Segmental Biomechanics

Although it may be clinically useful to describe the motions that occur at the cervical spine as separate motions, these motions correspond to the motion of the head alone, and do not describe what is occurring at the various segmental levels. It should be obvious that the range of head movement bears no relation to the range of neck movement, and that the total range is the sum of both the head and the neck motions.47

Flexion is described as an anterior osteokinematic rock/tilt of the superior vertebra in the sagittal plane, a superior-anterior glide of both superior facets of the zy-gapophysial joints, and an anterior translation/slide of the superior vertebra on the intervertebral disc. The produces a ventral compression and a dorsal distraction of the cervical disc. The uncovertebral joint lies on, or very near to, the axis of rotation for flexion and extension. Consequently, the main arthrokinematic motion that seems likely to be occurring here is an anterior spin (or very near spin).48 This appears especially probable because impairments of the uncovertebral joint seem to be unaffected by flexion or extension. It can be assumed then that the uncovertebral joint is only involved with side-flexion, and that uncovertebral restrictions will be detected in all cervical positions, although flexion partly disengages tlle joint due its posterior position on the vertebra.48

Although all of the following anatomic movement restrictors act to some degree on most of the components of flexion, the following act particularly on the associated movement component.

The anterior osteokinematic—restrained by the extensor muscles and the posterior ligaments (posterior longitudinal, interspinous, ligamentum flavum).

The superior-anterior arthrokinematic is restrained by the joint capsule, whereas the translation is restrained by the disc and the nuchal ligament.

Extension is described as a posterior osteokinematic sagittal rock, an inferior-posterior glide, and approximation of the superior facets of the zygapophysial joints, and a posterior translation of the vertebra on the disc. The uncovertebral joint undergoes a posterior arthrokinematic spin. The restrictors of the extension movement are the anterior prevertebral muscles and the anterior longitudinal ligament, which limit the osteokinematic; and the zygapophysial joint capsule, which restrains the arthrokinematic.48 The disc limits me posterior translation.

Glide of the ipsilateral uncovertebral join t, and a superior-lateral glide of the contralateral uncovertebral joint. A composite curved translation results. It is formed by the superior-inferior linear glides of the zygapophysial joints, the oblique inferior-medial and superior-medial glides of the uncovertebral joints, and the linear translation across the disc (Figure 14-8)

The osteokinematic rock can be limited by the contralateral scalenes and intertransverse ligaments. The uncovertebral and zygapophysial arthrokinematics can be limited by the joint capsule and the translation by the disc. If the side-flexion is limited, but the translation is okay, it is unlikely that the joint complex (the zygapophysial joint, disc, or uncovertebral joint) is impaired, and would tend to implicate muscle tightness.48 However, if the translation is also limited, there exists a problem with the joint complex.

Rotation is chiefly an osteokinematic rotation of the vertebra about a vertical axis that is coupled with ipsilateral side-flexion. Presumably, the translation follows the side-flexion, which is contralateral, resulting in the same uncovertebral and zygapophysial arthrokinematics that side-flexion does.48 With right rotation, the vertebral bodies (not the zygapophysial joints) of C2-4 flex and the vertebral bodies of C5-7 extend.

The clinician should be able to differentiate between a disc or zygapophysial joint impairment by using the end feel. A disc protrusion will result in a springy end feel, whereas a zygapophysial joint restriction will have an abrupt end feel.48

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