History
The term epidural merely denotes a space within the spinal canal but is applied to a variety of injection procedures. They may be classified as to region of interest: cervical, thoracic, or lumbar, and route of administration—caudal, interlaminar, or transforaminal. Each procedure involves directing a needle to a specific target employing an imaging modality to guide and document final needle position. This chapter limits discussion to fluoroscopic guidance. All of these procedures require injection of a contrast material to demonstrate the dispersal pattern of the injectates and documentation of that pattern with spot films. Finally, a report detailing the procedure, including specific technique, details of injected solutions (contrast material, local anesthetic, and corticosteroids), and recording the initial outcome is prepared for the permanent record.
There is a report in English literature that refers to the caudal injection approach for pain management in 1930. The first recorded use of corticosteroids injected into the epidural space for the treatment of “sciatica” was in 1952. The route of administration was one of the dorsal foramina of the sacrum, an early, blind, transforaminal technique. This technique was employed in Europe in the 1950s and 60s.
Interlaminar approaches to the lumbar epidural space were reported in the 1960s. Caudal and interlaminar techniques became standard practice in the United States, Britain, and most of continental Europe for the next quarter century. Interest in the transforaminal approach reemerged in the last quarter of the 20th century, in an attempt to deliver more target-specific injections. The cervical literature is sparse by comparison to that of the lumbar spine. The interlaminar approach for epidural injections was generally used in the 1980s. Cervical transforaminal injection was first reported in 1988. A descriptive outcome study by Bush and Hillier employing this approach followed in 1996. The transforaminal approach was adopted to deliver therapeutic agents to more specific targets influenced by observations that lumbar transforaminal injections appeared to be effective in treating lumbar radicular pain.
There are few reports of the origin of thoracic epidural steroid injections (ESIs) for treatment of spinal pain. A specific technique for thoracic transforaminal epidural injection was described in 2001.
A recent systematic review revealed an increase in the number of lumbosacral spine injection procedures performed in the last decade of the twentieth century. There was an increase of more than 270% noted between 1994 and 2001. Forty percent of these procedures were associated with the diagnosis codes for “sciatica,” “radiculopathy” or “herniated disc.” “Axial low back pain” diagnoses accounted for 36% and “spinal stenosis” 23%. A study of the Medicare population between 1993 and 1999 revealed that the annual number of cervical, thoracic, and lumbar epidural steroid injections peaked at more than 680,000 in 1998. These studies focused on the Medicare population, but it is likely that similar increases would be found for the general adult pain population.
A review of conservative care for sciatica published in 2000 surveyed 19 randomized controlled trials and pooled odds ratios calculated for several treatment types. The data indicated, “Epidural steroids may be beneficial for subgroups of nerve root compression.”
In 2009, Lavin published results of an extensive MEDLINE/PubMed search and searches of large review articles on the major interventional spine topics. This review was performed to find all prospective, double-blind, randomized, placebo-controlled trials in the English language interventional spine literature. He concluded “Fluoroscopically guided lumbosacral transforaminal epidural corticosteroid injections are effective in the treatment of acute/subacute lumbosacral radicular pain, and in preventing future surgeries. No firm conclusions were drawn about cervical epidural (CESI) injections or lumbosacral epidural (LESI) injections for the treatment of chronic radicular pain. A study of the American Society of Anesthesiologists (ASA) Closed Claims Project database revealed that epidural steroid injections account for more complications than any other interventional pain procedure.
Relevant Anatomy
The spinal epidural space is a continuous potential space in the vertebral canal extending from the foramen magnum to the sacral hiatus, lying between the dural sac and the osseoligamentous wall of the vertebral canal. The epidural space is bounded posteriorly by the lamina and ligamentum flavum. The anterior boundary is formed by the posterior disc margin, the posterior longitudinal ligament and the peridural membrane. This membrane attached to the upper and lower ring apophysis of each vertebra, blends with the disc annulus. It spans the waist of the vertebral body. Together these tissues form the floor of the vertebral canal. The lateral boundary of the epidural space is fenestrated by paired root canals or foramina at each segment. The vertebral pedicles lie between the root canals.
