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Ligaments of the vertebrae - ...
Numerous joints exist between the various bones of the vertebral axis. These are complex joints exhibiting a wide range of motion, from obvious, noticeable movements to subtle movements that are not easily observed. While some anatomists attempt to classify these joints into specific joint categories such as plane or hinge or pivot, the truth is, most of them are composite, complex joints with multiaxial ranges of motion. There are three types of intervertebral joints between the general bones of the vertebral column: synovial joints, fibrous syndesmoses, and cartilaginous symphyses. While the movement occurring at any individual intervertebral joint is not significant, the additive movement of many intervertebral joints can be quite significant. The synovial intervertebral joints occur between the superior and inferior articular facets of neighboring vertebrae. They vary from region to region, being more planar in the cervical and thoracic regions and forming reciprocally curved surfaces in the lumbar region. Numerous ligaments span between the vertebrae to form syndesmotic joints. These include the anterior longitudinal ligament spanning along the anterior surfaces of the vertebral bodies, the posterior longitudinal ligament coursing along the posterior surfaces of the vertebral bodies, the supraspinous ligament connecting the tips of the spinous processes, and the ligamentum flavum interconnecting the laminae of neighboring vertebrae. Between the bodies of vertebrae is the symphyseal intervertebral disc. The intervertebral disc is a strong fibrocartilaginous structure found between vertebral bodies from the second cervical vertebra to the sacrum. Movements of the vertebral column are defined and limited by the thickness of the intervertebral disc and by the shape and orientation of the synovial articular facets. A thicker disc allows more movement than does a thinner disc. The cervical region of the vertebral column shows the most extensive range of motion. The upward inclination of the superior articular facets allows for appreciable movements of extension and flexion. Lateral flexion is also significant, but because the superior articular facets also have a medial inclination. Lateral flexion is always accompanied by a slight rotation. The thoracic region is the least mobile region of the column. The presence of thin discs and vertically oriented facets limits the movements of flexion and extension to relatively minor motions. The orientation of the articular facets should provide for free lateral flexion, but this movement is limited by the presence of the ribs and sternum. The thoracic region shows the greatest freedom of rotational movement. The lumbar region shows considerable movement in the flexion-extension plane, with extension having a greater range of motion than flexion. The orientation of the articular facets facilitates these movements. Slight movements of lateral flexion and rotation are also possible.