Vasovagal

Vasovagal responses are not rare. About 1 in 14 patients undergoing cervical interlaminar epidural injection will experience a vagal response. Incidence varies by gender, women are at greater risk than men and with procedures, vagal response is five times more common in cervical than in lumbar procedures. Although they are usually a minor complication, vasovagal events may be quite severe. Vigilant screening is necessary to discover previous episodes; suspect “fainters.” Pretreat with atropine when suspicious and recognize the early signs (i.e., “I feel sick,” nausea, and slowing of pulse rate). However, these doses are much in excess of those required for any interventional pain procedure.

Contrast Material

Allergic reactions to modern contrast materials are extremely rare. Some may be related to preservatives such as methylparaben. Wang reviewed 84,928 intravenous contrast injections noting “allergic” reactions in 545 (0.6%).⁵² Seventy seven percent of the reactions were “mild,” primarily urticaria, successfully treated with diphenhydramine. Twenty one percent had moderate reactions with respiratory symptoms, facial edema, or both. Corticosteroids intravenously or by inhaler were effective in controlling these reactions. Two percent, eight women and three men, had severe reactions (0.0012%). Three were unresponsive; frank cardiorespiratory arrest occurred in one. There were no deaths and no long-term sequelae in 10 of the 11 patients with severe reactions.

Contrast material is employed to document where the injectate is spreading and to determine where it is not spreading. Modern nonionic contrast agents are safe for all epidural injections. Unintentional vascular or even subarachnoid spread will cause no problem. In those very rare instances of documented history of severe allergic reaction to nonionic contrast material, gadolinium may be employed as a substitute radiography contrast agent.⁵³

Diabetics taking metformin are at risk for contrast material nephropathy (CMN) if exposed to nonionic contrast material, during radiographic procedures. Solomon found no change in renal function in those subjects who had normal renal function prior to testing.⁵⁴ However, some patients with normal renal function exhibited increases of serum creatinine with high-contrast loads.⁵⁵ This should not be a problem with epidural injections because the contrast doses employed are limited and much lower than the volumes delivered in the radiologic procedures. Doses in excess of 100 mL are not unusual for enhanced CT or angiograms. However, diabetic patients with renal impairment should discontinue metformin, with approval of their primary physician.

Local Anesthetics

The local anesthetics employed in the epidural injections are lidocaine and bupivacaine. These amides are primarily metabolized in the liver and excreted in the urine. Their allergic potential is extremely low. Ester-based local anesthetics (procaine) have a higher incidence of allergic reaction. A large survey attests to the overall safety of the amides as spinal anesthetics.⁵⁶ For epidural injections, lidocaine may be employed in concentrations of 0.5% to 4.0% and bupivacaine at 0.25% to 0.75%. The percentage concentration of the anesthetic is reduced with increasing volume delivered. Although central nervous system and cardiovascular system toxicity can occur following the epidural, intravenous, or subarachnoid injection of local anesthetics, the toxic doses are far greater than the volumes employed in epidural injections—40 mL of 1.0% lidocaine (400 mg) delivered to the epidural space of test subjects resulted in average peak plasma concentrations safely below neurotoxic levels.⁵⁷ One author recommended the maximum epidural dose of lidocaine to be 500 mg and 225 mg for bupivacaine.⁵⁸

Acute cardiac complications, decreased cardiac output being one, can occur from intravascular injection of lidocaine or bupivacaine. Study has shown that normal cardiac function is maintained in subjects with lidocaine plasma levels of 4 to 8 mcg/mL. Plasma levels this high require doses of >400 mg of lidocaine.⁵⁹ In human volunteers slow intravenous (IV) injection of bupivacaine to produce plasma concentrations equivalent to those achieved during epidural injections did not cause significant cardiovascular change.⁶⁰ Between 3.0 and 7.0 mL of low concentrations of anesthetics for interlaminar injections and 0.75 to 2.0 mL of higher concentrations for transforaminal injections are not toxic in the epidural space. These doses are not toxic if technical misadventure results in delivery to the vascular system or subarachnoid space. Because of the longer half-life of bupivacaine, this anesthetic should be avoided in interlaminar epidural injections, particularly in the cervical spine. Inadvertent delivery into the subarachnoid or subdural space results in prolonged effects, specifically affecting respiratory function with misplaced cervical injection. Decreased concentration of anesthetics must be considered for interlaminar epidural injections in the cervical and thoracic regions in patients with respiratory or cardiovascular health problems because decreased cardiac output and heart rate can occur with sympathetic blockade, which occurs to some degree with all interlaminar epidural injections.

Corticosteroids

The steroid preparations most frequently employed in ESI are methylprednisolone acetate, triamcinolone acetonide, betamethasone sodium phosphate, betamethasone acetate, and dexamethasone sodium phosphate. All corticosteroids have systemic effects when injected in the epidural space. Side effects may include: fever, myalgia, malaise, fluid and electrolyte imbalance, hypertension, hyperglycemia, myopathy, ulcers, immunosuppression, behavioral changes, allergic reaction, and pituitary-adrenal suppression. Abrupt withdrawal after prolonged oral use may precipitate acute adrenal insufficiency. Most of these side effects are clearly associated with the systemic absorption of corticosteroid and subsequent transient hypercorticism, and likely account for many of the “minor” complications associated with epidural injections.

The cardiovascular system is affected directly and indirectly. Direct effects are due to steroid receptors on heart and smooth muscle. Indirectly, steroids increase sodium uptake and vascular tone, raising blood pressure. Judicious use is prudent in patients with cardiac disease, hypertension, and congestive failure. Dose and frequency of administration must be carefully monitored in this group.

In the central nervous system, nerve tissues exhibit increased excitability, EEG abnormalities are seen, subjects experience euphoria and behavioral changes. Rarely, these effects can be severe. A case report describes 67-year-old male who developed psychotic episodes within a week of a cervical ESI, along with other steroid injections in one treatment session. The symptoms spontaneously resolved in approximately 7 to 10 days.⁶¹ This case serves to remind us that we must always be cognizant of the doses we deliver, and remember patients may be receiving “steroid shots” from other physicians for unrelated problems.

Endocrine system alterations include decreased adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), and follicle-stimulating hormore (FSH), and testosterone. The changes are largely dose related. Bizarre responses do occur rarely. A 24-year-old man underwent a second cervical ESI of 60 mg of methylprednisolone for ongoing severe arm pain. A cushingoid appearance developed 1 month later. Serum cortisol was undetectable, there was no adrenal response to synthetic ACTH, and urinary-free cortisol was below normal at 12 weeks. Cortisol normalized in 4 months, however, the patient’s cushingoid appearance persisted for 12 months.⁶²

An epidural steroid injection of 160 mg of methylprednisolone will suppress adrenal function for weeks.⁶³ Does injection of corticosteroids increase the risk of infection? Infections do occur in patients following ESIs.⁶⁴ Postoperative infections are increased in hip replacement patients who received preoperative steroid injections.⁶⁵ No studies have been done on outcomes of spine surgery after ESI, but suppression of the immune system suggests there is inherent risk, especially in the first 4 weeks post injection.

Epidural administration of glucocorticoids results in potent suppression of insulin action. This should be taken into account when patients with diabetes receive ESIs.⁶⁶ Lumbosacral transforaminal and caudal epidural betamethasone injections are associated with statistically significant elevations in blood glucose levels in diabetic subjects. This effect peaks on the day of the injection and lasts approximately 2 days.⁶⁷ The administration of three epidural injections (250 mg prednisone equivalent) was followed by suppression of the corticotropic axis that persisted beyond 21 days. Plasma cortisol and ACTH and urinary free cortisol were markedly reduced at the day 1 and day 7 posttreatment visits, compared to baseline. At 21 days, these variables were still diminished.⁶⁸ We must be vigilant in follow-up of our diabetic patients.

The musculoskeletal system suffers from some bone mineral density loss, muscle weakness and wasting, and predisposition toward avascular necrosis with long-term oral steroid use. Although systemic corticosteroids may be associated with loss of bone mineral density, a prospective study of 204 patients followed for 1 year after standard doses of epidural steroids revealed no change in bone mineral density.⁶⁹

The currently used steroids contain preservatives. Bernat thought that seizures following intrathecal cortisone acetate were due to the preservative, 0.9% benzyl alcohol. Benzyl alcohol is common in depot steroids and is neurotoxic.⁷⁰ Hodgson reported that there was no concrete evidence of neurotoxicity of intrathecal steroids, but did not recommend purposeful delivery of these agents into the subarachnoid space.⁵⁶

Infection

Infection following epidural injection is a serious issue. It has been described as a rare complication.⁷¹ However, the possibility of procedure-related infection must be a concern for the injectionist. Analysis of the American Society of Anesthesiologists (ASA) Closed Claims database from 1970 to 1999 revealed that infection was the third most common complication of chronic pain procedures, accounting for 13% of all complications.²⁴ Any penetration of the skin surface with a needle then placed in deep spaces in and about the spine has the potential of introducing organisms with subsequent infection.⁷² Standard aseptic preparation and draping of the local injection site and good aseptic technique will minimize this complication. Diabetic and immunocompromised patients are a subgroup that should be recognized prior to procedures. Antibiotic prophylaxis should be considered for immunocompromised patients undergoing ESI.⁷³ Antibiotics should not be mixed with the contrast during any epidural injection. Accidental delivery of antibiotics into the subarachnoid space must be avoided.

Bleeding/Hematoma

Many veins lie in the needle path or near endpoint targets of transforaminal epidural injections (TFESI). Furman and colleagues reported the incidence of fluoroscopically confirmed “vascular uptake” occurring during lumbar⁷⁴ and cervical⁷⁵ transforaminal injections. Observing blood at the needle hub reliably predicts intravascular injection, (97% specific). But this finding has low sensitivity, (45% overall). The absence of blood in the needle hub despite aspiration is not reliable. The incidence of vascular uptake with lumbar procedures is about 11%. There is a higher incidence in the cervical spine where confirmed intravascular injection was observed in nearly 20% of patients. Kim and coworkers have recently reported a much higher rate of vascular uptake for cervical transforaminal injections, more than 50%.⁷⁶ Although neither author specified, most of the vascular uptake seemed to be venous. No complications occurred. Venous uptake during epidural injections is common and innocuous as long as it is recognized and needle adjustment is made before injecting physiologic solutions. Veins are less abundant in the posterior epidural space and venous uptake is less frequently seen during interlaminar epidural injections.

Three surveys of cervical interlaminar epidural injection on more than 2200 patients claim no major complications.^76–78 Minor adverse responses, such as increased headache, insomnia, vasovagal episodes, facial flushing, dural puncture, and short-term nocturnal fever were encountered. Similar response profiles occur with thoracic⁷⁹ and lumbar interlaminar injections and caudal epidurals as well. Most of these are likely a response to the corticosteroid and are unavoidable for the most part.

The incidence of epidural hematoma is approximated to be less than 1 in 150,000 epidural injections.⁸⁰ Clinically relevant hematoma may occur at any level, the majority of reported cases were associated with injections in the cervicothoracic area. Spinal epidural hematoma causing acute myelopathy is a rare complication. In a case report, Stoll and colleagues noted epidural hematoma after ESI in a young man with no predisposing factors.⁸¹ An older patient with apparently normal coagulation received multiple cervical ESIs for palliative pain control over several years. A hematoma that required surgical decompression occurred following the seventh procedure.⁸²

The potential for bleeding and hematoma formation is increased in patients with a coagulopathy, liver disease, or in patients taking anticoagulant medications. It is crucial that the injectionist be familiar with a patient’s coagulation status and with common anticoagulant and antiplatelet medications.⁸³ Anticoagulant therapy should not be interrupted until there is full understanding of the reason for the therapy. Actual discontinuation of anticoagulant therapy is usually best left to the physician managing and prescribing the patient’s anticoagulation. Epidural injections are elective procedures. Interrupting anticoagulant therapy may increase the risk of serious complications such as stroke, myocardial infarct, or pulmonary embolus.