The dural sac nearly fills the vertebral canal and extends from the foramen magnum terminating in the sacral canal at the level of the S1 to S2 segments. There is some variability and the thecal sac may terminate as high as the lumbosacral interspace or may extend to S3. At each vertebral segment paired dural root sleeves extend toward the root canals. The cervical and thoracic dural root sleeves are short and nearly horizontal in orientation, traversing the center of their respective root canals. The lumbar root sleeves are longer, increasing slightly in length and downward angle from L1 to the sacrum. Lumbar root sleeves turn laterally into grooves in the vertebral bodies and pedicles and are in intimate proximity to the medial/inferior border of the pedicles. This is the entrance zone of the root canal, or lateral recess of the vertebral canal. The dural root sleeve contains the dorsal and ventral rootlets of the segmental nerve. The dorsal ganglia lie generally in the midzone of the root canals, between the pedicles of adjacent vertebra. The dura and arachnoid membranes form a “water-tight” seal at the proximal end of the ganglia. Cerebrospinal fluid (CSF) fills the root sleeve but does not extend beyond the ganglia. Occasionally ectasia of a dural root sleeve will occur, resulting in extension of the subarachnoid space beyond usual boundaries. Referred to as cystic root sleeve dilatation or Tarlov cysts, they usually communicate freely with the subarachnoid space. They may occur at any level of the spine but are most frequent in the sacral region. Usually asymptomatic, they are rarely associated with symptoms.
There are accumulations of fat in the posterior vertebral canal, deep to the ligamentum flavum and posterior to the dural sac in the thoracic and lumbar spine. This posterior fat pad may be small or absent at the L5-S1 level when the dural sac is full size and is applied close to the lamina and ligamentum flavum, as it frequently is. Additional accumulations of fat are found laterally at the level of the discs within the root canals. There is little fat in the cervical epidural space. Midline sagittal spin echo (SE) T1 images of the spine demonstrate the lumbar and thoracic fat pads quite well. Fat is rarely visualized in the vertebral canal above the C7-T1 level. Ample fat fills the vertebral canal below the termination of the dural sac in the sacral vertebral canal.
A thin anterior membrane extends from the posterior longitudinal ligament to the anterior surface of the dural sac. This ventral meningovertebral ligament forms a nearly continuous septum, that functionally divides the ventral epidural space into left and right compartments in the lumbar region. A midline dorsal connective tissue band fixes the dural sac to the flaval ligaments. The appearance of the band varies from strands of connective tissue to a complete membrane.
A plexus of valveless veins occupies the anterior epidural space. Paired anterior internal epidural veins run the length of the vertebral canal. There are numerous interconnecting veins crossing the floor of the canal, the anterior internal vertebral venous plexus (AIVV). A smaller posterior internal venous plexus lines the roof of the epidural space in the lumbar and thoracic regions. Extending laterally around the vertebra, the peridural membrane encloses veins that course around the body of the vertebra. These veins communicate freely with the basivertebral veins, at the center of the posterior wall of each vertebral body and the anterior internal vertebral venous plexus. Several radicular veins traverse each root canal. They lie predominantly in the ventral root canal and connect the epidural venous plexus with the ascending lumbar veins and the vena cava.
Segmental arteries traverse the root canals at all spinal levels. They course in the anterior superior root canals along the anterior superior aspect of the segmental dural root sleeve. Some arterial branches perfuse the dorsal ganglia and segmental neural elements and, as such, are radicular arteries. Other branches penetrate the dura running along the segmental rootlets and may anastomose with the anterior spinal artery. They are, therefore, medullary arteries. Varying numbers of medullary arteries of differing sizes are found in the cervical, thoracic, and lumbar region, and contribute to the blood supply of the spinal cord.
The radicular and medullary arteries of the cervical spine arise primarily from the vertebral artery. Some arise from the ascending cervical and posterior cervical arteries. Medullary arteries penetrate the dura and divide into anterior and posterior branches, eventually reaching the anterior and paired posterior spinal arteries. Cervical medullary arteries are variable in size and distribution. There are usually two or three arteries of moderate size in the adult. They may be present at any segment and on either side.
