OSTEOLOGY OF THE VERTEBRAE

                        Structure of a typical Vertebra
Vertebrae have a common basic shape that changes in the different
segments of the spinal column to adapt to their various static needs.
Every vertebra with the exception of the first cervical (atlas, C1) vertebra has:        Parts:

• Vertebral body (corpus vertebrae), which is the anterior expanded part of the vertebra.
• vertebral arch(arcus vertebrae),located posteriorly to the body.It is bounded by the lamina arcus vertebrae and the pediculus arcus vertebrae.
• Vertebral foramen,foramen vertebrale.The vertebral body and arch enclose the vertebral foramen. All the vertebral foramina together form the vertebral canal, which houses the spinal cord. Corresponding to the increasing load, the size of the vertebrae increases from above down.
• Pedicle, Pediculus arcus vertebrae,the portion of the vertebral arch situated anteriorly between the body and transverse process as well as between the superior and inferior vertebral notches.
• Lamina, Lamina arcus vertebrae (vertebralis),the portion of the vertebral arch situated posteriorly between the transverse process and the spinous process.

                                       Processes:
 There are seven(7) processes extending from the vertebral arch,four(4) of which are articular processes,processus articularis, two(2) transverse,processus transversus and one(1) spinous,processus spinosus. 
 The body and transverse processes of the thoracic vertebrae bear joint facets for the ribs. Every vertebral arch at its origin from the vertebral body is marked above and below by a notch (incisura vertebralis, inferior and superior vertebral notch). The notches of two adjoining vertebrae form the intervertebral foramen,which transmits the spinal nerves.

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There are 7 cervical, 12 thoracic, 5 lumbar, 5 sacral and 4-5 coccygeal vertebrae. Each of these vertebral groups corresponds to a region of the vertebral column.Vertebral column contains 33-34 vertebrae in total.

                                      CERVICAL VERTEBRAE

The seven cervical vertebrae form a flexible framework for the

neck and support the head. The bone tissue of cervical vertebrae is more dense than that found in the other vertebral regions and, except for those in the coccygeal region, the cervical vertebrae are smallest. Cervical vertebrae have features which make them unique from other vertebrae.These features are :

• Large vertebral foramen. Because of this feature, the spinal cord is safest in the cervical vertebrae. 
• the presence of a transverse foramen,foramen transversarium in each transverse process.The vertebral arteries and veins pass through this opening as they contribute to the blood flow associated with the brain. 
• Cervical vertebrae C2–C6 generally have a bifid, or notched, spinous process. The bifid spinous processes increase the surface area for attachment of the strong nuchal ligament that attaches to the back of the skull. 
• The first cervical vertebra has no spinous process.
• The process of C7 is not bifid and is larger than those of the other cervical vertebrae.It can easily be palpated. Therefore, it is sometimes called the vertebra prominens.

  

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  C7

  
  

         The atlas (C1) is the first cervical, which differs from all other vertebrae.It has no body, it appears as a transverse ring composed of two arches(arcus anterior et posterior atlantis) and two lateral masses,massa lateralis atlantis.

  The axis (C2) is the second cervical vertebra. On the superior surface of its body, the axis bears a thick vertical process, the dens.The dens carries the anterior and posterior articular surfaces,and its apex.The dens corresponds to the body of the axis during during the developmental process.                                                           

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 clinical application:Muscle, bone, or ligament injury in this portion of the spinal column is relatively common in individuals involved in automobile accidents and sports injuries. Joint dislocation occurs commonly between the fourth and fifth or fifth and sixth cervical vertebrae, where neck movement is greatest. Bilateral dislocations are particularly dangerous because of the probability of spinal cord injury. Compression fractures of the first three cervical vertebrae are common and follow abrupt forced flexion of the neck. Fractures of this type may be extremely painful because of pinched spinal nerves.

                  THORACIC VERTEBRAE

     Twelve thoracic vertebrae articulate with the ribs to form the

posterior anchor of the rib cage. Thoracic vertebrae are larger

than cervical vertebrae and increase in size from superior (T1) to

inferior (T12). Unique features of thoracic vertebrae are:

• Each thoracic vertebra has a long spinous process,which slops obliquely downward.                                                             Facets (fovea) for articulation with the ribs.
• Round vertebral foramen.
• roughly heart shaped body(corpus).

                                     THE LUMBAR VERTEBRAE 

The five lumbar vertebrae, vertebrae lumbales(L1-L5), form the lumbar region of the vertebral column. They are characterized by the following structural features: 

•          Body is large and bean-shaped.
• Spinous processes are flattened and oriented in the sagittal direction.
• Long transverse processes.
• The external border of the superior articular process has a mamillary process.

