Chapter 8 Vertebral Column: Bones and Joints

The Laminae

Two flattened plates of bone, one passing towards the midline from each pedicle. They unite posteriorly in the midline to form the spinous process, and to complete the vertebral arch. (L. lamina = a plate, pl. laminae)

Pedicles

Two short rounded processes that extend posteriorly, one from each lateral margin of the dorsal surface of a vertebral body. (Pedicle = a little foot, a stock, stem, root)

3. Atlantooccipital Joints:

Two, right and left. Located between the atlas and occipital bone. Formed by an occipital condyle of the occipital bone articulating with the superior articular surface on the lateral mass of the atlas on the same side. Synovial condylar joints, permitting some flexion, extension, and slight lateral flexion.

Posterior Arch

is a curved structure that joins the posterior parts of the lateral masses together, completing a bony ring.

Sacram Canal

is a tubelike passage that extends through the sacrum from top to bottom. The vertebral channel with the fused bodies in front and the fused arches behind. The sacral and coccygeal nerves pass down in this canal.

Sacral Hiatus

is an opening in the sacral canal posteriorly at its lower end, causing a gap between the laminae of the fifth sacral segment.

Costal Pit

(NA) fovea costalis or facit, is a smooth round or semicircular smooth depression located on a vertebral body or its transverse process.

2. Interarticular Joints:

(NA) zygapophyseal joints; right and left; located between articular processes of the adjacent vertebrae on each side. Formed by the inferior articular process of one vertebra articulating with the superior articular process of the vertebrae below on the same side of the body. These are synovial gliding joints, the articular surfaces sliding over each other.

1. Intervertebral Joints:

(NA, intervertebral discs); Located between the flat articular surfaces of bodies of adjacent vertebrae from the second cervical vertebra to an including the lumbosacral joint between the fifth lumbar body and the sacrum.

S. 91 DETAILED STUDY OF THE JOINTS OF THE VERTEBRAL COLUMN

(p. 75)

6. Lumbosacral Joint:

A single joint, Located between fifth lumbar vertebra and the upper end of sacrum. Formed by the inferior articular surface of the fifrth lumbar vertebra and the superior articular surface of the sacrum. A cartilaginous joint with an intervertebral disc, similar to other intervertebral ones. (S. 91, p. 77)

The Vertebral Canal

A tubular passage extending form the foramen magnum of the skull to the lower sacrum. It is formed by the vertebral foramina of the vertebrae and the ligaments that join successive vertebral arches together. The spinal cord extends down through this canal.

Vertebral Foramen

An opening formed by the vertebral arch with tis pedicles and laminae, and the posterior surface of a vertebral body.

Intervertebral Foramen

An opening on each side of the arch, formed by an inferior notch of one vertebra and the superior notch of the vertebra below. A spinal nerve leaves the spinal cord through each of these openings.

Annulus Fibrosus

An outer pad of fibrous tissue and fibrocartilage.

Single Spinous Process

Extends posteriorly from the dorsal margin of each vertebral arch, at the junction of the right and left laminae. The bodies of vertebrae are composed of cancellous or spongy bone with a thin covering of compact bone. The arches and processes have a core of cancellous bone with an outer layer of compact bone. (S.88, p. 73)

S. 87 CURVATURES OF VERTEBRAL COLUMN

F. 8-1 (S. 87, p. 72)

Vertebral Notch

Formed by either the upper or lower curved surface of a pedicle; there is a superior and inferior notch on each side at each level, posteriorly the vertebral body.

Pelvic Curvature

Kyphotic Type, Concave surface anterior, similar to the thoracic curve. The sacrum and coccyx form the pelvic curvature.

Thoracic Curvature

Kyphotic type, with its concave surface directed anteriorly, and the convexity posteriorly. The midthoracic vertebrae project more posteriorly than the upper or lower thoracic.

7. Sacrococcygeal Joint:

Located between sacrum and coccyx. Formed by distal end of sacrum forming a joint with the first segment of the coccyx. Cartilaginous joint with a disc.

Lumbar Curvature

Lordotic Type, Convex curve anterior; The mid-lumbar bodies project more anteriorly than the upper or lower limb.