The following guidelines for performing spinal procedures in anticoagulated patients are based on the second American Society of Regional Anesthesia and Pain Medicine (ASRA) Consensus Conference on Neuraxial Anesthesia and Anticoagulation in 2003.⁸⁰ Warfarin therapy should be discontinued 4 to 5 days before spinal procedures and the international normalized ratio (INR) should be within normal range at the time of the procedure. Thienopyridine derivatives, (e.g., clopidogrel, ticlopidine) should be suspended 7 days and 14 days, respectively, prior to spinal procedures to allow for recovery of primary and secondary platelet aggregation and platelet-fibrinogen binding.

Low-molecular weight heparin should be held for at least 12 hours before the procedure in thromboprophylactic dosing and at least 24 hours in therapeutic dosing. Aspirin and nonsteroidal antiinflammatory drugs have not been found to have any contraindications for spinal procedures. It may be prudent to discontinue full dose aspirin therapy for 10 days in patients undergoing interlaminar procedures.

Dural Puncture

During interlaminar epidural injections, the dural sac is at risk. Transforaminal injections place the dural root sleeves at risk. Nonfluoroscopically guided interlaminar injections have increased incidence of dural puncture with prevalence up to 5.0% in cervical epidural injections.⁸⁴ Dural puncture is reportedly rare when the procedure is performed by “expert” interventionalists.⁸⁵ Minor complications, including headache secondary to dural puncture occurred in less than 0.5% in more than 4300 procedures. Dural puncture may occur with more frequency in the cervical spine above C7 and at L5-S1. In both areas there may be a paucity of epidural fat with the dural sac juxtaposed against the flaval ligament. Failure to recognize subarachnoid spread results in injection of anesthetic and steroid into the subarachnoid or subdural space. Delivery of anesthetics in sufficient quantity and concentration may produce significant spinal block, most serious at cervical levels where the block may impair respiration. These misadventures are avoided by selection of appropriate target, proper needle, good visualization, a cooperative, comfortable—but minimally sedated—patient and precise technique.

Subdural injections between the dural and arachnoid layers are rare but can and do occur. The injectionist must be able to recognize contrast injection into this space as noted by a cystlike appearance. Contrast injected into the subdural space can often be completely aspirated, which is not possible with subarachnoid or epidural injection.

Spinal Cord Puncture

Minimal direct cord injury occurs if there is puncture of the spinal cord. Injection of any solution into the substance of the cord is a major problem. Injury is proportionate to the volume of injectate. Direct puncture of the cord provokes pain and altered sensation in most subjects. Injection of solution into the substance of the cord adds to the trauma with ischemic pressure injury at the site of the injection in the cord. Hodges reported two cases of cervical cord injury secondary to cord injection. Both patients were heavily sedated an unable to respond.⁸⁶ Severe thoracic cord injury occurred when a low thoracic epidural injection was performed under general anesthesia.⁸⁷ Some cord punctures may not provoke pain.⁸⁸ Mayall reported permanent paraplegia resulting from multiple attempts at thoracic epidural injection in an awake patient. No lateral view was used during the procedure.⁸⁹ Surgery subsequently revealed multiple punctures of the cord. These complications are technical misadventures. They are minimized by careful attention and precise technique.

Brain and Spinal Cord Infarct

Arterial filling during transforaminal injections has been rarely reported. Only two cases of cervical medullary artery filling during transforaminal injection have been reported.^90,91 In both instances medullary artery filling was recognized during real time fluoroscopy and confirmed, in one instance, with digital subtraction angiography (DSA). Both procedures were aborted without further incident. A single case of lumbar radicular/medullary artery filling during transforaminal injection has been published.⁹² Filling of a small artery in the central canal during a right S1 transforaminal injection was recognized during real time fluoroscopy, but demonstrated more dramatically with DSA.

Transforaminal injections are hazardous because of important arterial structures in the target field. Delivery of a particulate steroid into an artery may result in embolization of particles, larger than capillaries, with subsequent ischemia and/or infarct of the perfused tissue. There were nonpublished, anecdotal reports of catastrophic neurologic complications associated with epidural injections circulating during the last decade. Brouwers and colleagues reported the first such occurrence in 2001.⁹³ The central cervical spinal cord infarct occurred in conjunction with a fluoroscopically guided C6 transforaminal injection. This was likely the result of embolization of the anterior spinal artery watershed by way of a reinforcing cervical medullary artery.³⁷

The next year Houten and colleagues reported the first cases of lower thoracic and conus infarct occurring as a result of lumbar transforaminal injections.⁹⁴ Two injections were performed at the L3-4 level, one on the left, the other on the right. The third was an injection at S1. The authors implied probable injection into an aberrant artery of Adamkiewicz.

A more likely hypothesis is injection into lumbar or sacral radiculomedullary arteries. In 1971, Lazorthes reported observing a well-developed anastomotic circulation to the conus and distal thoracic cord by way of lumbar and sacral arteries. In an experimental study, colloid material was injected into the aortic circulation, below the origin of the artery of Adamkiewicz and was subsequently identified in the distal cord and conus of the experimental animals.⁴¹ He postulated that these colloid emboli reached the anterior spinal artery circulation by way of reinforcing lumbar and sacral radiculomedullary arteries.

Glaser reported paraplegia following a thoracolumbar transforaminal injection in 2005.⁹⁵ Yin and Bogduk reported retrograde flow in a radicular arterial branch and subsequent filling of the thoracic anterior spinal artery. Retrograde flow into medullary arteries or the vertebral artery without direct cannulation can occur, providing an alternative mechanism of potential injury to the spinal cord or brain during transforaminal injections.⁹⁶

Since the first report in 2001, there has been a frightening number of case reports of catastrophic neurologic complications in the literature.⁹⁷ In a mail-in survey, Scanlon collected 287 responses from physician members of American Pain Society. There were 78 major neurologic complications associated with cervical TFE. All procedures involved injection of particulate steroid preparations. There were vertebrobasilar brain infarcts and cervical spinal cord infarcts.

The survey did not explore thoracic spinal cord and conus infarcts. There are more events than case reports; many are encountered in the context of medicolegal proceedings.⁹² One of the authors (CA) has reviewed six distal thoracic/conus infarcts in the last 2 years, none of which has been reported in the literature. Kennedy and colleagues reported two cases of distal thoracic cord and conus infarcts that occurred in conjunction with L3 TFE injections. A left L3 TFE was performed with fluoroscopic guidance, using betamethasone (Celestone) as injectate. A right L3 TFE was performed with CT guidance, using methylprednisolone acetate (Depo-Medrol). Paraplegia occurred almost immediately in both cases. Follow-up MRI scans demonstrated typical distal thoracic spinal cord and conus infarcts, with increased signal intensity in the central cord from about T9 to the tip of the conus.⁹⁸ Prevention of these complications begins with awareness that this can happen.

First, recognize intraarterial injection when it occurs.⁹¹ Careful real time fluoroscopy, in the frontal plane, during slow injection of an adequate volume of contrast to opacify vessels is mandated. Visualization of vessels can be enhanced by DSA.

Second, injection of a small test dose of concentrated local anesthetic before injecting steroids, especially with particulate varieties, to test for onset of neurologic signs may allow recognition of unexpected flow in the vertebral or medullary arteries.⁹⁹

Currently the presumed mechanism of spinal cord injury is an embolic shower of particles of the steroid preparation into the circulation of the anterior spinal artery.^100,101 A third safety measure is to avoid particulate steroids entirely for all transforaminal epidural injections.

Dexamethasone sodium phosphate is a nonparticulate steroid. Derby and associates found the particle size in this preparation to be approximately 10 times smaller than red blood cells and they do not appear to aggregate. They have lower density than the particles and aggregates of methylprednisolone acetate, triamcinolone acetonide, and betamethasone sodium phosphate/acetate, the most commonly used agents.¹⁰⁰ In a comparison study, Dreyfuss and colleagues reported that dexamethasone was slightly less effective than triamcinolone, but the difference was not statistically significant.¹⁰² There have been no reported infarcts when dexamethasone has been used for transforaminal injections. Two animal studies have demonstrated severe neurologic injury to the animals when particulate steroid preparations were injected into the carotid¹⁰³ and vertebral¹⁰⁴ arteries. There was no evident injury to the animals receiving intraarterial injections of the nonparticulate preparation, dexamethasone. A theoretically safer nonparticulate agent appears to be a valid alternative to the particulate agents that have been used to date.

Equipment

Intravenous Access

IV access should not be considered mandatory for routine injections of steroid into the epidural space, be it cervical, thoracic, lumbar, or sacral. Although some medical facilities mandate an IV, and at least one well respected guideline concerning spinal injections (ISIS) recommends the practice for transforaminal injections,¹¹⁸ it should not be considered standard of care. Although complications requiring the use of IV medications, (allergic reactions, severe vasovagal reactions, high intrathecal-spinal anesthetic block) are exceedingly rare, the high cost and risk/benefit ratio make routine intravenous cannulation questionable. Of course, use of sedation requires intravenous access.

Sedation

The administration of corticosteroids into the epidural space is minimally painful and the use of sedatives, hypnotics, amnestics, and analgesics is rarely medically indicated. Rather than by medical necessity, the use of these medications is more often governed by patient expectations of a completely pain-free procedure and physician intolerance of any patient movement or interaction during the procedure, and varies significantly from region to region within the country. If sedation is used, intravenous access is obviously required (except when only mild oral medications are given). Although light sedation may have a place in the markedly anxious patient, when carried to a point where the patient is unresponsive or minimally responsive to a painful stimulus, it must be considered dangerous and is never appropriate for epidural injections at any level or with any technique. At all times during the course of the procedure, the patient must be able to converse with the attending physician. If not obtunded prior to any untoward event, the patient will often give a vocal warning of unintentional misplacement of the needle. Unfortunately in many instances, sedation is used to conceal poor operator technique. Sedation can never take the place of technical competence.

One often overlooked aspect concerning the use of sedation in minimally painful procedures is the expectation created by their use, and the validation of complaints elicited from the patient. Routine use of sedation creates in the patient the presumption that the planned procedure is inherently excruciating to such a degree that sedation is required; this belief is self-fulfilling. In addition, the psychological overlay, often seen as a comorbid condition in the chronic pain patient, validates the patient’s idea of the extreme severity of the condition, because a procedure that requires sedation must be serious.

In competent hands, the optimum sedation is often attained by providing the patient with a detailed account of the anticipated procedure during the consent phase of the interaction, “talking the patient through” the procedure, for example, ensuring that he/she is aware prior to any sensory stimulation, engaging the patient in conversation, and perhaps using music, or other sensory stimulation, as a mild distraction.

Preparation and Drapes

When aseptic precautions are used, infection following epidural administration of corticosteroids is quite rare. The skin at, and around, the point of needle insertion is prepared using an iodine-based solution (e.g., povidone-iodine), or chlorhexidine, with or without alcohol, followed by sterile towels or fenestrated drapes to cordon off the area. A change in level or procedure, might be necessary because of unforeseen events, or individual anatomic variation or pathology and a larger skin “prep” than anticipated is never disadvantageous. Sterile technique is mandated throughout the procedure.

