What Is An Epidural Steroid Injection?
Research on pain and pain management estimates that approximately 90% of the population will be subject to pain that appreciably affects their life quality and ability to function normally during at least one point in their lifespan. Reports from the Centers for Disease Control (CDC) state that consistent (or chronic) pain, including that felt in the spinal or back region, is related to significant debility in some cases. This may lead to profound effects on the personal and professional lives of those affected.
Therefore, chronic pain may also be associated with significant economic burden. Some reports lead to the conclusion that this form of pain is related to billions in lost income every year. In addition, it may be a prominent factor in skipped work days and in occupational injury claims. Chronic and painful conditions are commonly linked to increased healthcare burden and reduced productivity in the workplace. Therefore, a considerable growth in the area of medical research dedicated to treating and managing this pain has taken place in the last few decades. The last decade has seen a significant rise in the number of robust clinical trials in new and more effective therapies for chronic pain.
An end-product of these trials that is in common use nowadays are epidural steroid injections. These are minimally-invasive medical techniques associated with efficacy and reliability in chronic conditions affecting the spine (i.e. the neck and back). Many major health and pain research authorities support epidural steroid injections as a treatment option with positive effects on life quality for patients who are affected by conditions such as:
- Chronic cervical (neck) pain
- Chronic lumbar (lower back) pain
- Radiculopathy (pain caused by damage to certain nerves that may also lead to chronic pain)
Epidural steroid injections are also recognized by as an aid to the restoration of normal function and daily activity levels.
Chronic spinal pain is a common topic in scientific literature, although interventions applied to this condition must undergo rigorous testing and trial processes before researchers will conclude that they are effective treatments for the condition(s) in question. This research has also found that there may be many underlying conditions that explain a particular type of pain, and that accurate diagnosis of these may affect the success of a certain therapy.
Epidural steroid injections have been found to be effective in cases of many of these disorders. This treatment has been shown to reduce or even eradicate pain in many cases. For patients who do not experience such pain relief after one injection, research has shown that a course of several injections over time may treat pain to an approximately equal effect. This treatment is associated with some side effects, mainly related to the drugs (i.e. steroids) included in the injections. These may include reductions in the control of bodyweight, emotional anomalies, the increased risk of arthritis development, and damage to the gastrointestinal tract.
Epidural injections were first introduced by the neurologist James Leonard Corning in 1885. Although his initial experiments incorporated cocaine (a socially-acceptable anesthetic at the time) as the injected material, it was not proposed specifically as a pain treatment for 16 years after this. By then, two other doctors were documented as using cocaine injections at a target in the base of the spine. The patients that this was tested on were described as suffering chronic pain of a form defined as intractable sciatica at that time (but may in fact have been a type of radiculopathy).
By the 1930s, a form of epidural injection known as a caudal injection was well-regarded in the literature as an effective form of pain relief. The formulations used were mostly local anesthetic medications, not steroids, however. The inclusion of steroids as part of the injection was first described in 1953. Since then, epidural steroid injections have received much clinical and empirical support as a treatment modality for chronic or severe pain. This procedure is particularly associated with relief in cases of radiculopathy, in which pain (which may be chronic) spreads from the spine into the extremities.
Epidural steroid injections may reduce pain mainly through their effects on inflammation. This is associated with the perception of pain, as the release of inflammatory molecules leads to chemical damage to nervous tissue, thus resulting in noxious (or painful) stimuli. Inflammation is thought to be a major factor in conditions such as arthritis and neuropathy. Steroids inhibit pro-inflammatory molecules, and thus may significantly reduce pain when introduced into tissues. These drugs also promote normal nerve membrane formation and modulate the molecular basis of nervous signaling. This may also contribute to the control of pain. However, some researchers assert that this is not the only effect on pain associated with epidural steroid injections.
The injection of fluid alone may also affect pain by promoting blood flow through the vessels located in the epidural space. This is thought to inhibit the conductance of pain signals to a degree. The injected material may also cleanse damaged nerve cells. This may add to pain relief by washing away inflammatory molecules present in the epidural space.
