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 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 ejaculation 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