Lumbar Spine Anatomy - Spine (2025)

• lumbar lordosis

  • average of 60°

    • normal range is 20-80°

  • apex of lordosis at L3

  • disc spaces responsible for most of lordosis

Components of vertebral bodies

• anterior vertebral body

• posterior arch

  • formed by

    • pedicles

      • project posteriorly from posterolateral corners of vertebral bodies

    • lamina

      • project posteromedially from pedicles, join in the midline

• spinous process

• transverse processes

• mammillary processes

  • separate ossification centers

  • project posteriorly from superior articular facets

• 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 moving distally

Landmarks

• midpoint of the transverse process is used to identify the midpoint of pedicle in the superior-inferior plane

• lateral border of pars is used to identify the midpoint in the medial-lateral plane

• pedicles angulate more mediallymoving distally in the spine

  • L1: 12°

  • L5: 30°

  • S1: 39°

Pedicle diameter

• L1 has the smallest diameter in the lumbar spine (T4 has the smallest diameter overall)

• S1 has an average diameter of ~19 mm

• segmental arteries

  • dorsal branches supply blood to the dura and 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

    • supply muscles, skin

    • medial branch supplies facet joints

  • ventral rami

    • supply 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 corresponding C8 pedicle) allows transition

  • horizontal (cervical) vs. vertical (lumbar) anatomy of nerve root

    • due to the vertical anatomy of a lumbar nerve root, a paracentral and foraminal disc herniation will affect different nerve roots

    • due to the horizontal anatomy of cervical nerve root, a central and foraminal disc herniation will affect the same nerve root

• sinuvertebral nerveis 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 associated figure)

• 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) is drawn intersecting the center of the femoral head

• the angle between these two lines is the pelvic tilt (see angle Z in associated figure)

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 associated figure)

• 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 can be therapeutic

• indication

  • 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

  • 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 ejaculation

• also referred to as

  • transpsoas approach

  • direct lateral

• patient position

  • lateral

  • usually performed on left side due to increased resistance 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, which can result in hip flexion and knee extension weakness

    • T12-L1

      • will need to remove rib and take down diaphragm

• anatomic risks

  • lumbar plexus

    • moves from dorsal to ventral going distally down the lumbar spine

  • ilioinguinal and iliohypogastric nerves

    • may be injured during retroperitoneal approach, which can result in groin paresthesias and abdominal paresis

  • segmental arteries

    • need to be stabilized or tied off when performing a corpectomy

  • aorta

    • important to place anterior retractors and prevent damage to aorta