The intervertebral symphysis is the joint between the bodies of adjacent vertebrae. It consists mainly of the intervertebral discs.
Below and above each vertebra are located 23 intervertebral discs (from C2 to S1), which are important for movements between vertebrae. The intervertebral discs join the articular surfaces of the vertebral bodies; they also play an important role in absorbing shock.
The vertebral column would be one-quarter of its length shorter without the intervertebral discs.
The intervertebral disc (discus intervertebralis)joins adjacent vertebrae, so the intervertebral joint (intervertebral symphysis) is formed.
The intervertebral disc consists of two parts, the:
Anulus fibrosus (anulus fibrosus) is peripheral part of the disc that contains many collagen fibers which form concentric lamellae.
Nucleus pulposus (nucleus pulposus) is central part of the disc composed of gelatinous mass (small number of collagen fibers, high percentage of water). It is supported by the anulus fibrosus, it is elastic and it forms a type of pillow against daily forces and pressure.
Prolapse or extrusion of the nucleus pulposus is called herniation of the intervertebral disc or it could also be called a slipped disc (see figures below). It is diagnosed most commonly in the lower, lumbar part of the vertebral column (usually between L3-L4, L4-L5 or L5-S1) like direct posterolateral herniation. The weak area of the annulus fibrosus predispose these places to prolapse of the nucleus pulposus. Normally in the other parts, the anterior and posterior longitudinal ligament reinforces the annulus fibrosus which lies under these ligaments. Disc extrusion impinges on the spinal nerve or even on the spinal cord and causes strong pain usually at the back or at the limb. The other symptoms are associated with distributions of damaged nerves. It may resemble sciatica.
Fracture of the vertebral column is a serious injury and spinal cord damage must always be considered.
Lumbosacral symphysis is a joint between the bodies of L5 and S1 (sacral bone in adults, after fusion of S1-S5.). It consists of:
- Intervertebral joint with a intervertebral disc between the bodies of the L5, and S1 (sacral bone in adults, after fusion of S1-S5.).
- Zygapophysial joints between which articular processes of these vertebrae are syndesmoses, like the ligamenta flava, anterior longitudinal ligament, posterior longitudinal ligament, interspinous ligament and the supraspinous ligament. There is one more ligament called the iliolumbar between the pelvis and the spine. Zygapophysial joints (facet joints) are synovial plane joints, so the lumbosacral joint can also be classified as the synovial joint.
Sacrococcygeal joint (articulatio sacrococcygea) contains the:
- Intervertebral joint with a thin intervertebral disc between apex of the sacrum and the body of the coccyx. Occasionally, the intercoccygeal joint is synovial.
- Joints between the sacral horn and the coccygeal horn.
- Following ligaments:
Superficial posterior sacrococcygeal ligament (ligamentum sacrococcygeum posterius superficiale) extends from median sacral crest to the coccyx and closes the sacral hiatus. It joins the sacral horn and the coccygeal horn. It is a prolongation of the ligamenta flava.
Deep posterior sacrococcygeal ligament (ligamentum sacrococcygeum posterius profundum) connects the posterior surface of the apex of the sacrum and the body of the coccyx. It is a prolongation of the posterior longitudinal ligament.
Anterior sacrococcygeal ligament (ligamentum sacrococcygeum anterius) connects the anterior surface of the apex of the sacrum, and body of the coccyx. It is a prolongation of the anterior longitudinal ligament.
Lateral sacrococcygeal ligament (ligamentum sacrococcygeum laterale) which connects the lateral sacral crest and the transverse process of the coccyx; it is analogous to the intertransverse ligament.
The ligaments that connect the synovial joints of the vertebral column include the:
- Ligamenta flava (ligamenta flava) which runs between the laminae of adjacent vertebrae, they limit vertebral flexion.
- Intertransverse ligaments (ligamenta intertransversaria) which are largely found at the cervical part, they are located between the transverse processes.
- Interspinous ligaments (ligamenta interspinalia) run from the root to the tip of each spine and they connect spinous processes of adjacent vertebrae. They limit vertebral flexion.
