THE VERTEBRAL COLUMN
The vertebral column, also called the spine, backbone, or spinal column, makes up about two-fifths of your total height and is composed of a series of bones called vertebrae (VER-te-bre¯; singular is vertebra)
The vertebral column, the sternum, and the ribs form the skeleton of the trunk of the body. The vertebral column consists of bone and connective tissue; the spinal cord that it surrounds and protects consists of nervous and connective tissues.
At about 71 cm (28 in.) in an average adult male and about 61 cm (24 in.) in an average adult female, the vertebral column functions as a strong, flexible rod with elements that can move forward, backward, and sideways, and rotate.
In addition to enclosing and protecting the spinal cord, it supports the head and serves as a point of attachment for the ribs, pelvic girdle, and muscles of the back and upper limbs.
The total number of vertebrae during early development is 33. As a child grows, several vertebrae in the sacral and coccygeal regions fuse. As a result, the adult vertebral column typically contains 26 vertebrae. These are distributed as follows:
What is the purpose of the spine?
- Support for the body – whilst allowing for movement
- Bending Forwards
- 7 cervical vertebrae (cervic- neck) are in the neck region
- 12 thoracic vertebrae (thorax chest) are posterior to the thoracic cavity
- 5 lumbar vertebrae (lumb- loin) support the lower back
- 1 sacrum (SA¯ -krum sacred bone) consists of five fused sacral vertebrae
- 1 coccyx (KOK-siks cuckoo, because the shape resembles the bill of a cuckoo bird) usually consists of four fused coccygeal vertebrae (kok-SIJ-e¯-al)
The cervical, thoracic, and lumbar vertebrae are movable, but the sacrum and coccyx are not.
Movement of the spine
- Most of the movement of the spine occurs in the facet joints
- The facets are covered in hyaline cartilage
- Facet joints are synovial
- There are joints between the vertebral bodies and these help to cushion and absorb shock by way of intervertebral discs
Normal Curves of the Vertebral Column
When viewed from the anterior or posterior, a normal adult vertebral column appears straight. But when viewed from the side, it shows four slight bends called normal curves. Relative to the front of the body, the cervical and lumbar curves are convex (bulging out); the thoracic and sacral curves are concave (cupping in).
The curves of the vertebral column increase its strength, help maintain balance in the upright position, absorb shocks during walking, and help protect the vertebrae from fracture.
The fetus has a single anteriorly concave curve throughout the length of the entire vertebral column. At about the third month after birth, when an infant begins to hold its head erect, the anteriorly convex cervical curve develops. Later, when the child sits up, stands, and walks, the anteriorly convex lumbar curve develops.
The thoracic and sacral curves are called primary curves because they retain the original curvature of the embryonic vertebral column. The cervical and lumbar curves are known as secondary curves because they begin to form later, several months after birth. All curves are fully developed by age 10. However, secondary curves may be progressively lost in old age.
Abnormal Curves of the Vertebral Column
Various conditions may exaggerate the normal curves of the vertebral column, or the column may acquire a lateral bend, resulting in abnormal curves of the vertebral column.
Scoliosis (sko¯-le¯ -O¯ -sis; scolio- crooked), the most common of the abnormal curves, is a lateral bending of the vertebral column, usually in the thoracic region. It may result from congenitally (present at birth) malformed vertebrae, chronic sciatica (pain in the lower back and lower limb), paralysis of muscles on one side of the vertebral column, poor posture, or one leg being shorter than the other.
Signs of scoliosis include uneven shoulders and waist, one shoulder blade more prominent than the other, one hip higher than the other, and leaning to one side. In severe scoliosis (a curve greater than 70 degrees), breathing is more difficult and the pumping action of the heart is less efficient.
Chronic back pain and arthritis of the vertebral column may also develop. Treatment options include wearing a back brace, physical therapy, chiropractic care, and surgery (fusion of vertebrae and insertion of metal rods, hooks, and wires to reinforce the surgery).