Periprocedure Techniques

Caudal Needle Placement

Caudal injection (i.e., access to the epidural space via the sacral hiatus) has been largely replaced by the slightly more selective, precise interlaminar and highly selective transforaminal approaches. However, if the practitioner’s training is questionable, L5 or S1 bilateral symptomatology is noted, or anatomic considerations prevent the use of other epidural approaches, a caudal injection might be entertained. Entry into the caudal canal involves needle placement though the sacral coccygeal ligament. Traditionally, this was accomplished by palpation of the sacral cornu and placement of the needle blindly. As documented previously, an unacceptably large percentage (>30%) of these injections failed to reach the caudal canal and nonfluoroscopically guided injections are no longer an acceptable routine practice. Caudal injections involve injectate being deposited between the S3-4 levels, with rostral spread hopefully reaching the pain generator two to four levels above, depending on needle tip location within the sacral canal. This injection at a distance may necessitate the use of a larger volume of injectate with reduced concentration of corticosteroid.

The patient is placed in the prone position (often a pillow under the hips provides increased access). Rotating the feet so that the toes are pointed medially and the heels lateral will relax the gluteal muscles and facilitate access to the entry point. In obese patients with large buttocks and a deep gluteal cleft, 3-inch surgical tape can be used to pull the buttocks apart and allow access to the needle insertion area over, or somewhat caudal, to the sacral cornu. The skin over the sacral hiatus, including the lower lumbar and sacral areas, is prepared and draped sterilely. The fluoroscope is positioned in lateral view because the sacral hiatus is usually quite difficult to identify using an anteroposterior (AP) fluoroscopic orientation. In a lateral view, the sacral lamina can be seen to extend down to S4 with an abrupt drop off noted identifying the sacral hiatus (Fig. 35-1, A). A metal pointer is positioned in the midline, over or slightly caudal to the sacral hiatus (see Fig. 35-1, B) and a 25-gauge needle is inserted (see Fig. 35-1, C). Anatomy allows the use of a 1.5-inch needle in the majority of cases. The needle will be felt to puncture the sacral coccygeal ligament and contact with os will be noted at the dorsal aspect of the S4 vertebral body in the ventral caudal canal. If the injectionist desires to advance the needle cephalad, a slightly more caudal insertion might be used. In this case, the needle can be advanced up the caudal canal to the level of S3—the level to which the dura extends in most individuals.

Figure 35-1 Lateral view of the sacrum. A, Arrows indicate extent of sacral hiatus. B, Pointer on skin at midline indicates needle insertion point over sacral hiatus. C, Needle in place penetrating sacral coccygeal ligament and contacting the dorsal S5 vertebral body.

When the needle is in position, contrast is injected under real time fluoroscopy. DSI (Fig. 35-2, A and B) often provides a more exact indication of the rostral contrast spread. Ventral flow through the ventral sacral foramen is often seen and can be extensive (see Fig. 35-2, C). Although an AP image is often obtained, the flow of contrast is usually better appreciated in the lateral view as is unintentional dural puncture. If appropriate spread of contrast is appreciated, the corticosteroid preparation with normal saline, 3 to 5 mL total is injected. Three milliliters of injectate will reach the L5-S1 disc level in approximately 80% of the injections (see Fig. 35-2, D). Larger volumes provide little added benefit. The extra epidural flow, as noted earlier, can severely limit the volume of active injectate actually reaching the pain generator (Fig. 35-3). Images documenting needle position prior to injection, and verifying contrast pattern and extent of coverage, must be saved for the medical record.

Figure 35-2 Lateral view of the sacrum. A, Digital subtraction imaging (DSI) at start of contrast injection. B, DSI at conclusion of contrast injection. Open arrows indicate extent of contrast within caudal canal. Black arrows indicate contrast flow through S2 and S4 ventral foramen. C, Lateral view at conclusion of contrast injection. Open arrows indicate extent of contrast within caudal canal. Solid arrows indicate contrast flow through S2 and S4 ventral foramen. D, Lateral view lumbosacral junction. Contrast is seen up to the L5 pedicle.

Figure 35-3 Anterior-posterior (AP) view of lumbosacral junction. Note partially sacralized L5 vertebral body on left. White arrows indicate extent of contrast within caudal canal. Black arrows indicate contrast flow through S1, S2, and S4 ventral foramen.

Lumbar Interlaminar

Because lumbar interlaminar (i.e., between the lamina) epidural injections place the active injectate closer to the area of pathology, they must be considered somewhat more selective than caudal administration of corticosteroids. These injections are often mislabeled as “translaminar,” that is, through the lamina. The needle is placed into the epidural space via a posterior approach, through the interlaminar space, and ligamentum flavum, but stopped prior to dural puncture. Injection is made into the dorsal epidural space (Fig. 35-4).

Figure 35-4 A, MRI axial T1 WI at L4-5. Arrow indicates needle track into epidural space. B, MRI sagittal T2 WI with arrows pointing to epidural space at L4-5 and L5-S1.

Interlaminar lumbar epidural injections of corticosteroid are the most often performed interventional pain procedure, even though their efficacy is questioned by many practitioners who are intimately involved with the discipline. Although most physicians within the specialty have patients who claim relief from these injections, interlaminar injections might be considered as “frequently performed procedures of unvalidated value.” However, interlaminar epidural injections performed with the use of fluoroscopy and targeted to level and side of pathology cannot be considered equivalent to the blind, nonvalidated injections of yore.

The patient is positioned prone, with a pillow under the abdomen to decrease the anatomic lordotic curve. Often with obese patients, the large abdomen will provide the proper anatomic position without additional padding. Placing the patient in sitting position where a fluoroscope is used in lateral view only, provides no benefit, has technical limitations, must be considered a bastardization of the technique taught to anesthesia residents, and indicates lack of training, understanding, and proficiency with the use of a fluoroscope for spinal injections. Although one wishes to place the needle in proximity to the underlying pathology, injectate of even a small volume will spread over several levels. Injectate placed within the epidural space in the midline dorsal position, will take the path of least resistance and may never reach the ventral aspect of the epidural space where the pain generator in the form of disc deformity or stenosis is found. However, if placement of the needle toward the side of complaint/pathology, and bevel control is used, contrast can be seen flowing to the ventral aspect of the epidural space and the intervertebral foramen, and the nerve root canals can be clearly identified.

Following appropriate positioning, the lumbosacral region is prepared and draped sterilely. The fluoroscope is used to examine the lumbar spine. Segmental anomalies such as sacralized L5 vertebral bodies, or nonsacralization of S1 should be noted and detailed on the procedure note. The targeted interlaminar space is then identified in an AP view (Fig. 35-5, A) caudal to the pathology unless a far lateral needle placement is contemplated. Because the majority of pathology is seen in the two lower lumbar levels, the L5-S1 and L4-5 interlaminar spaces are the most frequent targets. Cephalocaudal tilt results in the interlaminar space being seen at its maximum size, whereas a slight ipsilateral oblique view often provides easier access. When adequate visualization is obtained, the skin over the target is marked (see Fig. 35-5, B). Local anesthetic can then be injected (see Fig. 35-5, C) and the epidural procedure needle advanced. At this point, tactile feel is of utmost importance and can only be taught using “hands on” instruction in living subjects. The needle is felt to transverse through the various tissue layers until a midprocedure position is noted; resistance to needle advancement is noted secondary to contact with the ligamentum flavum (see Figs. 35-5, D and Fig. 35-6, A). Although some experienced practitioners make a point of contacting os on the superior aspect of the lamina caudal to the targeted space, the feel of contact with ligamentum flavum, is as distinct as this boney target. If contact with bone was sought, and contact was made, the needle is slightly withdrawn, redirected, and advanced until the distinct resistance of ligamentum flavum is noted. At times, insistence on contacting os prevents targeting a specific area of the interlaminar space. If os is not touched, the ligamentum flavum is engaged directly. Using a loss of resistance (LOR) technique with either constant pressure on the plunger of a glass/plastic LOR syringe with normal saline or short interval, light intermittent pressure with an air-filled LOR syringe, the needle is advanced. A very obvious loss of resistance to the saline or air is noted as the needle aperture exits the ventral aspect of the ligamentum flavum and enters the epidural space. At the present time, hanging drop and Macintosh balloons must be considered passé and of historical interest only. A lateral view can now be used to indicate needle depth (see Fig. 35-6, B) if necessary. However, if the needle is not placed in the exact midline, or a “true lateral” is not used, depth as noted by visual clues can be faulty due to the tangential imaging. No specific bony landmarks are available to verify needle tip entry into the epidural space. Special care must be taken when working above the L2-3 level because the spinal cord must be considered.

Figure 35-5 Anteroposterior (AP) image at lumbosacral junction. A, L5-S1 interlaminar space indicated by arrows. Note end plates of the L5-S1 disc are not parallel to beam to maximize interlaminar space (i.e., the target). B, Pointer indicates site of skin entry over target. C, Track of local anesthetic injected as a 25-gauge, 1.5-inch needle is withdrawn. D, 18-gauge epidural needle meeting resistance from ligamentum flavum.

Figure 35-6 Lateral image at lumbosacral junction. A, Needle is touching ligamentum flavum as noted by resistance to further advancement. Arrow indicates needle tip. B, Needle has been advanced through ligamentum flavum with loss of resistance to saline noted as tip (arrow) enters epidural space.

Aspiration, at this point, should evidence no or very minimal, clear or lightly blood-tinged fluid. As noted earlier, with the use of small needles, CSF return is not a reliable indicator of intrathecal needle placement. Images to document placement in AP, and possibly lateral views are obtained (see Figs. 35-6, B and 35-7, A). Injection of contrast, under active fluoroscopy in AP view is now performed to ensure needle position by contrast pattern (see Fig. 35-7, B-F). A nonhomogeneous, vacuolated pattern is apparent with epidural injection versus the homogeneous pattern noted with injection into the CSF. Although an AP view may make noting an intrathecal injection difficult, vascular uptake will be obvious because these structures are perpendicular to the needle, and visualization is transient owing to flow within the structure. A lateral view is now used to rule out intrathecal or subdural patterns and verify epidural spread of contrast in the dorsal epidural space (Fig. 35-8). Subdural injections between the dural and arachnoid layers will be cystic with clearly delineated margins. Subarachnoid injections of contrast in the lateral view will layer out in the ventral intrathecal space because it is heavier than CSF. Subdural injections mandate withdrawal of the needle dorsal to the liga-mentum flavum and reinserting toward a different target with LOR once again appreciated. If dural puncture is noted with an intrathecal pattern, the procedure can be attempted at an adjacent level or abandoned for that day.

Figure 35-7 Anteroposterior (AP) image at lumbosacral junction during injection of contrast. A, Needle is positioned in epidural space prior to injection of contrast. B, Digital subtraction imaging (DSI) at start of contrast injection. C, DSI at midinjection. Note development of nonhomogeneous, vacuolated pattern typical of epidural spread. D, Toward end of contrast injection. Note midline, spreading, nonhomogeneous, vacuolated pattern typical of epidural contrast. E, DSI and F, plain fluoroscopy, at end of contrast injection approximately 2.5 mL of contrast. Note midline, nonhomogeneous, vacuolated pattern typical of epidural spread. S1 nerve canals clearly identified, solid black arrows. Contrast beginning to outline the right L5 nerve root canal, open arrows, White arrows indicate rostral spread of contrast.