ESI Clinical Trial Papers
- Cohen et al. 2012
- Carette et al. 1997
- Arden et al. 2005
- Ghahreman et al. 2010
- Riew et al. 2000
- Sayegh et al. 2009
- Kraemer et al. 1997
- Meadeb et al. 2001
- Vad et al. 2002
- Wilson-MacDonald et al. 2005
- Nam & Park 2011
- Dilke et al. 1973
The Anatomy Of The Spine
An understanding of how epidural steroid injections work is aided by a basic grounding in the anatomical features of the spine. This structure is made up of small bones called vertebrae. There are 33 of these in total. They are partially hollow, having a large gap in the center, surrounded by thin horizontal processes of bone. Most of them stack up (when viewed vertically) to form a canal by lining up their central holes. This is the vertebral (or spinal) column, also known as the “backbone.” Most of the vertebral column is located in the back of the main trunk of the body. The function of this column is to support and protect the spinal cord, and to contribute to upright movement, i.e. standing.
The spinal column may be described as forming a number of discrete regions. At the top of the column is the cervical curve (or region), which encompasses the neck. The thoracic region, which includes the next 12 individual vertebrae, descends from this and forms the upper back region (or thorax). The lumbar region, which contains five vertebrae, is known as the lower back. The remainder of the spine is the sacral region, consisting of the four vertebrae of the coccyx (the tailbone) and the sacral spine, which form joints with the pelvis.
The spinal cord is the thick band of tissue traveling the length the vertebral column. This contains long bundles of nervous tissue that conduct signals to the brain, where they are processed as information about the body and about any potential or actual harm to it. The cord joins the brain at the beginning of the cervical region and proceeds downward within the column until it reaches the lumbar region. The human spinal cord is associated with master control of motor, sensory, and reflex properties. Damage to the spinal cord may result in a range of problems with these functions, ranging from mild sensory abnormalities to paralysis. Therefore, the spinal cord must be defended at all cost from damage, shock, and other trauma. This is accomplished not only by the vertebral column, but by a number of membranes (or meninges).
These protective membranes wrap around the spine, and also extend into the skull to line the brain. The meninges include the arachnoid, the dura mater, and pia mater, which form distinct layers around the brain and spine. The dura (Latin, “tough”) mater is a resilient membrane that is capable of protecting these structures from a certain degree of damage. This membrane is inflexible and durable, and also contains cerebrospinal fluid. This material is present to supply some nutrition to nervous tissue and for additional protection.
One may guess the location of the epidural space at this point; epi-dural: outside or around the dura. It is located in the periphery of the spinal cord near the bony column. It roughly surrounds the dura mater. The epidural space is the site of lymph tissue (which removes toxins from tissues), the roots of spinal nerves, adipose (fat) tissue, and blood vessels. This space is not present in the brain, but begins at the top of the cervical region and ends at the bottom of the sacral region.
Spinal nerve roots are junctions between nerves that split off from the spinal cord to extend into the body. Vertebrae contain small gaps to allow these nerves to leave the spinal cord. Damage or irritation of these nerve roots may be associated with chronic pain. This may also be associated with reductions in muscle control (or paresis, which may be perceived as increased weakness or loss of muscle function). It may also lead to the loss of motor control (i.e. paralysis).
How Are Epidural Steroid Injections Performed?
The epidural space is often chosen as a target for medical intervention as it is near enough to one’s spinal cord to offer access to spinal nerve roots without excessive infiltration into areas such as the layer of cerebrospinal fluid as described above. The epidural space is present in all spinal regions, meaning that pain in many areas of the body may be addressed by the application of epidural steroid injections. Injection into this area is commonly regarded as far safer than injection into other areas, such as the sub-arachnoid space or directly into nervous tissue, when wishing to deliver pain-relieving medication directly to the spine.
