Chapter 25 Spinal Injection Techniques
Spine pain is a common reason for physician visits, as approximately one fourth of Americans report at least 1 day of low back pain in the last 3 months, and 14% have similar reports of neck pain.59 Low back pain is the main reason that patients younger than 45 years limit their activities.39,126 Although 90% of episodes of low back pain resolve within 6 weeks, there is a 60% to 80% rate of recurrence within 2 years.185
Direct costs of low back pain have been estimated to be between $20 and $50 billion per year, with indirect costs reaching more than $100 billion.58,147,185 In addition, there has been a large increase in utilization of invasive interventional procedures.77,200 Within the Medicare population, lumbar epidural injections increased by 271% and lumbar zygapophysial joint injections increased by 231% from 1994 to 2001.77
As the population has been growing older and living longer, these treatments have become increasingly popular. We advocate a comprehensive multidisciplinary approach to the treatment of spinal pain. Spinal interventional procedures certainly have a role, but should be used judiciously within the armamentarium of the physiatrist’s nonsurgical treatments. Careful patient selection is imperative to increase efficacy, decrease risk, and reduce cost of unnecessary procedures. The following chapter is not intended to substitute for clinical and technical experience. Because these procedures are clearly an integral part of the rehabilitation management program for spinal pain, we aim to provide a basis for understanding the indications and techniques for interventional spine procedures, their potential side effects and complications, and data regarding their efficacy.
Primum non nocere: “First, do no harm.” All spinal interventions carry inherent risk and have the potential to cause complications ranging from mild medication side effects to significant morbidity and mortality. The practitioner must be able to recognize risks in order to minimize them and weigh them against the potential benefit of the planned procedure for each patient.
The absolute contraindications to spinal injections include pregnancy, infection within the procedural field, and the inability of the patient to give informed consent.25 Informed consent must be obtained from the patient before all spinal procedures. The patient must understand the purpose of the intervention as well as the associated risks.
Considering underlying medical conditions such as tumor, infection, inflammatory disease, or trauma as a cause of spinal pain is important before performing spinal procedures.60,151,176,187 Although the incidence of these conditions is low, any delay in diagnosis can worsen the prognosis.60 Red flags are signs associated with an increased likelihood of an underlying medical condition as a cause of pain. These include the following101,180,190:
Spinal interventions carry an inherent risk of bleeding complications because of the highly vascular nature of the spine. The reported incidence of a clinically significant epidural hematoma is rather low (1 in 70,000 to 1 in 190,000).3,205 However, severe morbidity such as paraparesis or quadriparesis can be associated with an epidural hematoma.32,202
Identifying patients with an increased bleeding tendency is essential, and several guidelines exist for performing spinal procedures in patients with an increased bleeding tendency.97,121 Information including a medical and family history of coagulation disorders, a careful medication history to identify the use of anticoagulants, and a history of prolonged bleeding after trauma or prior surgery should be obtained from every patient. If a coagulation disorder is diagnosed and managed, spinal procedures may be considered after evaluation and disclosure of the expected risks and benefits.181,196
Existing guidelines for spinal procedures in patients receiving antiplatelet and anticoagulant therapy vary by the type of medication.96,97,108,121 Nonsteroidal antiinflammatory drugs (NSAIDs), including aspirin, reduce platelet aggregation, but have not been implicated in increased bleeding risk or complications in lumbar epidural injections.96 In patients with otherwise normal coagulation status, discontinuation of these drugs is not required.
