Vertebral Column

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I. THE VERTEBRAL COLUMN consists of 33 vertebrae |Cl-7, Tl-12, Ll-5, Sl-5 (sacrum), and Co 1—4 (coccyx)]. The vertebral canal contains the spinal cord, dorsal nerve root, ventral nerve root, and meninges. The spinal nerve is located outside the vertebral canal by exiting through the intervertebral foramen.

A. Vertebral levels (Table 1-1) are used to reference the location of important anatomic structures. Knowledge of these vertebral levels is helpful when answering clinical vignette questions. For example, a clinical vignette question may describe a pulsatile swelling locaced at vertebral level T2. Knowing that the arch of the aorta is found at T2 suggests the correct answer: aortic arch aneurysm.

B. Curves

1. Primary curves are the thoracic and sacral curvatures that form during the fetal period.

2. Secondary curves are the cervical and lumbar curvatures that form after birth as a result of lifting the head and walking, respectively.

3. Kyphosis is an exaggeration of the thoracic curvature that may occur in elderly persons as a result of osteoporosis or disk degeneration.

4. Lordosis is an exaggeration of the lumbar curvature that may be temporary and occurs as a result of pregnancy, spondylolisthesis, or potbelly.

5. Scoliosis is a complex lateral deviation, or torsion, that is caused by poliomyelitis, a leg-length discrepancy, or hip disease.

C. Joints

1. Atlanto-occipital joints. Nodding the head (e.g., indicating "yes") occurs at the atlanto-occipital joints between CI (atlas) and the occipital condyles. These are synovial joints and have no intervertebral disk. The anterior and posterior atlanto-occipital membranes limit excessive movement at this joint.

2. Atlanto-axial joints. Turning the head side-to-side (i.e., indicating "no") occurs at the atlanto axial joints between CI (atlas) and C2 (axis). These are synovial joints and have no intervertebral disk. The alar ligaments limit excessive movement at this joint.

D. Clinical considerations

1. Atlanto-axial dislocation a. Tearing of the transverse (cruciform) ligament because of trauma (e.g., Jefferson fracture) or rheumatoid arthritis allows the dens (part of the axis) to move within the vertebral canal. This mobility contributes to the risk of injury to the

Table 1-1.

Vertebral Levels as Reference Points

Vertebral Level Anatomic Structure

C4 Hyoid bone

Bifurcation of common carotid artery C5 Thyroid cartilage

Carotid pulse palpated C6 Cricoid cartilage

Start of trachea Start of esophagus T2 Sternal notch

Arch of the aorta T4 Sternal angle

Junction of superior and inferior mediastinum Bifurcation of trachea T5—7 Pulmonary hilum

T8 Inferior vena cava hiatus

T9 Xiphisternal joint

T10 Esophageal hiatus

T12 Aortic hiatus

T12—L1 Duodenum

T12 Celiac artery

Upper pole of left kidney L1 Superior mesenteric artery

Upper pole of right kidney

End of spinal cord in adult (conus medullaris) and pia mater L2 Renal artery

L3 End of spinal cord in newborn

Inferior mesenteric artery Umbilicus

L4 Iliac crest

Bifurcation of aorta

51 Sacral promontory Start of sigmoid colon

52 End of dural sac, dura, arachnoid, subarachnoid space, and cerebrospinal fluid

53 End of sigmoid colon cervical spinal cord (leading to quadriplegia) and medulla (respiratory paralysis, leading to sudden death).

b. The dens is secured in its position by the following structures: transverse ligament, alar ligaments, apical ligament, and tectorial membrane (which is a continuation of the posterior longitudinal ligament).

c. Widening of the atlanto-dental interval (distance from the anterior arch of CI to the dens) suggests tearing of the transverse ligament.

2. Denervation of zygapophyseal (facet) joints a. The zygapophyseal (facet) joints are synovial joints between the inferior and superior articular processes. These joints are located near the intervertebral foramen.

b. If these joints are damaged as a result of trauma or disease (e.g., rheumatoid arthritis), a spinal nerve may be impinged and cause severe pain. To relieve the pain, medial branches of the dorsal primary ramus are severed (dorsal rhizotomy).

3. Dislocations without fracture occur only in the cervical region because the articular surfaces are inclined horizontally. Cervical dislocations stretch the posterior longitudinal ligament.

4. Dislocations with fracture occur in the thoracic and lumbar regions because the articular surfaces are inclined vertically.

5. Stability of the vertebral column is determined primarily by four ligaments: anterior longitudinal ligament, posterior longitudinal ligament, ligamentum flavum, and inter spinous ligaments.

6. Breast, lung, and prostate cancers metastasize to the brain because the internal vertebral venous plexus, basivertebral veins, and external vertebral venous plexus that surround the vertebral column communicate with the cranial dural sinuses and veins of the thorax, abdomen, and pelvis.

7. Spina bifida occulta is a common congenital malformation in which the vertebral arch is absent. The defect is covered by skin and usually is marked by a tuft of hair. This condition is not associated with any neurologic deficit.

8. Hemivertebrae occurs when a portion of the vertebral body does not develop. This condition can lead to scoliosis.

9. Sickle cell anemia is associated with "fish mouth vertebra" (seen radiographi-cally), in which central depressions occur in the vertebral body.

10. Spondylolysis is a chronic stress fracture of the pars interarticularis (an area between the pedicle and lamina of a vertebra). It often is seen in adolescent athletes, most commonly at vertebra L5. On an oblique radiograph of the lumbar vertebrae, the fracture appears as a "collar" around the neck of the Scottie dog.

11. Spondylolisthesis occurs when the pedicles of a lumbar vertebra degenerate or do not develop properly. As a result, the body of the lumbar vertebra moves anterior with respect to the vertebrae below it, causing lordosis. Degenerative spondylolisthesis usually occurs at vertebral level L4—5. Congenital spondylolisthesis usually occurs at vertebral level L5—SI.

12. Spondylosis is a degenerative process that is characterized by the formation of osteophytes and bone spurs. It typically occurs in the cervical region of elderly patients.

13. Ankylosing spondylosis (rheumatoid spondylitis, or Marie-Stumpel disease) is an inflammatory osteoarthritis that usually affects the lumbar vertebrae and sacroiliac joint. The annulus fibrosus of the intervertebral disks may become ossified, producing severe spinal immobility. The ossification bridges the disks at various levels, forming a "bamboo spine." Most of these patients are positive for histocompatibility antigen HLA-B27.

14. Osteomyelitis is a bacterial infection that may occur within vertebral bodies. Staphylococcus aureus and Pscudomonas aeruginosa (in immunosuppressed patients and intravenous drug users) are causative agents.

15. Protrusion of the nucleus pulposus a. An intervertebral disk consists of the annulus fibrosus (fibrocartilage) and nucleus pulposus (remnant of the embryonic notochord). The nucleus pulposus usually herniates posterolateral^ and compresses a nerve root.

b. Table 1-2 shows important features of a herniated disk at various vertebral levels. From the clinical signs listed in Table 1-2, you should be able to deduce which nerve root is compressed and then identify the appropriate herniated disk on a radiograph or an MRI.

Table 1-2.

Vertebral Levels of Herniated Disk"

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