Back Anatomy Notes

Surface Anatomy of the Back

  • Clinical Perspective:
    • Palpation and visual examination.
    • Observation of spinous processes, muscle orientation, and bony protrusions.
    • Focus on the posterior aspect, primarily the back region.

Vertebral Column

  • Composition:
    • 33-34 vertebrae.
    • Intervertebral discs between most vertebrae.
  • Function of Intervertebral Discs:
    • Shock absorption.
    • Facilitation of movement.
    • Prevention of bone-on-bone friction.
    • Thick fibrocartilage outer layer with a gel-like center for compression.
  • Vertebral Column Regions:
    • Cervical (neck): 7 vertebrae.
    • Thoracic: 12 vertebrae with rib attachments.
    • Lumbar: 5 large vertebrae.
    • Sacrum (sacral region): 5 fused vertebrae.
    • Coccyx (tailbone): 3-5 fused vertebrae (variation in number).

Curvatures of the Vertebral Column

  • Primary Curvatures:
    • Present at birth.
    • Located in the thoracic and sacral regions.
  • Secondary Curvatures:
    • Develop after birth.
    • Cervical curvature develops as the baby gains head control (around six months).
    • Lumbar curvature develops as the baby starts to stand and walk (six months to one year).
  • Spinal Curvature Variations:
    • Scoliosis: Lateral bend in the thoracic region (pathological).
      • Can be C-shaped or S-shaped.
      • Early intervention with braces or physical therapy is important.
      • Severe cases may require surgery.
    • Kyphosis: Hunching of the back, over-accentuation of thoracic curvature (not always pathological).
      • Common in elderly individuals due to weakened core muscles and decreased bone density.
      • Congenital kyphosis is rare (e.g., Quasimodo).
    • Lordosis: Over-accentuation of lumbar curvature (not always pathological).
      • Can be congenital or developed through activities (e.g., gymnastics, dance).

General Vertebra Characteristics

  • Common Features (Slide 6):
    • Body: Anterior-facing.
    • Superior and Inferior Articular Processes: Allow for vertebral stacking.
    • Pedicle: Connects the articular processes to the body.
    • Transverse Process: Lateral projection.
      • Modified in cervical vertebrae to have a foramen for the vertebral artery.
      • In thoracic vertebrae, it has articulation points with the ribs.
    • Lamina: Connects the transverse processes to the spinous process.
    • Spinous Process: Posterior projection, gives the spine its name.
    • Intervertebral Foramen: Formed by stacking vertebrae, spinal nerves pass through.
    • Vertebral Foramen: Large opening for the spinal cord.

Cervical Vertebrae

  • 7 Cervical Vertebrae (C1-C7):
    • C1 (Atlas) and C2 (Axis) are unique.
    • Typical cervical vertebrae: C3-C7.
  • Characteristics of Typical Cervical Vertebrae:
    • Wider body compared to thoracic and lumbar.
    • Lighter weight.
    • Transverse foramen for the vertebral artery (branch of the subclavian artery).
    • Superior articular processes with facets facing superior-posteriorly.
    • Large, triangular vertebral foramen.
    • Bifurcated spinous process (except C7).
    • C7: Transitional vertebra with elongated transverse processes and a non-bifurcated spinous process (vertebral prominence).

Atlas (C1)

  • Most modified vertebra.
  • Superior articular processes (facets)
  • No real body or spinous process.
  • Transverse processes are present with transverse foramen.
  • Lateral masses: areas of increased bone density
  • Posterior tubercle (instead of spinous process)
  • Inferior articular processes (facets)
  • Facet for articulation with the odontoid process (dens) of C2.

Axis (C2)

  • Spinous process: bifurcated
  • Dens (odontoid process): finger-like projection, articulates with C1.
  • Superior and inferior articular
  • Transverse processes and transverse foramen: present, but smaller.
  • Hangman Fracture:
    • Fracture of the odontoid process, typically at the base.
    • Displacement: posterior displacement of the odontoid process.
    • Posterior displacement can compress the spinal cord, leading to death.