Cervical Curvature

Lordotic type, with an anterior convexity. The midcervical vertebrae therefore project more anteriorly than the upper or lower cervical vertebrae

4. Atlantoaxial Joints:

One median and two lateral, right and left located between the atlas and axis.

Inferior Articular Processes

Right and left, Project caudally (downwards) from the junction of each pedicle and lamina. Their smooth articular surfaces are directed anteriorly. The IAP of on vertebra form joints with the SAP of the vertebra below. As the IAP lie posterior to the corresponding superior processes a forward displacement of the upper of the two vertebrae cannot occur unless there are defects in the IAP of the upper vertebrae. If present these might be congenital or due to some injury, and will result in spondylolisthesis.

Transverse Processes

Right and left, extend laterally from the junction of each pedicle and lamina on each side.

Superior Articular Processes

Right and left, extend up towards the head from the junction of each pedicle and lamina. Their smooth articular surfaces are directed somewhat posteriorly.

Interarticular Joints,

Similar to No. 2 above are also present between the inferior articular processes of the fifth lumbar vertebra and articular processes of upper end of sacrum; gliding joints, right and left.

Cervical Vertebrae

Small, with spinous processes usually forked or bifid/double. There are openings in each of the transverse processes -- a foramen transversarium or transverse foramen through which the vertebral artery passes to reach the skull. The superior and inferior articular processes on each side of the vertebrae are united to form a pillar or column of bone behind the transverse process. The articular facets, or foveae on the columns are inclined slightly posteriorly form the horizontal. They do not lie vertically as do those of other vertebrae. Three cervical vertebrae have alternate names and special features.

1. Body of the Vertebra

Solid anterior part shaped like a cylinder, with the posterior surface flattened.

2. Arch of a Vertebra

The curved posterior part enclosing an opening. The arch has two pedicles and two laminae that, together with the posterior surface of the body, form a vertebral foramen.

S. 89 CHARACTERISTICS THAT IDENTIFY SOME OF THE VERTEBRAE

The vertebrae becomes progressively larger from the cervical to the lumbar divisions.

3. Seven Processes:

Transverse Process (2), Superior Articular Processes (2), Inferior Articular Processes (2), Single Spinous Process (1)

S. 88 STRUCTURE OF A VERTEBRA

Vertebra = a bone of the vertebral column. pl. vertebrae, adj. vertebral (L. vertere = to turn) A vertebra has a body, an arch, seven processes and a vertebral foramen. (p. 72)

S. 86 DIVISIONS OF THE VERTEBRAL COLUMN

Vertebral column is composed of 5 parts or divisions according to the location: (p. 72) 1. Cervical vertebrae, 7 in the neck 2. Thoracic vertebrae, 12 in the thorax 3. Lumbar vertebrae, 5 posterior to the abdoment 4. Sacrum, 5 fused vertebrae in the pelvis 5. Coccyx, 4 or 3, or 5 incomplete, in pelvis

(3) Intervertebral Disc

a flat circular plate lying between the articular cartilages covering each bone, and consisting of: (S. 91, p. 76)

5. The coccyx:

adj. coccygeal, The coccyx is usually formed by four (or occasionally three, or five) incompletely developed vertebrae. The segments often remain as separate bones. The upper end of the coccyx forms a joint with the apex of the sacrum.

3. The Lumbar Vertebrae

are larger than the thoracic, and become progressively larger towards the sacrum. Their spinous processes are directed almost horizontally and posteriorly. Their transverse processes have no foramina and no costal pits.

2. The Thoracic Vertebrae

are larger then the cervical. Their spinous processes are directed almost vertically caudally (towards the tail end of the body). The tip of one of these may lie opposite the inferior margin of the vertebra below the one to which it is attached. The thoracic vertebrae have costal pits named foveae. (s. fovea)

Superior and Inferior Facets (foveae)

are located on the superior and inferior surfaces of each lateral mass. The superior one articulates with a condyle of the occipital bone on the same side. The inferior ones articulate with the superior articular processes of the second cervical vertebra below.

