The Back

Chapter 1 The Back

I. Typical Vertebra

• Body, vertebral arch, processes for muscular attachment and articulation with adjacent vertebrae, and vertebral foramen (Figure 1-1)

A. The Body

1-1 Typical cervical vertebrae. A, Superior view of a typical cervical vertebra. B, Lateral view of articulated cervical vertebrae.

(From Greene, W B: Netter’s Orthopaedics. Philadelphia, Saunders, 2006, Figure 13-4.)

Anterior weightbearing cylinder

B. Vertebral Arch

a. U-shaped component attached to posterior aspect of body

b. Provides attachment for spinous, transverse, and articular processes

2. Pedicle has superior and inferior vertebral notches.

3. Lamina fuses in posterior midline with opposite lamina.

C. Transverse Processes

D. Articular Processes

1. Superior and inferior articular processes project from junction of pedicle and lamina separated by pars interarticularis

2. Form synovial zygapophysial (facet) joints with articular processes of adjacent vertebrae

Zygapophysial joints are synovial joints that may develop osteoarthritis with age or trauma.

E. Vertebral Foramen

1. Space enclosed by vertebral arch and body

2. Collectively form vertebral canal for spinal cord and meninges

F. Intervertebral Foramina

1. Formed between inferior and superior vertebral notches in pedicles of adjacent vertebrae

2. Transmit spinal nerves and related blood vessels

Compressing spinal nerve in intervertebral foramen may cause radiculopathy.

Any space-occupying lesion in an intervertebral foramen may compress the spinal nerve or its roots and produce back pain that may radiate into an extremity. Motor nerve fibers may become involved, resulting in loss of strength.

II. Vertebral Column

• Comprises 33 vertebrae in normal adult: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, 4 coccygeal

7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal vertebrae

A. Cervical Vertebrae (see Figure 1-1; Table 1-1)

1. Typical cervical vertebrae: C3-C6

a. Spinous processes allow neck extension because they are short.

b. Articular processes with nearly horizontal facets allow relatively free movement in all directions at the expense of stability.

c. Transverse foramen in each transverse process allows passage of vertebral artery and vein.

TABLE 1-1 Features of Vertebrae

The vertebral artery ascends transverse foramina of vertebrae C1-6.

2. C1 (atlas) (Figure 1-2; see Table 1-1)

a. Midline anterior tubercle on anterior arch and posterior tubercle on posterior arch

b. Sulcus for vertebral artery on posterior arch on each side

3. C2 (axis) (Figure 1-3; see Table 1-1)

1-2 Atlas (C1) from superior view.

(From Greene, W B: Netter’s Orthopaedics. Philadelphia, Saunders, 2006, Figure 13-4.)

1-3 Axis (C2) and atlantoaxial joints. A, Posterosuperior view of axis. B, Posterosuperior view of articulated atlas and axis. Posterior articular facet of dens is for articulation with transverse ligament of atlas at median atlantoaxial joint. C, Open mouth radiograph of atlantoaxial joints.

(From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 17.)

The dens (odontoid process) and body of the axis develop from separate ossification centers. The ossification centers may fail to fuse, and this anomaly must be distinguished from an odontoid fracture in patients with cervical trauma. The dens also may be congenitally absent.

The dens may be congenitally absent or fail to fuse with the body of the axis.

a. Called vertebra prominens because of its long spinous process, which helps in counting vertebrae.

Vertebra prominens is helpful in counting vertebrae.

b. Small transverse foramen does not contain vertebral artery.

Dislocations without fracture occur only in cervical spine.

Dislocations may cause cervical vertebra to move out of alignment because articular surfaces lie in nearly a horizontal plane and are less stable. Although the spinal cord may be compressed, it may escape severe injury because of the large vertebral canal. Nevertheless, all movement of patients suspected of having a neck injury should be minimized until the cervical spine is properly stabilized. Injury to the cervical spinal cord may not appear on a radiograph.

Failure of segmentation of cervical vertebrae results in congenital fusion, causing Klippel-Feil syndrome, which is characterized by a short, stiff neck.

Klippel-Feil syndrome is congenital fusion of cervical vertebrae.

B. Thoracic Vertebrae (Figure 1-4; see Table 1-1)

• Articular processes are oriented to favor lateral bending and rotation, although range of movement is limited by the rib cage, thin intervertebral discs, and overlapping spinous processes.