Kyphosis (kı¯-FO¯ -sis; kyphoss- hump; -osis condition) is an increase in the thoracic curve of the vertebral column that produces a “hunchback” look. In tuberculosis of the spine, vertebral bodies may partially collapse, causing an acute angular bending of the vertebral column.
In the elderly, degeneration of the intervertebral discs leads to kyphosis. Kyphosis may also be caused by rickets and poor posture. It is also common in females with advanced osteoporosis.
Lordosis (lor-DO¯ -sis; lord- bent backward), sometimes called hollow back, is an increase in the lumbar curve of the vertebral column. It may result from increased weight of the abdomen as in pregnancy or extreme obesity, poor posture, rickets, osteoporosis, or tuberculosis of the spine.
Spina bifida (SPI¯-na BIF-i-da) is a congenital defect of the vertebral column in which laminae of L5 and/or S1 fail to develop normally and unite at the midline.
The least serious form is called spina bifida occulta. It occurs in L5 or S1 and produces no symptoms. The only evidence of its presence is a small dimple with a tuft of hair in the overlying skin.
Several types of spina bifida involve protrusion of meninges (membranes) and/or spinal cord through the defect in the laminae and are collectively termed spina bifida cystica because of the presence of a cyst like sac protruding from the backbone.
If the sac contains the meninges from the spinal cord and cerebrospinal fluid, the condition is called spina bifida with meningocele (me-NING-go¯ -se¯ l).
If the spinal cord and/or its nerve roots are in the sac, the condition is called spina bifida with meningomyelocele (me-ning-go¯ -MI¯-e¯ -lo¯ -se¯ l).
The larger the cyst and the number of neural structures it contains, the more serious the neurological problems. In severe cases, there may be partial or complete paralysis, partial or complete loss of urinary bladder and bowel control, and the absence of reflexes.
An increased risk of spina bifida is associated with low levels of a B vitamin called folic acid during pregnancy. Spina bifida may be diagnosed prenatally by a test of the mother’s blood for a substance produced by the fetus called alpha-fetoprotein, by sonography, or by amniocentesis (withdrawal of amniotic fluid for analysis).
Fractures of the Vertebral Column
Fractures of the vertebral column often involve C1, C2, C4–T7, and T12–L2.
Cervical or lumbar fractures usually result from a flexion–compression type of injury such as might be sustained in landing on the feet or buttocks after a fall or having a weight fall on the shoulders.
Cervical vertebrae may be fractured or dislodged by a fall on the head with acute flexion of the neck, as might happen on diving into shallow water or being thrown from a horse. Spinal cord or spinal nerve damage may occur as a result of fractures of the vertebral column if the fractures compromise the foramina.
- Outer annulus fibrosus: strong annular (circle shaped) fibres distribute pressure evenly across the disc, and contain the:
- Nucleus pulposus:
– several layers of fibrocartilage.
– contains loose fibres suspended in a mucoprotein gel (consistency of jelly).
– acts as a shock absorber and keeps vertebrae separate.
- The disc can be likened to a jam doughnut:
- The annulus fibrosis = the dough and the nucleus pulposus = the jam
- If the front of the doughnut is pressed, the jam moves posteriorly
- When a disc prolapses the jam/nucleus pulposus is forced out of the doughnut/disc and may put pressure on local nerves
- Referred pain e.g. sciatica may result
Intervertebral discs (in-ter-VER-te-bral; inter- between) are found between the bodies of adjacent vertebrae from the second cervical vertebra to the sacrum and account for about 25% of the height of the vertebral column. Each disc has an outer fibrous ring consisting of fibrocartilage called the annulus fibrosus (annulus ringlike) and an inner soft, pulpy, highly elastic substance called the nucleus pulposus (pulposus pulplike).
The discs form strong joints, permit various movements of the vertebral column, and absorb vertical shock. Under compression, they flatten and broaden.