Two Auricular Surfaces

are located one on each lateral surface of the sacrum. These rough areas join the auricular surfaces of the iliac bones to form the sacroiliac joints. (Auricle = ear, or earlike).

Lateral Masses

are solid masses of bone that lie one on either side of the foramen and support the articular facets (fovae). These masses are joined anteriorly by an anterior bony arch, and posteriorly by a posterior arch of bone.

Cornua

are two small bony processes that extend up from the posterior surface of the coccyx to meet similar cornua of the sacrum.

Sacral Cornua

are two small bony projections that extend caudally from the lower sacrum posteriorly, one on each side of the sacral hiatus. They form joints with similar cornua of the coccyx. (L. cornu - a horn)

The Superior Articular Processes

extend up from the posterolateral margins of the sacrum on each side. Their articular surfaces are directed posteriorly and form joints with the inferior articular processes of the fifth lumbar vertebra.

Anterior Arch

forms the front wall of the foramen by uniting the two lateral masses here.

Vertebra Prominens or Seventh Cervical Vertebra

has a longer and larger spinous process than the other cervical vertebra. It is readily palpable at the base of the neck posteriorly. Because it is so easily palpated it is used as a landmark to count the spinous processes of the thoracic vertebrae lying below it. (S. 89, p. 74)

Axis or Second Cervical Vertebra

has a tooth shaped process extending upwards from its body. This dens or odontoid process fits into the anterior arch of the atlas above. It forms a pivot joint with this arch, allowing rotation of the head and atlas upon the axis. (Axis -- a straight line or an axle about which turning occurs) (L. dens = a tooth or toothlike process)

Apex of the Sacrum

is its small inferior end which articulates with the first segment of the coccyx.

Vertebral Foramen

is large and formed in front by the anterior arch, laterally by the lateral mass, and behind the posterior arch. A transverse ligament passes across from one lateral mass to the other dividing the foramen into two parts. The anterior part is occupied by the dens (odontoid process) of the second cervical vertebra, while the posterior part contains the spinal cord.

The Promontory of the Sacrum

is the prominent anterior margin of the upper sacral segment.

Ala

is the winglike upper part of each end consisting of the upper surface of the body of the first sacral segment and the alae on either side.

(2) The lateral Parts (lateral masses)

of the sacrum lie one on either side of the fused bodies, lateral to the sacral foramina. Each lateral part is made up of the fused transverse processes and costal elements of the 5 fused vertebrae. (S. 89, p. 75)

Four Dorsal Sacral Foramina

open into the canal on either side. They lie lateral to the fused bodies and transmit the dorsal branches of the sacral nerves from the sacral canal.

Four Pelvic (Anterior) Sacral Foramina

open into the sacral canal on each side from the pelvic surface of the sacrum. They transmit anterior branches of the sacral nerves to the pelvis.

(1) Costal Pit of a Thoracic Vertebra

or a facet, lies on the lateral surface of a thoracic vertebra close to its posterior margin, to articulate with the head of the rib. As some semilunar pits, one on the upper and the other on the lower margin, rather than one circular pit at the center of the body. The tenth, eleventh, and twelfth vertebrae have a single pit on each side as they form joints with one rib only.

(1) The Body of the Sacrum

or central part is the largest curved area that is formed from the fused bodies of the 5 sacral segments. The transverse ridges on the pelvic (anterior) surfaces at each level denote the points of union of these segments.

Atlas

or first cervical vertebra, has no body and no spinous process. Instead it has two lateral masses of bone and two arches. These together surrond the vertebral foramen.

4. The Sacrum

pl. sacra, adj. sacral, is made up of five vertebrae that have become united to form a single bone. In the fetus and young child the sacral segments are separated by cartilages. The sacrum has a central part of body, two lateral parts, an arch, and a sacral canal.

Nucleus pulosus

the pulpy center of a disc in the center of an anulus fibrosus and surrounded by it.

(2) Costal Pit on a Transverse Process:

this rounded pit lies on the anterior surface of a transverse process of thoracic vertebrae. If it forms a joint with a tubercle of a rib.