Spinal Column Anatomy

• Spinal Column Anatomy
• Presented by Kevin McCarthy, CNIM, Director of Education and Training
• Presented by Kent Rice, REPT, CNIM, DABNM, Sr. Manager Education and Training

Learning Objectives

• List the major components of a vertebra
• List the unique features of the cervical vertebra and spine
• Describe the curvatures of the spine by spinal section
• Describe the number of vertebra by spinal section
• Describe the component of a vertebral disc
• Know the 3 column model of stability

Spinal Column

• Cervical Column: 7 vertebrae

• Vertebral Arteries

• Lordotic Curve

• Smallest Vertebrae

• Most Flexible for Rotation

• Atlas (C1) and Axis (C2)

• Thoracic Column: 12 vertebrae

• Greater Rigidity and Less Flexible

• Kyphotic Curve

• Rib Attachments form a box

• Lumbar Column: 5 vertebrae

• Flexibility and Heavy Loads

• Largest Vertebrae

• Lordotic Curve

• Sacral Column: 5 vertebrae

• Hip and Pelvic Attachments

• Fused Segments

Morphology and Section Size

• Sections vary by size to handle increasing loading forces
• Sections vary by shape specific to function (e.g., transverse foramen)
• Sections vary in rigidity and flexibility based on vertebral shape and function

Cervical Spinal Column

• 7 vertebra from C1 to C7
• Superiorly it joins the cranium, known as the occipital-cervical or atlanto-occipital junction
• Specialized components of the cervical spine include:
  • Vertebral foramen of the transverse process
  • Atlas (C1), axis (C2)
  • The odontoid process of C2.

External Craniocervical Ligaments

• Connection between the cranium and the cervical spine
• Supports the head and neck; allows for flexion, extension, and rotation
• Vertebral arteries running through the transverse foramina are susceptible to injury from neck trauma, with potential for significant CNS ischemic event

Cervical Vertebrae – Atlas (C1) Axis (C2)

• The 2 most superior vertebrae are unique in their form and function
• Their form is derived from the necessary function of supporting and rotation of the skull
  • Cervical vertebra 1 (C1) is the Atlas
  • Cervical vertebra 2 (C2) is the Axis

Specific Features of the Atlas & Axis

• Superior and inferior articular facets form the rotating joint between C1 and C2
• Dens (odontoid process): the pivot center for rotation of the skull on the spinal column

Cervical Vertebrae

• The smallest bodies, lamina, and pedicles
• The transverse processes contain the transverse foramen (vertebral arteries)
• The most flexible region in anterior/posterior, lateral and rotational movement

Cervical Instrumentation

• Anterior fixation is achieved with a vertebral body screw and plate
• Posterior cervical screws are usually placed in the lateral mass

Thoracic Spinal Column

• 12 vertebrae from T1-T12
• A natural kyphosis of 20-40° to accommodate vital organs within the rib cage
• Rib attachments at each thoracic vertebra make the thoracic spine more rigid and less flexible than cervical or lumbar regions

Thoracic Vertebrae

• Facets are articulating surfaces for spinal joints (facet joints)
• Ribs attach at the body and transverse process

Lumbar Spinal Column

• 5 vertebra from L1 to L5
• The conus medullaris of the spinal cord ends at the level of L1
• The cauda equina, pelvic, and lower limb nerve roots, are present from L1 through the sacral regions
• Largest vertebra, separated by 5 lumbar discs
• Discs bear the most force and are at greatest risk for herniation

Lumbar Vertebrae

• Specific features of the lumbar vertebra
  • The largest vertebral body and spinous process
  • Largest pedicles of any vertebra
• Removal of the lamina and spinous process (called a laminectomy), is done to facilitate cauda equina decompression

Lumbar Pedicle Screw Instrumentation

• The pedicle is a secure location for fixation of the spine, especially in the lumbar and thoracic spine
• Medial malpositioning of the pedicle screw endangers nerve root or spinal cord

Important Ligaments of the Spinal Column

• The ligaments provide support and protection for the spine
  • Anterior Longitudinal Ligament (ALL)
  • Posterior Longitudinal Ligament (PLL)
  • Supraspinous ligament
  • Interspinous ligament
  • Ligamentum Flavum

Sacral Spinal Column

• 5 fused vertebral levels S1 to S5
• No intervertebral disc
• Lumbosacral junction at L5-S1
• Coccyx bone at tip

Vertebral Discs

• Intervertebral discs are between each vertebra and cushion force load axially onto the spinal column
• The nucleus pulposus absorbs most force and is held in by the firm annulus fibrosus
• Thinning or tears in the annulus fibrosus can lead to bulging of the disc and compression of neurological structures
• The intervertebral disc is an avascular structure deriving its nutrients from the vertebral end plate

Nucleus and Annulus

• Nucleus Pulposus (NP) - granular, semi-gelatinous
• Annulus Fibrous (AF) - striated, multi-layered fibrous material
• Two cartilaginous vertebral end-plates (VEP)

Vertebral Discs

• The nucleus absorbs and distributes force evenly against the annulus.
• The annulus supports the loading force on the disc
• Abnormal forces overstress the annulus and can course herniation or rupture
• Common spinal surgery is for a HNP, herniated nucleus pulposus

Spinal Instability

• The loss of ability of the spine under physiological loads to maintain its pattern of displacement so that there is no initial or additional neurological deficit, no major deformity, and no incapacitating pain
• A stable spine should be one that can withstand axial forces anteriorly through the vertebral bodies, tension forces posteriorly, and rotational stresses
• Total of 5 or more = instability

2-Column Models

• Considers the anterior and posterior segments, grouping fractures as stable and unstable
• The posterior elements were considered the most important in spinal stability
• Failed to recognize "clinical instability" i.e., burst fractures, where the posterior elements (all structures posterior to PLL) are intact
• Ability to protect the neural elements is compromised

3-Column Models

• Classifying instability into three degrees, according to mechanical and/or neurological involvement
• First degree or Mechanical: disruption of posterior elements, neuro intact, potential for chronic instability "Spine can buckle" i.e. Seat-belt and distraction injuries
• Second degree or Neurological: still neurologically intact, but spinal canal has been violated, posing risk to its contents i.e. burst fractures
• Third degree or Mechanical and Neuro compromise: burst and fracture dislocations with neuro involvement

3-Column Model

• It is the current model used to determine spinal instability and spinal instrumentation construct The 3 columns are:
  • Posterior: pedicles, facts, lamina, etc
  • Middle: posterior half of vertebral body
  • Anterior: anterior half of vertebral body

Linked to 3 degrees of instability

• 1º Mechanical: structural damage only to the posterior column
• 2° Neurological: spinal canal violated by posterior and/or middle column high risk of neurological injury
• 3° Mechanical & Neurological: ighly unstable involving anterior and middle column and possibly posterior column and neurological changes