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Lumbar Spine Anatomy

Topic updated on 01/03/14 4:04pm
Alignment
  • Sagittal plane
    • lumbar lordosis
      • average of 60 degrees
        • normal range is 20 to 80 degrees
      • apex of lordosis at L3
      • disc spaces responsible for most of lordosis
Lumbar Osteology
  • Lumbar spine has the largest vertebrae bodies in the axial spine
  • Components of vertebral bodies  
    • anterior vertebral body
    • posterior arch
      • formed by
        • pedicles
          • pedicles project posteriorly from posterolateral corners of vertebral bodies
        • lamina
          • lamina project posteromedially from pedicles, join in the midline
    • spinous process
    • transverse process
    • mammillary processes
      • separate ossification centers
      • project posteriorly from superior articular facet
    • pars interarticularis
      • mass of bone between superior and inferior articular facets
      • site of spondylolysis  
  • Articulations
    • intervertebral disc 
      • act as an articulation above and below
    •  facet joint (zygapophyseal joint)
      • formed by superior and inferior articular processes that project from junction of pedicle and lamina
      • facet orientation
        • facets become more coronal as you move inferior
Lumbar Pedicle Anatomy
  • Landmarks  
    • midpoint of the transverse process used to identify midpoint of pedicle in superior-inferior dimension 
    • lateral border of pars used to identify midpoint in medial-lateral dimension
  • Pedicle angulation
    • pedicles angulate more medial as you move distal
      • L1: 12 degrees
      • L5: 30 degrees
      • S1: 39 degrees
  • Pedicle diameter 
    • L1 has smallest diameter in lumbar spine (T4 has smallest diameter overall) 
    • S1 has average diameter of ~19mm
Lumbar Blood Supply
  • Lumbar vertebral bodies supplied by
    • segmental arteries
      • dorsal branches supply blood to the dura & posterior elements
Lumbar Neurologic Structures
  • Nerve roots
    • anatomy
      • nerve root exits foramen under same numbered pedicle
        • central herniations affect traversing nerve root  
        • far lateral herniations affect exiting nerve root   
      • dorsal rami
        • supplies muscles, skin
      • ventral rami
        • supplies anteromedial trunk
    • key difference between cervical and lumbar spine is 
      • pedicle/nerve root mismatch
        • cervical spine C6 nerve root travels under C5 pedicle (mismatch)
        • lumbar spine L5 nerve root travels under L5 pedicle (match)
        • extra C8 nerve root (no C8 pedicle) allows transition
      • horizontal (cervical) vs. vertical (lumbar) anatomy of nerve root
        • because of vertical anatomy of lumbar nerve root a paracentral and foraminal disc will affect different nerve roots
        • because of horizontal anatomy of cervical nerve root a central and foraminal disc will affect the same nerve root
  • Cauda equina
    • begins at ~L1
Lumbar-Pelvic Sagittal Alignment
  • Pelvic incidence   
    • pelvic incidence = pelvic tilt + sacral slope
    • a line is drawn from the center of the S1 endplate to the center of the femoral head
    • a second line is drawn perpendicular to a line drawn along the S1 endplate, intersecting the point in the center of the S1 endplate
    • the angle between these two lines is the pelvic incidence (see angle X in figure above)
    • correlates with severity of disease 
    • pelvic incidence has direct correlation with the Meyerding–Newman grade  
  • Pelvic tilt   
    • sacral slope =  pelvic incidence - pelvic tilt
    • a line is drawn from the center of the S1 endplate to the center of the femoral head
    • a second vertical line (parallel with side margin of radiograph) line is drawn intersecting the center of the femoral head
    • the angle between these two lines is the pelvic tilt (see angle Z in figure above)
  • Sacral slope   
    • pelvic tilt = pelvic incidence - sacral slope
    • a line is drawn parallel to the S1 endplate
    • a second horizontal line (parallel to the inferior margin of the radiograph) is drawn
    • the angle between these two lines is the sacral slope (see angle Y in the figure above)
Image-Guided Interventions
  • Overview
    • performed using CT or fluoroscopic guidance
    • 22G-25G needle usually used for injection of local anesthetic and corticosteroid
  • Selective Nerve Root Injections
    • indications
      • unilateral radicular symptoms
      • used for therapeutic and diagnostic purposes
    • technique
      • transforaminal (outside-in) technique usually used
  • Facet joint injection 
    • indications  
      • to confirm facet joint as pain generator (diagnostic)
      • also a therapeutic procedure
  • Epidural injection 
    • indications  
      • lumbar spinal stenosis
  • Discography  
    • indications
      • very controversial
      • to prove that pain arises from the intervertebral disc ("concordant pain") rather than other sources ("discordant pain")
    • technique
      • small amount of dilute contrast injected into the disc and pain response is recorded
      • contrast helps assess disc morphology and diagnose annular tears
Surgical Approaches
  • Posterior 
    • posterior midline approach
      • can be used for PLIF or TLIF
    • Wiltse paraspinal approach 
  • Anterior 
    • retroperitoneal (anterolateral) approach 
      • aorta bifurcation found at L4/5
      • superior hypogastric plexus on L5 body
        • damage causes retrograde ejaculation

 

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(OBQ10.260) A patient with severe multi-level spinal stenosis is scheduled to undergo decompression and fusion from T12-L4. Both pedicle screw length and diameter are measured pre-operatively. Which of the following pedicles would be templated for the smallest diameter screw? Topic Review Topic

1. T12
2. L1
3. L2
4. L3
5. L4

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