Dalley, 10th Edition

101

Vertebral Column

are long, thin, and broad in the cervical region, thicker in the thoracic region, and thickest in the lumbar region. These lig aments resist separation of the vertebral lamina by limiting abrupt exion of the vertebral column and thereby prevent injury to the IV discs. The strong, elastic yellow ligaments help preserve the normal curvatures of the vertebral column and assist with straightening of the column after exing. Adjoining spinous processes are united by weak, often membranous interspinous ligaments and strong brous su praspinous ligaments (Fig. 2.20). The thin interspinous ligaments connect adjoining spinous processes, attaching from the root to the apex of each process. The cord-like band forming the supraspinous ligaments connects the tips of the spinous processes from C7 to the sacrum and merge superiorly with the nuchal ligament at the back of the neck (Fr. nuque , back of the neck) (Fig. 2.20A). Unlike the interspinous and supraspinous ligaments, the strong, broad nuchal ligament (L. ligamentum nuchae ) is composed of thickened broelastic tissue. It extends as a median band from the external occipital protuberance and posterior bor der of the foramen magnum to the spinous processes of the cervical vertebrae. Because of the shortness and depth of the C3–C5 spinous processes, the nuchal ligament provides at tachment for muscles that attach to the spinous processes of vertebrae at other levels. The intertransverse ligaments ,

connecting adjacent transverse processes, consist of scat tered bers in the cervical region and brous cords in the thoracic region (Fig. 2.20B). In the lumbar region, these ligaments are thin and membranous. CRANIOVERTEBRAL JOINTS There are two sets of craniovertebral joints, the atlantooc cipital joints , formed between the atlas (C1 vertebra) and the occipital bone of the cranium, and the atlantoaxial joints , formed between the atlas and axis (C2 vertebra) (Fig. 2.22). The Greek word atlanto refers to the atlas (C1 vertebra). The craniovertebral joints are synovial joints that have no IV discs. Their design gives a wider range of movement than in the rest of the vertebral column. The articulations involve the occipital condyles, atlas, and axis. Atlantooccipital Joints. The articulations are between the superior articular surfaces of the lateral masses of the atlas and the occipital condyles (Fig. 2.22; see Fig. 2.8A, B). These joints permit nodding of the head, such as the exion and extension of the head occurring when indicating approval (the “yes” movement). These joints also permit sideways tilt ing of the head. The main movement is exion, with a little lateral exion and rotation. They are synovial joints of the condyloid type and have thin, loose joint capsules.

2

Tectorial membrane (cut) Alar ligament

Occipital bone

Articular facet of dens for transverse ligament of atlas (part of median atlantoaxial joint)

Left atlantooccipital joint

Capsule of atlantooccipital joint

# *

#

Superior longitudinal band Transverse ligament of atlas Inferior longitudinal band

Atlas (C1)

Tectorial membrane (accessory part) Capsule of right lateral atlantoaxial joint Posterior longitudinal ligament becoming tectorial membrane (cut)

Cruciate ligament (cut)

Axis (C2)

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Dens of axis

(A) Posterior view

Atlantoaxial joints

Median Lateral

Atlas (C1)

Margins of foramen magnum Occipital condyle # *

Axis (C2)

(B) Anterior view

Craniovertebral joints

FIGURE 2.22. Capsules, ligaments, and tectorial membrane of craniovertebral joints. A. Ligaments of atlantooccipital and atlantoaxial joints. The tectorial membrane and the right side of the cruciate ligament of the atlas have been removed to show the attachment of the right alar ligament to the dens of C2 (axis). B. Median and lateral atlantoaxial joints. Sliding movements in opposite directions occur at the lateral atlantoaxial joints as the atlas rotates around the dens.