A typical epidural steroid injection procedure may be performed in an outpatient clinic or physician’s office, and takes about 15 minutes. Before an epidural steroid injection is performed, equipment to monitor vital signs (e.g. heart rate, respiration, and blood pressure) may be connected to the patient, especially if intravenous sedation is required. The physician or specialist may first clean and prepare the skin above the area to be injected.
The patient lies face down, so that the spine will be easily accessible. A steroid injection usually only requires topical local anesthesia to numb the skin. The epidural space of the region targeted is visualized using imaging techniques such as fluoroscopy. This enhances the accuracy of the specialist or physician as he or she inserts a needle and extends it within the vertebra toward the appropriate space. The use of contrast dye may also help ensure accurate needle insertion. Once accurate placement of the needle has been achieved, the steroids are injected in a volume sufficient to cover the area necessary (e.g. to reach and act on the nerve roots in question). An excessive volume of medication over too large an area may affect the risk of adverse events resulting from this procedure.
Epidural steroid injections tend to take the following forms:
- Interlaminar—This approach is probably in the most widespread use. It involves the placement of a needle between two vertebrae. This allows drug delivery to nerves on the left and right halves of the spinal column. Interlaminar injection is associated with efficacy in studies including patients with radiculopathy resulting from damage to the discs of cartilage found between every pair of vertebrae. The interlaminar approach is also associated with pain relief in cases of failed back surgery syndrome, other forms of neuropathy, and spinal stenosis. Interlaminar injections are regarded as being more specific in aim than other approaches (e.g. caudal; see below). In other words, steroids injected between vertebrae may have a higher probability of reaching their targets on both sides of the spine. The interlaminar approach is linked to the requirement of smaller volumes compared to the caudal approach. However, this approach is associated with an increased risk of the dural membrane being pierced with the needle. This is known as dural puncture.
- Transforaminal—In this approach, a needle is inserted at an angle relative to a vertebra into the epidural space above a nerve root. Unlike the approach above, this targets nerves on only one side of the spine. It is often applied to patients who may have surgical pins, rods, or bone grafts as a result of spinal surgery in the region to be treated. Transforaminal injections may require more guidance from imaging, as the needle must be inserted into empty space to the side of the spinal column. However, this approach is regarded as being comparable in specificity to the interlaminar approach. Transforaminal injections may be associated with reduced risks of dural damage. Some research indicates that this approach is superior in efficacy in cases of spinal pain associated with neuropathy in comparison with the injections completed using either the caudal or interlaminar approach.
- Caudal—This approach goes into the epidural space of the sacral region at the end of the spine. This approach confers the option for larger volumes of steroids to be injected, if necessary. This is one of several potential benefits of the caudal approach. Another is the relatively small risk of dural puncture. Some analysis of the data on caudal injections indicates their beneficial effects in several chronic pain conditions. These include pain originating from intervertebral disc damage. The effects of the caudal approach in cases of pain associated with surgery and spinal stenosis are less well studied, but evidence on these topics indicate positive results. Injections done using the caudal approach may be less accurate than those completed using the translaminar or transforaminal approaches.
The use of all of these approaches is supported by high-quality evidence and research. Many patients report near-immediate pain relief as a result of these procedures. The duration of this may vary from patient to patient, and may range from a few weeks to a year. The factors associated with these individual differences in response have not yet been completed defined. The number of injections needed for an expected treatment effect may also vary from patient to patient. In some cases, multiple injections scheduled a few weeks apart may be required for optimal pain relief. The data concerning the best schedules for epidural steroid injections is limited. Some researchers disagree on this topic. Some assert that multiple injections result in no appreciable benefit. These scientists theorize that injection schedules need to be specialized for each individual patient, particularly in instances of a first-time injection resulting in appreciable benefit.
The treatment effect of epidural steroid injection may vary, depending on certain factors. These may be common to other similar interventions. The factors that may affect the result of a steroid injection include:
- The skill and training of the physician performing the injection
- Symptoms duration prior to treatment
- The disease or disorder associated with the pain
This may have an impact on the extent of the pain relief and on the long-term condition of the patient. Research suggests that the time elapsed before diagnosis and the start of treatment is inversely related to the pain relief experienced as a result of the epidural steroid injection.