The upper and midthoracic cord is supplied by medullary arteries arising from branches of the costocervical trunk and spinal branches of the aorta. There is usually a single large medullary artery arising from the aorta and supplying blood to the lower half of the thoracic cord and conus. This large medullary artery, the artery of Adamkiewicz, has a variable origin but usually originates on the left side (80% of patients), between T7 to L4, most often between T9 and T11. In a study of 4000 spinal cord angiograms, there were three instances in which the major medullary artery of the distal thoracic cord originated at the fourth lumbar artery.
Paired lumbar arteries originate from the aorta at each lumbar segment. These give rise to spinal branches that include radicular and medullary branches. Most lumbar spinal branches are small. Some may be 1.0 to 2.0 mm in diameter. There is potential for a medullary artery of substantial size to be present in any root canal.
Spondylogenic Pain
Spondylogenic pain arises from a component of the spine or its supporting structures, and is synonymous with other terms such as nonspecific or idiopathic spinal pain. The International Association for Study of Pain (IASP) published a taxonomy, defining clinical terms used to describe pain, in an effort to standardize the use of terms.
Somatic pain results from noxious stimulation of a musculoskeletal component of the body and arises as a result of stimulation of nociceptive nerve endings in bone, ligament, joint, muscle or tendon. Visceral pain occurs with noxious stimulation of a body organ or its capsule. Both somatic and visceral derangements cause pain in the location of the source structure, but it is often vague and ill defined.
Referred pain is pain perceived in areas adjacent to or remote from the source of pain. Convergence is the physiologic basis for referred pain. Sensory neurons from different peripheral sites converge on common neurons in the spinal cord and thalamus that relay to higher centers in the brain. Without additional sensory input, the brain may not be able to determine the specific site of the initial input. Referred pain is a misperception of the origin of the signal that reaches the brain.
Somatic spinal pain syndromes may be expressed topographically as neck, midback, or low back pain. Local pain in these areas is often accompanied by referred pain. Somatic neck pain may be perceived with pain referred to the shoulder girdle or upper extremity.
Lesions of the midback refer to the chest wall and low back pain is commonly associated with pain in the buttocks and lower extremity. Somatic referred pain is typically diffuse, deep, and ill defined, aching in quality and aggravating.
Radicular pain occurs when there is irritation or injury of a spinal nerve or its roots. In the lumbar spine, simple compression of a normal nerve or nerve root does not provoke pain. Alone, pressure on a spinal nerve or its roots may produce a conduction block of axons. Sensory axon conduction block results in loss of sensation or “numbness.” Motor axon block results in weakness. Compression alone can result in radiculopathy, without radicular pain. Pressure on a previously injured or damaged nerve or root provokes pain. Local ischemia or inflammation can induce ectopic impulses in a dorsal root canal ganglion resulting in radicular pain. Lumbar radicular pain is discretely localized, “bandlike” in distribution, and shooting, lancinating, or shocking in quality and can have a cutaneous component.
Preprocedure Evaluation
A practitioner of spinal interventions may be a managing physician directing the care of a patient with a painful spinal condition or a consultant to whom a patient has been referred for a procedure. With each encounter, the responsibility for assessing the clinical condition and the appropriateness and risks of a given procedure, rests with the physician injectionist. The practitioner must attempt to understand the pain and associated disability. The patient is the primary source of that information.
What is the primary complaint? Is this an acute or chronic problem; a constant or recurring problem? Is local pain somatic or visceral? Is there a radicular or somatic referred component? One must localize the somatic component and the location of radiating pattern. The character and intensity are as important as the location. What are the mechanical aspects, that is, what provokes and relieves the pain? An example: A 35-year-old female presents with recent onset of left posterior and lateral aching neck pain for no apparent reason. Constantly present, the aching varies from moderate to severe on occasion. There is diffuse aching of left posterior shoulder girdle muscles. She has recurring episodes of severe, “sharp, stabbing” left upper extremity pain, extending along the posterior arm, medial forearm, and into the left long finger. No arm weakness, frequent “tingling” of the whole upper extremity and normal strength and reflexes are observed. Prolonged sitting, particularly at a console or working at a desk, aggravates the neck pain. Neck extension and left side bend induces a painful “shocking” sensation in the left arm. Though intermittent, the arm pain is the dominant complaint. She has axial somatic neck pain, with somatic referred pain to the left shoulder girdle and left upper extremity radicular pain, without radiculopathy.