Clopidogrel (Plavix) and ticlopidine (Ticlid) inhibit adenosine diphosphate–induced platelet aggregation, but bleeding risk after spinal injection has not been studied. Based on labeling precautions, surgical literature, and interventional cardiology and radiology data, it is recommended that before spinal intervention, clopidogrel be discontinued for 7 days and ticlopidine for 14 days.108,121
Glycoprotein IIb/IIIa receptor antagonists such as abciximab, eptifibatide, and tirofiban inhibit the binding of thrombocytes to fibrinogen and von Willebrand factor, thereby inhibiting platelet aggregation. This class of medications is an absolute contraindication to spinal procedures. Because these medications are used in the management of acute coronary syndromes, the physician is unlikely to encounter them when assessing for a spinal procedure. Discontinuation of eptifibatide and tirofiban for 8 hours before an intervention, and for 24 to 48 hours for abciximab, is recommended by guidelines for regional anesthesia.97
Warfarin has a profound impact on coagulation as a vitamin K antagonist. Active use of warfarin results in an increased risk of spinal hematoma after lumbar puncture.97 The use of warfarin for therapeutic anticoagulation is therefore considered a contraindication for spinal interventions. Warfarin should be discontinued for 4 to 5 days before any spinal intervention to allow the prothrombin time and international normalized ratio to return to the normal range. For invasive procedures such as spinal interventions and surgery, an international normalized ratio of 1.5 or less is considered safe in most guidelines.97,108
Low-molecular-weight heparin (LMWH) is administered either for thrombus prophylaxis or therapeutically at higher doses. After a prophylactic dose of LMWH, it is recommended that spinal procedures be postponed for 12 hours. The medication must be held at least 24 hours before the procedure when a patient is receiving a therapeutic dose of LMWH, and cannot be administered until 24 hours after the procedure.125
Unfractionated heparin is administered either as a prophylactic or therapeutic dose. Prophylactic low-dose unfractionated heparin is not a contraindication for spinal procedures.192 Therapeutic doses of heparin should be discontinued 2 to 4 hours before any spinal procedure and a normal activated partial thromboplastin time documented before the procedure. Heparin may be restarted 1 hour after the procedure.125
The risk for a spinal hematoma is present regardless of the patient’s hemostasis status. The outcome after spinal hematoma is highly dependent on the time interval between symptom onset and treatment with surgical decompression. The prognosis of spinal hematoma is poor without definitive treatment within 8 to 12 hours after onset of symptoms.161 Warning symptoms include sensory and/or motor block longer than expected, recurrence of sensory and/or motor block after initial resolution, diffuse sensory and/or motor block beyond what was expected, and unexplained spine pain with or without radicular pain.116,161 These symptoms are not specific and can present immediately or be delayed several hours to days.116 Specific postprocedure instructions, including a contact if symptoms are encountered, are essential. Emergent magnetic resonance imaging (MRI) is required for diagnostic evaluation, followed by emergent decompressive surgery if a spinal hematoma is present.
Review for any prior history of allergic reaction to medication is essential. Assessing the type of reaction for each medication can prove helpful. A positive history for urticaria, swelling, rashes, or breathing problems should be considered severe and potentially of the anaphylactic type. Although many “reactions” to medications are not truly allergic, it is prudent to clarify this if the patient consents to receive a similar medication.
Often the first medication administered in the procedure suite is a sedative. One case of a severe anaphylactoid reaction to midazolam has been reported,78 although the risk for an allergic reaction to sedatives is exceedingly low.
Allergy to contrast is more common and is usually an anaphylactoid type of reaction. There are several mistaken beliefs about contrast allergy. Iodine is present in ionic and nonionic contrast agents, and many who believe they are allergic to contrast dye believe incorrectly that they have an allergy to iodine. Iodine is a naturally occurring substance found throughout the body and in table salt, and true iodine allergy has not been cited. Another misconception is that those who are allergic to shellfish are allergic to iodinated contrast. The allergy to shellfish is to the muscle protein tropomyosin, which does not correlate to an iodinated contrast agent allergy.114 Likewise, allergy to topical iodine solutions is not an allergy to iodine, but to other agents within the solution.114 Similarly, allergy to iodinated contrast dye is not actually due to iodine.6 Consequently a patient should not be considered allergic unless the patient has had an allergy to contrast dye.
Anaphylactic food allergies in general (including shellfish, fish, eggs, milk, and chocolate), however, do correlate with an increased risk of contrast allergy, with a 5.7% incidence, whereas persons with allergic asthma have a 7.7% incidence.114 Screening for atopic reactions of any kind can help determine those at higher risk of a contrast allergy.