1. Typical thoracic vertebrae: T2-T9

a. Costal demifacets on the body articulate with the head of the corresponding rib and the inferior rib.

b. Costal facet on transverse process articulates with tubercle of corresponding rib

2. T1 and T10-T12

a. Complete facet on the body articulates with the entire head of the corresponding rib.

b. Inferior demifacet on body of T1 articulates with superior part of head of rib 2

1-4 Typical thoracic vertebra. A, Superior view. B, Lateral view.

(From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 154.)

Traumatic injury to the thoracic vertebrae may produce dislocation with fracture because articular facet joints are arranged vertically. An aortic aneurysm may cause left-sided erosion to bodies of T5-T8 as seen on a radiograph.

An aneurysm of the descending thoracic aorta may erode bodies of vertebrae T5-8 on the left side.

C. Lumbar Vertebrae (Figures 1-5 and 1-6; see Table 1-1)

• Articular processes with facets oriented to favor flexion and extension

1-5 Lumbar vertebrae. A, Superior view of a typical lumbar vertebra. B, Lateral view of articulated lumbar vertebrae. Intervertebral foramina transmit spinal nerves.

(From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 155.)

1-6 A, Oblique radiograph of lumbar spine showing characteristic “Scottie dog” form (B). The appearance of a collar indicates a fracture of the pars interarticularis.

Traumatic injury to lumbar vertebrae may produce dislocation with fracture because articular surfaces are arranged vertically.

Stress fractures of the pars interarticularis occur frequently in lumbar vertebrae (spondylolysis), with the posterior part of the vertebral arch separating from the anterior part to cause back pain. It occurs commonly in L5 in adolescent athletes involved in sports that require repeated spinal hyperextension. The vertebral column is not misaligned in unilateral fractures, which show up in oblique lumbar radiographs as a collar on the neck of the “Scottie dog” (Figure 1-6).

Spondylolysis is a fracture of pars interarticularis that may cause spondylolisthesis.

In spondylolisthesis, a vertebral body is displaced forward on the vertebral body immediately below. It occurs frequently at the L5/S1 level and is often secondary to bilateral pars interarticularis fractures. Alignment of the vertebral column is compromised, and the cauda equina may be affected. Patients with spondylolisthesis may encounter difficulty during childbirth because of the resulting narrowed pelvic inlet.

Spondylolisthesis may interfere with childbirth.

Degenerative changes in the lumbar spine and ligamenta flava may cause narrowing of the spinal canal (spinal stenosis). The resulting compression of neural structures produces pain on walking or standing that is relieved by bending forward or sitting (neurogenic claudication). This differs from vascular claudication of the lower extremities that is relieved by standing still.

Neurogenic claudication from lumbar spinal stenosis differs from vascular claudication in being unrelieved by standing still.

1. Wedge-shaped bone formed by fusion of five sacral vertebrae

2. Articulates superiorly with L5 at lumbosacral joint and laterally with hip bones at sacroiliac joints

3. Four pairs of anterior sacral foramina for anterior rami and four pairs of posterior sacral foramina for posterior rami of spinal nerves S1-S4

4. Sacral canal contains dural sac down to lower border of S2.

5. Sacral hiatus in place of spine and laminae of S5 (and sometimes S4) with sacral cornua located laterally

When administering caudal epidural anesthesia, sacral cornua are used as landmarks to locate the sacral hiatus.

Sacral cornua are landmarks for caudal epidural anesthesia.

• Triangular bone formed from fusion of four coccygeal vertebrae; often C1 is not fused.

III. Joints and Ligaments of Vertebral Column

A. Joints between Vertebrae

1. Intervertebral discs (Figure 1-7)

a. Fibrocartilaginous joints between bodies of adjacent vertebrae except C1/C2, sacrum, and coccyx

1-7 Ligaments connecting vertebrae.

(From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 158.)

There is no intervertebral disc between vertebrae C1/C2.

b. Separated from each vertebral body by thin plate of hyaline cartilage

c. Permit little movement between adjacent vertebrae but cumulatively allow considerable flexibility of column

d. Function as shock absorbers

(1) Anulus fibrosus

(a) Fibrocartilaginous portion of disc surrounding nucleus pulposus; thinner posteriorly

(b) Firmly attached to anterior and posterior longitudinal ligaments

(2) Nucleus pulposus

(a) Incompressible gelatinous center of intervertebral disc located closer to its posterior surface

(b) Produces shock-absorbing quality of disc

(c) Loses water temporarily during daily activities and permanently with age as it gradually becomes replaced by fibrocartilage

The nucleus pulposus loses water temporarily each day and permanently with age.

