Lumbar Spine Anatomy - Spine (2024)

  • 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 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

    • Intervertebral Disk

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

      • Nerve fibers present along periphery of annulus fibrosus only

    • 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

      • 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)

  • 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 Lateral

      • 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

Lumbar Spine Anatomy - Spine (2024)
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