If patients have a history of a contrast allergy, they can be premedicated with prednisone, 20 to 50 mg orally via several different regimens. Oral administration must be given, however, at least 6 hours before contrast administration. Intravenous dosing immediately before the procedure is not effective.114 Ranitidine, 50 mg orally 2 hours precontrast, and diphenhydramine, 25 to 50 mg orally 2 hours precontrast or intravenously 10 minutes precontrast, can also be helpful. Use of gadolinium is also considered acceptable. However, these measures do not completely prevent an anaphylactoid reaction.134
Anesthetics can also cause an allergic reaction. The ester subgroup is metabolized by plasma pseudocholinesterase into para-aminobenzoic acid (PABA). This can lead to an allergic reaction in persons sensitive to PABA in other products (such as sunscreen). It is important to realize that those with an allergy to esters are not usually allergic to amide anesthetics, and vice versa.
An allergic reaction to corticosteroid is rare, but a case of sustained urticaria after spinal injections has been reported in which the patient skin tested positive to 21 of 26 corticosteroids.154 Also, adjuvants and preservatives commonly added to glucocorticoids could potentially cause an allergic reaction.
Allergic reactions might not be avoidable, and preparation including basic monitoring and advanced cardiac life support training is recommended. Unfortunately, many practitioners are unaware of what is considered appropriate treatment.198
Treatment with high–flow rate oxygen delivered by facemask is appropriate when oxygen saturation falls below 92%.198 Fluid is administered regardless of whether hypotension is present, because allergic reactions, especially those caused by contrast agents, are worsened by dehydration.198 Subcutaneous or intravenous epinephrine is indicated, although the intravenous route has a more dependable uptake, particularly when a patient becomes hypotensive.198 Diphenhydramine can be given, but is contraindicated if the patient is hypotensive. Consequently it has limited use in an emergent anaphylactic reaction.7 Corticosteroids do not modify the acute symptoms in an anaphylactoid reaction and should not be given as the sole treatment.198
The use pattern of sedatives for spinal procedures is variable. Some physicians think sedatives cloud the diagnostic value of injections, while others think they are necessary and decrease anxiety and the incidence of vasovagal reactions.68 Their use should be judicious, in view of the obvious risk of respiratory depression from overdose. Many procedures require a responsive patient to minimize risk, and oversedation could lead to serious complications. Some patients are more susceptible to conscious sedation than others; therefore slow titration is recommended.127
The use of sedatives requires that there are no gastric contents at risk of being aspirated. The recommendation, therefore, is that the patient should have no clear liquids for 2 hours and no solids for 6 hours before the procedure. This guideline is generally followed even when sedation is not planned. Patients who have not followed this recommendation should have their procedures delayed.8
Using the lowest possible dose of the nonionic form of contrast in most spinal procedures helps to minimize the risk of developing renal toxicity. In those patients with normal renal function, even in the setting of diabetes mellitus, multiple myeloma, and metformin treatment, the risk of renal toxicity is low.114 Minimizing the dose and ensuring precontrast hydration are recommended to decrease nephrotoxicity.49
Various medications can interact with iodinated contrast agents. Metformin can increase the risk of renal toxicity and precipitate severe lactic acidosis in diabetic patients. It might be prudent to withhold metformin after use of iodinated contrast agents in spinal procedures as well. Combining iodinated contrast administration with any nephrotoxic medication (even NSAIDs) increases the risk of toxicity.134 Neural, cardiac, and osmotic toxicity are also possible but more rare.114
In spinal procedures, 0.2 to 15 mL of contrast containing between 200 and 300 mg/mL of iodine is generally used. Keeping the iodine dose below 3 g minimizes toxicity.114 Gadolinium can be used in place of iodinated contrast and has less toxicity.
