Dr. Safriel is the lead neuroradiologist in the Dunedin
NeuroSpine Institute, University of South Florida, Radiology Associates
of Clearwater, Clearwater, FL.
Pain of spinal origin is a
significant public health concern in the United States and is among the
most common reasons people seek medical care.1–4 It is the also the second leading, medically related reason for missed work, resulting in 40% of lost workdays annually.2 Between 1997 and 2006, the use of interventional pain management procedures increased by 235% in the Medicare population.2 The cost-per-injection also doubled, from $115 to $227, between 1994 and 2001.1
While clinical trials are difficult to perform due to the multiple
factors that can influence a patient’s perception of pain, evidence is
building that early imaging and intervention result in better outcomes.1–9
approaches to pain management utilize medication, rehabilitative
therapies and behavioral approaches. Interventional pain management
approaches employ diagnostic and therapeutic techniques to assist in
identifying and relieving pain. Compared to traditional pain management
methods, which have shown mixed outcomes, 10–12 interventional therapies that rely on injection procedures have demonstrated promising results.5–22
back and neck pain is most easily classified into 3 broad categories
according to its anatomical origin: disc degeneration, disc
protrusions/herniations and facet degeneration. The primary role of
imaging is to exclude causes of nondegenerative pain (e.g., compression
fractures, tumors, neural disorders and traumatic injuries) and indicate
which of the above three categories may be the primary pain generator.
article describes procedural techniques developed through extensive
experience, a thorough literature review, and feedback from spine and
neurosurgeons. It is important to recognize that the techniques outlined
here are among many possible options.
This paper will first
review the safety profile of injection procedures as a guide to
obtaining informed consent and outline the pertinent differences between
lumbar and cervical injections. Then, epidural, nerve block and facet
injections will each be examined separately, with a particular focus on
outlining the differences between lumbar and cervical therapy.
arsenal of interventional pain management includes many other injection
procedures, such as stellate ganglion blocks and trigger point,
sacroiliac joint, synovial cyst rupture, and intradiscal steroid
injections. A complete review of all these procedures is beyond the
scope of this article.
But by initially focusing on epidural
injections/nerve blocks and facet injections—the most common
procedures—the interventional musculoskeletalor neuroradiologists can
subsequently expand their practices to include other procedures.
Safety profile: What you need to know for informed consent
The safety of both lumbar and cervical epidural steroid injections
(ESI) and nerve blocks has been confirmed by multiple large studies
ranging from 322 to 5,334 patients, with no permanent adverse procedure
related outcomes and a complication rate of <1% requiring additional
treatment.23–27 In all studies, both lumbar and cervical
procedures were performed in outpatient settings, though not necessarily
in ambulatory surgery centers. A Carm (portable or fixed) or CT was
used for guidance. There is no evidence in the literature comparing
fluoroscopic to CT guidance in either the lumbar or cervical spine
(although many operators are passionate on their choice of imaging
modality). Ultimately, operators will choose the imaging modality that
best suits their technique.
One aspect that may favor
fluoroscopic over CT guidance is the risk of intravascular injections in
the superior-inferior plane (Figure 1) that may not be visualized on
CT. This risk is higher in the cervical spine with transforaminal
injection due to: 1) tortuosity of the vertebral artery (Figure 2); 2)
direct injection into the cord; and 3) injection into microvasculature
that supplies the spinal cord. Isolated reports, documenting lower cord
infarction and cauda equinalike symptoms,28,29 emphasize the
importance of avoiding intravascular injection. As these techniques
utilize contrast for guidance, complications relating to contrast
administration must also be considered. In patients who are not
candidates for nonionic contrast, gadolinium may be substituted.30,31
The most common complications in neck and back procedures are pain23,25
and needle misplacement, primarily in the subarachnoid space (Figure
3). Transforaminal cervical injections are more controversial. While
some studies have shown their safety,32,33 many physicians have reconsidered performing these34,35 due to an unfavorable safety profile shown by other studies. 36–42 Cervical nerve blocks that target the nerve along its extraspinal course using fluoroscopy may be a safer alternative.26,27
Epidural steroid injections
Rationale and patient selection
The literature is replete with articles describing the benefits of ESIs.5–22 These injections are of value to patients with both spinal stenoses and acute herniations.17,22 In
cases of chronic stenosis, especially among the elderly, patients can
remain functional despite a relatively high degree of pain, but they are
often incapacitated by acute exacerbations. Pain management injections
are very useful in combating these episodes and returning the patient to
baseline function. The alternatives to injection may be surgery or, in
those for whom surgery is not an option, a life of pain. The patient
should understand that one injection is not a permanent cure. Back pain
that returns with activity, requiring reinjection at the same location,
does not mean the original injection was a failure. Many patients settle
into a routine of bi- or triannual injections to control pain.
