A simple outline format of the spinal vertebral joints and ligaments.
Joints of the Vertebral Column
The vertebrae from C2 to S1 articulate with one another at joints between their bodies and between their articular processes.
Joints of the Vertebral Bodies
The anterior intervertebral joints are secondary cartilaginous joints (symphysis) which are designed for strength and weight bearing.
The articulating surfaces of the adjacent vertebrae are covered with hyaline cartilage and are connected by a fibrocartilaginous intervertebral disc and ligaments.
The intervertebral discs provide the strongest attachment between the bodies of the vertebrae. In addition to these discs, strong anterior and posterior longitudinal ligaments unite the bodies.
In the cervical and lumbar regions, the discs are thick anteriorly making them wedge shaped. This structure of the discs is related to the normal curvatures in these regions.
The anterior longitudinal ligament
This is a strong, broad fibrous band that covers and connects the anterior aspects of the bodies of the vertebrae and intervertebral discs.
This ligament is thickest when opposite the discs.
It extends from the pelvic surface of the sacrum to the anterior tubercle of C1 (atlas) and the occipital bone of the skull, anterior to the foramen magnum.
The fibres of this ligament firmly attach to the intervertebral discs and the periosteum of the vertebral bodies.
This strong ligament helps to maintain the stability of the joints between the vertebral bodies and helps prevent hyperextension of the vertebral column.
The posterior longitudinal ligament
This is a narrower, weaker band than the anterior longitudinal ligament. It runs along the posterior aspect of the vertebral bodies, within the vertebral canal.
It is broadest superiorly where it is continuous with the tectorial membrane, which is attached to the occipital bone on the interior aspect of the foramen magnum.
It is attached to the intervertebral discs and the posterior edges of the vertebral bodies from the axis (C2) to the sacrum.
The posterior longitudinal ligament also helps to prevent hyperflexion of the vertebral column and posterior protrusion of the nucleus pulposus of the disc.
The Intervertebral Discs
These are plates of fibrocartilage corresponding to the shape to the articular surfaces of the vertebral bodies.
The discs play a leading role in weight bearing and a lesser role in movement.
Each disc is composed of an external anulus fibrosus, which surrounds the internal gelatinous nucleus pulposus.
The anuli fibrosi insert into the smooth, rounded rims on the articular surfaces of the vertebral bodies.
The nuclei pulposi contact the hyaline cartilage plates, which are attached to the rough articular surfaces of the vertebral bodies.
There is no disc between C1 (atlas) and C2 (axis). The most inferior functional disc is between L5 and S1.
The Anulus Fibrosus
This is the fibrous ring of the intervertebral disc. It is composed of concentric lamellae of fibrocartilage, which run obliquely from one vertebra to another.
Some fibres in one lamella are at right angles to those in the adjacent ones. This arrangement, while allowing movement between vertebrae, provides a very strong bond between them.
The lamellae are thinner and less numerous posteriorly than they are anteriorly or laterally.
The Nucleus Pulposus
This is the central core of the intervertebral disc. It is more cartilaginous than fibrous and is normally highly elastic.
It is located more posteriorly than centrally and has a high water content until old age.
The nucleus pulposus (L. pulpa, fleshy) acts like a shock absorber for axial forces and like a semi-fluid ball bearing during flexion, extension, rotation, and lateral flexion of the vertebral column.
It becomes broader when compressed.
The nucleus pulposus is avascular. It receives its nourishment by diffusion from blood vessels at the periphery of the anulus fibrosus and from the adjacent surfaces of the vertebral bodies.
Protrusions of the nucleus pulposus usually occur posterolaterally, where the anulus fibrosus is weak and poorly supported by the posterior longitudinal ligament. The protruding part of the nucleus pulposus may compress an adjacent spinal nerve root, causing severe lower back pain and/or leg pain.
Joints of the Vertebral Arches
Zygapophyseal Joints (facet joints)
These are synovial joints between the interior articular process of superior vertebrae and the superior articular process of inferior vertebrae. These plane joints are known as zygapophyseal joints (facet joints).
The flat surfaces of the articular facets are covered with hyaline cartilage.
Each joint is surrounded by as thin, loose articular capsule that is attached to the articular margins of the processes.
The fibrous capsules are longer and looser in the cervical region than in the thoracic and lumbar regions. The fibrous capsule of each joint is lined with a synovial membrane.
The facet joints permit gliding movements between the vertebrae.
In the cervical and lumbar regions, these joints bear some weight, sharing this function with the intervertebral discs.
These joints control flexion, extension, and rotation of adjacent cervical and lumbar vertebrae.
Most of the movement in the vertebrae occur in these two areas.
Accessory Ligaments of the Intervertebral Joints
The laminae of adjacent vertebral arches are joined by broad, elastic bands called ligamentum flava (yellow ligaments), which extend almost vertically from the lamina above to the lamina below.