Corticosteroids are thought to relieve pain by reducing inflammation and by blocking transmission of nociceptive C-fiber input. They have been shown to directly inhibit the activity of phospholipase A2 within the inflammatory cascade.93 In addition to their antiinflammatory actions, corticosteroids also have another pain-relieving mechanism of action via nerve membrane stabilization through inhibition of ectopic impulses, ion conductance, C-fiber transmission, and hyperpolarized spinal neurons.57,88,89,104
Local tissue toxicity has been demonstrated with corticosteroids. Dexamethasone was shown to decrease proteoglycan concentration in human chondrocytes.183 Although there had been some concern about neural toxicity with spinal administration, no concrete evidence of neurotoxicity from intrathecally administered corticosteroids has been reported.94
Corticosteroids have systemic side effects that should be considered when assessing risk. A single epidural steroid injection (ESI) can cause adrenal suppression and hypothalamic-pituitary-adrenal axis imbalances for 1 to 5 weeks.136 Complete adrenal suppression is usually limited to 4 to 7 days, but the level of incomplete suppression can be similar to that of low-dose oral corticosteroids. Some individuals are more susceptible to suppression and long-term effects, but clinical prediction of these individuals is not possible.69 An ESI precipitates more prolonged suppression than does an intraarticular injection.209 Intraarticular injection studies have shown that the duration of both systemic and local effects increased with decreased corticosteroid solubility. The degree of cortisol suppression was dependent on the number of joints injected, independent of the corticosteroid dose.10
Specific guidelines for the acceptable cumulative dose of spinal corticosteroids do not exist. Many physicians advise no more than three ESIs per year or a 6-month limit of 5 mg per kilogram of body weight.182 There are no published data, however, of an evidence-based definitive guideline. Nonetheless, judicious use is recommended because the additive local effect on the spinal structures is unknown, and the systemic effects of prolonged adrenal suppression are detrimental.
Patients with diabetes mellitus have an increased risk from the effects of adrenocortical suppression. After an ESI, persons with diabetes can have elevated blood glucose levels particularly during the first 4 to 7 days postinjection. Some studies have found the severity of this glucose increase related to the hemoglobin A1c level at the time of injection.209 Blood glucose levels can exceed 400 mg/dL, with an attendant risk of ketoacidosis.
The general infection risk is elevated in all patients after glucocorticoid injection, secondary to immunosuppression. An almost immediate suppression of T lymphocytes occurs.209 Newly acquired viral infections and reactivation of latent herpes virus are more likely to occur after glucocorticoid administration. Any existing infection is a contraindication to injection of glucocorticoids. Local infection at the site of proposed injection is a contraindication to injection, even when glucocorticoids are not being administered.
Preexisting immunosuppression in a patient requires careful assessment. All patients with diabetes mellitus are relatively immunosuppressed, and this varies with their blood glucose levels. The patient should also be screened for other causes of immunosuppression in the medical history.
Long-term effects such as osteoporosis can occur with ESIs. No large clinical studies have assessed this risk. However, the fact that systemic absorption can approximate the effects of low oral dosing for at least 30 days suggests that bone density loss is likely after ESIs.182
Glucocorticoids potentiate the risk of gastrointestinal bleeding, especially when used in conjunction with NSAIDs. Although no data clearly indicate that patients have to discontinue NSAIDs before spinal procedures because of the risk for bleeding at the site of injection,96 several studies have reported approximately a twofold increase in gastrointestinal bleeding risk for those taking NSAIDs and glucocorticoids combined compared with NSAIDs alone.145,195 This may provide enough reason to withhold NSAIDs when performing spinal procedures with glucocorticoids.