Self-pain rating, employing a specific method such as the visual analog scale (VAS) is essential. What is the intensity rating at the time of assessment? Range of intensity is determined by noting the pain rating at its best and worst. Patients can express their pain on pain drawings, which should be correlated with the description of symptoms. These instruments are very useful in assessing the immediate response to an intervention.
Simple psyche screening questionnaires to assess anxiety, depression, self-perception of disability, and somatization are useful in assessing pain behavior. What has been the response to any previous interventions or procedures? Finally, what medications, at what doses have been used to treat and what has been the response? Psychological factors contribute to pain and influence the outcome of interventions. There is no simple screening tool. Therefore, one must know his or her patient and history.
Medical history includes review of all allergies and idiosyncratic reactions, any current illness or infection and chronic conditions such as cardiovascular disease, diabetes, seizures, respiratory and renal disorders. All these factors affect how procedures will be performed.
The history of all surgical procedures and their outcomes should be explored. A complete list of current medications is mandatory. A general review of systems should include information about sleeping pattern. Social habits such as tobacco and alcohol use or abuse are important. Patient’s work and/or avocations may pertain to complaints and should be explored. A family history may contribute to recognition of an underlying hereditary disorder.
The physical examination on a first encounter is general but with focus on primary and secondary complaints. Developmental status, any deformities or postural aberrations should be recorded. The level of distress during interview and examination, patient’s willingness and ability to cooperate with interview/examination and the patient’s demeanor and orientation should be observed and recorded along with routine vital signs. Examination may include assessment of gait and both sitting and standing postures. Passive or active movements of the cervical, thoracic, or lumbar spine through their range of motion are observed. Palpation of regional musculature and bony prominences helps to localize somatic pain. Epidural procedures are injections into the spinal neuraxis and require a basic neurologic examination prior to the procedure. On a case-by-case basis, examination of core and extremity strength, weakness, range of motion, and reflexes contribute to formulating a working hypothesis.
Spine imaging plays a definite role in the evaluation of spine pain complaints both in demonstrating relevant pathology and aiding in planning a safe and efficient approach for procedures. Modern imaging modalities provide excellent depictions of spine anatomy. However, many lesions, evident in the maturing spine, are clinically insignificant. Imaging studies often demonstrate pathology that is irrelevant. Computed tomography (CT) or magnetic resonance imaging (MRI) may demonstrate a left C3-4 disc protrusion in a patient complaining of right arm pain and altered sensation radiating to the right forearm, thumb, and index finger. It cannot be overstated that there is a significant incidence of pathology in asymptomatic subjects. A focal disc protrusion on the right at L3-4 may be clearly defined by MRI, in a patient complaining of left buttock pain extending to the left calf. Scans should be reviewed overall, but with particular attention to areas that might be related to the patient’s underlying complaints, as gleaned from the interview and examination. One should carefully study the left L4-5 and L5-S1 root canals in a patient with pain extending from the left buttock to the left anterolateral leg and dorsum of the foot. Recently 150 patients with unilateral leg pain, and MRI confirming neural compression by prolapsed disc or foraminal stenosis had lumbar transforaminal epidural injections (LTFE) at appropriate sites. These were effective in relieving their pain initially, and only18% of these patients required surgery at a minimum 1-year follow up. Not all abnormalities need be targeted but rather those most likely to be associated with the expressed symptoms and physical findings.
Indications: This clinical process should provide a basis for a hypothesis as to the nature of the underlying spinal disorder. Epidural injections are indicated when a patient expresses constant or frequently recurring episodes of radicular pain, but also patients with somatic spinal pain associated with mixed somatic referred and radicular pain referred to one or both extremities or the chest wall.
Contraindications: Absolute contraindications include a bleeding diathesis, systemic infection or local infection in the procedure field, pregnancy, and inability or unwillingness to cooperate and participate in the procedure. Relative contraindications include significant competing disease—that is, uncontrolled hypertension, diabetes, congestive heart failure, and anticoagulation therapy.
