Chapter 45 Selective Nerve Root Blocks and Transforaminal Epidural Steroid Injections Flashcards
KEY POINTS 1. Epidural steroid injections are indicated in patients with lumbosacral radiculopathy. The beneficial effect of the steroids is secondary to its anti-inflammatory effect and specific antinociceptive effect. The antiinflammatory effect is probably related to inhibition of phospholipase A2. Local application of methylprednisolone inhibits the transmission of impulses through the C-fibers but not in the Ab fibers. 2. Epidural steroids are more effective in patients with acute lumb
The pain from “sciatica”
can be caused by
mechanical compression by herniated discs, chemical irritation from ruptured disc, foraminal stenosis secondary to spondylosis, or vascular compromise.
the most likely cause of radicular pain is from
chemical inflammation around the nerve root
Human discs contain high levels of
phospholipase A2 (PLA 2) along with other inflammatory mediators such as metalloproteases and nitric oxide
phospholipase A2 PLA2
the enzyme
responsible for the liberation of arachidonic acid from cell
membranes at the site of inflammation, and levels are increased
in herniated discs relative to normal discs. PLA 2 also acts as a catalyst in generating prostaglandins, leukotrienes, platelet activating factor, and lysophospholipids, all
of which cause inflammation
methylprednisolone was applied directly to neural structures.
a reduction of inflammation
Corticosteroids suppress inflammation by
The mechanism of action is most likely related to the steroids ability to inhibit phospholipase A2 activity.
Steroids may also have a
local anesthetic and antinociceptive effect
mainstay of conservative
management of radicular pain
Epidural steroid injections
The evolution of the transforaminal approach was based on the idea that
injecting a concentrated steroid around inflamed neural structures will provide better and longer lasting relief of radicular
pain than introducing the same steroids in the dorsal epidural space.
radicular pain occurs because of pathology in the
ventral epidural space from disc protrusion, extrusion, leakage of
nucleus pulposus, or mechanical compression. Axial back
and neck pain are more complicated in that it can be caused by both ventral and dorsal elements.
Irritation of the posterior longitudinal ligament or internal disc disruption can cause the same type of pain that
muscle strains/ sprains, facet arthropathy, or ligamentum flavum pain.
The more cephalad the
injection, the higher the risk for
catastrophic complications such as spinal cord injury or stroke.
The cervical level is the most “risky” in that the
vascularity in the foramen is extensive,
and susceptible arteries are in the immediate vicinity of the foramen at the C3–C6 levels.
The foramen at the cervical level face slightly
anterior and oblique; thus, the supine or lateral position is optimal.
The cervical foramina are bounded
posteriorly by the superior articular process (SAP) of the lower vertebra and anteriorly by the lower end of the upper vertebral body, the uncinate process of the lower vertebra, and the intervertebral disc. Its
roof and floor are formed by the pedicles of consecutive vertebrae.
The superior and lower portion of the foramen contains
The superior portion of the foramen contains epiradicular veins and the lower most portion contains the spinal
nerve.
Arterial branches arise either from the
vertebral arteries
or the deep or ascending cervical arteries to supply the
nerve roots (radicular arteries) and spinal cord (medullary arteries).
at most risk of penetration during a cervical transforaminal epidural steroid injection (TFESI) or SNRB.
branches off of the cervical arteries
At the thoracic level, the foramen faces more
posterior and lateral relative to the cervical level.
at risk of penetration at the lower
thoracic levels.
the ribs, pleura, and mediastinum are the surrounding structures along with the radicularis magna
The foramina at the lumbar levels face
laterally.
Border of foramina at the lumbar levels
The anterior border includes the upper vertebra and intervertebral disc, the posterosuperior and the posteroinferior borders are comprised of the inferior articular process
(IAP) and SAP, respectively, with the pedicles forming the
roof and the floor.
main arterial supply to the lower two-thirds of the spinal cord.
artery of Adamkiewicz. It enters the spinal canal anywhere from T7 to L4, usually on the left side between T9 and L1 vertebrae.