The particulate size of corticosteroids is another property that can contribute to adverse events during epidural injection.165 Accidental intraarterial injection of particulates can cause serious harm in the cervical, thoracic, and even the lumbosacral spine by causing a spinal cord infarction.182 The cervical transforaminal epidural approach with particulate corticosteroid has been associated with serious neurologic compromise including death, stroke, and quadriplegia in at least 70 cases.165
All corticosteroid preparations used for epidural injection are particulate except dexamethasone and betamethasone sodium phosphate.21 Dexamethasone has not been implicated in any of the embolic events associated with epidural injection. Although no large-scale studies have compared the efficacy of different corticosteroids, one smaller study suggests some slightly longer term effects with particulate corticosteroid in the cervical spine compared with dexamethasone.62
Anesthetics inhibit migration of sodium ions into the axon to slow conduction, and reduce the potassium conductance to slow repolarization. Anesthetics have known systemic toxicity, which limits the total dose (Table 25-1). There are two chemical subgroups of anesthetics, the amides and the esters. The amides are metabolized in the liver and excreted in the urine, whereas the esters are metabolized by plasma pseudocholinesterase into PABA.54,148 Systemic toxicity for all anesthetics affects the central nervous system (CNS). The initial symptoms frequently are uneasiness, tinnitus, metallic taste, and visual auras. These symptoms can progress to shivering and then to seizures. The management of CNS toxicity is airway protection and benzodiazepine administration for control of seizures.148
Cardiac effects of anesthetic toxicity are manifested through decreased cardiac conduction and atrioventricular block. Bupivacaine is 16 times more potent for cardiac QRS prolongation than is lidocaine. Bupivacaine also has a slow “on” and slow “off” binding to the sodium channels, which makes its duration of action longer for the anesthetic affect, but also for its toxicity. Cardiac toxicity with bupivacaine often precedes the CNS toxicity, and once present is rarely reversed, with a high fatality rate despite adequate resuscitation efforts.148
Epidural anesthetics have been shown to locally inhibit platelets, fibrinolysis, and leukocyte function. It has been proposed that reduced granulocyte migration and metabolic activation at surgical sites infiltrated with lidocaine might be a mechanism of decreased pain postsurgically. This could also be a mechanism for the duration of pain relief exceeding the anesthetic action in spinal procedures.148 Lidocaine and bupivacaine have been shown to have an antiinflammatory effect on nucleus pulposus–induced nerve injury, and to increase intraradicular blood flow in an animal nerve root compression model.206,207
Prevention of infection starts with the proper preparation, including a sterile procedural field and maintaining sterile equipment and medications. Risk of infection cannot be completely eliminated and might occur with any spinal injection. A 1% to 2% infection rate is reported for all spinal injections, but only a 0.01% to 0.1% rate for severe infections.65 The infection can spread through Batson’s plexus. Malposition of the needle, such as into the pelvic cavity, could cause infection with enteric organisms.203
Placement of the spinal needle outside the target area can result in deleterious consequences. Dural puncture, disk entry, intraabdominal puncture, pelvic puncture, pneumothorax, intravascular injection, nerve trauma, and spinal cord trauma are all possible with spinal interventions. They are best avoided with proper use of fluoroscopy and radiopaque contrast.85
The use of fluoroscopy is essential for spinal procedures. Radiation exposure is inherent and must be considered as part of the risk for both the patient and the interventionalist. Radiation doses to the interventionalist are approximately 0.39 mrem at the glasses per 100 cases, with a mean of 15 seconds per case.38 This is well within radiation exposure safety guidelines, but protective lead aprons, thyroid shields, and glasses are recommended along with increasing distance from the x-ray beam.38 Patients have higher levels of exposure per procedure, and consent for the procedure should include radiation exposure.71 Pregnancy is an absolute contraindication to fluoroscopy. The radiation risk should be taken even more seriously in younger patients.
The concept of injecting medication into the epidural space has been around since the early 1950s.123 Initial reports in the United States from the 1960s described treatment for sciatica using the caudal and interlaminar (IL) approaches.20,83 By the mid 1970s and 1980s, nerve root injections were described for the treatment of radicular pain. The transforaminal (TF) route of administering medication to the epidural space has become more popular in the past decade. This was largely prompted by the introduction of fluoroscopic guidance and reviews reporting that epidural corticosteroids administered by the conventional routes were not as effective as claimed in uncontrolled studies.27,109,113 Studies by Derby et al.56 and others in the 1990s described outcome improvements with prospective studies evaluating the TF route for radicular pain.132 The last decade has been characterized by a more detailed look at the efficacy of epidural steroids, with a number of reviews conducted. The proportion of these published studies that were randomized controlled trials, however, remains very small. The findings of many of these studies are described below.
The usefulness of cervical, thoracic, and lumbar epidural injections remains controversial. Underlying this controversy is the dramatic increase in lumbosacral injections in the Medicare population from 1994 to 2001. Friedly et al.77 reported that less than half of these epidural injections were performed for sciatica or radiculopathy, where the greatest evidence of benefit is available.