instances of multilevel disease, selective nerve blocks may help in
planning the extent of fusion surgery, or a series of successful facet
blocks may shift attention to the posterior column. Surgeons may also
use these procedures as a gatekeeper in selecting patients for surgery.7,43 As
a tool for predicting 1-year surgical outcome, spinal injections have a
reported sensitivity between 65% and 100%, a specificity between 71%
and 95%, and a positive predictive value as high as 95%.7
ESIs can result in significant pain relief,18,19 decreased operative rates43 and cost savings,44 particularly in those over 65 years of age. Acute lesions and radicular pain respond better to ESI;6,8,45 disc herniations respond better than spinal stenoses (61% vs. 38%).8 In spinal stenoses, however, patient response is independent of the degree of stenosis.46 Injections
may be the only effective pain relief mechanism for patients with
multilevel disease (especially in the cervical spine, where there are no
FDA approved devices for fusions of greater than three levels), or
those who cannot undergo surgery.
Fluoroscopic needle guidance is needed for optimum efficacy.47–49
The epidural space can be reached via caudal, interlaminar or
transforaminal approaches. Of the three, the transforaminal and
interlaminar approaches are employed most often (Figures 47).4,16 The caudal approach is the least used24 but easiest to perform and aimed at the sacral notch (Figure 4).
the lumbar interlaminar approach, the patient is positioned prone on
the table. Tilting the Carm at an approximately 5-degree angle
ipsilateral to the side of entry and a 2-degree to 5-degree
caudal/Ferguson tilt may better expose the apex of the interlaminar
space (Figure 5). Optimal needle position is at the midline (Figure 5).
Needle placement too far from the midline may result in the injectate
remaining ipsilateral and not crossing the midline.50 In the
cervical spine, due to the smaller size of the epidural space more
superiorly, the injection is almost always performed at C7T1 or C6C7.42
A lateral projection usually is of little value, due to the shoulders’
obscuring the lower cervical spine. Therefore, an alternative approach
entails obtaining an obliquity of approximately 45 degrees contralateral
to the side of injection. Correct position is achieved when the needle
tip is in the spinolaminar line (Figure 6). The injectate is then
directed upward by turning the needle (with a curved tip or side hole)
The lumbar transforaminal approach may require a
steeper angulation of approximately 30 degrees ipsilateral to the entry
site. A cephalad/reverse Ferguson tilt should be obtained until the
endplates of the target level overlap (the angle will be most severe at
L5S1 and least at L2L3). Optimal needle position is in a ‘safe triangle’
bounded by the exiting nerve at its base with the sides made up by the
undersurface of the transverse process and the lateral margin of the
vertebral body (Figure 7). The target point is underneath (i.e., 6
o’clock) the pedicle (Figure 7). There is a posterolateral variation to
the lumbar transforaminal approach that places the needle more medially
and advances the needle until it arrives at the posterior portion of the
foramen on the lateral view.51 An S1 injection involves
only minimal ipsilateral obliquity and a 20-degrees-of-cephalad tilt of
the Carm until the posterior and anterior S1 foramina overlap. A lateral
projection is used to ensure that the needle is not advanced too deeply
beyond the sacrum.
