Lumbar Spine Anatomy - Spine (2024)

• 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

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

• 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

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

• 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

• segmental arteries

  • dorsal branches supply blood to the dura & posterior elements

• 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

• Sinu-vertebral nerve is responsible for nociception and proprioception of disk

• Nerve fibers present along periphery of annulus fibrosus only

• begins at ~L1

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

• pelvic tilt = pelvic incidence - sacral slope

• 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

• sacral slope = pelvic incidence - pelvic tilt

• 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)

• performed using CT or fluoroscopic guidance

• 22G-25G needle usually used for injection of local anesthetic and corticosteroid

• indications

  • unilateral radicular symptoms

  • used for therapeutic and diagnostic purposes

• technique

  • transforaminal (outside-in) technique usually used

• indications

  • to confirm facet joint as pain generator (diagnostic)

  • also a therapeutic procedure

• 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

• posterior midline approach

  • can be used for PLIF or TLIF

• Wiltse paraspinal approach

• retroperitoneal (anterolateral) approach

  • aorta bifurcation found at L4/5

  • superior hypogastric plexus on L5 body

    • damage causes retrograde ejacul*tion

• also referred to as

  • transpsoas approach

  • direct lateral

• patient position

  • lateral

  • usually performed on left side due to increased strength of aorta to injury

• target levels

  • ideal for access for

    • L1/2

    • L2/3

    • L3/4

  • less ideal access

    • L4/5

      • highest risk of iatrogenic nerve injury to lumbar plexus and resulting hip flexion and knee extension weakness

    • T12/L1

      • will need to remove rib and take down diagphragm)

• anatomic risks

  • lumbar plexus

    • moves dorsal to ventral moving down the lumbar spine

  • ilioinguinal and iliohypogastric nerves

    • may be injured during retroperitoneal approach resulting in groin paresthesias and abdominal paresis

  • segmental arteries

    • need to be stabled or tied off corpectomy performed

  • aorta

    • important to place anterior retractors so damage to aorta is prevented