 A laminectomy is the surgical removal of the spinous processes and their supporting vertebral laminae in a particular region of the vertebral column. A laminectomy may be performed to relieve pressure on the spinal cord or nerve root caused by a blood clot, a tumor, or a herniated (ruptured) disc. It may also be performed

on a cadaver to expose the spinal cord and its surrounding meninges.

THE SACRAL VERTEBRAE

The wedge-shaped sacrum provides a strong foundation for the pelvic girdle. It consists of four or five sacral vertebrae that become fused after age 26. The sacrum has an extensive auricular 

surface on each lateral side for the formation of a slightly 

movable sacroiliac (sak''ro-il'e-ak) joint with the ilium of the 

hip. A median sacral crest is formed along the dorsal surface 

by the fusion of the spinous processes. Posterior sacral foramina 

on either side of the crest allow for the passage of nerves from 

the spinal cord. The sacral canal is the tubular cavity within the 

sacrum that is continuous with the vertebral canal. Paired superior 

articular processes, which articulate with the fifth lumbar 

vertebra, arise from the roughened sacral tuberosity along the 

posterior surface.

 The smooth pelvic surface of the sacrum forms the posterior surface of the pelvic cavity. It has four transverse lines denoting

the fusion of the vertebral bodies. At the ends of these 

lines are the paired pelvic foramina (anterior sacral foramina).

The superior border of the anterior surface of the sacrum, called 

the sacral promontory, is an important obstetric 

landmark for pelvic measurements.

                    

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THE COCCYX

The triangular coccyx (“tailbone”) is composed of three to five fused coccygeal vertebrae. The first vertebra of the fused coccyx has two long coccygeal cornua, which are attached by ligaments to the sacrum. Lateral to the cornua are the transverse processes.

  clinical application:When a person sits, the coccyx flexes anteriorly, acting as a shock absorber. An abrupt fall on the coccyx, however, may cause a painful subperiosteal bruising, fracture, or fracturedislocation of the sacrococcygeal joint. An especially difficult childbirth can even injure the coccyx of the mother. Coccygeal trauma is painful and may require months to heal. 

                THE VERTEBRAL COLUMN AS A WHOLE

The vertebral column consists of a series of irregular bones called

vertebrae, separated from each other by fibrocartilaginous intervertebral discs. Vertebrae enclose and protect the spinal cord,support the skull and allow for its movement, articulate with the rib cage, and provide for the attachment of trunk muscles. The

intervertebral discs lend flexibility to the vertebral column and absorb vertical shock.The vertebral column has a length of about 70 cm and it accounts for about 25% of the length of a human.

  The vertebral column (“backbone”) and the spinal cord of the

nervous system constitute the spinal column. The vertebral column has four functions:

1. to support the head and upper extremities while permitting

freedom of movement;

2. to enable bipedalism;

3. to provide attachment for various muscles, ribs, and visceral

organs; and

4. to protect the spinal cord and permit passage of the

spinal nerves.

 The vertebral column is typically composed of 33 individual vertebrae, some of which are fused. There are 7 cervical, 12 thoracic, 5 lumbar, 3 to 5 fused sacral, and 4 or 5 fused coccygeal vertebrae; thus, the adult vertebral column is composed of a total of 26 movable parts. Vertebrae are separated by fibrocartilaginous intervertebral discs and are secured to each other by interlocking processes and binding ligaments. This structural arrangement permits only limited movement between adjacent vertebrae but extensive movement for the vertebral column as a whole. Between the vertebrae are openings called intervertebral foramina that allow passage of spinal nerves. When viewed from the side, four curvatures of the vertebral column can be identified. The cervical, thoracic, and lumbar curves are identified by the type of vertebrae they include. The pelvic curve (sacral curve) is formed by the shape of the sacrum and coccyx. The curves of the vertebral column play an important functional role in increasing the strength and maintaining the balance of the upper part of the body; they also make possible a bipedal stance.

 The four vertebral curves are not present in an infant. The cervical curve begins to develop at about 3 months as the baby begins holding up its head, and it becomes more pronounced as the baby learns to sit up. The lumbar curve develops as a child begins to walk. The thoracic and pelvic curves are called primary curves because they retain the shape of the fetus.The cervical and lumbar curves are called secondary curves because they are modifications of the fetal shape.

  THE CURVATURES OF THE VERTEBRAL COLUMN The vertebral column possesses the following curvature:

• Lordoses - anterior curvatures,present in the cervical and lumbar regions(cervical and lumbar lordoses).
• Kyphosis - posterior curvatures, present in the thoracic and sacral regions(thoracic and sacral kyphosis).

         The curvatures are associated with the upright body posture in humans. They absorb shocks placed on the vertebral column, aid in balance maintenance and increase the thoracic and pelvic cavities. In the thoracic region, there is a slight curvature to the right( a physiological scoliosis) caused by a well developed right upper limb.

Kamal Umar Labaran

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