Approach selection depends on the location of
disc pathology and the nerves involved. A patient with subarticular or
posterolateral impingement on a nerve root (Figure 8) would benefit from
a transforaminal injection at that level or the level below (as flow in
the epidural space is often preferentially cephalad, along the nerve
roots as they track back to the thecal sac). A patient with a
broad-based disc bulge may benefit more from an interlaminar injection,
although the location of the injection must consider that the epidural
space may be located either above or below the disc (Figure 9). In the
postoperative spine where laminectomy has removed the posterior epidural
space, transforaminal injections or an approach above or below the
surgical level may be necessary (Figure 10). Foraminal herniations
present a particular challenge. While they may be easily accessed by the
transforaminal route, the narrowing of the foramen may make such
injections very painful (Figure 11). Systematic reviews of foraminal
injections as well as our own experience have found marginal benefit
over interlaminar injections in pain relief.4,16
Needles for ESI
The type and size of needles
available for epidural injections vary considerably; there is little
evidence to support choosing one needle over another (Figure 12). There
are curved and straight needles. Among the straight variety, a 22-gauge
spinal Quincke (end hole/ spinal) needle may be used in the lumbar
spine, while a 25-gauge needle may be used in the cervical spine. Many
operators prefer a 22-gauge Whitacre or Pajunk (sidehole) needle in the
cervical spine; some use this needle in the lumbar spine, as well. A
blunt-tip Whitacre or Pajunk needle will require an introducer to
penetrate the skin. A 1.5-inch, 18-gauge standard injection needle is
adequate for this purpose, although some manufacturers make special
introducer sheath/needle combinations. The curved (Tuohy) needle is an
alternative to the straight needle. The use of a curved needle requires a
minimum of 22-gauge. Ultimately, the choice of needles depends on
Medication for ESI
The choice of injectate is
operator dependent, with many combinations reported. The injectate
consists of a contrast agent followed by local anesthesia and a steroid.
Some operators inject the local anesthesia separately, followed by the
steroid, while others mix the two.
Contrast is used to verify
epidural location and to indicate the distribution of injectate. Some
physicians use contrast as a volume expander while others prefer saline
for this use. The contrast is typically nonionic and lowosmolar. In
patients with contrast allergies gadolinium can be safely used in most
lumbar procedures.30,31,52,53 If using gadolinium, the amount
should be just enough to document epidural injection. Gadolinium should
not be used as a substitute for volume expander. The typical amount of
contrast or contrastsaline mixture used for either cervical or lumbar
interlaminar epidurography is 4 cc to 5 cc (less in nerve blocks; see
below). A smaller amount will not provide sufficient contrast for an
epidurogram to evaluate for adhesions or distribution of injectate. For
coding purposes, an epidurogram is considered to have been performed
when approximately 4 cc to 5 cc of contrast is injected regardless of
the route (transforaminal or interlaminar). The report, CPT code, and
amount billed must be adjusted if an epidurogram is not performed. The
amount of contrast injected may be reduced in spinal stenosis. Many
patients will feel pressure or leg cramping from almost any volume, no
matter how small. Patients undergoing first-time injections may confuse
this with pain. Careful questioning and reassurance that pressure is
normal will be adequate in most cases. The injectate volume should be
reduced if significant pain is experienced.
The choice and amount
of epidural anesthetic agent is subjective. Lidocaine 1% and 2%; and
Marcaine 0.25%, 0.5% and 1% have all been used. The epidural anesthetic
agent should not contain epinephrine. Marcaine will have a stronger
effect than lidocaine. While lidocaine is FDA-approved for use in the
epidural and intrathecal space, Marcaine is used off label for this
purpose. Generally, the stronger the local anesthesia, the greater the
chance the patient will have difficulty ambulating and may fall after a
procedure. The use of Marcaine is generally less prevalent in the
literature 6,23,25,30,43,46 and there have been no studies on
the use of Marcaine in ESIs. Regardless of the type of epidural
anesthetic agent, all patients receiving such an agent can not drive
themselves immediately after the procedure to avoid the potential of
foot drop while driving. Patients who do not have an accompanying driver
should be kept in the office for 60 minutes to 120 minutes.
the author’s practice 3 cc to 4 cc of lidocaine 1% is used. In cases
where injectate volume must be reduced (due to spinal stenosis) but a
full anesthetic effect is still desired, 2 cc of lidocaine 2% may be an
alternative (injectate amounts for nerve block are reduced). Evaluating
the patient’s response to the anesthetic agent while the patient is
still monitored in the suite may indicate whether the injection
correctly targeted the pain generator. Many operators do not use
epidural anesthetic agents in the cervical spine due to the risk of
anesthesia in the C3, C4 and C5 regions of the cord responsible for
diaphragmatic function. These areas, if anesthetized, may cause
diaphragmatic paralysis and respiratory arrest.
