Spine

Spine Structure and Function

  • Overview of the spine

Physiologic Curves

  • Types of Curves:

    • Lordosis:

    • Locations: Cervical & Lumbar regions

    • Orientation: Anterior

    • Kyphosis:

    • Locations: Thoracic & Sacral regions

    • Orientation: Posterior

  • Line of Gravity:

    • Transects the spinal curves ensuring balance anteriorly and posteriorly

    • Deviation in one portion of the spinal column results in shifting to compensate and maintain balance

  • Flexibility of the Curves:

    • Provides 10 times the axial strength compared to a straight column

    • Importance of weight bearing (WB):

    • Supine position: no WB

    • Sitting position: maximum WB

    • Flexibility is crucial to withstand effects of gravity and other external forces

Components of Physiologic Curves

  • Anterior Portion:

    • Vertebral bodies and disks: responsible for weight bearing

  • Posterior Portion:

    • Facets (zygapophyseal joints)

    • Vertebral arches, spinous processes, & transverse processes: responsible for muscle attachment

Motions of the Spinal Column

Sagittal Plane Motion

  • Flexion:

    • Vertebral bodies approximate (spinous processes separate)

  • Extension:

    • Vertebral bodies separate (spinous processes approximate)

Frontal Plane Motion

  • Lateral Flexion (Side Bending):

    • The edges of vertebrae separate on one side and approximate on the opposite side

Transverse Plane Motion

  • Rotation (Thoracic):

    • Rotation to the right results in superior vertebra body moving to the right and spinous process to the left

    • Named based on the movement of the top vertebrae (for example, L4 rotates to the right on L5 = L4 R Rotation)

Other Motions

  • Anterior/Posterior Shear:

    • Superior vertebral body translates forward or backward on the body below

  • Lateral Shear:

    • Superior vertebral body translates side to side on the body below

  • Distraction/Compression:

    • Separation or approximation of vertebral bodies through longitudinal forces

    • Longitudinal stretching vs. weight bearing (WBing)

    • Elongation vs compression

Fryette’s Laws

  • Principle I:

    • In neutral spine, side bending to one side causes rotation to the opposite side

    • Observed in type I somatic dysfunction with multiple vertebrae misaligned

    • Extreme dysfunction resembles scoliosis

  • Principle II:

    • In flexed or extended (non-neutral) positions, side bending on one side results in rotation on the same side

    • Related to type II somatic dysfunction where one vertebral segment is restricted

  • Principle III:

    • Introducing motion in one plane modifies (reduces) motion in other planes

    • Dysfunction in one plane negatively affects other planes of motion

Cervical Spine

  • Anatomy and Function:

    • Upper portion of the spine with a lordotic curve

    • Composed of OA and AA joints plus 6 typical joints

    • OA Joint:

    • Primary motion: capital flexion and extension (nodding)

    • AA Joint:

    • Primary motion: rotation

    • Typical Joints:

    • Capable of all motions (Flex, Ext, Rot, SB) at zygapophyseal joints

    • Facet orientation: 45 degrees

Atlas and Axis Anatomy

  • Atlas (C1):

    • No spinous process or vertebral body

    • Transmits forces to lower cervical vertebrae

    • Articulates with occipital condyles allowing capital flexion/extension

    • Nodding motion results from convex occipital condyles moving on the concave portion of the atlas

  • Axis (C2):

    • Provides stability via ligaments surrounding the odontoid process

    • Owing to a unique shape, allows for significant rotation in the cervical spine

Motion of the Sacrum

  • Nutation:

    • Base moves anteriorly and inferiorly; apex moves posteriorly and superiorly

  • Counter Nutation:

    • Base moves posteriorly and superiorly; apex moves anteriorly and inferiorly

Intervertebral Disc

  • Largest avascular structure, no direct blood supply

  • Functions:

    • Allows intervertebral motion and increases weight-bearing capacity

    • Accounts for 20-33% of the total length of the spinal column

    • Cushioning between vertebrae; acts as a shock absorber

  • Nucleus Pulposus:

    • Nourished by synovial fluid absorbed during movement

    • Increases size when not loaded (i.e., overnight)

  • Annulus Fibrosis:

    • Encapsulates nucleus pulposus; provides structural stability

Forces on the Lumbar Spine

  • Moment due to applied load

  • Erector Spinae Force

  • Disc Shear Force (perpendicular to long axis of vertebrae)

  • Disc Compressive Force (parallel to long axis of vertebrae)

Stability in the Spine

  • Three Subsystems of Stability:

    • Passive: inert structures, bones, and ligaments

    • Active: muscles and Valsalva Maneuver

    • Neural control: brain coordination of muscles

Ligaments of the Spine

  • Anterior Longitudinal Ligament:

    • Limits hyperextension

  • Posterior Longitudinal Ligament:

    • Prevents excessive flexion, varies in thickness

  • Interspinous Ligaments:

    • Connect successive spinous processes

  • Ligamentum Nuchae:

    • Replacement for interspinal ligaments in cervical spine

  • Iliolumbar Ligament:

    • Stabilizes L5 vertebra to the iliac crest

Common Vertebral Column Pathologies

  • Thoracic Outlet Syndrome:

    • Nerve/vessel compression in upper extremities

  • Torticollis:

    • Unilateral SCM contracture causing neck side bending

  • Sciatica:

    • Entrapment of the sciatic nerve

  • Spondylosis:

    • Degenerative osteoarthritis of the spine

  • Herniated Discs:

    • Bulging of intervertebral discs

  • Spondylolisthesis:

    • Displacement of vertebra leading to instability

  • Compression Fractures:

    • Resulting from falls or trauma

Conclusion

  • The spinal column's intricate structure and various functional systems provide both stability and flexibility necessary for mobility and load-bearing tasks.