Epidural steroid injections are performed to relieve pain. It is an intervention that has the advantage of being largely painless and time-efficient. Epidural steroid injections are often an outpatient procedure, which makes them an attractive alternative to more invasive techniques to alleviate chronic pain in many conditions. Epidural steroid injections may also reduce any debilitating effects of these disorders on normal movement and function. For example, patients who have missed or left work may be able to resume this as a result of an epidural steroid injection. Disability caused by pain can be a vicious cycle. Reduced mobility related to chronic pain may be a factor in more long-term impairments in movement.
Possible Adverse Effects
Epidural steroid injections may be recommended in many reputable pain clinics and general practices. However, the epidural spinal injection procedure is associated with some complications, which is common to many similar interventions. The incidence of these is relatively reduced, but may include:
- Delays in sleep onset, reduced ability to remain asleep, or reductions in sleep quality
- Hot flashes
- Increased risks of bleeding
- Sensations of flushing and warmth and a general perceived temperature increase; this may last a number of days after the administration of steroids
- Temporary increases in blood sugar, which is particularly relevant to diabetic patients
- Transient increases in pain
- Water retention
Reduced sensation in an extremity affected by pain for which the steroid injection has been recommended may occur in some cases. However, this is usually resolved in about eight hours. Severe adverse reactions to an epidural steroid injection are less common. These may include extensive blood loss, immune reactions, infection, nerve damage, and paralysis. In very rare cases, epidural steroid injection may be related to cases of meningitis (the irritation or infection of the membranes around the spinal cord).
Some patients may be more susceptible to the adverse effects of epidural injections than others. These people may be advised to consider other forms of treatments. Some factors that may influence the risk of complications include:
- Untreated hypertension
- Patients who also take medications to reduce blood clotting
- Patients with pre-existing blood clotting disorders
- Patients with pre-existing infections
- Patients with cardiovascular conditions
- Patients with pre-existing hypersensitivity to steroids
Factors Affecting Treatment Effectiveness
The failure of this treatment, or a response below the threshold normally expected as a result of epidural steroid injection, depends on many variables. These contribute to both the risk of treatment failure and recurrence of the existing pain condition. Variables that modify this risk may include:
- Age: The outcomes of many treatments, including epidural steroid injections, may be affected by advancing age
- A history of habitual smoking
- A history of opioid medication intake
- A history of spinal surgery
- Education status
- Occupational satisfaction, i.e. happiness or fulfillment at work
- Concurrent pain of other types
- Pre-existing anxiety disorders
- Pre-existing depressive disorders
- Individual pessimistic or hopeless opinions concerning the ability to recover from pain
- Reduced ability to cope with pain
- Pain catastrophization, or disproportional reactions of anxiety, fear, and discomfort in response to or in anticipation of pain (catastrophization may lead to reduced coping, hopelessness, anxiety and depressive symptoms, as well as the reduced ability to recover from pain)
- Increased pain-rating scores and functional decline prior to treatment
- The failure of previous different treatment options
- Increased negative reactions to fear
- Pain sensitivity; some people may be more sensitive to pain than others
- Chronic pain that is not affected by activity levels
Conditions Related To Epidural Steroid Injections
Epidural steroid injections are recommended for many pain conditions and disorders. This recommendation depends on an accurate diagnosis of the underlying condition responsible for pain, however. This is likely to begin with in-depth interviews with a physician or pain specialist concerning the symptoms, symptom severity, as well as the location and duration of symptoms experienced by the patient. This may ensure accurate diagnosis and an idea of which region of the spine an epidural injection should target. In some cases, the symptoms and their characteristics are not specific enough to give a concrete diagnosis. In these cases, the physician may diagnose based on the elimination of possible conditions. For example, in cases of lower back pain, the doctor may try to eliminate the possibilities of the most common conditions related to this, such as nerve root damage, before proceeding.