During the course of a day the discs compress and lose water from their cartilage so that we are a bit shorter at night. While we are sleeping there is less compression and rehydration occurs, so that we are taller when we awaken in the morning. With age, the nucleus pulposus hardens and becomes less elastic. Decrease in vertebral height with age results from bone loss in the vertebral bodies and not a decrease in thickness of the intervertebral discs.
Since intervertebral discs are avascular, the annulus fibrosus and nucleus pulposus rely on blood vessels from the bodies of vertebrae to obtain oxygen and nutrients and remove wastes.
Certain stretching exercises, such as yoga, decompress discs and increase general blood circulation, both of which speed up the uptake of oxygen and nutrients by discs and the removal of wastes.
Parts of a Typical Vertebra
Vertebrae in different regions of the spinal column vary in size, shape, and detail, but they are similar enough that we can discuss the structures (and the functions) of a typical vertebra.
Vertebrae typically consist of a vertebral body, a vertebral arch, and several processes.
The vertebral body, the thick, disc-shaped anterior portion, is the weight-bearing part of a vertebra. Its superior and inferior surfaces are roughened for the attachment of cartilaginous intervertebral discs. The anterior and lateral surfaces contain nutrient foramina, openings through which blood vessels deliver nutrients and oxygen and remove carbon dioxide and wastes from bone tissue.
Two short, thick processes, the pedicles (PED-i-kuls little feet), project posteriorly from the vertebral body and then unite with the flat laminae (LAM-i-ne¯ thin layers) to form the vertebral arch. The vertebral arch extends posteriorly from the body of the vertebra; together, the vertebral body and the vertebral arch surround the spinal cord by forming the vertebral foramen. The vertebral foramen contains the spinal cord, adipose tissue, areolar connective tissue, and blood vessels.
Collectively, the vertebral foramina of all vertebrae form the vertebral (spinal) canal. The pedicles exhibit superior and inferior indentations called vertebral notches. When the vertebral notches are stacked on top of one another, they form an opening between adjoining vertebrae on both sides of the column. Each opening, called an intervertebral foramen, permits the passage of a single spinal nerve carrying information to and from the spinal cord.
Seven processes arise from the vertebral arch. At the point where a lamina and pedicle join, a transverse process extends laterally on each side. A single spinous process (spine) projects posteriorly from the junction of the laminae. These three processes serve as points of attachment for muscles.
The remaining four processes form joints with other vertebrae above or below. The two superior articular processes of a vertebra articulate (form joints) with the two inferior articular processes of the vertebra immediately above them. In turn, the two inferior articular processes of that vertebra articulate with the two superior articular processes of the vertebra immediately below them, and so on.
The articulating surfaces of the articular processes, which are referred to as facets (FAS-ets or fa-SETS little faces), are covered with hyaline cartilage. The articulations formed between the vertebral bodies and articular facets of successive vertebrae are termed intervertebral joints.
Regions of the vertebral column
The five regions of the vertebral column, beginning superiorly and moving inferiorly. The regions are the cervical, thoracic, lumbar, sacral, and coccygeal. Note that vertebrae in each region are numbered in sequence, from superior to inferior. When you actually view the bones of the vertebral column, you will notice that the transition from one region to the next is not abrupt but gradual, a feature that helps the vertebrae fit together.
Vertebral Regions—Cervical Vertebrae
The bodies of the cervical vertebrae (C1–C7) are smaller than all other vertebrae except those that form the coccyx.
Their vertebral arches, however, are larger.
All cervical vertebrae have three foramina:
- One vertebral foramen
- Two transverse foramina
The vertebral foramina of cervical vertebrae are the largest in the spinal column because they house the cervical enlargement of the spinal cord. Each cervical transverse process contains a transverse foramen through which the vertebral artery and its accompanying vein and nerve fibers pass. The spinous processes of C2 through C6 are often bifid—that is, they branch into two small projections at the tips.