Figure 35-8 Lateral image at lumbosacral junction at end of contrast injection. Note spread in dorsal epidural space with minimal contrast identified ventrally. L5 and S1 segmental nerves identified, black arrows, White arrows denote spread of contrast between L4 and S1 emphasizing the nonselective nature of interlaminar injections.

After validation of epidural injection is obtained and images are saved, the physician can now proceed with the injection of corticosteroid in a total volume of 2 to 4 mL. Larger volumes will result in wider dispersion of a less concentrated mixture, neither of which factors is beneficial if a specific pathology has been targeted. A so-called “washout” or postinjection film can be saved to document final dispersion of material within the epidural space (Fig. 35-9).

Figure 35-9 Anteroposterior (AP) “washout” image at lumbosacral junction after injection of 3 mL corticosteroid and normal saline. L5 and S1 segmental nerves identified (black arrows). Spread of contrast between L4 and S2 emphasizing the nonselective nature of interlaminar injections (white arrows).

Because one is often treating a unilateral, or one side dominant, pain complaint, one of the authors (ML) targets the side of pathology/symptomatology. Fig. 35-10) illustrates this alternative approach where flow into the ventral epidural space and segmental nerve canals is routinely observed with a proposed increase in efficacy.

Figure 35-10 AP image at lumbosacral junction. A, Needle is in epidural space as noted by loss of resistance to saline. Note far lateral needle placement under lamina. B, Digital subtraction imaging (DSI) and C, plain fluoroscopic images of the lumbosacral junction at completion of contrast injection. Right unilateral epidural contrast pattern with L5 and S1 segmental nerve canals clearly identified (black arrows). D, Lateral “washout” image at lumbosacral junction following contrast and 3 mL injection of corticosteroid and normal saline. Contrast is clearly evident in the ventral epidural space and L4, L5, and S1 segmental nerves are identified (arrows).

Normal saline or local anesthetic can be used as the diluents with corticosteroid, realizing that local anesthetic provides no diagnostic information and adds significantly to the morbidity profile without added therapeutic value and requires a lengthier postprocedure monitoring period. Because no arterial structures are present in the epidural space that could lead to catastrophic complications, a particulate corticosteroid is not contraindicated for this procedure. Mild transient low back pressure or a mild transient pressure paresthesia may be experienced by the patient. This is often concordant with the patient’s usual pain complaint and does not require discontinuance of the procedure, unless the pain is severe.

Thoracic Interlaminar

The thoracic interlaminar technique involves additional risks because the spinal cord lies millimeters ventral to the ligamentum flavum. In addition, the dorsal epidural space is narrower than in the lumbar region (Fig. 35-11). This procedure should not be attempted by any physician who has not had extensive training and experience working in the lumbar region.

Figure 35-11 MRI thoracic spine axial T2 WI. Arrow indicates dorsal epidural space.

As with all interlaminar injections, the patient is best placed in a prone position and an appropriate sterile preparation of the skin and draping at the proposed skin entry site are completed. Because the lamina of the thoracic spine resemble overlapping shingles on a roof, excellent visualization of the interlaminar space is often impossible. Anatomically, the interlaminar space will always be found ventral to the spinous process of the rostral level. Using the fluoroscope, the targeted interlaminar space is identified and optimum visualization is obtained using cephalocaudal tilt of the image intensifier (Fig. 35-12, A). A paramedical approach is advocated because the orientation of the lamina and spinous process often makes a midline approach difficult, especially if any degree of rotoscoliosis is present. This becomes quite evident in the midthoracic region, T4-10.

Figure 35-12 AP image of thoracic spine. A, T10-11 interlaminar space is noted by dark arrowB, Pointer marking needle skin entry for T10-11 interlaminar epidural needle placement, paramedian and one level below target. C, Loss of resistance has indicated needle tip as having entered the epidural space. Arrow indicates position of needle tip when lamina first contacted. D, Lateral image of thoracic spine. LOR has indicated needle tip as having entered the epidural space. Note tip of needle appears dorsal to posterior elements (double-headed arrow), indicating that tactile information and experience alone, versus visual clues, are of paramount importance in the performance of this injection.

Using an AP orientation with caudal tilt of the image intensifier, the skin entry point is marked, slightly more than one level below the target and lateral to midline (see Fig. 35-12, B). Therefore if the T10-11 interspace is targeted, the skin entry would be over the T12 lamina. A local anesthetic track toward the lamina above is completed to a depth of ~1.5 inches. The epidural needle is advanced toward the targeted midline interlaminar space and os is contacted over the lamina (T11) of the vertebra just caudal and lateral to the target (see Fig. 35-12, C). The needle is then slightly withdrawn and advanced slowly toward the spinous process rostral to the target (T10). The distinctive resistance of the ligamentum flavum will be noted and advancement of the needle is halted. A lateral view may be obtained at this point and the needle tip will be noted lying dorsal to the epidural space. Using the LOR technique as described earlier, the needle is advanced slowly through the ligamentum flavum.

It is important to realize that the anatomy of the thoracic spine differs from that of the lumbar spine in that the transverse processes angle to a greater extent dorsally, and the superior articular processes (SAP) lie ventral to their anatomic position in the lumbar spine. The needle, when within the dorsal thoracic epidural space, will appear dorsal to the lamina and SAP (see Fig. 35-12, D). Images precontrast, AP, and lateral, to document needle position are archived. After negative aspiration for CSF and blood, contrast is injected and flow is verified in the dorsal epidural space (Figs. 35-13 and 35-14). Because of the narrowness of the epidural space in the thoracic spine, spread of a small volume of contrast can be extensive with 2 to 3 mL covering greater than five levels with flow to the ventral spinal canal being minimal (see Fig. 35-14).

Figure 35-13 AP images of thoracic spine with needle in epidural space. A, Plain fluoroscopic image prior to contrast injection. B-D, Sequential series of digital subtraction imaging (DSI) during contrast injection. Note wide spread of contrast and vacuolated epidural pattern typical of a thoracic epidural injection. B, Beginning of contrast injection, volume ~0.75 mL. C, Midinjection. Volume ~1.75 mL. D, End of contrast injection, volume ~2.5 mL. Note wide spread of contrast (arrows) and vacuolated epidural pattern typical of a thoracic epidural injection. E, Plain x-ray image at end of injection. Approximate volume 2.5 mL. Note wide spread of contrast (arrows), and vacuolated epidural pattern typical of a thoracic epidural injection.

Figure 35-14 Lateral image of thoracic spine at end of injection. Approximate volume 2.5 mL. Note dorsal epidural pattern and wide spread of contrast (arrows) covering levels typical of a thoracic epidural injection.

When epidural placement of the needle is verified, the corticosteroid of choice can be injected using a diluent of either normal saline or local anesthetic. Volumes of greater than 3 mL are rarely required. Mild, transient dorsal pressure is often experienced by the patient. As with any injection into the epidural space, no validated positive diagnostic value can be ascertained whether or not local anesthetic is used.

Cervical Interlaminar

…one forgets the tiger heart that pants beneath it; and would not willingly remember, that this velvet paw but conceals a remorseless fang.

Herman Melville

Interlaminar injections may appear elementary in the hands of an expert, but significant morbidity and mortality has occurred when the inexperienced injectionist has not heeded the aforementioned advice. Access to the cervical epidural space via the transflaval approach can be accomplished safely if quality instruction is received, proper technique is used, care and vigilance is practiced, and significant, extensive experience at other levels is obtained prior to attempt of this seemingly easy procedure. The cervical epidural space is narrow, 3 to 5 mm, and the tactile clues differ significantly from the lumbar or thoracic levels. The anatomy is unique especially in regard to the dorsal angle of the laminae, presenting imaging uncertainty when assessing depth within the central canal. In patients with short necks or large body habitus the shoulders may prevent adequate lateral visualization at C7-T1 or even C6-7. In addition to the anatomic variation, knowing that only millimeters separates an injection into the dorsal epidural space from penetration of, and injection into the spinal cord, creates an apprehension knowing that death or quadriplegia can easily result from a slight needle misadventure.

Prior to any placement of a needle into the cervical canal, a recent high quality MRI or CT scan must be evaluated by the physician planning the injection (Fig. 35-15). Canal diameter must be assessed prior to the injection to ensure adequate space within the epidural space. The epidural space must be assessed to see if an interlaminar injection can be performed safely. The normal diameter of the spinal canal is 12.5 mm or greater, with a cord diameter of ~9 mm. Cerebral spinal fluid (CSF) should be identified surrounding the cord on axial views. An AP diameter of less than 11 mm is considered to be relative spinal stenosis, whether congenital (i.e., owing to short pedicles) or secondary to acquired pathology (i.e., disc protrusion or spondylosis). An AP diameter of less than 10 mm is significant and placement of a needle at any level with this degree of compromise, is questionable, especially if no epidural fat is noted dorsally on imaging.

Figure 35-15 A, MRI sagittal T2 WI at midline. Note minimal epidural space at C6-7 (black arrow); increasing at C7-T1(white arrow); “large” at T2-3 (open arrow). A small protrusion is noted at C6-7. B. MRI axial T2 WI at C7-T1. Black arrow points to the epidural space. Double headed arrow indicates an adequate sagittal spinal canal diameter with cerebrospinal fluid (CSF) noted surrounding the cord.

Because the dorsal epidural space thins markedly above C6, interlaminar injections above the C6-7 level are never appropriate and pose an undue risk to the patient. Dr. Richard Derby, an outstanding, experienced, and well known interventional pain physician from an anesthesia background, stated that, “a cervical epidural injection rarely should be performed above C7-T1.”¹¹⁹ Because the most common levels of pathology occur at C5-6 or C6-7, this makes the C7-T1 interlaminar spaces ideal to target. If pathology, anatomy, or postsurgical changes necessitate, the T1-2 interlaminar space can be chosen. In a series of patients by one of the authors (CA), CT scan approximately 15 minutes post-interlaminar injection, using small volumes at the lower cervicothoracic junction, has shown contrast covering the entire cervical epidural space. Therefore, precision of level might be a moot point and of little significance regarding cervical interlaminar injections.

The patient is placed in the prone position with the neck slightly flexed. The posterior upper dorsal and cervical regions are prepped and draped in a sterile manner. The AP fluoroscopic view is obtained (Fig. 35-16, A) and the targeted interlaminar space identified. Using cephalocaudal tilt, the image intensifier is positioned to maximize the interlaminar space (see Fig. 35-16, B).

Figure 35-16 A, Scout AP view cervicothoracic spine. B, Slight right oblique view cervicothoracic spine. Arrow indicates maximized C6-7 interlaminar space.

In most cases, a slight paramedian approach provides the easiest access, and a slight ipsilateral oblique view may be helpful. Some practitioners advocate a midline approach, perpendicular to the ligamentum flavum and the dorsal dura. However, the feel of the needle contacting and traversing the ligamentum flavum is an important technical aspect of this procedure. Because the resistance noted by contact with the ligamentum flavum is correlated to the distance traversed through it, this resistance is increased when entering at any decreasing angle from perpendicular to this structure. In addition, needle contact with the dura at a 90-degree angle is more apt to result in trespass into the intrathecal space, with subarachnoid injection, or cord penetration. Dural contact at a less acute angle would be expected to distort or “tent” the dura without penetration, with fewer expected cases of intrathecal encroachment. The LOR technique with saline will increase this “dural tenting” because a low-volume stream of pressurized saline will be injected into the potential epidural space before extensive needle entry, distorting the dura and providing some additional space and margin of safety. Therefore, a paramedian approach (Fig. 35-17) with a LOR technique with saline, might be considered a safer alternative.

