The (the craniocervical junction) is the most mobile section of the vertebral column. Because the occipital-atlanto-axial joint is capable of extremely complex patterns of motion, we will subdivide the upper cervical spine into two motion segments (C0/C1 and C1/C2), where each of these two motion segment consists of two adjacent bony structures and their associated soft tissues.
By summing the contribution of the two motion segments, we are able to account for the total range of motion of the upper cervical spine. Always keep in mind that the occiput, atlas, and the axis function as a unit whose individual movements are closely coupled one to another.
The clinical phenomenon of restricted vertebral motion can be attributed to factors that influence the capacity of paired facets, of the motion segment under investigation, to open and close. When we speak of the capacity of facets to and , we are referring primarily to the accordion-type movement that occurs during flexion (forward-bending) and extension (backward-bending), not separation-type movement. Under normal conditions, interverterbral facets open during flexion and close during extension (Click here to visualize normal flexion and extension from a -- -- -- .
Because of the orientation of the apophyseal joints, the shape of the vertebral disks, and the universal joint characteristics of the vertebral bodies, sidebending and rotation are coupled to the same side (Type II Mechanics). Join Dr. Philip E. Greenman, D.O., F.A.A.O., as he discusses Type II motion mechanics of typical cervical vertebrae.
The functionality of motion segments is most easily evaluated by employing translatory movement to the right and to the left to introduce a sidebending component. When testing a nonsymptomatic subject, the physician should feel translational resistance that is smooth and symmetric, indicating that the left and right facets are freely opening and closing as left and right sidebending occurs. Abnormal resistance to translation is an indication that either one facet is unable to fully open or that the contralateral facet is unable to fully close. For example, translating C5 from left to right on C6 tests the capacity C5 to left sidebend and left rotate on C6. Translation from left to right without abnormal resistance depends upon the ability of the left facet to close and the right facet to open. If there is resistance to translation from left to right, then there is restriction of left sidebending and left rotation of C5 on C6. It is inferred that this condition results from either the left facet being unable to close or the right facet being unable to open. In this , be sure to note that translation of the vertebra from right to left produces the same effect on the facets as right sidebending, and that translation of the vertebra from left to right produces the same effect as left sidebending.
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