The first two cervical vertebrae differ considerably from the others.
The atlas (C1), named after the mythological Atlas who supported the world on his shoulders, is the first cervical vertebra inferior to the skull. The atlas is a ring of bone with anterior and posterior arches and large lateral masses. It lacks a body and a spinous process. The superior surfaces of the lateral masses, called superior articular facets, are concave. They articulate with the occipital condyles of the occipital bone to form the paired atlanto-occipital joints. These articulations permit you to move your head to signify “yes.” The inferior surfaces of the lateral masses, the inferior articular facets, articulate with the second cervical vertebra. The transverse processes and transverse foramina of the atlas are quite large.
The second cervical vertebra (C2), the axis, does have a vertebral body. A peglike process called the dens ( tooth) or odontoid process projects superiorly through the anterior portion of the vertebral foramen of the atlas. The dens makes a pivot on which the atlas and head rotate. This arrangement permits side-to-side movement of the head, as when you move your head to signify “no.”
The articulation formed between the anterior arch of the atlas and dens of the axis, and between their articular facets, is called the atlanto-axial joint. In some instances of trauma, the dens of the axis may be driven into the medulla oblongata of the brain. This type of injury is the usual cause of death from whiplash injuries.
The third through sixth cervical vertebrae (C3–C6), correspond to the structural pattern of the typical cervical vertebra previously described.
The seventh cervical vertebra (C7), called the vertebra prominens, is somewhat different. It has a large, nonbifid spinous process that may be seen and felt at the base of the neck, but otherwise is typical.
Cervical spine movement
- Flexion = forward
- Extension = backward
- Lateral flexion
- Support for movements of the head
- Strong ligaments
- Movement is through facet joints
Cervical spine stress points
- Odontoid peg #
- Junction of C7 / T1
- Hyoid bone
- Spondylosis (degeneration)
- Facet joint narrowing
- Intervertebral disc degeneration
Vertebral Regions—Thoracic Vertebrae
Thoracic vertebrae (T1–T12) are considerably larger and stronger than cervical vertebrae.
In addition, the spinous processes on T1 through T10 are long, laterally flattened, and directed inferiorly. In contrast, the spinous processes on T11 and T12 are shorter, broader, and directed more posteriorly.
Compared to cervical vertebrae, thoracic vertebrae also have longer and larger transverse processes. They are easily identified by their costal facets (cost- rib), which are articular surfaces for the ribs.
The feature of the thoracic vertebrae that distinguishes them from other vertebrae is that they articulate with the ribs. Except for T11 and T12, the transverse processes of thoracic vertebrae have costal facets that articulate with the tubercles of the ribs.
Additionally, the vertebral bodies of thoracic vertebrae have articular surfaces that form articulations with the heads of the ribs. The articular surfaces on the vertebral bodies are called either facets or demifacets. A facet is formed when the head of a rib articulates with the body of one vertebra. A demifacet is formed when the head of a rib articulates with two adjacent vertebral bodies.
Each side of the vertebral body T1 has a superior facet for the first rib and an inferior demifacet for the second rib. On each side of the vertebral body of T2–T8, there is a superior demifacet and an inferior demifacet as ribs two through nine articulate with two vertebrae, and T10–T12 have a facet on each side of the vertebral body for ribs 10–12.
These articulations between the thoracic vertebrae and ribs, called vertebrocostal joints, are distinguishing features of thoracic vertebrae. Movements of the thoracic region are limited by the attachment of the ribs to the sternum.