Rupture of the nucleus pulposus through the anulus fibrosus causes a herniated intervertebral disc. Herniated discs usually occur in lumbar (L4/L5 or L5/S1) or cervical regions (C5/C6 or C6/C7) of individuals younger than age 50 and may impinge on spinal nerves or their roots. Herniations may follow degenerative changes in the anulus fibrosus or be caused by sudden compression of the nucleus pulposus. Herniated lumbar discs usually involve the nerve root descending to exit the intervertebral foramen inferior to the vertebra below (traversing root) rather than the nerve root leaving the vertebral canal at the level of the disc (exiting root) (Figure 1-8).

1-8 Herniated lumbar intervertebral disc. Herniation usually occurs posterolaterally and affects traversing root, not exiting root (i.e., herniation at L4-L5 affects L5 root, whereas herniation at L5-S1 affects S1 root).

An intervertebral disc usually herniates posterolaterally just lateral to posterior longitudinal ligament.

Intervertebral discs herniate most commonly at L4/L5 and L5/S1 and compress traversing nerve root.

2. Facet joints (zygapophysial/zygapophyseal joints)

a. Synovial joints between superior and inferior articular facets of adjacent vertebrae

b. Provide varying amounts of flexion, extension, rotation, or lateral bending depending on vertebral level

Facet joints diseased by osteoarthritis (degenerative joint disease) border the intervertebral foramen, and osteophytes may impinge on an adjacent spinal nerve, causing severe pain. Lumbar zygapophysial joints may be denervated by surgical or percutaneous radiofrequency neurotomy (percutaneous rhizolysis) to relieve low back pain. Each joint is innervated by medial branches of two adjacent posterior rami, and both branches must be sectioned.

Osteoarthritis is degenerative joint disease from aging or trauma.

Osteophyte on zygapophysial joint may compress spinal nerve

B. Ligaments Connecting Vertebrae (Table 1-2; see Figure 1-7)

TABLE 1-2 Ligaments of Vertebral Column

Ligament	Attachment	Comments
Supraspinous	Connects tips of spinous processes	Limits flexion of vertebral column; expanded in cervical region as ligamentum nuchae
Interspinous	Connects spinous processes of adjacent vertebrae	Limits flexion of vertebral column
Anterior longitudinal	Attached to anterior surface of vertebral bodies and intervertebral discs	Limits extension of vertebral column; supports anulus fibrosus and may be strained or torn in whiplash
Posterior longitudinal	Attached to posterior surface of vertebral bodies and intervertebral discs and lies within vertebral canal	Limits flexion of vertebral column; supports anulus fibrosus and directs herniation of intervertebral disc posterolaterally
Ligamentum flavum	Paired ligament that connects laminae of adjacent vertebrae	Limits flexion of vertebral column; yellowish due to elastic tissue

Because its presence reinforces the intervertebral disc in the posterior midline, the posterior longitudinal ligament reduces the incidence of disc herniations that may compress the spinal cord and cauda equina.

The cervical spinal cord may be injured without x-ray evidence of vertebral damage.

The cervical spinal cord may be injured by transient inward bulging of the ligamentum flavum during sudden forced hyperextension. A radiograph may not show vertebral damage.

Whiplash (cervical extension sprain) is forceful hyperextension of the cervical spine that stretches the anterior longitudinal ligament and adjacent structures. Rear-end automobile collisions often cause whiplash, and symptoms include neck pain, headache, and pain and numbness radiating into the upper extremities.

Rear-end automobile collision causes whiplash injury.

C. Craniocervical Joints and Ligaments

1. Atlantooccipital joint (Figure 1-9)

a. Paired synovial joint between occipital condyle and superior articular facet of atlas

b. Allows flexion/extension of head (nodding head “yes”) and some lateral flexion but no rotation

c. Posterior atlantooccipital membrane penetrated by vertebral artery and suboccipital nerve

2. Atlantoaxial joint (see Figure 1-9)

a. Paired lateral atlantoaxial joints and median atlantoaxial joint with dens held against anterior arch of atlas by transverse ligament of atlas

b. Allows rotation of head (shaking head “no”) but not flexion, extension, or lateral bending

1-9

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Jun 16, 2016 | Posted by admin in ANATOMY | Comments Off

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