The epidural space is a tissue plane between the dura mater and periosteum and ligaments within the vertebral canal. It is contained anteriorly by the posterior longitudinal ligament and the vertebral bodies, and posteriorly by the laminae and ligamentum flavum. Its lateral borders are the pedicles and intervertebral foramina (Figure 25-1).
FIGURE 25-1 Lumbar spinal anatomy. all, Anterior longitudinal ligament; altif, anterior layer thoracolumbar fascia; dr, dorsal rami; ds, dural sac; esa, erector spinae aponeurois; grc, grey rami communicantes; i, intermediate branch; IL, illiocostalis lumborum; IVD, intervertebral disc; l, lateral branch; LT, longissimus thoracis; m, medial branch; M, multifidi; p, pia; pll, posterior longitudinal ligament; pltif, posterior layer thoracolumbar fascia; PM, psoas major; QL, quadratus lumborum; svn, sinovertebral nerve; st, sympathetic trunk; VB, vertebral body; vr, ventral rami; zj, zygapophysial joint.
The epidural space contains the spinal nerve roots and their dural sleeves, the internal vertebral venous plexus, loose areolar tissue, segmental blood supply, and lymphatics. The epidural veins form an arcuate pattern, positioned laterally at the level of each vertebral body. This is an important consideration for ESIs because venous puncture is more likely to occur laterally than with midline approaches.158
Key anatomic features of the cervical spine include a thin ligamentum flavum (unfused in the midline in approximately half of individuals), absence of the interspinous ligament, and a small posterior epidural space (distance between the ligamentum flavum and dura mater).95,158 At C6–C7 and C7–T1 the epidural space has a mean width of 3 mm (1 to 4 mm).5
The laminae and spinous processes overlap in the midthoracic region, making a midline approach extremely difficult. The posterior epidural space is about 2 mm in the upper thoracic region and increases to about 5 to 6 mm in the lumbar region.
The artery of Adamkiewicz is a concern for thoracic and lumbar interventional procedures. It is the largest radiculomedullary artery and the major supplier of the anterior spinal artery in the lumbar region. The artery enters the spinal canal through a single intervertebral foramen in 85% of individuals between T9 and L2,53,98 and is located 63% of the time on the left side.29 This structure has been implicated in paraplegia after lumbar nerve root block.98
The primary cause of radicular pain is attributed to the inflammatory effect on the nerve from the nearby disk herniation. During surgery and on myelography, nerve roots appear swollen in patients with radiculopathy.22,163 A herniated nucleus pulposus induces marked inflammatory responses in the dura, nerve roots, and the spinal cord with high levels of phospholipase A2 activity.164 The level of phospholipase A2 activity in extracts from human disk herniations was found to be 20 to 10,000 times more than that in any other human source.164 Herniated disk specimens have also demonstrated increased levels of matrix metalloproteinase activity, nitric oxide, prostaglandin E2, and interleukin-6.82,106
Unfortunately, there are no standardized practices for administering an ESI (Table 25-2). Across disciplines and institutions the content and volume of the injectant vary significantly. A Corticosteroid–local anesthetic mixture is the most common medication used for ESIs in both academic institutions and private practices. The results for other medications vary, with a minority of centers adding opioids clonidine, or using local anesthetic alone for their injections.51
The volume of the injectant varies based on the approach used. In cervical and thoracic epidural injections, a total of up to 3 to 5 mL might be used for ESIs in which the IL approach is used. In cervical and thoracic TF ESIs, however, clinicians generally use a maximum total volume of 1.5 to 2 mL. The volume used for lumbar ESIs is slightly greater, generally not exceeding 3 to 4 mL for TF ESIs, 6 to 10 mL for IL ESIs, and 20 mL for a caudal approach.48
ESIs have been used to treat a variety of spinal disorders. They are primarily and most effectively used to treat radicular symptoms. Currently, supportive evidence is lacking for the utility of ESIs in conditions such as postlaminectomy syndrome, degenerative disk disease, annular tears, spondylosis, spondylolisthesis, and vertebral fractures.