Figure 35-17 MRI axial T2 WI at C7-T1. A needle path from a left paramedian approach to midline (black solid arrow) if inadvertently advanced will puncture the dura and enter the spinal cord. However, a needle targeting a lateral target within the epidural space (white broken arrow) will possibly miss the cord if overly advanced and may never puncture dura.

Using the paramedian approach, a point on the skin is marked lateral to midline over the superior lamina of the level below (Fig. 35-18, A) and local anesthetic is injected (see Fig. 35-18, B). Care must be used because the average depth from skin to epidural space at C6-7 and C7-T1 is 57 mm (2.25 inches) and 54 mm (2.12 inches) at T1-2¹²⁰, in an exceedingly slender person a 1.5 inch needle might be long enough to reach the spinal canal with intrathecal injection of local anesthetic resulting in a “high spinal block,” or spinal cord injection. The epidural needle is then advanced through the anesthetized tissue toward one of two endpoints. Many practitioners advocate contact with the most rostral aspect of the lamina to provide a reliable measure of depth (see Fig. 35-18, C). However, if this bony contact cue is missed due to imaging uncertainty or inexperience, the injectionist while expecting this firm contact with os, might unknowlingly advance the needle through the ligamentum flavum, dura, and into the spinal cord. When os is contacted, a lateral view can be obtained and depth can be verified as dorsal to the spinolaminar line. The needle is then slightly withdrawn, redirected to slide off os, and the ligamentum flavum is contacted. A more experienced physician, who has gained a tactile sense of the needle passing through distinctive tissue layers, may omit the touching of the lamina and advance the needle directly toward the interlaminar space until the distinct feel of the ligamentum flavum is noted.

Figure 35-18 A-D, Slight ipsilateral oblique view cervical spine. C6-7 interlaminar space maximized. A, Pointer on skin over target indicating rostral aspect of the C7 lamina caudal and slightly lateral to interlaminar space. B, Needle placement for local anesthetic injection. C, Epidural needle advanced and touching lamina below and lateral to interlaminar space target. D, Needle through ligamentum flavum, verified by loss of resistance to saline and air. Negative aspiration for cerebrospinal fluid (CSF) and blood. E, AP view cervical spine. Needle in epidural space at dorsal midline. F, Not true lateral view cervical spine. Note margins of neural arch not aligned (arrows). Needle appears somewhat ventral to spinolaminar line (broken line) due to suboptimal imaging. Compare to Figure 35-21, A.

When the ligamentum flavum is contacted, the LOR syringe is attached and the needle is slowly advanced until loss of resistance with saline or air, as described earlier, is noted (see Fig. 35-18, D). A quasi feel of loss of resistance is often present in the cervical spine as the needle transverses the tissue between the interspinous ligament and ligamentum flavum, and only experience may be able to differentiate this from the “true” loss of resistance as one enters the epidural space. In addition, a false loss of resistance can also be appreciated when in close proximity to periosteum prior to the tactile sensation of laminar os being contacted. When the needle has traversed the ligamentum flavum and is in the epidural space (see Fig. 35-18, E) aspiration should be negative for CSF and blood. If CSF is noted, the needle must be withdrawn and either epidural placement attempted at a different level or, possibly a better option, the procedure discontinued and the patient discharged to return at a future date. If frank blood is noted, the needle is withdrawn dorsal to the ligamentum flavum is redirected, and loss of resistance is once again sought at a slightly different area.

Although a true lateral view with identification of the needle at the spinolaminar line has been advocated to verify depth prior to injection of contrast, this technique can be fraught with misleading information (see Fig. 35-18, F). A single lateral view is not sufficient to gauge depth because the laminae in the cervical spine are not orthogonal, perpendicular to the x-ray beam; they slope at approximately 45 degrees (see Fig. 35-19). Lateral images are further distorted secondary to the displacement of the needle tip from midline. For every aberration, the lateral image becomes progressively less valid. To exactly calculate needle tip position, the AP view provides information about the rostral-caudal and medial-lateral placement, whereas a tangential image through the lamina opposite which the tip of the needle lies (i.e., the contralateral oblique view) delineates needle depth—although being dependent on the precise degree of obliquity can be deceptive as to the reality of needle tip position. Exact knowledge of needle placement requires tactile clues as to tissues penetrated, multiple fluoroscopic views, and the training, experience, and expertise to evaluate each unique situation. Unlike many other injections, two views, AP and lateral, do not always provide sufficient information to accurately place the tip of the needle in a safe position. All images indicating that the needle is in a safe final position, prior to contrast injection, are archived.

Figure 35-19 MRI axial T2 WI at C7-T1. Solid white lines indicate ~45-degree orientation of the cervical lamina. The solid black arrow represents a needle within the epidural space to the right of midline. White broken lines represent a true lateral fluoroscopic view. Black broken lines represent a contralateral, left, oblique fluoroscopic view. Note distance between the most dorsal epidural space (black dot) and the needle tip.

When access to the epidural space is evidenced through the use of LOR and possibly by imaging, contrast is injected under active fluoroscopy (see Figs. 35-20 to 35-23) in a volume that will ensure that the injection is being made within the epidural space, and that intrathecal, subdural, and vascular flow are absent. A volume of 2 to 3 mL is usually adequate. Images of contrast verifying safe needle position and appropriate contrast flow are saved for the historical record. Verification of needle position with contrast is followed by injection of the active pharmaceutical compound, corticosteroid. Diluents of either normal saline or low concentration local anesthetic can be used safely with the understanding that neither has a therapeutic or diagnostic role and local anesthetic can be assumed to have a higher morbidity profile.

Figure 35-20 Series of AP view cervical spine. A, Needle in epidural space prior to contrast injection. B-E, Sequential digital subtraction imaging (DSI) during contrast injection. B, Early in injection. C, Early midinjection. D, Later at midinjection. E, Contrast with bilateral spread. Note nonhomogeneous vacuolated pattern consistent with epidural injection. F, Fluoroscopic image at end of contrast injection, ~2.5 mL. Contrast evidences bilateral spread. Note nonhomogeneous vacuolated pattern consistent with epidural injection. G, AP view cervical spine with intervertebral disc end plates squared. Image at end of contrast injection, ~2.5 mL. Note nonhomogeneous vacuolated pattern consistent with epidural injection. Spread of contrast is bilateral and extends between C5 and T1 (arrows).

Figure 35-21 A,True lateral view cervical spine. Compare with figure 35-18, F. Note needle tip at spinolaminar line (arrow). Image at end of contrast injection, ~2.5 mL. Note nonhomogeneous vacuolated pattern at spinolaminar line consistent with dorsal epidural injection. Spread of contrast is seen ventrally and extends rostral to C4-5. B, Oblique view cervical. Note needle tip at spinolaminar line. Image at end of contrast injection, ~2.5 mL. Note nonhomogeneous vacuolated pattern at spinolaminar line consistent with dorsal epidural injection. This view is often required when body habitus prevents adequate lateral imaging of the lower cervical levels.

As in the lumbar region, the patients chief complaint, and index pain is often unilateral or one-side dominant. Again, one of the authors (ML) feels compelled to target the side of pathology/symptomatology, especially when as noted, a less than perpendicular approach to the epidural space may provide a margin of safety as the anatomy in Figure 35-17 indicates. Figs. 35-22 and 35-23illustrate this alternative approach where flow into the ventral epidural space and segmental nerve canals is routinely observed with a theoretical increase in efficacy.

Figure 35-22 Needle in position at C7-T1 following penetration of the ligamentum flavum evidenced by loss of resistance. Far left lateral targeted interlaminar epidural injection. A, AP view. Note needle under the left medial laminar border. B, Lateral view. Note needle tip (arrow) appears to have passed through the spinal canal illustrated by broken lines. Suboptimal image secondary to patient body habitus. C, Right oblique view (i.e., contralateral to needle tip position). Tip of needle (arrow), is positioned at the left ventral laminar line. Lamina (L). D, Left oblique view (i.e., ipsilateral to needle tip [arrow]). Note that needle appears to have transversed the spinal canal and is ventral to the right ventral laminar line.

Figure 35-23 Cervical spine after injection of contrast, ~2.5 mL, at C7-T1. A, AP view. Note essentially unilateral, vacuolated contrast pattern extending from C5 to T2. Flow of contrast into spinal nerve canals is present (broken arrows). Compare to Figure 35-22, AB, Lateral view. Suboptimal image secondary to patient body habitus. Note wide contrast column, not confined to the dorsal epidural space, indicating spread of contrast into the lateral and ventral epidural space covering the proposed pathology. Compare to Figure 35-22, BC, Right oblique view (i.e., contralateral to needle tip position). Note contrast clearly in the dorsal epidural space ventral to the spino-laminar line. Compare to Figure 35-22, CD, Left oblique view (i.e., ipsilateral to needle tip). Note marked vacuolated epidural pattern (solid arrows). When the image is corrected for obliquity, the tubular structure, indicated by open arrows, would be situated over left uncinate line and is consistent with spread of contrast around the vertebral artery, indicating that the injectate is covering the ventral lateral recess, vertebral foramen, and neural contents. Compare to Figure 35-22, D.

During injection, it is common for the patient to note some neck pain as well as transient, mild pressure paresthesia into the upper extremity, in addition to a feeling of “warmth” and “pressure,” in the chest. These symptoms do not necessitate discontinuing the injection unless they are severe.

Transforaminal Injections versus Selective Spinal Nerve Blocks

Corticosteroids placed into the epidural space via the intervertebral foramina are often described as selective spinal nerve blocks. This is a gross misunderstanding of the anatomy involved and the rationale behind the procedure. The target of the injection is the pain generator, known in the case of radicular pain to be the dorsal root ganglion (DRG), and the associated pathology being deformity of the outer intervertebral disc margin (i.e., protrusion, extrusion, sequestration, or spinal stenosis.) These pathologies usually involve the medial aspect of the foramen and/or spinal canal. Therefore, for the active injectate to be of benefit, it must flow through the foramen into the epidural space. Corticosteroids are antiinflamatory medications and the intent is not to “block” neural transmission. The local anesthetic, neural blocker, often used as part of the injection is not therapeutic and is merely “along for the ride,” although it might provide negative diagnostic information, and validate the corticosteroid as having been placed in close proximity to the pain generator. The fact that epidural spread is desired (whether or not local anesthetic is used) invalidates the concept of “selective” because any medication placed within the epidural space is in contact with multiple neural structures and is, by definition, nonselective. Even the concept of a “selective epidural” must be considered a gross misrepresentation of the procedure and a failure to understand the pertinent anatomy.

Selective spinal nerve blocks (SSNB), are injections into the foramen, with an extremely small volume, 0.3 to 0.5 mL, of concentrated local anesthetic (e.g., lidocaine 4%). They are at best a “quasidiagnostic procedure” which is neither selective nor validated as diagnostic. If limited to the foramen, questions about the level of symptomatology might be addressed. Because neural structures within the intervertebral foramen include the dorsal root ganglion, spinal nerve, dorsal ramus, medial branch, intermediate branch, lateral branch, ventral ramus, sinuvertebral nerve, and gray ramus communicans, local anesthetic limited to the foramen can hardly be called “selective” in any sense of the word, and is of limited positive diagnostic use.

