes of the in vitro cervical vertebral canal and its cast form during flexion, extension, and lateral bending.

OBJECTIVE: The purpose of this study was to investigate and measure morphological changes in the vertebral canal and its cast form at the level of the cervical spine in vitro during flexion, extension, and lateral bending in cadaver specimens. METHODS: The morphological changes of vertebral canal and its contents were investigated and measured during experimental flexion, extension, and lateral bending of the cervical spine with 10 fresh specimens (Chinese); the cross-sections and sagittal diameters were also measured by pouring liquid wax into the intervertebral canal. RESULTS: During lateral bending, the nucleus pulposus was pushed to the opposite side and the inferior cervical nerve roots of the opposite side were stretched. Cross-sectional diameter at the level of C6-7 during flexion was larger than that in lateral bending (P < .05). Comparing extension with flexion, we found that changes in all segments' areas were significant (P < .05). There was no significant difference in the sagittal diameter at any segment during all postures (P > .05). CONCLUSIONS: During lateral bending, the nucleus pulposus of neck were pushed into the opposite side, and inferior cervical nerve roots of the opposite side were stretched. The C5, C6, and C7 nerve roots appeared to undergo excessive stretch when an excessive lateral bending beyond the physiologic range was undergone. This study provides some additional evidence about the mechanics of cervical spine motion.