Thoracic spine movement
- Limited flexion and extension (movement is mainly though lumbar spine)
- Limited lateral flexion and rotation
- Provides support for rib cage which protects vital organs
- Allows for movement of the ribs during breathing, joint between ribs and thoracic vertebrae
Thoracic spine stress points
- Junction of C7 / T1
- Junction of T12 / L1
- Thoracic spine is well supported / strong elsewhere
- Intervertebral discs become narrowed
- Spondylosis of facet joints
- Wedge fractures
Vertebral Regions—Lumbar Vertebrae
The lumbar vertebrae (L1–L5) are the largest and strongest of the unfused bones in the vertebral column because the amount of body weight supported by the vertebrae increases toward the inferior end of the backbone.
Their various projections are short and thick. The superior articular processes are directed medially instead of superiorly, and the inferior articular processes are directed laterally instead of inferiorly.
The spinous processes are quadrilateral in shape, are thick and broad, and project nearly straight posteriorly. The spinous processes are well adapted for the attachment of the large back muscles.
Lumbar spine movement
Most of the movement of the back is through the lumbar spine
- Considerable flexion
- Limited extension
- Lateral flexion
- Strong spinal ligaments support the back
- Good muscle tone and posture help
Lumbar spine stress points
- Junction of T12 / L1
- Junction of L5 / S1
- Intervertebral discs become narrowed
- Degeneration of the joints between the vertebrae
- Facet joint involvement
- Narrowed intervertebral disc spaces
- Osteophyte formation
- A defect of a lumbar vertebra, affecting the pars interarticularis
- Usually L4 or L5
- Pars interarticularis = the part between the articular suraces
- Prone to hyperextension, wear and tear
- Sometimes results in a fracture through the pars interarticularis, however this is not trauma – it is a result of degeneration and repetitive strain.
Vertebral Regions—Sacral and Coccygeal Vertebrae
The sacrum (SA¯-krum) is a triangular bone formed by the union of five sacral vertebrae (S1–S5).
The sacral vertebrae begin to fuse in individuals between 16 and 18 years of age, a process usually completed by age 30. Positioned at the posterior portion of the pelvic cavity medial to the two hip bones, the sacrum serves as a strong foundation for the pelvic girdle.
The female sacrum is shorter, wider, and more curved between S2 and S3 than the male sacrum.
The concave anterior side of the sacrum faces the pelvic cavity. It is smooth and contains four transverse lines (ridges) that mark the joining of the sacral vertebral bodies. At the ends of these lines are four pairs of anterior sacral foramina.
The lateral portion of the superior surface of the sacrum contains a smooth surface called the sacral ala (A¯ L-a wing; plural is alae,A¯ L-e¯), which is formed by the fused transverse processes of the first sacral vertebra (S1).
The convex, posterior surface of the sacrum contains a median sacral crest, the fused spinous processes of the upper sacral vertebrae; a lateral sacral crest, the fused transverse processes of the sacral vertebrae; and four pairs of posterior sacral foramina. These foramina connect with anterior sacral foramina to allow passage of nerves and blood vessels.
The sacral canal is a continuation of the vertebral cavity. The laminae of the fifth sacral vertebra, and sometimes the fourth, fail to meet. This leaves an inferior entrance to the vertebral canal called the sacral hiatus (hı¯-A¯ -tus opening). On either side of the sacral hiatus is a sacral cornu (KOR-noo; cornu horn; plural is cornua, KOR-noo-a), the inferior articular processes of the fifth sacral vertebra. They are connected by ligaments to the coccyx.
The narrow inferior portion of the sacrum is known as the apex. The broad superior portion of the sacrum is called the base. The anteriorly projecting border of the base, called the sacral promontory (PROM-onto ¯-re¯), is one of the points used for measurements of the pelvis.
On both lateral surfaces the sacrum has a large ear-shaped auricular surface that articulates with the ilium of each hip bone to form the sacroiliac joint.
Posterior to the auricular surface is a roughened surface, the sacral tuberosity, which contains depressions for the attachment of ligaments. The sacral tuberosity unites with the hip bones to form the sacroiliac joints. The superior articular processes of the sacrum articulate with the inferior articular processes of the fifth lumbar vertebra, and the base of the sacrum articulates with the body of the fifth lumbar vertebra to form the lumbosacral joint.