Trauma to artery of Adamkiewicz
lead to anterior spinal artery syndrome and paraplegia
The indications for SNRBs and transforaminal epidural steroid injections are the same and include:
l Radiculitis/radiculopathy
l Lumbar disc displacement without myelopathy
l Axial pain
l Diagnostic for vague symptoms or multilevel pathology
l Postlaminectomy with recurrent pain
l Spinal/foraminal stenosis
Contraindications SNRBs and transforaminal epidural
steroid injections
l Patient refusal
l Bleeding disorders
l Elevated coagulation studies
Equipment and materials for SNRBs and transforaminal epidural
steroid injections include the following:
l C-arm fluoroscope (CT also used) and fluoroscopic table
l Monitors
l 22- or 25-gauge Quincke needle, variable length up to 7 in, depending on patient size
l Corticosteroid—methylprednisolone, triamcinolone,
betamethasone, dexamethasone
l Contrast dye—Omnipaque M-185 or Isovue M-200
techniques for SNRB and transforaminal epidural
steroid injection are essentially the same except for the
final needle location
The final needle position is slightly lateral to the intervertebral foramen for the SNRB, and the tip is guided more toward the center rather than subpedicular and anterior. For the cervical level, the needle is kept
more lateral to the foramen to avoid spread of contrast
to adjacent levels along with lower volumes of local anesthetic
LUMBAR TECHNIQUE
The procedure can be done prone or lateral, most practitioners
prefer prone. Fluoroscopy is utilized to determine the correct level of injection and approach. The area
is prepped with either chlorohexanol or Betadine and draped in usual sterile fashion.
LUMBAR TECHNIQUE
The C-arm is then positioned
obliquely to visualize the foramen optimally, usually 15 to 30 degrees, Scotty dog view, with the transverse process over the vertebral body. A less oblique view can be utilized to keep the needle lateral to the foramen and better target a single nerve
Lumbar Techniques
The goal is for the needle to be
coaxial with the C-arm, just under the pedicle and lateral to the pars interarticularis, above the superior articular process inferiorly. This approach avoids the nerve root, and thus avoids periprocedural paresthesias.
Lumbar Techniques
An anteroposterior view is obtained with the fluoroscope to determine the
mediolateral location of the needle
Lumbar Techniques
If the needle tip encounters bony resistance, this is most
likely
the pars interarticularis and the needle should be walked just inferior, anterior, and medial past this level.
Lumbar technique
Once the needle tip is just under the pedicle medially, the fluoroscope is rotated to the
lateral view and the needle is advanced slowly into the foramen until the tip is in the anterior one-third of the foramen, just under the
pedicle
Lumbar Techniques
The patient may experience a paresthesia, at which
point it is best to
slightly withdraw; the paresthesia must
disappear prior to injection of contrast. After negative
aspiration for blood, 1 to 2 ml of radiographic contrast is
injected under live fluoroscopy to confirm anterior epidural
spread in the case of the transforaminal injection, or
nerve root spread for the SNRB
For
the L1 and L2 levels, digital subtraction angiography
should be utilized in the AP and lateral view to better
detect potential vascular spread and the needle tip should
be kept slightly posterior in the foramen to avoid the
artery of Adamkiewicz.
L5 level presents unique challenges
iliac crest is in the line of the needle and
may obstruct its path to the foramen. Normally, this can be
avoided by angling the C-arm more cephalad to line up the
inferior end plates of the L5 vertebral body.
At the L5 level the path
of the needle is
a triangular area formed by the superior
articulating process of S1, the inferior border of the transverse
process of L5, and the iliac crest. The needle
is advanced from a lateral to a medial direction, medial to
the iliac crest, until the tip of the needle projects inferior
to the pedicle.
Patient and C arm position for blockade of the S1 nerve root.
The patient lies prone for blockade of the S1 nerve root. The C-arm is in straight anterior–posterior (AP) projection or with 5 to 10 degrees of ipsilateral lateral angulation
blockade of the S1 nerve root
The needle is advanced through the posterior sacral foramen until the first sacral root is encountered.
in the lumabr technique, Once the appropriate contrast pattern is seen in the anterior epidural space, an AP image is then obtained to confirm
spread of contrast perineurally and/or epidurally as well as
confirmation that no vascular or intrathecal spread has occurred
in the lumbar technique the final target for the SNRB is for the needle
to be extraforaminal whereas with the transforaminal epidural, it is ideal to be in the anterior and superior portion of the foramen
in the lumbar technique, Once appropriate spread of contrast is seen in the ventral
epidural space without vascular or intrathecal uptake
a mixture of 1 ml of saline (or 1% lidocaine or 0.25% bupivicaine)
and either 40 to 80 mg of triamcinolone, 6 mg of betamethasone, or 4 to 8 mg of dexamethasone are injected incrementally
THORACIC TECHNIQUE
The C-arm position
The T9 to T12 levels are done similarly to the L1 and L2 levels. The C-arm is not rotated quite as oblique to avoid
potential pneumothorax, and the needle is not advanced quite as anterior to avoid the artery of Adamkeiwicz For the T1 to T8 levels, the C-arm should not be rotated more than 15 degrees to avoid pneumothorax, and to
maintain better visualization of the foramen.