Thoracic Vertebrae

  • Spinous Processes:
    • Elongated, angled inferiorly and posteriorly, not bifurcated.
  • Transverse Processes:
    • True transverse processes with facets for rib articulation.
  • Superior and Inferior Articular Processes:
    • Shortened.
  • Body:
    • Heart-shaped.
  • Vertebral Foramen:
    • Smaller, rounded.
  • Rib Articulation:
    • T10-T12 bodies have single facets.
    • T2-T9 have demifacets on the superior and inferior aspects of the body.
  • Rib Structure:
    • Two ends: sternal and vertebral.
    • Vertebral end: head and tubercle.
    • Head articulates with the vertebral body.
    • Tubercle articulates with the transverse costal facet.
  • Movements:
    • Rotation only
  • Costovertebral Joints:
    • Articulation of the head of the rib with vertebral bodies and intervertebral discs.
  • Costotransverse Joints:
    • Articulation of the tubercle of the rib and transverse process.

Lumbar Vertebrae

  • Characteristics:
    • Large and robust.
    • Thick body: supports the weight of the upper body.
    • Triangular, squished vertebral foramen.
    • Spinal cord ends at L1-L2 in adults.
    • Meninges continue down.
    • Filum terminale: pia mater extension that anchors to the coccyx.
  • Anchoring:
    • Prevents pulling or shearing of spinal nerves.
    • Wide, narrow and tapered transverse processes.
  • Posterior view: Resembles a moose.
  • Movement:
    • Flexion and extension only.

Sacrum

  • Fused Vertebrae:
    • Consists of five fused vertebrae.
  • Structures:
    • Body:
      • Visible from a superior view.
    • Fused Transverse Processes:
      • Ala (fused rib elements).
    • Sacral Crest:
      • Replaces spinous processes.
    • Sacral Foramina:
      • Anterior and posterior, replacing intervertebral foramina.
    • Sacral Canal:
      • Replaces vertebral foramen.
    • Sacral Hiatus:
      • Opening where the sacral canal ends and attaches to the coccyx.
    • Sacral Promontory (center of gravity):
      • Located 1 cm posterior to the body on the superior aspect.
      • Angle of the pelvis impacts center of gravity location.

Coccyx

  • Tailbone:
    • 3-5 fused vertebrae.
    • Sacrum's tag-along friend.

Atlanto-Occipital and Atlanto-Axial Articulations

  • Atlanto-Occipital:
    • Articulation between the atlas (C1) and the occipital bone of the skull.
  • Atlanto-Axial:
    • Articulation between the atlas (C1) and the axis (C2).

Intervertebral Discs

  • Composition:
    • Make up 20% of the vertebral column length.
    • Annulus Fibrosis:
      • Tough, fibrous cartilage outer layer.
    • Nucleus Pulposus:
      • Gel-like center; allows compressibility.

Spinal Ligaments

  • Transverse Ligament of the Atlas:
    • Holds the dens of the axis in place.
  • Apical Ligament of the Dens and Alar Ligaments:
    • Connect the atlas and axis to the skull and C3.
  • Zygopophysial Joints:
    • Joints between articular processes.
  • Uncovertebral Joints:
    • Congenital, form around age 10 (develop on the superior border) between cervical vertebrae particularly in the C5 region.
    • Can lead to pain and disc herniation.
  • Anterior Longitudinal Ligament:
    • Wide; runs along the entire length of the vertebral bodies.
  • Posterior Longitudinal Ligament:
    • Narrow runs along the vertebrae, but is disrupted by the spinous processes.
  • Ligamentum Flavum:
    • Connects adjacent lamina.
  • Interspinous Ligaments:
    • Connect adjacent spinous processes.
  • Supraspinous Ligament:
    • Runs along the tips of the spinous processes, prevents pointiness.

Bone Disorders: Osteoporosis

  • Definition:
    • Osteoclast activity outpaces osteoblast activity, leading to decreased bone density.
  • Effects:
    • Compressive fractures in the spine, common in postmenopausal women.
    • Fractures can occur from normal activities (e.g., walking).

Disc Herniations

  • Process:
    • Nucleus pulposus (gel-like center) herniates through the annulus fibrosis (outer layer).
  • Vulnerability:
    • Posterolateral regions of the annulus fibrosis are thinner, posing risk.
  • Stages of Disc Herniation and Severity:
    • Disc Degeneration: initial breakdown of annulus fibrosis tissue.
    • Disc Prolapse: the outermost fibers of the annulus fibrosis, that contain the nucleus pulposus, are still intact (results in a pinched nerve and pain).
    • Disc Extrusion: nucleus pulposus ruptures through the annulus fibrosis.
    • Disc Sequestration: nucleus pulposus breaks down and oozes into local tissue (may result in fusion of vertebrae).
  • Nerve Rootlets:
    • In extrusion, nerve rootlets grow into the open area of the intervertebral disc, causing pain.