S1 Transforaminal Corticosteroid Injection Technique

Of the lumbar intervertebral discs, L5-S1 is the second most common to suffer from protrusion, or extrusion, often with S1 segmental nerve involvement. Therefore, instillation of corticosteroid around the S1 DRG is a procedure frequently employed by the interventional pain physician and constitutes one of the core procedures of our specialty. This injection requires placing a needle through the dorsal foramen of S1, thereby accessing the S1 nerve canal.

The patient is placed in a prone position. The lower lumbar and sacral areas are prepared and draped as detailed previously. Using an AP view, the fluoroscope is oriented to identify the area just caudal to the S1 pedicle on the symptomatic side (Fig. 35-24, A). The superior end plate of S1 is squared (see Fig. 35-24, B) and a slight ipsilateral obliquity is used until the dorsal foramen is visualized directly caudal to the S1 pedicle and medial to the lateral wall of the S1 nerve canal (Fig. 35-24). The target should be seen as distinct from and slightly rostral to the larger, and often more obvious, S1 ventral foramen (see Fig. 35-25, A and B).

Figure 35-24 AP image at lumbosacral junction. A, Superior end plate of S1 is not parallel to beam. B, Superior end plate of S1 parallel to x-ray beam (black arrow). Lateral wall of the left S1 nerve canal is identified by white arrows.

Figure 35-25 Ipsilateral oblique view, 5 to 10 degrees, of the lumbosacral junction. A, Lateral wall of the S1 nerve canal labeled with white arrows. Dorsal foramen, DF1, and ventral foramen, VF1 of S1 outlined by black line. Dorsal, DF2, and ventral, VF2, foramen of S2 indicated by white broken linesB, Identical unlabeled image for comparison.

The skin entry point is marked over, or just caudal to the target, Fig. 35-26, A, and if desired local anesthetic injected. A 25- or 22-gauge spinal needle is then advanced toward the lateral-caudal aspect of the foramen (Fig. 35-26, B), just medial to the lateral nerve canal wall in that the course of the S1 segmental nerve is medial (see Fig. 35-26, B). Slight reduction in resistance to needle insertion will be felt as the needle enters the foramen. As the needle is advanced, it may contact the lateral wall of the nerve canal or the dorsal aspect of the S1 vertebral body (i.e., the ventral canal). The bent needle technique will allow continued precise advancement. A lateral view is used to note appropriate depth with the needle tip lying between the lamina and anterior canal (see Fig. 35-26, C). At this point, AP and lateral images are saved for the permanent medical record to document needle position prior to injection of contrast.

Figure 35-26 Ipsilateral oblique view, 5 to 10 degrees, of the lumbosacral junction. A, Pointer on skin indicating needle insertion point. Black circle represents needle target at the lateral rostral aspect of the S1 dorsal foramen. B, Needle is positioned within the S1 nerve canal. C, Lateral view of the lumbosacral junction. A needle is seen within the S1 nerve canal with its tip (black arrow) close to the ventral canal wall (white arrows).

Using an AP view, contrast is injected slowly under active fluoroscopy, with DSI if available (Fig. 35-27, A-F). The contrast should be flow proximally toward the L5-S1 intervertebral disc without significant vascular uptake. Although medullary arteries are not seen at this level,¹²¹ retrograde venous filling toward the conus might be appreciated and would necessitate repositioning of the needle. If the majority of contrast is noted to travel distally through the ventral foramen, the needle should be repositioned until contrast is covers the targeted structure. A lateral view then demonstrates filling of the S1 nerve canal with minimal contrast flowing out of the ventral foramen (see Fig. 35-27, G).

Figure 35-27 Ipsilateral oblique view of 5 to 10 degrees. A, Plain fluorography image preinjection of contrast. B-E, Sequential digital subtraction imaging (DSI) during injection of contrast. No vascular pattern is noted flowing toward, and stopping at, the midline in the area designated by the oval. B, DSI at start of injection, ~ 0.1 mL. C, DSI, volume of injection ~ 0.5 mL. D, DSI, volume of injection ~1.0 mL. E, DSI and end of injection ~1.75 mL. F, AP fluoroscopic image following contrast injection. Cephalad contrast flow noted to the L5-S1 disc level (arrow). G, Lateral image following contrast injection. Contrast flow noted to the L5-S1 disc level (black arrow). Note contrast flow filling the S1 nerve canal and flowing through the ventral foramen (white arrows).

Corticosteroid can now be injected with normal saline or local anesthetic. Because particulate corticosteroids have had catastrophic consequences when injected within a neural foramina, solutions are preferable (i.e., dexamethasone 10 to 15 mg). A total volume of 1.5 to 2.0 mL is usually adequate to cover the targeted area. Appropriate volume can be estimated by the previous flow of contrast. When the corticosteroid is mixed with lidocaine (Xylocaine) 4%, a concentration that can be depended on to provide sensory blockade is obtained, which can validate that the pain generator was addressed and provide negative diagnostic information.

Lumbar Transforaminal

Injection into the lumbar intervertebral foramen with corticosteroid for radicular pain is of known therapeutic value. Because the L4-5 intervertebral disc is most susceptible to injury, the most common level for this procedure is the L5-S1 foramen, covering the L5 dorsal root ganglion and segmental nerve. Segmental anomalies of sacralized L5 or nonsacralized S1 vertebral bodies occur in approximately 15% of patients, and care must be taken to ensure the correct level is being injected. The targeted foramen can be identified in an AP image by being bounded in a cephalocaudal orientation by the pedicle above and below, and medial to lateral by the medial and lateral pedicular lines. For the majority of cases, positioning of the needle in a subpedicular position, and in the middle foramen in the dorsal-ventral orientation, is safe, and distances the needle tip from the possible position of the medullary artery (i.e., artery of Adamkiewicz, as discussed earlier). A so-called “retroneural” positioning of the needle has been described¹²²; however, this technique can be considered a slight variant of the standard technique. Occasionally, because of marked degenerative changes, no access to the foramen is available via the subpedicular approach. In this case, an alternative infraneural technique can be used that targets the caudal ventral aspect of the foramen, and will be described following the standard approach.

The patient is placed in prone position with a pillow under the lower abdomen to decrease the lumbar lordotic curve. After a sterile preparation and draping of the skin at the injection site, the fluoroscope is positioned to obtain an AP view with the pedicle shadow bounding the upper aspect of the targeted foramen, in the center of the fluoroscope monitor (Fig. 35-28, A). As in the majority of spinal injections, to obtain a true AP image, cephalocaudal tilt of the image intensifier is used so that the vertebral end plate closest to the target is “squared,” (i.e., the x-ray beam is parallel to the end plate, which appears as a solid line rather than an ovoid structure). In the case of an L5-S1 transforaminal injection this would be the inferior end plate of L5 (see Fig. 35-28, B), for an L4-5 transforaminal injection the inferior end plate of L4, and so on.

Figure 35-28 AP image at lumbosacral junction. A, Note the superior end plate of S1 is not parallel to the x-ray beam. B, Inferior end plate of L5, closest to target, is parallel to x-ray beam indicating a true AP view. C, Left oblique view. Note that the SAP of S1 appears to lie under the 6:00 o’clock position of the L5 pedicle. Circle represents needle target. D, Left oblique view. A 25-gauge, 3.5-inch Quincke pointed spinal needle is seen having been advanced into the L5-S1 foramen caudal to the 6:00 o’clock position on the pedicle. E, MRI subpedicular axial L4-5 T1 WI. Representation of needle insertion into the left midforamen. F, Lateral view of the lumbosacral junction. The tip of the 25-gauge, 3.5-inch spinal needle is seen in a subpedicular position in the midsection of the L5-S1 foramen. Broken white line indicates needle was inserted parallel to the inferior end plate of L5, showing correct initial AP positioning of the C-arm (see Fig. 35-28, B).

An ipsilateral oblique projection is now obtained so that the tip of the superior articular process (SAP) of the level below is positioned under the approximate “6 o’clock” position of the pedicle when seen as a clock face. In the case of the L5-S1 transforaminal injection, the fluoroscope is positioned so that the S1 SAP is seen as positioned under the L5 pedicle (see Fig. 35-28, C). Anatomically, if a needle is now advanced into the subpedicular position, and the tip does not stray medial to the rostral tip of the SAP and 6 o’clock position of the pedicle, the spinal canal is safe from trespass. If desired, a skin wheal can be considered, especially if needles greater than 25 gauge are used. The procedure needle is advanced using a down-the-beam, “tunnel vision,” technique toward the inferior aspect of the pedicle shadow (see Fig. 35-28, D).

In most cases, a needle of 5 inches is needed to enter the L5-S1 foramen due to the greater depth required secondary to the cephalad tilt of the image intensifier, as required to obtain a true AP at this level. As the needle is advanced, the operator needs to be ever conscious of depth—realizing that os will in all probability be contacted, and to prevent further insertion, at one of four structures: the lamina, SAP, transverse process, or vertebral body. If the three former boney structures are contacted, the bent needle can be used to maneuver around them. If the lamina, SAP, and transverse process are passed, tactile clues will indicate passage through the dorsal leaf of the intertransversarii muscles. At this point, a lateral view can be used to verify that the needle has entered the foramen (see Fig. 35-28, F). If the needle is advanced so that the dorsal vertebral body is contacted in the ventral foramen, a lateral view will note this and the needle is withdrawn a few millimeters. An AP view will ensure that the needle has not been excessively advanced medially, past the 6 o’clock position of the pedicle, where entry into the dural root sleeve might be expected (Fig. 35-29, A). Lateral and AP views are saved to document final needle position and provide a permanent record of the procedure (see Figs. 35-28, F and Fig. 35-29, A).

Figure 35-29 AP digital subtraction imaging (DSI) and plain fluoroscopic images prior to, during, and postcontrast injection. A, Precontrast. The needle tip is noted as lying under the 6:00 o’clock position (black arrow) of the L5 pedicle within the “safe triangle”. The segmental nerve (broken lines) courses caudal, medial, and ventral to the needle tip. B-E, Sequential DSI during injection of contrast. Arrows indicate contrast caudal to the pedicle within the L5-S1 foramen and flowing medially into the epidural space. No vascular pattern is noted flowing toward the midline in the area designated by oval. B, DSI image at start of contrast injection, volume ~0.2 mL. C, DSI, ~0.5 mL of contrast injected. D, DSI, ~0.75 mL of contrast injected. E, DSI, at end of injection, ~1.2 mL of contrast. F, AP image after ~1.2 mL of contrast is injected. Contrast is clearly covering the course of the L5 segmental nerve and dorsal root ganglion (DRG). Arrow indicates contrast flow through the foramen into the epidural space. G, Lateral image after ~1.5 mL of contrast is injected. The white arrow notes contrast within the ventral L5-S1 foramen, while the black arrow indicates spread of contrast cephalad to the L4-5 disc level.

An AP view is now used for injection of contrast under active fluoroscopy because the structures that present danger, the medullary artery or retrograde flow to the conus, are perpendicular to the beam and will be well visualized. DSI can be used if available, and the operator has been trained in its use, but is not considered standard of care at this juncture. Contrast should be seen to flow medially through the foramen into the epidural space (see Fig. 35-29, B-F). Contrast will often be seen following the medial border of the pedicle spreading toward the intervertebral disc at the level above. If the majority of contrast is seen to flow laterally along the ventral ramus, it shows that a significant portion of the injectate will not come in contact with the pathology, and pain generator, one wishes to treat. Repositioning of the needle is then recommended. Minimal venous uptake is not a contradiction to completing the procedure. However, if marked venous flow is seen, this necessitates repositioning of the needle and reevaluation with contrast.