- Supraspinous ligaments (ligamentam supraspinalia) which connect the tips of the spinous processes from C7 to the median sacral crest, they limit vertebral flexion.
- Nuchal ligament (ligamentum nuchae) from the external occipital crest to all spinous processes of the cervical vertebrae, which limits vertebral flexion.
- Anterior longitudinal ligament (ligamentum longitudinale anterius) which extends from the pharyngeal tubercle and pass along the bodies of the vertebrae to the anterior sacrococcygeal ligament, it limits vertebral extension.
- Posterior longitudinal ligament (ligamentum longitudinale posterius) that extends from the internal surface of the clivus and pass along the bodies of the vertebrae (posterior surface) to the posterior sacrococcygeal ligament, it limits vertebral flexion.
Ossification of the Posterior Longitudinal Ligament (OPLL) is commonly associated with cervical myelopathy or certain rheumatic conditions. OPLL of the spine can cause spinal cord compression.
The superior articular processes of each vertebra form two synovial joints with the inferior articular processes of the vertebra above. The inferior articular processes form two synovial joints with the superior articular processes of the vertebra below. Both are called the zygapophysial joints.
Atlanto-occipital joint (articulatio atlantooccipitalis) is formed between the occipital condyles and superior articular surfaces of the lateral masses of the atlas. The cavities of that articulation are surrounded by capsules and also by anterior and posterior atlanto-occipital membranes (membrana atlantooccipitalis anterior et posterior)which extend from the arches of the atlas to the skull (around foramen magnum).
Movement: flexion, extension, lateral flexion and circumduction of the head.
Atlanto-axial joint (articulatio atlantoaxialis) consists of:
- Median atlanto-axial joints (articulatio atlantoaxialis mediana) are synovial joints which have the anterior median jointbetween the odontoid process (anterior articular surface) and the anterior arch of the atlas (facet for dens) and the posterior median joint between the odontoid process (posterior articular surface) and the transverse ligament of atlas as part of the cruciate ligament of atlas (transverse ligament of atlas)
- Lateral atlanto-axial joints (articulatio atlantoaxialis lateralis) are synovial joints between lateral masses of atlas and superior articular surfaces of axis. The articular surfaces are formed by the inferior articular surface of atlas and superior articular surface of axis.
Behind the odontoid process passes the cruciate ligament (ligamentum cruciforme atlantis)which restrains excessive flexion and extension movements. It consists of a strong transverse part (ligamentum transversum atlantis)and a smaller part, the longitudinal bands (fasciculi longitudinales). The transverse ligament of atlas has an articular surface, lying between lateral masses of atlas and form an articular surface of the posterior median joint of the median atlantoaxial joint.
Two ligaments connect the odontoid process with the skull: the apical ligament of dens (ligamentum apicis dentis) from the apex of the dens to the anterior margin of the foramen magnum and the alar ligaments (ligamenta alaria) from the lateral sides of the odontoid process to the medial sides of the occipital condyles. The alar ligamentsattaches the axis to the occiput and the lateral masses of the atlas and they limit rotation.
The membrana tectoria, which is superior continuation of the posterior longitudinal ligament, is located posteriorly. It overlies the transverse ligament of the atlas. It protects the spinal cord before the trauma of dens.
Movements: rotation of the head. Movements of the atlanto-occipital and atlanto-axial joints depend on the flexibility of the cervical part of the vertebral column.
Two ligaments pass along the vertebral column and connect the bodies and intervertebral discs anteriorly and posteriorly. These are the:
- Anterior longitudinal ligament (ligamentum longitudinale anterius) extends from the pharyngeal tubercle of the occipital bone and pass along the bodies of the vertebrae to the anterior sacrococcygeal ligament
- Posterior longitudinal ligament (ligamentum longitudinale posterius) extends from the anterior margin of the foramen magnum and pass along the bodies of the vertebrae to the posterior sacrococcygeal ligament.
Zygapophysial joints (articulationes zygapophysiales), apophyseal or posterior intervertebral joints are formed by the articular processes of adjacent vertebrae (see Fig. 2-25). Superior articular processes of vertebra located below, connect with the inferior articular processes located above. There are 23 pairs of these joints.