There is risk of a major depressive disorder in patients with chronic pain. Pure psychogenic pain is rare and used pejoratively. Almost all chronic pain can be altered by psychological adjustments and issues. Without these being addressed, successful diagnosis and treatment is unlikely.
Absolute contraindications include active psychosis and homicidal or suicidal ideation. Studies have shown a relationship between physical and sexual abuse and various types of pain. Correlation of failed low back surgery with childhood trauma has revealed definite risk factors. These include physical, psychological, and/or sexual abuse, emotional neglect, abandonment, and chemical dependence and/or loss of a primary caregiver. Relative contraindications include personality disorders, bi-polar disorder, severe depression, lack of social support, and drug dependence/abuse.
Negative predictors are external locus of control, “just fix me,” unstable relationships, poor vocational adjustment, neurocognitive deficits, inability or unwillingness to participate in active rehabilitation, unreasonable expectation of procedures, ongoing litigation, symptoms inconsistent with pathology, high fear avoidance, inability to actively exercise, and catastrophizing cognitive style.
Positive predictors are history of adherence to treatment regimen, positive support system, compliance (currently and historically), and appropriate expectations.
A Few Medical Issues
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%). 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.
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. However, some patients with normal renal function exhibited increases of serum creatinine with high-contrast loads. 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. 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. One author recommended the maximum epidural dose of lidocaine to be 500 mg and 225 mg for bupivacaine.
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. 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. 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. 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.
An epidural steroid injection of 160 mg of methylprednisolone will suppress adrenal function for weeks. Does injection of corticosteroids increase the risk of infection? Infections do occur in patients following ESIs. Postoperative infections are increased in hip replacement patients who received preoperative steroid injections. 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. 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. 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. 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.
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. 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.
Major Complications
Directing a needle deep into the tissues in and about the spine approaches sensitive spaces and structures of the neural axis. There is a spectrum of possible major complications.
Infection
Infection following epidural injection is a serious issue. It has been described as a rare complication. 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. 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. 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. 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 lumbar and cervical 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%. 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. 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 thoracic 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. 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. 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.
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. 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. 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. Dural puncture is reportedly rare when the procedure is performed by “expert” interventionalists. 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. Severe thoracic cord injury occurred when a low thoracic epidural injection was performed under general anesthesia. Some cord punctures may not provoke pain. Mayall reported permanent paraplegia resulting from multiple attempts at thoracic epidural injection in an awake patient. No lateral view was used during the procedure. 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. 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. 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. 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.
The next year Houten and colleagues reported the first cases of lower thoracic and conus infarct occurring as a result of lumbar transforaminal injections. 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. 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. 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.
Since the first report in 2001, there has been a frightening number of case reports of catastrophic neurologic complications in the literature. 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. 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. Prevention of these complications begins with awareness that this can happen.
First, recognize intraarterial injection when it occurs. 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.
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. 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. In a comparison study, Dreyfuss and colleagues reported that dexamethasone was slightly less effective than triamcinolone, but the difference was not statistically significant. 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 carotid and vertebral 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.
Epidural Injection Techniques
Equipment
Fluoroscopy
Fluoroscopy is mandated for all interventional spinal procedures, including injections performed for the diagnosis or treatment of pain of spinal origin. Although “blind,” nonfluoroscopically guided, interlaminar injections for peri- and postoperative analgesia are the norm in the anesthesia arena, the specialty of interventional pain or non-surgical spine, demands precise needle placement, selective administration of medications, validation of the procedure, and a historical record. The literature documents that in experienced hands, successful epidural needle placement is to be expected in only 60% to 70% of cases where fluoroscopy is not used. A 30% to 40% failure rate does not provide a sufficient probability of success on which to base a diagnostic or therapeutic modality. Therefore, interventional spinal pain procedures performed using nonfluoroscopically guided (i.e., blind) techniques should be considered as highly inappropriate and possibly sham, and fraudulent procedures whether being performed for diagnostic or therapeutic objectives. Rationalizations that the cost of fluoroscopy is prohibitive, equipment unavailable, historical precedent, or the “vast experience and skill” of the practitioner, usually belies economic impairment or poor, insufficient training and cannot be used as an excuse for the substandard practice of medicine.
