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Spine Anatomy - Advanced

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Spine Anatomy - Advanced

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The Spine (aka, vertebral column, spinal column)

Summary

  • The spine extends from the skull to the pelvis.

Overview

Vertebrae comprise

  • Vertebral body (anterior)
  • Vertebral arch (posterior)
    • Made up of pedicles, laminae, and processes.

Terminology

Anatomical/Embryological synonyms (but not the same):

  • Vertebral arch is synonymous with Neural arch
  • Vertebral body is synonymous with Centrum

Vertebral Column

  • The vertebral body is the disc-shaped weight-bearing portion of the vertebra.
  • The vertebral arch encloses the vertebral foramen through which the spinal cord passes.

The vertebral arch

It comprises (from anterior to posterior):

  • Paired pedicles, which abut the vertebral body,
  • Paired laminae, which meet medially at the:
  • Singular spinous process, which extends posteriorly; it serves as an attachment site for ligaments and muscles of the vertebral column.
  • Transverse processes to which trunk muscles and ligaments attach.
  • Articular processes.

Processes

  • A process is a bony prominence.

Each Vertebra comprises:

  • 1 Spinous process
  • 2 Transverse processes
  • 4 Articular processes (2 sup., 2 inf.)

Facet joints

As a mneomnic, use BU(M) for the orientation of the superior facet joint:

  • Backward
  • Upward
  • Medial (sometimes)

Articular facets

Articular facets (zygapophysial joints) form at adjacent articular processes.

Intervertebral discs

  • Lie sandwiched between the vertebral bodies.
  • They comprise:
    • Nucleus pulposus, which is an inner gelatinous substance, and,
    • Annulus fibrosus, which is the outer ring of collagen and cartilage.
  • The intervertebral disc absorbs shock and acts as a cushion between the vertebrae, and allows for spine flexibility.

Bone histology

  • The center of the vertebral body comprises spongy bone.
  • The periphery comprises compact bone.

Intervertebral foramen

The laterally-oriented opening between the vertebral arches of stacked vertebrae.

  • A spinal nerve passes through the foramen.
  • The inferior vertebral notch lies beneath the top pedicle.
  • The superior vertebral notch lies above the pedicle on bottom.

Numbering

  • There are roughly 33 vertebrae.
  • There are 31 spinal nerves.

Number of Vertebrae:

  • 7 cervical
  • 12 thoracic
  • 5 lumbar
  • 5 fused sacral
  • 3 – 4 fused coccygeal

Number of paired spinal nerves:

  • 8 cervical
  • 12 thoracic
  • 5 lumbar vertebrae
  • 5 sacral
  • 1 coccygeal

Nerve root exit pattern

  • Cervical roots exit above their corresponding vertebra, thoracic roots and below, exit below it.

See Spinal Nerves

Full Text

  • Here we will learn the anatomy of the spine, which is enclosed within the vertebral column (aka, spinal column, aka, spine): it extends from the skull to the pelvis.

Overview

  • To begin, start a table.

Denote that the vertebrae comprise:

  • Vertebral body (anterior)
  • Vertebral arch (posterior), which comprises pedicles, laminae, and processes.

Orientation

  • We'll draw let's draw axial and lateral views of the vertebral column, using a prototypical thoracic vertebra: bear in mind that skeletal differences on to the vertebra exist at the different spine segment levels.
  • Label posterior and anterior.
  • Draw the vertebral body, which is the disc-shaped weight-bearing portion of the vertebra.
  • Next, draw the vertebral arch.
    • Indicate that it encloses the vertebral foramen through which the spinal cord passes.

Terminology

  • Next, let's address some important, easily confused terminology.
  • Write that the following are anatomical terms:
    • Vertebral arch
    • Vertebral body
  • And then write their embryological synonyms:
    • Neural arch
    • Centrum
  • However, although these terms are similar and are often used interchangeably, they do have different meanings and conflating the terms spawns confusion.
  • Show that the vertebral arch comprises (from anterior to posterior):
    • Paired pedicles, which abut the vertebral body,
    • Paired laminae, which meet medially at the:
    • Singular spinous process, which extends posteriorly; it serves as an attachment site for ligaments and muscles of the vertebral column.
    • Then, label the transverse processes to which trunk muscles and ligaments attach.
    • Finally, show the superior articular processes.
  • Now, write that a process is a bony prominence.

For each typical vertebra, there is:

  • 1 Spinous process
  • 2 Transverse processes
  • 4 Articular processes (2 sup., 2 inf.)

Lateral View

  • Next, let's draw two stacked vertebrae in lateral view.
  • Label anterior and posterior.
  • First, draw the vertebral bodies;
  • Then, the vertebral arches.
  • On each, label the transverse process (coming towards us).
  • Spinous process going backwards.
  • On the upper vertebra, indicate the inferior articular process.
  • And on the lower vertebra, indicate the superior articular process.
  • Show facet joints on each, which abut one another.

Superior Facet Joint Acronym

  • As a mneomnic, write BU(M) for the orientation of the superior facet joint, which stands for:
    • Backward
    • Upward
    • Medial (sometimes)
  • In our terminology, include that articular facets (zygapophysial joints) form at adjacent articular processes.

We discuss their significance in spine pain, elsewhere.

  • Sandwiched between the vertebral bodies, draw intervertebral discs.
  • Indicate that the intervertebral disc comprises:
    • The nucleus pulposus, which is an inner gelatinous substance, and,
    • The annulus fibrosus, which is the outer ring of collagen and cartilage.
    • The intervertebral disc absorbs shock and acts as a cushion between the vertebrae, and allows for spine flexibility.
      Then, within both the axial and lateral views of the spine, show that the center of the vertebral body comprises spongy bone whereas the periphery comprises compact bone.

Intervertebral Foramen

  • Now, show that the spinal cord descends through the vertebral canal.
  • Then, label an intervertebral foramen, which is the laterally-oriented opening between the vertebral arches of stacked vertebrae;
  • Show a spinal nerve pass through the foramen.
  • Label the inferior vertebral notch beneath the top pedicle.
  • And the superior vertebral notch above the pedicle on bottom.

Vertebrae and Exiting Spinal Nerves

Finally, let's address the relationship between the vertebrae and the spinal nerves.

  • Draw a skull.
  • Then, draw the length of the vertebral column.
  • Indicate that there are roughly 33 vertebrae.
  • Whereas there are 31 pairs of spinal nerves.

Vertebral Levels

Demarcate that vertebrae divide into:

  • 7 cervical
  • 12 thoracic
  • 5 lumbar vertebrae

Then, that there are:

  • 5 fused sacral
  • 3 – 4 fused coccygeal vertebrae.

Spinal Nerves

Next, demarcate that the spinal nerves divide into:

  • 8 cervical
  • 12 thoracic
  • 5 lumbar vertebrae
  • 5 sacral
  • 1 coccygeal

Numbering

  • Highlight the difference between the cervical and spinal numbering, this has important consequences.
  • Write that cervical roots exit above their corresponding vertebra, thoracic roots and below, exit below it.

Lastly, let's see why.

  • Draw the vertebrae for C7 and T1. (The cervical spine ends at C7).
  • Show that the C7 spinal nerve exits above its vertebra.
  • Then, show that C8 exits below C7.

So where must T1 go?

  • Show that it exits below the T1 vertebra.