http://upload.orthobullets.com/topic/2071/images/pedicle diameter illustration 3.jpg
http://upload.orthobullets.com/topic/2071/images/ap xr.jpg
http://upload.orthobullets.com/topic/2071/images/facet orientation.jpg
http://upload.orthobullets.com/topic/2071/images/l4 vs l5 3.jpg
  • 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
    • transpoas approach
      • lumbar plexus moves dorsal to ventral moving down the lumbar spine
      • L4-L5 is lowest accessible disc space, highest risk of iatrogenic nerve injury

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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? Review Topic





















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Pedicle screws are often used for spine stabilization procedures in both elective and trauma situations. Understanding of pedicle anatomy is essential to safe and effective screw placement. Ebraheim et al in their studies investigated pedicle dimensions of thoracic and lumbar spine, including linear and angular measurements, as well as the average distance from the projection point of the lumbar pedicle axis to the midline of the transverse process. The smallest pedicle diameter was most consistently found at the L1 level. The information from their studies can be helpful during pre operative templating and operative placement of screws into lumbar and thoracic pedicles.

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