Muscles of the Back

  • Categories:
    • Extrinsic:
      • Superficial: Trapezius and Latissimus dorsi.
      • Deep: Levator scapulae, Rhomboids major and minor.
      • Intermediate: Serratus posterior inferior and Serratus posterior superior (help elevate ribs/respiration, primarily in COPD patients).
  • Intrinsic: postural muscles, for stability and movement of the neck and spine.

Extrinsic Muscles

  • Trapezius:
    * Manipulates the shoulder and upper limb/anchoring itself to the skull, the spinous processes, and the spine of the scapula.
  • Latissimus dorsi:
    * coughing muscle, also an important muscle for doing pull up.
  • Levator Scapulae
    * levitates or pulls up on the scapula, and it helps with that medial rotation of the scapula.
  • Rhomboid minor and major
    * helps with that medial kind of, posterior medial rotation of the scapula
    * helps hold the scapula in place.

Intrinsic Muscles

  • Superficial:
    • Splenius capitis and splenius cervicis (attaches directly to the skull).
  • Deepest Intrinsic Muscles(Erector Spinae):
    • Iliocostalis:
      • iliocostalis lumborum, iliocostalis thoracis, and then iliocostalis cervicis.
    • Longissimus:
      • thoracus, cervicis, and then capitis.
    • Spinalis:
      • spinalis thoracus.
  • Deepest Intrinsic Muscles:
    +semispinalis (thoracic, cervicis, and capitis)
    +rotatores
    +multifidus
    +intertransversarii (Transverse process.)
    +interspinalis (Spinous process.)
    +Spinous process to superior articular process.
    *Levator costarum longus and brevis muscles also in here.

The Suboccipital Triangle

  • Location
    • Located in the suboccipital area (cut out trapezius/ semisthenalis capitis.
  • Suboccipital triangle muscles (3) *Contents:
    • Suboccipital nerve.
    • Suboccipital venous plexus.
    • A part of the vertebral artery
  • Associated Syndrome:
    • Vertebrobasilar syndrome: Compression of suboccipital triangle acutely can cause a vertebral artery syndrome.

Spinal Cord

  • Termination:
    • Ends at the level of L1-L2 in adults (conus medullaris).
  • Continuation:
    • Cauda equina: nerve roots extending from the conus medullaris; branching through intervertebral foramen and sacral foramina.
    • Filum terminale: extension of pia mater anchoring spinal cord to coccyx.

Spinal Cord Cross-Section

  • Gray and White Matter:
    • Gray matter: unmyelinated interneurons, terminal ends of sensory neurons, bodies/dendrites of motor neurons.
    • White matter: myelinated axons coming into or out of spinal cord.
  • Nerve fibers Types:
    • Commissural fibers: travel one region to another in the spinal cord.
    • Ascending fibers: (sensory) afferent pathway.
    • Descending fibers: (motor) efferent pathway.
  • Dorsal and Ventral Roots
    • Dorsal (posterior) root: sensory neurons.
    • Ventral (anterior) root: motor neurons.
    • Dorsal root ganglion: enlargement before convergence.
      *Root organization: Northbound (sensory) and southbound (motor) are separate
  • Neoron types:
    *Visceral: impulse to and from our internal organs:
    *Somatic: to and from skeletal muscles and skin.
    *Dermatomes/Myomes: Sensory/Motor neurons in regards to sensations (paresthesia) and motor/movement(paralysis)
  • the vessels are in the epidural space as well.

Lumbar Puncture and Epidural Anesthesia

  • Lumbar Puncture (Spinal Tap):
    • Purpose: collect cerebrospinal fluid
    • Location: L4-L5 interspace (below spinal cord termination).
    • Positioning: patient in fetal position to open vertebra.
    • Procedure: stylet passed into intervertebral foramen through meninges.
  • Epidural Anesthesia:
    • Location: epidural space (fatty area upon the dura).
    • Procedure: catheter threaded to desired level after stylet.
  • Caudal Epidural Anesthesia:
    • Location: sacral hiatus
    • Blocks pudendal nerve
    • Used for pain management in vaginal childbirth

Spina Bifida

  • Definition:
    • Failure of vertebral arches to form or fuse, usually in the lumbar region.
  • Types:
    • Spina bifida occulta: least severe, cannot be seen with the naked eye.
    • Closed spinal dysraphism: development of lipoma.
    • Meningocele: cyst-like structure of the meninges and cerebrospinal fluid.
    • Myelomeningocele: open spinal cord with meninges, cerebrospinal fluid, and nervous tissue.