Of the several steroid preparations available, Dexamethasone sodium phosphate (Decadron®,
Sicor Pharmaceuticals Inc, Irvine, CA) is the only steroid FDA-approved
for intravenous use. In theory, it would be the safest in case of
accidental intravenous administration. However, due to the short-acting
nature of dexamethasone, it has not gained widespread use in pain
management as evidenced by the fact that there have been very few
reports on its effects as compared with other preparations.54 Of the longeracting preparations, the most soluble and least particulate is Betamethasone sodium phosphate (Celestone Soluspan®,
Schering, Kenilworth, NJ). 6 mg of Betamethasone is equivalent to 0.75
of Dexamethasone. It will not elicit the arachnoiditis that may occur
with other steroids in the event of accidental intrathecal injection.55,56 The
greater solubility of Celestone compared to other preparations results
in a lower chance of embolism in the event of accidental intravascular
administration.57 Typically, 12 mg of Celestone is used (less in nerve blocks; see below). In vitro data also show that more soluble steroids (such as Decadron and Celestone) are safer than particulate steroids (DepoMedrol® and Kenalog®) in the cervical spine.58
steroid preparations are methylprednisolone acetate (DepoMedrol,
Pfizer, New York, NY) and triamcinolone acetonide (Kenalog, BristolMyers
Squibb, Princeton, NJ). A typical dose is 80 mg for both (less in nerve
blocks; see below) which is equivalent to 12 mg of betamethasone.
DepoMedrol and Kenalog are semi-particulate solutions that are less
soluble than Celestone and, therefore, theoretically may have poorer
spread in the epidural space. DepoMedrol is available as an 80mg
preparation that may be helpful if the injectate volume must be reduced
due to spinal stenosis. There have been reports of arachnoiditis due to
the neurotoxic polyethylene glycol component of methylprednisolone
acetate.56,58,60 There has been a report of Kenalog crystals found in the epidural space at surgery in patients with recent ESIs.61
The literature is conflicting as to whether Kenalog or Celestone is better for pain relief,62,63 with some suggesting that the crystallization of Kenalog provides better longterm benefit62 and others noting that the soluble properties of Celestone provide quicker onset of action.63 It
is important for both the operator and patient to understand that the
steroid may take up to 3 days to begin providing symptomatic relief.
Nerve block injections
Rationale and patient selection
Nerve blocks may
be performed as part of the workup for potential surgery as both
diagnostic and therapeutic procedures. There is no agreement in the
literature on what defines a positive nerve block result or “good” pain
relief. Smaller volumes are used in nerve blocks to limit the effect to
only one nerve. Patients may have a single or multiple level nerve
block. Multiple blocks may be performed at the same session or
sequentially (but still on the same day) until the pain generator is
found. When these are performed sequentially, the patient is brought
into the procedure suite for the first block. Thereafter they are
monitored in an observation area for approximately 30 minutes where
their response to the anesthetic agent is assessed. If the patient
experiences less than approximately 80% relief, then the next nerve
level is treated (on the same day), and so on. Once approximately 80%
relief is obtained, no further injections are needed as the patient will
not be able to distinguish further relief. If a total of approximately
80% pain relief is not attained, another source of pain should be
considered. Bilateral blocks can be performed, but care should be taken
as the patient may have difficulty ambulating after these injections.
For this reason some operators do not perform bilateral nerve blocks on
the same day.