THORACIC TECHNIQUE
patient’s position
At these levels, only the prone position is utilized, but theoretically, the lateral position can be used.
THORACIC TECHNIQUE
a needle is advanced coaxially with the C-arm
of the fluoroscope to the posterior and medial portion of the
foramen. Once
the needle tip is seen just medial and inferior to the pedicle, real-time fluoroscopy with the injection of 1 to 2 ml of contrast under AP and lateral imaging is utilized to confirm
appropriate spread
THORACIC TECHNIQUE
substance injected
The substances injected are the same as for the lumbar technique, but, methylprednisolone
is not recommended because of its larger particle size
CERVICAL TECHNIQUE
patients position
The cervical level is usually approached in the supine position
with the head neutral and a shoulder roll in place. A cushion is useful to keep the patient comfortable and to keep the head in place. The head maybe turned for the lower levels if it makes the needle entry easier. For C1 to C4 levels, the lateral position may be ideal, but for C4 to C8, the supine position is better to keep the shoulders out of the way of the image
CERVICAL TECHNIQUE
C-arm position
image is now a PA rather
than an AP image unless the C-arm is inverted.24 The fluoroscope
is rotated oblique ipsilaterally to visualize all of the
borders of the foramen.
CERVICAL TECHNIQUE
The initial target is the
most posterior and inferior part of the foramen in order to avoid the vertebral artery anteriorly or placing the needle to medially into the spinal canal
CERVICAL TECHNIQUE Goal
The goal is to make contact with the superior articular process posteriorly to gauge the medial safety margin. In order to do this, a coaxial
view of the needle is crucial. Once the needle contacts the
posterior portion of the foramen, the needle can be walked
slightly anteriorly into the foramen. The fluoroscope is then rotated back to PA to determine the medial
location of the needle tip.
Digital subtraction
angiography (DSA) should be used for all
cervical transforaminal or selective nerve root injections because
the consequence of not detecting intravascular spread of contrast can lead to catastrophic complications
CERVICAL TECHNIQUE
Needle postion
The needle should not be advanced more than
one-third of the facet column on the AP view. If perineural or epidural spread is not noted, the needle can be advanced slightly farther in the PA plane. Once appropriate epidural or perineural spread is noted without vascular uptake, a mixture of 1 ml of saline (or 1% lidocaine) and either 40 mg of triamcinolone, 6 mg of betamethasone, or 4 mg of dexamethasone are injected slowly.
The presence of pain during an SNRB is not a very reliable sign that
needle touched the nerve root sheath.The needle may have irritated sensitive structures such as
the joint capsule, periosteum, and annulus fibrosus and may cause referred pain to the leg
Causes of SELECTIVE NERVE ROOT BLOCKS
herniated disc,
lateral recess stenosis, central canal stenosis, or pedicular kinking
COMPLICATIONS
Spinal injections may cause infectious, cardiovascular, neurologic, and bleeding complications. Exposure to x-ray
radiation and adverse, allergic, and anaphylactic reactions to the medications and the dye are added risks
Risks specific to TFESI and SNRBs include
trauma to the spinal nerve,
intrathecal injection if the needle penetrates the dural root
sleeve, or segmental epidural when the medication is injected
into the epidural space via the neural foramen
Trauma to the artery of Adamkiewicz may cause
paraplegia and trauma to the segmental artery, which travels with the nerve root, may result in segmental cord infarct.
Cervical TFESIs and SNRBs are inherently riskier
Spinal cord trauma, arterial injury, blindness, and brain or spinal cord infarct are added risks
methylprednisolone use in lumbar selective nerve root injections NOT cervical SNRBs
methylprednisolone has the largest particle size of all of the steroids and easily precipitates. If injected through the any of the susceptible arteries including the vertebral, ascending
cervical and deep cervical arteries, it may cause a segmental
spinal cord infarct or settle in an end-artery in the brain causing a small infarct.
Steroids used in cervical SNRBs
Triamcinolone has intermediate particle and maybe used. Betamethasone has the smallest size and should preferably be used if available
indication for epidural steroid injections is
nerve root irritation
The lumbar stabilization program consisted of
exercises emphasizing hip and hamstring flexibility and abdominal
and lumbar paraspinal strengthening.