The coccyx, like the sacrum, is triangular in shape.
It is formed by the fusion of usually four coccygeal vertebrae, as Co1–Co4. The coccygeal vertebrae fuse somewhat later than the sacral vertebrae, between the ages of 20 and 30.
The dorsal surface of the body of the coccyx contains two long coccygeal cornua that are connected by ligaments to the sacral cornua. The coccygeal cornua are the pedicles and superior articular processes of the first coccygeal vertebra. They are on the lateral surfaces of the coccyx, formed by a series of transverse processes; the first pair are the largest.
The coccyx articulates superiorly with the apex of the sacrum. In females, the coccyx points inferiorly to allow the passage of a baby during birth; in males, it points anteriorly
Age-Related Changes in the Vertebral Column
With advancing age the vertebral column undergoes changes that are characteristic of the skeletal system in general. These changes include reduction in the mass and density of the bone along with a reduction in the collagen-to-mineral content within the bone, changes that make the bones more brittle and susceptible to damage.
The articular surfaces, those surfaces where neighboring bones move against one another, lose their covering cartilage as they age; in their place rough bony growths form that lead to arthritic conditions.
In the vertebral column, bony growths around the intervertebral discs, called osteophytes, can lead to a narrowing (stenosis) of the vertebral canal. This narrowing can lead to compression of spinal nerves and the spinal cord, which can manifest as pain and decreased muscle function in the back and lower limbs.
Chiropractic (kı¯-ro¯ -PRAK-tik; cheir- hand; -praktikos efficient)
A holistic health-care discipline that focuses on nerves, muscles, and bones. A chiropractor is a health-care professional who is concerned with the diagnoses, treatment, and prevention of mechanical disorders of the musculoskeletal system and the effects of these disorders on the nervous system and health in general.
Treatment involves using the hands to apply specific force to adjust joints of the body (manual adjustment), especially the vertebral column. Chiropractors may also use massage, heat therapy, ultrasound, electric stimulation, and acupuncture. Chiropractors often provide information about diet, exercise, changes in lifestyle, and stress management. Chiropractors do not prescribe drugs or perform surgery.
Craniostenosis (kra¯ -ne¯ -o¯ -sten-O¯ -sis; cranio- skull; -stenosis narrowing)
Premature closure of one or more cranial sutures during the first 18 to 20 months of life, resulting in a distorted skull. Premature closure of the sagittal suture produces a long narrow skull; premature closure of the coronal suture results in a broad skull. Premature closure of all sutures restricts brain growth and development; surgery is necessary to prevent brain damage.
Craniotomy (kra¯ -ne¯ -OT-o¯ -me¯ ; cranio- skull; -tome cutting)
Surgical procedure in which part of the cranium is removed. It may be performed to remove a blood clot, a brain tumor, or a sample of brain tissue for biopsy.
Laminectomy (lam-i-NEK-to¯ -me¯ ; lamina- layer)
Surgical procedure to remove a vertebral lamina. It may be performed to access the vertebral cavity and relieve the symptoms of a herniated disc.
Lumbar spine stenosis (sten- narrowed)
Narrowing of the spinal canal in the lumbar part of the vertebral column, due to hypertrophy of surrounding bone or soft tissues. It may be caused by arthritic changes in the intervertebral discs and is a common cause of back and leg pain.
Spinal fusion (FU¯ -zhun)
Surgical procedure in which two or more vertebrae of the vertebral column are stabilized with a bone graft or synthetic device. It may be performed to treat a fracture of a vertebra or following removal of a herniated disc.
Injury to the neck region due to severe hyperextension (backward tilting) of the head followed by severe hyperflexion (forward tilting) of the head, usually associated with a rear-end automobile collision.
Symptoms are related to stretching and tearing of ligaments and muscles, vertebral fractures, and herniated vertebral discs.