Nerve block technique, medication, and needles
Injectate consists of 1 cc of a contrast agent, a half-dose of
steroid compared to the ESIs above and 1 cc of lidocaine 2%. Broadly
speaking, the technique for lumbar nerve root injection is similar to
the transforaminal injection. Some variation exists in the lumbar
approach; some operators may attempt to position the needle tip more
laterally compared with a transforaminal ESIs to prevent reflux into the
epidural space. Cervical extraforaminal nerve root blocks may be
performed safely with correct technique:26,27 The Carm is
tilted approximately 20 degrees to 30 degrees ipsilateral to the side of
choice, with the target point at the junction of the middle and lateral
third of the articular pillar just below the foramen of the nerve root
to be treated (Figure 13).
Rationale and patient selection
Facet pain often
overlaps disc pain and may coexist with disc disease. Facets are
synovial joints and, therefore, they can be affected by arthritis in a
fashion similar to other synovial joints (e.g., the knee, hip, etc.).
Symptoms include pain in the paraspinal region, buttocks, thigh or
shoulder in cervical spine; pain worsened on hyperextension following
flexion and pain accompanied by paraspinal tenderness. Age, a prior
history of low back pain, abnormal gait, absence of leg pain, muscle
spasms, and aggravation of pain on valsalva may indicate pain with its
origin in the facet joint.63
Medial branch block injections are often directed at groups of facets. There is a known placebo effect with single blocks64–66 and therefore, prior to surgery or rhizotomy a patient should have two successful (80% relief) blocks.64–66
The decision on whether to perform an intraarticular injection or
medial branch facet nerve block depends on several factors: Medial
branch blocks are more useful in patients who are candidates for
rhizotomy, where uncertainty exists over the origin of back pain and in
those where the facets are so overgrown and deformed by osteophytes that
intraarticular injection is not possible.67–70 In the cervical spine, intraarticular injections have shown little efficacy whereas medial branch blocks have shown benefits.14
Radiologic guidance (fluoroscopy or
CT) is essential, as facets at different levels have different
orientations (Figures 14, 15). As little as 1 cc of injectate can
rupture a nondiseased facet capsule.71 Studies have
postulated that facet capsule rupture is associated with increased pain
relief possibly due to injectate bathing the medial ramus feeding the
facet and spreading to the epidural space.67,68,71 Despite
the presumed benefits of extracapsular spread of injectate, initial
needle placement within the facet joint provides better pain relief than
extracapsular injection.68 There is a dual innervation to
each lumbar facet joint. Each facet is innervated by the medial branches
of the posterior rami of the spinal nerves above and below the joint.
Thus, the L4L5 facet is innervated by the L5 medial branch (coursing
over the L5 transverse process) and the L4 medial branch (coursing over
the L4 transverse process). An exception to this rule is the C2C3 facet
joint, which is innervated by the third occipital nerve and the C1
medial branch that courses superolaterally to the C1 foramen. The medial
branch of levels other than C2C3 and S1 is approached by tilting the
Carm at approximately 20 degrees ipsilateral to the nerve in question
(Figure 16) and aiming for the junction of the transverse process and
the superior articulating process (i.e., the ear and nose of the
“Scottydog”). Medications and needles for medial branch blocks are
similar to those described for nerve blocks. In all cases contrast
(±0.5cc) should be injected to exclude a vascular injection and, in
intraarticular injections, to perform a facet arthrogram (if this is not
performed, the report and CPT charge should be adjusted). This is then
followed with a 1:1 steroid/local anesthetic mix at half the volume of a
nerve block (i.e., the total steroid/steroid/local anesthetic volume
should be approximately 1 cc). Many operators will use 20 mg Depo-Medrol
per facet joint injection as Depo-Medrol is FDA-approved for joint
injections and there is little risk of intrathecal injection. For
similar reasons, either Marcaine or lidocaine may be used in facet
injections. Some operators only use medial branch blocks as a diagnostic
technique, in which case no steroid is injected.
pain management procedures benefit patients who are both operative and
non-operative candidates as determined by clinical parameters and
imaging (Figure 17). In those patients who are not operative candidates,
spinal injections can help identify anterior column (disc herniations
and degeneration) versus posterior column (facet) disease. Minimally
invasive techniques can produce long-term relief. In patients who are
operative candidates, pain-relieving injections can assist in
identifying the level of surgery in multilevel disease and temporizing
pain while the patient awaits surgical scheduling.
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