These procedures are not without risks, and some of the complications can be catastrophic, although infrequent. Transient complications encountered during epidural injections include insomnia, nonpositional headaches, increased back pain, facial flushing, vasovagal reactions, nausea, and increased leg pain.36 Reported complications with lumbar ESIs include infection, hematoma, intravascular injection of medication, direct nerve trauma, subdural injection of medication, air embolism, disk entry, urinary retention, radiation exposure, and hypersensitivity reactions.36 Cervical TF or IL injections are associated with relatively frequent minor adverse events (5% to 20%); however, serious adverse events are very uncommon (<1%).46 In a 2008 review of complications of lumbar IL and TF ESI, Goodman et al.85 concluded that most if not all serious adverse events can be avoided by careful technique, sterile precautions, and a thorough understanding of the relevant anatomy and fluoroscopic contrast patterns.
Various technical approaches are available to access the cervical, thoracic, and lumbosacral epidural space. Despite the body of evidence that supports the use of fluoroscopy and the utility of the TF approach, the technical approach for ESIs varies widely. The three most common approaches include IL, TF, and caudal. The following technique descriptions are not intended to serve as a stand-alone reference for conducting the procedures.
In a 2002 survey of academic and private practices, a significant variance in the use of fluoroscopy for spinal procedures was noted. Private practices used fluoroscopy with more regularity than academic institutions, most notably in the cervical region where 73% of private practices and only 39% of academic institutions polled used fluoroscopy.51
A paucity of literature on thoracic epidurals is available. This is most likely due to the significantly smaller incidence of acute herniated disks in the more stable thoracic spine. The incidence of thoracic disk injuries is 1 in 1 million persons per year, and these injuries account for only 0.25% to 0.75% of all disk herniations.9 IL and TF approaches are described for this region. Often a cervical technique is used for the upper thoracic region, and a lumbar technique is used for the lower thoracic region.
Access to the epidural space in the thoracic spine is somewhat more difficult secondary to the unique anatomic properties of the thoracic region. These include the closer proximity of the spinal cord and a narrower epidural space than the lumbar region. The overlapping laminae and spinous processes in this region limit midline access to the epidural space. It is also difficult to view the IL space on radiographs or using fluoroscopy. Botwin et al.35 describe an overall prevalence of complications per injection of 20.5%. All were transient and resolved without any residual morbidity.
One argument for using the TF approach in preference to the IL approach is the ability to deliver the medication directly to the ventral epidural space. Injectant within the epidural space will tend to flow in the direction of least resistance. Studies evaluating contrast patterns generally support this concept, although some conclusions are conflicting.
Kim et al.111 conducted a recent analysis of epidurography contrast patterns for cervical IL epidural injections using the midline approach. The rate of ventral epidural spread from this posterior approach was 56.7% with 1 mL of injectant and 90% with 2 mL. Botwin et al.37 evaluated the contrast patterns in lumbar IL injections in 2004 and found that approximately one third revealed ventral contrast flow and 16% were bilateral. In contrast, Manchikanti et al.139 evaluated lumbar TF ESI flow patterns and demonstrated ventral epidural filling in 88% of the procedures and nerve root sleeve filling in 97% of procedures. In a prospective evaluation of contrast flow patterns with fluoroscopically guided lumbar ESI via the lateral parasagittal IL approach versus the TF epidural approach, Candido et al.43 found the parasagittal IL approach superior to the TF approach for placing contrast into the ventral epidural space, with reduced fluoroscopy times and improved spread.
The effectiveness of TF versus IL ESIs has been compared, and the results are mixed. Schaufele et al.166 evaluated the effectiveness of TF versus IL ESI for the treatment of symptomatic lumbar disk herniations and found TF injections resulted in better short-term pain improvement and fewer long-term surgical interventions than the IL ESI. A literature review on the management of cervical radiculitis with IL versus TF ESI concluded that there was insufficient evidence supported by prospective studies to determine whether one technique was more effective or safer than the other.100 Ackerman and Ahmad4 compared TF, IL, and caudal approaches for the treatment of lumbar disk herniations and found that pain relief was significantly more effective with TF injections.4
The IL technique achieves access to the epidural space using the paramedian or midline approaches. The route of penetration from superficial to deep includes the skin, subcutaneous tissue, paraspinal muscles (paramedian approach) or interspinous ligament (midline approach), ligamentum flavum, and then entry into the epidural space. The most common technique includes a “loss of resistance approach” used to identify entry into the epidural space. Fluoroscopy with contrast is used to confirm the location (Figure 25-2).
