HTMS SELF ASSESSMENT HIGH YIELD ANATOMY (BACK) POINTS

BACK

Vertebral Column

I. General Characteristics

II. Typical Vertebra

III. Intervertebral Disks

IV. Regional Characteristics of Vertebrae

V. Ligaments of the Vertebral Column

VI. Vertebral Venous System

Soft Tissues of the Back

I. Superficial Tissues

II. Deep Tissues

III. Suboccipital Area

Spinal Cord and Associated Structures

I. Spinal Cord

II. Spinal Nerves

III. Meninges

IV. Structures Associated with the Spinal Cord

V. Dermatome, Myotome, and Sclerotome

VI. Development of Back Structures

HIGH YIELD POINTS: 

Vertebral column consists of 33 vertebrae, including the 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 4 fused coccyx or 26 vertebrae (if the sacrum and coccyx are considered as a fused 1 bone each).

■ Atlas is the C1 vertebra, supports the skull and helps make nodding movements possible. The axis has a dens that helps the head to rotate.

■ Alar ligament prevents excessive rotation of the head. The ligamentum nuchae is the extension of the supraspinous ligament in the cervical region. The ligamentum flavum connects adjacent laminae.

■ Intervertebral disks consist of a central nucleus pulposus with a surrounding annulus fibrosus and serve as shock absorbers. The nucleus pulposus arises from the embryonic notochord and may herniate through the ruptured annulus fibrosus, thereby impinging on the roots of the spinal nerve. Most herniated disk occurs at L4 to L5.

■ Primary curvatures are located in the thoracic and sacral regions and develop during embryonic and fetal periods, whereas the secondary curvatures are located in the cervical and lumbar regions.

■ Spina bifida is a defective closure of the vertebral arch associated with maternal folic acid deficiency and includes (a) spina bifida occulta—a failure of the vertebral arch to fuse (bony defect only with a small tuft of hair over the affected area of skin), (b) meningocele—a protrusion of the meninges through the unfused arch of the vertebra (spina bifida cystica), (c) meningomyelocele—a protrusion of the spinal cord and the meninges, and (d) myeloschisis (rachischisis)—a cleft spinal cord due to failure of neural folds to close.

■ Lumbar spondylosis (ankylosis) is a degenerative joint disease affecting the lumbar vertebrae and intervertebral disks, causing pain, muscle weakness, and stiffness, sometimes with sciatic radiation resulting from nerve root pressure by associated protruding disks or osteophytes.

■ Klippel–Feil syndrome is a congenital defect manifested as a short, stiff neck resulting from reduction in the number of cervical vertebrae or extensive fusion of the cervical vertebrae.

■ Arnold–Chiari (or Chiari) deformity is a congenital cerebellomedullary malformation in which the cerebellum and medulla oblongata protrude down into the vertebral canal through the foramen magnum.

■ Atlantooccipital joint is a condylar synovial joint and involved in flexion, extension, and lateral flexion of the head. The atlantoaxial joints consist of two lateral plane joints and one median pivot joint (between the anterior arch of the atlas and the dens of the axis), and are involved in rotation of the atlas and head as a one unit on the axis.

■ Atlantoaxial dislocation (subluxation) occurs after rupture of the cruciform ligament caused by trauma or rheumatoid arthritis. It may result from a congenital absence of the dens, a fracture of the dens, or a direct trauma frequently caused by traffic accidents.

■ Compression fracture is produced by collapse of the vertebral bodies resulting from trauma, results in kyphosis or scoliosis, and may cause spinal nerve compression.

■ Whiplash injury of the neck is produced by a force that drives the trunk forward while the head lags behind, causing the head (with the upper part of the neck) to hyperextend and the lower part of the neck to hyperflex rapidly, as occurs in rear-end automobile collisions.

■ Herniated (slipped) disk is a protrusion of the nucleus pulposus through the annulus fibrosus of the intervertebral disk into the intervertebral foramen or into the vertebral canal, compressing the spinal nerve root. It commonly occurs posterolaterally.

■ Sciatica is pain in the lower back and hip, radiating into the buttock and into the lower limb and is most commonly caused by herniation of a lower lumbar intervertebral disk, compressing or irritating roots of the sciatic nerve. It causes muscular weakness, numbness, tingling, and pain along the path of the sciatic nerve.

■ Hangman fracture is a fracture of the pedicles of the axis (C2), which may occur as a result of judicial hanging or automobile accidents. In this fracture, the cruciform ligament is torn and the spinal cord is crushed, causing death.

■ Spinal cord occupies approximately the upper two-thirds of the vertebral canal, is enveloped by three meninges, and has cervical and lumbar enlargements for nerve supply of the upper and lower limbs, respectively. It has a conical end known as the conus medullaris, which terminates at the level of L2 vertebra.