Vascular flow of contrast laterally, or to the contralateral side, can be presumed to be venous, whereas flow to the midline, with or without evidence of cephalad extension, must be considered arterial and the procedure must be terminated. Following verification of a safe contrast pattern with AP imaging, a lateral view (see Fig. 35-29, G) will confirm contrast in the targeted foramen, often with spread in the ventral epidural space to the pedicle above. Lateral and AP images with and without contrast are archived to verify that the procedure has been performed as stated, with technical competence, and as a record for any medical legal questions which might arise at a future date.

As noted earlier, because of anatomic variation, such as severe degenerative disc disease with intervertebral disc narrowing or marked osteophytic lesions, subpedicular access to the foramen may be limited. In this case, an infraneural approach to the foramen over the intervertebral disc might be chosen. The end plates at the specific level are squared to the x-ray beam. An ipsilateral oblique view is then obtained so that the SAP of the level below is situated under the approximate midpoint of the inferior end plate of the level above. After the skin infiltrate of local anesthetic, the procedure needle is advanced toward the intervertebral disc, just lateral to the SAP. This technique is analogous to that used to access the intervertebral disc during discography, with advancement halted within the foramen prior to entering the disc annulus. Resistance will be noted as the annulus is contacted and a lateral view obtained to verify needle depth. (Fig. 35-30, B). The needle will be seen lying in the inferior aspect of the foramen, possibly adjacent to the intervertebral disc. An AP view is checked to ensure the needle is within the foramen in a medial-lateral orientation (see Fig. 35-30, B). When the infraneural technique is used, flow around the pedicle will not be seen in many instances. The contrast will be noted to flow through the foramen and spread within the lateral epidural space both in a rostral and caudal direction (see Fig. 35-30, C-G).

Figure 35-30 Transforaminal L4-5 injection using the infraneural approach. A, AP image with needle in position in the caudal foramen. Needle tip (arrow) lies between the lateral and medial pedicular lines (white broken lines), illustrating position within the foramen. The L4 segmental nerve (black broken lines), passes rostral and ventral to the needle (see B). B, Lateral view with needle in place. Needle is noted to be in an infraneural position within the caudal foramen. Segmental nerve is outlined. C-E, AP digital subtraction imaging (DSI) sequence during injection of contrast. C, Image after injection of ~0.25 mL. Contrast (black arrow) is seen within the L4-5 foramen without spread into the epidural space. No flow is evident medial to the medial pedicular line (white broken line) and into the epidural space. D, After injection of ~1.0 mL flow is noted through the L4-5 foramen and into the epidural space. E, End of contrast injection of ~1.75 mL. Contrast is clearly seen flowing through the L4 foramen and into the epidural space. Contrast is also noted in the L5 nerve canal (arrows). F, Plain fluoroscopic image at end of contrast injection of ~1.75 mL. Contrast is clearly seen flowing through the L4-5 foramen, into the epidural space, covering the position of the L4 dorsal root ganglion (DRG) and segmental nerve. Contrast is also noted in the L5 nerve canal (arrows). G, Lateral view at end of injection. Contrast is noted within the L4-5 foramen, covering the segmental nerve and the dorsal root ganglion (DRG).

When the injection of contrast produces a satisfactory pattern, the corticosteroid injectate, preferably as a solution, can be injected with confidence that safety is ensured, and the coverage of the pain generator may provide pain relief. Use of 4% lidocaine (Xylocaine) combined with the corticosteroid solution can provide a final concentration that ensures sensory blockade. As noted, this can afford only negative diagnostic information, but is often a worthwhile addition.

As previously noted, some practitioners have advocated the use of a “test dose” of local anesthetic prior to the corticosteroid injection. From a single reported case study,¹²³ it is theorized that if injection into the medullary artery were to occur, local anesthetic would flow into the anterior spinal artery, thereby anesthetizing the spinal cord and producing temporary motor and sensory deficit. The corticosteroid injection would then be abandoned and any detrimental effects of the corticosteroid injection would be prevented. This chain of suppositions depends on the assumption that a solution of corticosteroid injected into the medullary artery will cause a greater deleterious effect to the spinal cord than a solution of local anesthetic. Cord infarctions with the postulated etiology involving injection into the medullary artery, resulting in cord ischemia in the watershed of the anterior spinal artery, have been reported only with the use of particulate corticosteroid preparations. Therefore, if one limits corticosteroid use in transforaminal injections to solutions, this problem should be preventable. In addition, using a test dose 2 minutes prior to injection of the corticosteroid presumes that the needle tip will not move during this period of time: a questionable supposition.

Thoracic Transforaminal Injections

Fluoroscopic imaging of the thoracic spine lacks the conspicuity of the cervical and lumbar regions. The lungs, heart, great vessels, and ribs impart radiopaque shadows, and movement of the heart, chest wall, and the variability in radiolucency from the differing tissue radiolucency and air exchanges during inspiration and expiration often makes interpretation of images challenging. In addition, most practitioners have minimal experience with the thoracic spine because pain complaints in this region occur less frequently than in the lumbar and cervical areas and training specific to the thoracic spine is uncommon. Thoracic transforaminal injections are rarely indicated rostral to T4 because pathology is infrequently seen in these segments.

To access the thoracic intervertebral foramina, the patient is placed prone on the procedure table. After a sterile preparation of the skin and draping, the proposed level for injection is identified. Because individual characteristics of the twelve thoracic levels are not easily identifiable (i.e., “all thoracic levels look the same”), it is of utmost importance to be compulsive about ascertaining the correct level. The authors recommend counting down from T1 and marking the skin over the pedicles of the chosen level with a marking pen ensuring that the end plate closest to the target is squared. One then counts up from T12, ensuring that this second enumeration of the specified level matches with the first (Fig. 35-31, A). If any question remains, additional examinations are performed until no doubt exists in the mind of the physician injectionist that the correct level is being targeted.

Figure 35-31 AP image of the thoracic spine. A, Inferior end plate of T9 and superior end plate of T10 are not parallel to beam. B, Inferior end plate of T9 and superior end plate of T10 are parallel to x-ray beam (black arrows).

A true AP view is obtained by squaring the inferior end plate of the chosen level; (i.e., T9 if the T9-10 foramen has been chosen to access (see Fig. 35-31, B). The C-arm is rotated in an ipsilateral oblique motion so that the pedicle will appear to move medially toward the midline with the rib head following. The lateral pedicular line, or SAP, is placed between one third and one half the distance over the vertebral body (Fig. 35-32, A). The foramen can be accessed anywhere between the boundary pedicles. Because the medullary artery, artery of Adamkiewicz, is found within the rostral-ventral aspect of the foramen, usually lies caudal to T7, but can be highly variable in location, one of the authors (ML) prefers an infraneural approach, over the intervertebral disc, rather than a subpedicular, needle placement. The target is an area of hyperlucency in the form of a rectangle seen over the intervertebral disc (see Fig. 35-32, B). This so called “magic box” is bounded laterally by a line formed by connecting the medial rib heads; the lateral pedicular line/SAP; and the inferior and superior end plates of the specific level. Local anesthetic can be infiltrated and a 25- or 22-gauge spinal needle can be advanced toward the target using frequent intermittent fluoroscopy (Fig. 35-33, A). As long as the needle is directed medial to the rib head, costovertebral joint, and lateral to the lateral pedicular line, pneumothorax and central canal encroachment is nearly impossible. Often during insertion of the needle, os will be contacted. Because the needle is traversing a space between the proximal rib and SAP, rotation of the bent needle tip will permit continued advancement. Resistance will be noted as the needle contacts the annulus of the intervertebral disc, and further advancement is halted (Fig. 35-33, B and C).

Figure 35-32 Left oblique images of the thoracic spine. The pedicles appears to have moved medially with the rib heads following. White broken line indicates medial rib heads, costovertebral joint. Black broken line delineates midpedicular line that closely approximates the lateral lamina and SAP. A, a small radiolucent so-called “magic box” is noted over the intervertebral disc, bounded by the inferior end plate of T9 (white line), the superior end plate of T10 (black line), the medial pedicular line (white broken line), and the medial rib head line (black broken line). B, Needle target over intervertebral disc (circle) is shown in this magnified image of A.

Figure 35-33 Needle within the T9-10 foramen. A, Oblique view, needle has been advanced over the intervertebral disc between the medial rib head line and midpedicular line. B, Lateral view. Note that the needle tip (arrow) is in the infraneural position caudal and ventral within the foramen in proximity to the dorsal intervertebral disc. C, CT axial bone window image of the midthoracic spine. Note safe needle access (arrow) to the foramen between the rib head (RH) and superior articular process (SAP). As long as the needle is advanced within the “magic box”, medial to the rib head and lateral to the SAP, the lung and central spinal canal are not at risk. Black lines indicate lateral margin of the central canal.

Acceptable needle placement in lateral and AP views is now confirmed and images are saved (see Fig. 35-33, B and Fig. 35-34, A). The needle tip as will be seen in a lateral view as lying in the caudal-ventral foramen, and the AP image will note its foraminal placement between the medial and lateral pedicular lines.

Figure 35-34 Needle is placed within the T9-10 foramen. A, AP image precontrast injection. Needle tip is in the lateral foramen (arrow) as is evident by relationship to pedicle shadow. B-E, Sequential digital subtraction imaging (DSI) series during injection of contrast. Note flow of contrast medial through foramen (black arrows). No vascular flow is evident into the midcanal (white oval), which might indicate a medullary artery injection. B, Volume ~0.25 mL. Arrow indicates flow into epidural space. C, Volume ~0.5 mL. D, Volume ~ 1.0 mL. E and F, DSI and plain fluoroscopic images at completion of contrast injection—final volume ~1.75 mL. Note the extent of spread of a relatively small volume within the foramen and epidural space. Only a small proportion of the injectate is noted lateral along the ventral ramus (open arrows).

Injection of contrast using active AP fluoroscopy, with DSI if available, will provide confirmation of flow through the foramen into the lateral epidural space without worrisome vascular uptake as detailed previously (see Fig. 35-34, B-F). The lateral view will confirm foraminal and epidural injection (Fig. 35-35).

Figure 35-35 Lateral fluoroscopic image after injection of final contrast volume ~1.75 mL. Contrast is seen within the entire foramen with the targeted anatomic structure, the T9 segmental nerve, and dorsal root ganglion (DRG) clearly outlined (arrows).

Injection of the nonparticulate corticosteroid with normal saline or local anesthetic as the diluent in a total volume of 2 to 3 mL can proceed when a safe contrast pattern that encompasses the targeted neural structure is noted.

Cervical Transforaminal

As stated previously, in recent years as more physicians with differing levels of training are pursuing interventional pain procedures, a rise in the number of catastrophic outcomes from injection of particulate corticosteroids into the cervical foramen has been realized. This is a procedure that should be shunned by those novices who have not had years of extensive experience and training in regard to the anatomy of the region and correct technique. However, the authors are not aware of any catastrophic events occurring when due diligence was practiced, all images were saved indicating safe needle placement, and a solution injectate was used.