The evidence is moderate for short- and long-term relief in managing cervical radiculopathy. In managing lumbar radiculopathy, the evidence is strong for short-term relief and limited for long-term relief.2,33 The evidence is indeterminate in the management of neck pain, low back pain, and lumbar spinal stenosis.
The lumbar TF approach is considered to be more specific and allows for the smallest aliquot of injectant to be delivered to the site of pathology. The technique involves using fluoroscopy to identify a subpedicular target within the intervertebral foramen. The needle is advanced to achieve a perineural location in the “safe” triangle that lies just below the pedicle and above the dural sleeve of the target nerve root (Figure 25-3). Precautions are taken to avoid advancing the needle tip medial to the “six-o’clock” position of the pedicle in the anteroposterior view (Figure 25-4).
A slightly different technique is used to deliver medication to the S1 nerve root in its foramen. The approach is analogous to that of the subpedicular approach at lumbar levels. The target point for an S1 TF injection is on the caudal border of the S1 pedicle, just dorsal to the internal opening of the S1 anterior sacral foramen. The needle is inserted into the posterior sacral foramen just short of the floor of the sacral canal.25
The technique for cervical TF injections is similar to that for lumbar TF injections. The correct oblique view of the target foramen is obtained with fluoroscopy. An entry point overlying the posterior half of the target foramen is used for initial needle placement. Care is taken to ensure that the tip of the needle is positioned over the anterior half of the superior articular process to ensure that it is not prematurely inserted too far into the foramen. The needle is advanced to the superior articular process and then readjusted to enter the foramen tangential to its posterior wall, opposite the equator of the foramen. Accurate placement is confirmed in multiple planes with radiopaque contrast and fluoroscopy.159
Epidural injection literature uses the terms selective nerve root block (SNRB) and TF injection interchangeably. The term SNRB implies selectivity of the TF approach, enabling the interventionalist to implicate a specific nerve root as a pain generator by anesthetizing it. It has recently been demonstrated that L4 and L5 SNRBs are often nonselective or at least only partially selective.193 Furman et al.81 observed that with as little as 0.5 mL of contrast, 30% of lumbosacral TF ESIs were no longer selective for the specified root level. The selective nature of the nerve root block applies to where the injectant travels, and the literature demonstrates that this might not be confined to a specific nerve root. The use of the term SNRB should consider these observations.
Although the evidence in the literature is often conflicting, two recent randomized controlled trials support the efficacy of TF ESI. The first is a study by Riew et al.160 that considered avoidance of surgery as the outcome measure, comparing patients treated with lumbar TF injections of bupivacaine plus betamethasone with those treated with bupivacaine alone. Significantly fewer (29%) of the patients treated with corticosteroid preparation than those treated with bupivacaine alone (67%) required surgery. The second study compared outcomes of patients treated with lumbar TF injections of corticosteroids with those treated with paraspinal injections of saline. At 12 months’ follow-up, 84% in the TF ESI group reported greater than 50% reduction in pain scores, compared with 48% treated with paraspinal injections.186
The evidence for cervical TF ESI in managing cervical nerve root pain is moderate for short- and long-term improvement. For lumbar TF ESI, the evidence for managing lumbar nerve root pain is strong for short-term and moderate for long-term improvement. The evidence is limited in managing lumbar radicular pain in post–lumbar laminectomy syndrome. The evidence is indeterminate in managing axial low back pain, axial neck pain, and lumbar disk extrusions.2 In a systematic review of TF ESI for low back and lower limb pain, the evidence for TF lumbar ESI is Level II-1 for short-term relief and Level II-2 for long-term improvement (Table 25-3).40