Alignment Sagittal plane lumbar lordosis average of 60° login to view 1 more bullet apex of lordosis at L3 disc spaces responsible for most of lordosis Lumbar Osteology Lumbar spine has the largest vertebral bodies in the axial spine Components of vertebral bodies anterior vertebral body posterior arch formed by login to view 4 more bullets 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 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 login to view 1 more bullet Lumbar Pedicle Anatomy 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 Pedicle angulation pedicles angulate more medially moving 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 Lumbar Blood Supply Lumbar vertebral bodies supplied by segmental arteries dorsal branches supply blood to the dura and posterior elements Lumbar Neurologic Structures Nerve roots anatomy nerve root exits foramen under same numbered pedicle login to view 2 more bullets dorsal rami login to view 2 more bullets ventral rami login to view 1 more bullet key difference between cervical and lumbar spine is: pedicle/nerve root mismatch login to view 3 more bullets horizontal (cervical) vs. vertical (lumbar) anatomy of nerve root login to view 2 more bullets Intervertebral disk sinuvertebral 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 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) 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 can be therapeutic Epidural injection 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 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 login to view 1 more bullet 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 login to view 3 more bullets less ideal access login to view 4 more bullets anatomic risks lumbar plexus login to view 1 more bullet ilioinguinal and iliohypogastric nerves login to view 1 more bullet segmental arteries login to view 1 more bullet aorta login to view 1 more bullet