The patient is placed in supine position with a pillow under the shoulders to slightly extend the cervical region. The anterior and procedural side of the cervical region is prepared and draped sterilely. Whereas in most procedures the C-arm fluoroscope is positioned laterally, perpendicular to the patient, some experienced injectionists, including one of the authors (ML), prefer it to be positioned at the head of the procedure table for ease of obtaining views in all planes of projection. This technique lends itself to the operator sitting on the side to be targeted. The C-arm is maneuvered to obtain an oblique view with caudal tilt of the image intensifier, so that the foramina are seen at their widest diameter in respect to both cephalocaudal and ventral-dorsal dimensions. This is the so-called “foraminal” view (Fig. 35-36). In this position, the x-ray beam is focused parallel to the exiting nerve and foramen. An essential understanding of the shape of the foramen is paramount to the safe conduct of this procedure. In this foraminal view, the actual foramen is not an aperture as it appears. In actuality, it is shaped like a funnel (Fig. 35-37) with the central part appearing hyperlucent, whereas the actual outer edge is ill defined and indistinct because it lies over the posterior and anterior boney elements. The target is the SAP of the level below, dorsal to what appears to be the sharp dorsal border of the foramen and approximately one fourth to one third cephalad of the foramen’s most caudal aspect (Fig. 35-38).

Figure 35-36 Oblique, foraminal view of cervical spine. Foramina are at their widest extent both in dorsal-ventral and cephalocaudal diameters. A, Inner dashed circle represents the inner circumference of the most medial aspect of the foramen. The white circle represents the true margin of the foramen. The needle target is indicated by a black dotB, Identical image for comparison.

Figure 35-37 MRI axial T2 WI. Shape of cervical foramen seen as “funnel”. Note medial diameter is smaller than lateral diameter.

Figure 35-38 Oblique, foraminal view of cervical spine. Target foramen is seen at its widest extent both in dorsal-ventral and cephalocaudal diameters. Black dashed circle represents the inner circumference of the most medial aspect of the foramen. The white circle represents the true margin of the foramen. The two broken lines represent the approximate position of the vertebral artery overlying the uncinate line. The pointer indicates the needle target over the midportion of the C7 SAP dorsal to the foramen.

The skin is marked and if desired, a skin wheal of local anesthetic can be injected. A small-gauge needle is then inserted to contact bone, SAP, dorsal to the apparent foramen (Fig. 35-39). One of the authors (ML) prefers a slight bend on the tip of the needle to increase maneuverability and control. However, an opposing opinion (CA) prefers a straight needle because the radius circumscribed by a bent needle tip with rotation can be considered a “cutting weapon” and might damage any neural or vascular structures that are encountered. Because the actual distance between skin and foramen is rarely greater than 1.5 inches, and a slight misdirection of the needle can easily lead to placement into a potentially perilous structure (Fig. 35-40), a technique in which the needle is advanced quickly under active fluoroscopy is thought to be safest. In addition, if pressure is applied with a blunt instrument during needle insertion, soft tissue is distracted, and the actual depth to target is usually less than one-half inch. This pressure is then released and the skin draws back over the needle, securing it in place. This technique can be accomplished in less than 1 second, and some radiation exposure to the dominant hand is inevitable (see Fig. 35-39). Using pulsed, low-dose fluoroscopic modes, the radiation dose is low, and the perceived safety factor afforded by this technique is appealing. This technique is analogous to that used for cervical discography and stellate ganglion blocks.

Figure 35-39 Oblique, foraminal view of cervical spine. Foramina are at their widest extent both in dorsal-ventral and cephalocaudal diameters. Indicating the target and with pressure providing distraction of soft tissues and decreasing the skin-target distance, the needle is advanced quickly, and the C7 superior articular process (SAP) is contacted dorsal to the apparent foramen.

Figure 35-40 MRI axial T2 WI. Solid arrow indicates correct needle trajectory contacting the superior articular process dorsal to the foramen. The broken arrow indicates targeting of what appears to be the dorsal aspect of the radiolucent foramen when seen in an oblique, foraminal view. A very small miscalculation in the angle of insertion can result in marked morbidity as the vertebral artery or spinal canal is entered. Note left lateral extrusion (black arrow).

When the SAP is contacted dorsal to the perceived foramen, all further advancement of the needle is immediately stopped until depth can be ascertained (Fig. 35-41, A). If the needle is additionally inserted at this point, entry into the central spinal canal can easily occur (see Fig. 35-40). An AP view (Fig. 35-41, B) verifies medial-lateral position. The needle tip should be seen as lying over the mid-aspect of the articular pillar. The needle can be advanced toward the uncinate because the dural root sleeves in the cervical spine do not extend laterally to the degree observed in the lumbar spine and vascular structures are less prevalent in this area.

Figure 35-41 A, Oblique, foraminal view of cervical spine. The needle in position contacting the C7 superior articular process (SAP) dorsal to the apparent foramen. Needle is dorsal to the vertebral artery (broken white lines). B, AP view of cervical spine. The needle tip (white arrow) in position contacting the SAP over the midsection of the articular pillar (black double-headed arrow). Note distance from uncinate line that indicates the most lateral extent of dural root sleeve position and possible spinal canal trespass. The vertebral artery (white dashed lines) is ventral to the needle position in the dorsal foramen.

At this juncture, images documenting precontrast needle position are archived. The foraminal view (Fig. 35-41, A) shows the needle in the dorsal foramen contacting the SAP, whereas the AP view (see Fig. 35-41, B) documents that encroachment of the central canal has not occurred. A needle inadvertently placed ventral within the foramen owing to slight error in angle of insertion, might easily puncture the vertebral artery.

Using active fluoroscopy in the AP view, with DSI if available, contrast is injected to ensure a safe pattern. Flow should be seen through the foramen and into the lateral epidural space (Fig. 35-42). If marked foraminal stenosis is present, minimal contrast may be seen entering the spinal canal. A transient mild to moderate, pressure paresthesia is often noted by the patient secondary to neural stimulation. If significant venous uptake is evident, the needle can be repositioned slightly, either medially toward the uncinate process or laterally, while staying in touch with the SAP. One then reinjects contrast until a safe pattern is noted. If vascular flow to the midspinal canal is evident, the medullary artery may have been cannulated, and the procedure must be terminated. If apparent filling of a tubular structure is noted lateral to the uncinate process in AP view, and over the uncinate line in foraminal view, vertebral artery injection—either intramural or intraluminal—must be considered strongly and the procedure terminated. If there is any question in the operator’s mind about the safety of the injection, the procedure should be terminated immediately.

Figure 35-42 Sequential AP views of the cervical spine during injection of contrast. No vascular injection is evident either flowing towards, at the midline which might indicate an injection into the medulary artery with flow into the anterior spinal artery. See area bounded by the oval. No tubular contrast enhanced structure is noted coursing in a cephalocaudal orientation lateral to the uncinate line indicating vertebral artery injection. A, At start of contrast injection, approximate volume is 0.2 mL. Note extent of foramen clearly is identified (black arrows). If one wished to perform a so-called “selective spinal nerve block” (SSNB), a volume ≤0.3 mL of concentrated local anesthetic might provide selectivity. B, Injection at an approximate volume of 0.75 mL. At this point, contrast is seen entering the spinal canal. Lateral flow along ventral ramus is seen (arrow). C, Injection at an approximate volume of 1.25 mL. At this point, contrast is seen entering the spinal canal (white arrow). Increasing lateral flow along ventral ramus is evident (black arrow). D, Injection at an approximate volume of 1.75 mL. At this point, contrast is clearly noted within the spinal canal (white arrows). The dorsal root ganglion (DRG) is identified within the foramen. Increased lateral flow along ventral ramus continues (black arrow). E, AP view of cervical spine contrast volume of ~1.75 mL. At this point, contrast is clearly noted within the spinal canal (white arrows). The DRG is identified within the foramen. Increased lateral flow along ventral ramus continues (black arrow).

As noted above, some injectionists, including one of the authors (CA), prefer to inject a test dose of local anesthetic prior to the corticosteroid and wait 2 minutes looking for neurologic sequelae correlated with an anesthetized spinal cord. When a safe contrast pattern has been obtained in both AP and foraminal views (see Figs. 35-42, E and 35-43), images are saved for the historical record of the procedure. The nonparticulate corticosteroid can be injected with diluent of choice.

Figure 35-43 Oblique, foraminal view of cervical spine. Contrast is noted within the dorsal foramen and epidural space. No contrast is noted filling a tubular structure over the uncinate [i.e., the vertebral artery (parallel white brokenlines]. Foraminal contrast over articular pillar is evident (arrows).

Postprocedure Care

Following the injection, whether cervical, thoracic, or lumbar, the needle is removed and the skin is cleansed of the antiseptic solution and any blood. A sterile self-adhesive dressing can be applied if desired.

The patient is taken to a recovery area for observation where physiologic monitoring is continued until discharge. Recovery room personnel should be trained to recognize any emergent situations that may present. Complications require diagnosis and treatment in a timely and appropriate manner. Although rarely needed, immediate access to oxygen, airway supplies, and emergency medications must be available. Because sensory and/or motor deficit is often noted when local anesthetics are used, neurologic assessment is of particular importance. If a lumbar injection has been completed, it is prudent to ascertain that the patient has sufficient control of the lower extremities to stand and walk, and assistance on rising should be initially provided. Any motor deficit will rapidly reverse if reasonable doses of local anesthetic were used.

Prior to discharge, if a more selective injection (i.e., transforaminal versus interlaminar) was completed with local anesthetic, the patient is evaluated for degree of pain relief compared with initial, preprocedure level. Assessment by the physician, or other trained personnel, must include those provocative movements which initiate an increase in the index pain. Appraisal of pain intensity change following a procedure with the patient lying comfortably in a bed is of no value. Following an L5-S1 transforaminal injection, the postprocedure neurologic examination would be expected to evidence weakness in extensor hallucis longus, and sensory decrease of the dorsal foot and great toe. These findings validate the procedure because if present, a response to the corticosteroid might be reasonably expected. If sensory deficit in the selected target dermatome was noted, but the patient continued to realize his initial level of pain, either a technical problem occurred or the diagnosis of L5 radicular pain must be reconsidered. This postprocedure evaluation must be included in the specific, detailed, accurate procedure note dictated following any medical intervention (see appendix A and B).

On discharge, written instructions should be provided to the patient. These instructions should detail information about a follow-up appointment, care of the injected area, and on contacting medical help if the patient experiences a complication due to the procedure.

Summary

Corticosteroids placed within the epidural space are rationally used for treatment of radicular type pain thought to originate from inflammation whether lumbar, thoracic, or cervical. Common sense dictates that an injection specifically and precisely targeting the pain generator with a concentrated active component will have more benefit when compared to a dilute preparation placed in an area distanced from the pathology. This is borne out in the literature where precise, selective, transforaminal epidural placement of corticosteroids have shown long-term benefit. Conversely, nonfluoroscopically guided “epidurals,” more precisely designated “injections of corticosteroid placed somewhere in or near the spine,” have been shown to have no clinically significant efficacy. Blind, nonfluoroscopically validated “epidural” injections, can no longer be considered to meet a contemporary standard of medical care, and ethics dictate that this practice be relegated to historical interest only.

In addition, the questionable practice of “a series of three epidurals” must be abandoned as having no scientific rationale. Evaluation of the patient following each injection and basing further treatment on some evidence of past benefit and a rational expectation of future pain relief is the essence of evidence-guided medicine.

Today, for the vast majority of patients with radicular pain, prior to any surgical intervention, transforaminal injection of corticosteroid must be considered the treatment of choice. That these routine procedures are “special,” “dangerous,” or noneffective speaks to the questionable training of those espousing these sentiments.

As with all medical interventions, there is a risk-benefit ratio that must be considered. Transforaminal and interlaminar epidural injections can involve significant morbidity and even mortality. However, with prudence, vigilance, and meticulous technique, these risks are well managed by a fully trained Interventional Pain Management/Nonsurgical Spine Specialist.