It is imperative that all physicians performing fluoroscopically guided spinal injections have training in the interpretation of real time fluoroscopic images whether cervical, thoracic, lumbar, or sacral. This training must be beyond the level of a residency and most current “pain” fellowships. Expertise in radiologic interpretation is far beyond the training and proficiency of nurse anesthetists (CRNAs), physician assistants (PAs), and other so-called “mid level nonphysician providers.” Performance of interventional pain procedures constitutes the practice of medicine as noted by at least one judicial body within the United States, and numerous medical specialty societies including the American Medical Association, the International Spine Intervention Society, and the American Society of Anesthesiologists.
The fluoroscopic instrument of choice is the C-arm, which can be moved in any plane to provide optimum imaging to direct needle insertion and to verify, and document, final needle position and contrast spread. Radiation-saving modalities such as low dose, pulsed mode, collimation, and saving of last image are essential and ensure safe practice. Digital subtraction imaging (DSI), although not at present standard of care, can provide significant useful information when used correctly.
The majority of interventional pain procedures are performed where the C-arm fluoroscope is used to align the skin entry point with the target. A needle can then be advanced parallel to the beam. Using this down-the-beam technique, the correct angle of needle insertion is unmistakable, and when the injectionist is familiar with the anatomy lying between the skin and target, it offers the safest approach. For precise work, parallax demands that the target is placed in the center of the image.
To use the C-arm, an x-ray-compatible procedure table is required. Although some operating room tables will suffice, most have metal incorporated into their structure, which limits certain fluoroscopic projections. Carbon fiber tables, with the pedestal at the foot, are now quite affordable and provide unlimited access and unrestricted imaging possibilities.
Radiation safety precautions, including the use of lead aprons, thyroid shields, and radiation exposure monitors must be provided for all personnel in the procedure room. Some have advocated the use of lead glasses.
One often overlooked aspect of radiation safety is the radiologic technician, RT, actually controlling the C-arm. A competent RT will not only assist in obtaining the correct images for safe needle placement, but should also control collimation and the power output of the fluoroscopy equipment to ensure that the physician performing the procedure is acquiring the least radiation while maintaining adequate imaging quality throughout the procedure. However, obtaining the correct image required for an injection procedure is the responsibility of the physician alone, and the essential “fine tuning” to provide this image is best handled personally.
Regarding radiographic guidance, although the use of CT guidance has been advocated by a small minority of radiologists, most radiologists within the interventional pain community reject the use of this imaging modality for the placement and validation of safe needle position. Using CT allows one to accurately delineate the skin entry point; however, the advancement of the needle toward the target is accomplished crudely, without imaging assistance. This adds to the physical discomfort of the patient, the time required to complete the procedure, and the chance for needle misadventures. CT necessitates the injection of contrast for verification of needle placement without the benefit of active, real time imaging. Vascular injections will, in all likelihood, escape detection owing to the rapid “washout” of contrast secondary to blood flow within the vein or artery. In addition, the marked increase in total radiation exposure to the patient, as inherent in CT, should be of concern. No literature exists in which evidence indicates any benefit to the use of CT for routine spinal injections. Specialty group guidelines published by the International Spine Intervention Society (ISIS) and the Physiatric Association of Spine, Sports, and Occupational Rehabilitation (PASSOR), specifically do not mention CT use for epidural injections, whether transforaminal or interlaminar. As noted previously, severe permanent neurologic sequelae following the use of CT for cervical and lumbar transforaminal epidural injections have been reported in the literature and medical legal documents. These cases involved paraplegia, quadriplegia, and death secondary to cord infarct.
A historical record of all procedures must be archived either with hard or digital images. Multiple images must clearly identify that the needle is in safe position prior to injection of contrast, and that the contrast pattern represents a safe flow of the injectate.
Miscellaneous Supplies
Aseptic technique demands the use of sterile gloves. Although their effectiveness in the control of infection in regard to minimally invasive spinal injections has never been demonstrated, some have advocated the use of masks, hats, and gowns.