The ligamentum flavum was given its name because of its fibres consist mainly of yellow elastic tissue (L. flavus, yellow).
The ligaments are attached superior to the anterior surfaces of the inferior borders of a pair of laminae, and inferiorly to the posterior surfaces of the superior border of the next succeeding pair.
Some of their fibres extend to the articular capsule of the facet joints and contribute to the posterior boundaries of the intervertebral foramina.
The ligamentum flava help to preserve the normal curvature of the vertebral column and to straighten the column after it has been flexed.
Interspinous and Supraspinous Ligaments
Weak interspinous ligaments and a strong cord-like supraspinous ligament joint adjacent spinous processes.
These ligaments are represented superiorly by the ligamentum nuchae, a triangular medial septum between the muscles on each side of the posterior aspect of the neck.
These are ligaments connecting adjacent transverse processes, consists of a few scattered fibres, except in the lumbar region where they are membranous and more substantial.
The Craniovertebral Joints
The suboccipital joints are between the skull and C1 (atlas), and between C1 and C2 (atlas and axis). They are called the atlanto-occipital and atlanto-axial joints.
The main differences between these joints and others in the vertebral column are (1) they are synovial only, there are no intervertebral discs, and (2) there are no zygapophyseal joints (facet).
The Atlanto-occipital Joints
These articulations are between C1 (atlas) and the occipital condyles. They permit nodding of the head (i.e., the flexion and extension of the neck that occurs when indicating approval).
The atlanto-occipital joints, one on each side, are between the superior articular facets on the lateral masses of C1 and the occipital condyles.
They are condyloid type of synovial joints.
They have thin, loose articular capsules that are lined with synovial membrane.
The skull and C1 are also connected by anterior and posterior atlanto-occipital membranes, which extend from the anterior and posterior arches of C1 to the anterior and posterior margins of the foramen magnum.
They prevent excessive movement of the atlanto-occipital joints.
The transverse ligament of the atlas is a strong band extending between the tubercles on the lateral masses of C1 vertebrae.
It holds the dens of C2 against the anterior arch of C1. There is a synovial joint between them.
Vertically oriented superior and inferior bands pass from the transverse ligament to the occipital bone superiorly and to the body of C2 inferiorly.
They form the cruciform ligament (L. crux, cross) which was given this name because of its resemblance to a cross.
The alar ligaments extend from the sides of the dens to the lateral margins of the foramen magnum.
These short, strong, rounded cords attach the skull to C2 vertebra.
They check rotation and side-to-side movements of the head.
The Atlanto-axial Joints
These are synovial joints between C1 and C2 vertebrae. There are two lateral joints and one medial joint.
The movement of these joints is rotation, which allows the head to be turned from side to side.
During this movement, the skull and C1 rotate as a unit on C2.
Alar ligaments prevent excessive rotation of these joints.
Movements of the joints between the skull and C1 and between C1 and C2 vertebrae are augmented by the flexibility of the neck owing to movements of the joints of the vertebral column in the middle and inferior cervical regions.
During rotation of the head, the dens of C2 is held in a collar formed by the anterior arch of the atlas and the transverse ligament of the atlas.
The articulation of the dens with C1 is a pivot joint.
Movements of the Vertebral Column
The range of movement of the vertebral column varies considerably according to the individual.
The extreme extension exhibited by acrobats who can put their heads between their lower limbs would be hyperextension in almost everyone.
The normal range of movement is limited by (1) the thickness and compressibility of the intervertebral discs, (2) the resistance of the muscles and ligaments of the back, and (3) the tension of the articular capsules of the zygapophyseal (facet) joints.
Movements between adjacent vertebrae take place on the resilient nuclei pulposi of the intervertebral discs and at the facet joints.
Although movements between adjacent vertebrae are relatively small, especially in the thoracic region, the summation of all of the small movements produces a considerable range of movements of the vertebral column as a whole.
Movements of the vertebral column are freer in the cervical and lumbar regions than elsewhere. These regions are also the most frequent sites of aches, pain and serious injuries.
The thoracic region of the vertebral column is relatively stable owing to its connection to the sternum via the ribs and costal cartilages. In addition, the intervertebral discs are slightly thinner and their spinous processes overlap.
Extension is most marked in the lumbar region and generally is more extensive than flexion.
Flexion is greatest in the cervical region and is almost non-existent in the thoracic region.
During flexion of the lumbar region, the nucleus pulposus moves posteriorly, putting tension on the posterior part of the anulus fibrosus.
This is the major reason that posterolateral herniations of the nucleus pulposus through the anulus fibrosus are most common in the lower lumbar and lumbosacral regions.
Lateral flexion is greatest in the lumbar region; it is restricted by the ribs in the thoracic region. Because of the greater rotation and gliding movements between its vertebrae, rotation is most marked in the thoracic region.