■ Denticulate ligaments are 21 pairs of lateral extensions of the pia mater; the filum terminale internus is an inferior extension of the pia mater; CSF is formed by vascular choroid plexuses in the ventricles of the brain and is contained in the subarachnoid space; and the cauda equina (horse’s tail) is formed by dorsal and ventral roots of the lumbar and sacral spinal nerves.

■ Tethered cord syndrome is a congenital anomaly resulting from defective closure of the neural tube. It is characterized by the abnormally low conus medullaris, which is tethered by a short thickened filum terminale, leading to such conditions as progressive neurologic defects in the legs and feet and scoliosis.

■ Spinal nerves consist of 31 pairs of nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal). The cervical spinal nerves exit above the correspondingly numbered vertebrae except the eighth cervical nerves, which emerge below the seventh cervical vertebra; the remaining spinal nerves exit below the correspondingly numbered vertebrae.

■ Shingles (herpes zoster) is caused by the varicella zoster virus that remains latent in the dorsal root ganglia of spinal nerves and the sensory ganglia of cranial nerves. It results from activation of the virus, which travels down the sensory nerve to produce severe neuralgic pain, an eruption of groups of vesicles, or a rash in the dermatome of the nerve.

■ Caudal (epidural) anesthesia is used to block the spinal nerves in the epidural space by injection of local anesthetic agents via the sacral hiatus located between the sacral cornua.

■ Saddle block is the introduction of anesthesia into the dural sac in the region corresponding with the areas of the buttocks, perineum, and medial aspects of the thighs that impinge on the saddle in riding.

■ Lumbar puncture (spinal tap) is the tapping of the subarachnoid space in the lumbar region (lumbar cistern), usually between the laminae of vertebrae L3 and L4 or vertebrae L4 and L5. It allows measurement of CSF pressure and withdrawal of a fluid sample for microbial or chemical analysis and also allows introduction of anesthesia, drugs, or radiopaque material into the subarachnoid space.

■ Meninges consist of a pia mater (innermost layer), arachnoid mater (transparent spidery layer), and dura mater (tough fibrous outermost layer). The subarachnoid space between the pia and arachnoid maters contains CSF, the subdural space between the arachnoid and dura maters contains moistening fluid, and the epidural space external to the dura mater contains the internal vertebral venous plexus.

■ Meningitis is inflammation of the meninges caused by viral or bacterial infection. Bacterial meningitis (purulent meningitis) is an extremely serious illness and may result in brain damage or death, even if treated. Meningitis is also caused by fungi, chemical irritation or drug allergies, and tumors.

■ Vertebral artery arises from the subclavian artery and ascends through the transverse foramina of the upper six cervical vertebrae.

■ Vertebral veins are formed in the suboccipital triangle by tributaries from the venous plexus around the foramen magnum and the suboccipital venous plexus and descend through the transverse foramina.

■ Internal vertebral venous plexus lies in the epidural space and communicates superiorly with the cranial dural sinuses and inferiorly with the pelvic veins and with both the azygos and caval systems in the thoracic and abdominal regions. This venous plexus is the route of early metastasis of carcinoma from the lung, breast, and prostate gland or uterus to bones and the CNS.

■ External vertebral venous plexus lies in front of the vertebral column and on the vertebral arch and communicates with the internal vertebral venous plexus.

■ Superficial muscles of the back are involved in moving the shoulder and arm and are innervated by ventral primary rami of the spinal nerves.

■ Intermediate muscles are muscles of respiration.

■ Deep muscles of the back are responsible for extension of the spine and head and are innervated by dorsal primary rami of the spinal nerves.

■ Triangle of auscultation is bounded by the latissimus dorsi, trapezius, and scapula (medial border) and is the site where breathing sounds can be heard most clearly. The lumbar triangle is formed by the iliac crest, latissimus dorsi, and external oblique abdominal muscles. It may be the site of an abdominal hernia.

■ Suboccipital triangle is bounded by the rectus capitis posterior major, obliquus capitis superior, and obliquus capitis inferior muscles. The suboccipital muscles are innervated by the suboccipital nerve (dorsal primary ramus of C1).

■ Accessory nerve consists of a cranial portion that joins the vagus nerve and a spinal portion that supplies the sternocleidomastoid and trapezius muscles.

■ Dorsal scapular nerve (C5) supplies the rhomboid major and minor and levator scapulae muscles.

■ Suboccipital nerve (C1) supplies the muscles of the suboccipital region. The greater occipital nerve (C2) is derived from the dorsal primary ramus and communicates with the suboccipital and third occipital nerves and may supply the semispinalis capitis.

Reference: 

1. BRS Gross anatomy.

2. Gross Anatomy: The Big Picture. 

3. High Yield Gross Anatomy.

4. Clinical Anatomy by Regions, Snell. 

5. Grays Anatomy .

6. LAST Anatomy