A sterile cover for the C-arm image intensifier allows the physician to control and direct the image during the periprocedural period. In addition, this prevents contaminating detritus from falling onto the sterile field from the equipment. A sterile, long, 6- to 12-inch, radio-opaque pointer, combined with a skin marking pen enables the injectionist to mark the proposed skin entry site in a radiation safe manner.
A variety of needles and syringes are required and these vary according to the specific procedure intended. For interlaminar injections, prepared trays offered by a number of companies are often the most efficient, and cost effective, option. Hustead, Crawford, or Tuohy epidural needles of 18 or 20 gauge, 3.5-inch are ideal for most situations. Occasionally a 5-inch needle is required. Interlaminar injections require the use of tactile sense by tissue resistance for realization of needle tip position during needle insertion. This ability to identify needle tip position by feel is lost when smaller gauge needles, 22 or 25 gauge, are used and will result in a higher incidence of dural puncture. In addition, the valuable identification with aspiration of CSF with intrathecal placement, or blood when intravascular, cannot be relied on if these needlessly small needles are used. The adequate use of local anesthetic renders the insertion of an 18 gauge needle no less comfortable than the use of a smaller gauge instrument. Sharp, cutting needles designed for intrathecal placement, Chiba or Quincke type, were not designed for use in accessing the epidural space via the interlaminar approach because the variation of resistance of the tissue layers trespassed cannot be as readily appreciated. A 5 mL loss of resistance (LOR), glass or plastic syringe is unique to the interlaminar approach. Injections into the most caudal aspect of the epidural space through the sacral hiatus can, in most instances, be undertaken with a 25-gauge 1.5-inch needle.
Transforaminal epidural injections are best accomplished with 25-or 22-gauge needles. In nearly all cases, 3.5- or 5-inch lengths suffice. Quincke or Chiba beveled needles are used by the majority of experienced practitioners. A small bend of the tip, opposite the bevel, is used by experienced physicians to allow precise directional control during insertion. Occasionally, an intertransverse fusion mass may prevent the direct insertion to the target. This might require the use of a two needle technique: an introducer needle of larger diameter, (18 gauge) placed at the correct target depth, and a procedure needle with a large bend capable of maximum lateral movement, inserted through the introducer. Although some practitioners have advocated the use of blunt needles to prevent unintentional arterial uptake, no evidence exists as to this claim as has been addressed in detail. In addition, blunt needles require an introducer needle to puncture the skin, are difficult to control, and (in at least one small study) have been shown not to decrease the incidence of vascular puncture.
In addition to the procedure needles specific to any technique, a 25-gauge needle for skin localization and an 18 gauge for drawing up of medications are used. Syringes, in the 3 to 10 mL range, for local anesthetic, contrast, and injectate must be provided.
To prevent needle movement during attachment of multiple syringes to the needle hub after optimal needle position is obtained, a small-bore, low-volume extension tube can be of great help. These are available in various lengths (3 to 30 inches), and volumes (0.23 to 0.5 mL), depending on operator preference. Extension tubing also allows the physician to keep his/her hands out of the x-ray beam during injection of contrast using active fluoroscopy as mandated for safety.
Medications
Local anesthetics are used in nearly all spinal injections. A comprehensive review of these medications is beyond the scope of this chapter and can be found in a vast number of anesthesia references. Amide type local anesthetics (lidocaine and bupivacaine) are the preferred choice, have an extremely safe profile when compared to the ester-based (procaine, chloroprocaine and tetracaine) choices. Epinephrine, added 1:100,000 to 1:400,000, increases morbidity and has no use in the practice of pain intervention. True allergic reactions to amide-type local anesthetics are rare, in the range of 1:100,000. Para-aminobenzoic acid (PABA), used as a preservative, or as a metabolic product of the ester-type local anesthetics, can initiate an allergic reaction and their use is, therefore, highly questionable. With the small doses of local anesthetics used in interventional pain procedures, doses capable of causing neurologic or cardiovascular problems should never be encountered.
For patient comfort and acceptance, anesthetizing the skin and underlying tissues prior to procedure needle insertion is suggested. Although skin localization may not be required when 25-gauge needles are used, insertion of needles in the 17 to 22 gauge range can be quite uncomfortable. One percent (1%) preservative-free lidocaine, 4 to 5 mL, is ideal for this use. Using a 25-gauge, 1.5-inch needle, excellent conditions for any epidural injection can be easily and safely obtained.
Injection of local anesthetic into the epidural space is highly dependent on practitioner practice. Patients are selected, as previously discussed, for radicular-type pain secondary to a proposed inflammatory neuropathology. These patients frequently suffer from chronic complaints. Because local anesthetics provide only 1 to 3 hours of neuroblockade, no long-term relief can be expected from the local anesthetic. However, in a patient who presents in moderate-to-severe pain, even the short relief noted by addition of local anesthetic might warrant its use after the added risk profile is considered.
Local anesthetic placed in the epidural space has no positive diagnostic value, whether via the interlaminar or transforaminal route. Nerves are ubiquitous within the epidural space and spread of injectate is nonselective. However, in transforaminal epidural injections, the use of local anesthetic in a concentration high enough to cause sensory block, can provide the physician with reliable negative information. If a patient presents with right lower extremity radicular-type pain, and pathology correlates well with this symptom, a transforaminal injection at the appropriate level would appear to be indicated. In this case, corticosteroid alone might be expected to provide long-term benefit owing to its antiinflammatory action. If the corticosteroid were administered with local anesthetic, and the patient saw excellent relief of preprocedure pain, little inference can be made. However, if the patient saw minimal or no relief and significant numbness in the specific dermatome of the segmental nerve that was targeted, one can make the assumption that the cause of the pain is not associated with that specific level. This is helpful in ruling out this level as associated with the pain generator.
Although there are a number of corticosteroids that have been used epidurally by interventional pain physicians for more than 50 years, none have been approved for intraspinal use by the United States Food and Drug Administration (FDA). All corticosteroids must, therefore, be described as “off label.” Methylprednisolone, betamethasone, triamcinolone, and dexamethasone have all been advocated. Of the aforementioned corticosteroids, the first three are suspensions, only dexamethasone is a solution that is commercially available. Regarding transforaminal injections, there appears to be correlation between the use of particulates and spinal cord and brain infarctions owing to arterial occlusion. Therefore, for cervical, thoracic, or lumbar injections into the intervertebral foramen, the solution, dexamethasone, would appear to offer a real safety benefit.
The use of nonionic, water soluble contrast media is mandated for all fluoroscopically guided spinal injections. Iohexol (Omnipaque) or iopamidol (Isovue) in concentrations of 180 to 300 mg/mL are safe—with allergic reactions occurring in the 1:100,000 to 1:500,000 range. Injection of contrast validates that the needle is in correct position and that the active injectate will cover the targeted anatomic structure. In addition, the pattern of contrast will ensure that the needle tip has not unintentionally strayed into a position where injection might cause significant morbidity. Training in “normal,” aberrant, and potentially dangerous contrast patterns is essential.
Although emergent situations are rare during the practice of interventional pain procedures, vigilance and preparedness are essential. One never knows when a situation requiring immediate intervention will occur. Physicians performing spinal injections must be proficient in emergency protocols including airway management and cardiovascular resuscitation. A basic course such as Advanced Cardiac Life Support (ACLS) should be considered a minimum requirement. In addition, well-trained, and practiced, procedure room personnel who are able to assist the physician and monitor the patient provide a safeguard to ensure immediate and appropriate patient care, should the unexpected occur. Whether the procedure is performed in an office, ambulatory surgery center, or hospital setting, emergency equipment, pharmaceuticals, oxygen, airway supplies, suction, and other resuscitation provisions must be immediately available and checked regularly to ensure proper function.
Monitoring devices such as pulse oximetry, noninvasive blood pressure, and ECG, must at the least be immediately available, and their use is required if any sedation is contemplated. An ongoing conversation with the patient is always an appropriate and accurate monitor of the patient’s comfort, level of consciousness, cardiac and respiratory status pre-, peri-, and postprocedure.
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, 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.
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.
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 ).
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.