A doctor may also assess the patient for characteristics that affect the success of this treatment or of the likelihood of the recurrence of pain after an injection. These are also referred to as yellow flags, and may help the physician design a treatment plan appropriate to the individual patient. Yellow flags, depending on the pain research authority or association providing diagnostic tools to assess them, may include some of the psychosocial factors affecting treatment failure that are mentioned above.
The vast majority of people may expect to be subject to some form of spinal pain at one point or another in their lifetime. Pain in the neck or back is associated with many factors, which may depend on the structure of the back. Some of these relate to the deterioration of the many types of tissue (e.g. bone, cartilage) that make up the spine. These effects may extend to other tissues or structures that attach the spine to the rest of the body (e.g. joints, ligaments, or muscles). Despite all these possibilities, some cases of pain arise without the detectable presence of any factors listed so far. This is known as idiopathic or unexplained pain.
In many cases, spinal damage or disorder results in pain or discomfort localized in the spinal region in question, which may also spread outward into the limbs. This pain may manifest in many different forms, or types, of pain. Some patients may describe their pain as being a concentrated stabbing sensation, while others may perceive it as less localized and duller. The characteristics of a particular disorder may change over time. In other words, some conditions may be associated with episodic pain, which persists over a certain period of time, then remits for another period of time to recur again for another. Some symptoms are specific to certain disorders. On the other hand, others may be a characteristic of many different conditions.
These may include:
- Muscle stiffness or cramping
- Muscle spasming
- Spreading pain
- Weakness, numbness, or tingling in extremities
- Pain onset, or sensitivity, to pressure or touch
Some conditions associated with consistent pain may not be treated with conventional treatments such as oral painkillers. Patients who experience these may be better suited to epidural steroid injection.
Epidural steroid injection is commonly recommended to patients with:
- Intervertebral disc herniation: In these cases, the discs of cartilage that support vertebrae may impinge on spinal nerves or the spinal cord. This may require corrective surgery in some cases, but in less severe forms may be managed with pain-relieving interventions.
- Osteoarthritis: This is the chronic deterioration (or degeneration) of cartilage, associated with inflammation and pain.
- Spondylolisthesis: Spondylolisthesis is a progressive spinal deformity. This is caused by the degeneration of the joints between vertebrae over time. This condition may not result in pain, but can become painful if the spinal cord or nerve roots are compressed by the increased deformation of spinal structure. Some reports estimate that approximately 5% of the population suffer from spondylolisthesis.
- Whiplash: This is a relatively common form of cervical pain, in which the tissues within the cervical area are damaged by abrupt and violent jolting movements. These are typically linked to motor vehicle collisions and other high-impact events. Whiplash may be associated with chronic pain.
- Spinal stenosis: This is the compression of spinal nerves or the spinal cord, caused by the abnormal accumulation of tissue on the inside of the vertebral column. This may be associated with chronic pain that intensifies in response to activity, such as walking.
- Vertebral fractures: This is a degeneration of the normal structure of vertebrae, which may be associated with direct damage, conditions such as osteoporosis, or advancing age.
- Spinal deformities: These are conditions that cause abnormalities in the structure of the spine, and may be genetic. These disorders include kyphosis or scoliosis. Spinal deformity may affect all regions of the spine.
- Spinal infections: Some patients with back pain have been found to be affected by infections of the spine. This possibility should always be eliminated in the diagnosis of patients presenting with pain accompanied by fever. Infection may also be considered if a patient is recovering from spinal surgery, may be immunocompromised, or has a history of regular medication intake or drug abuse.
- Degenerative disc disease: This condition is associated with wear and tear to the discs over time. This results in injury to one or more discs, which may result in chronic pain. It can affect any region of the spine. The pain may spread to other areas or remain concentrated around the disc in question.
- Lumbar radiculopathy: This is associated with nerve damage located in the lumbar region. This condition is associated with pain that spreads through a lower extremity.
- Cervical radiculopathy: A similar condition in which a nerve in the cervical region is damaged. This causes pain to radiate along an arm.
- Failed back surgery syndrome: This often results from inadvertent nerve damage sustained in the course of surgery to correct another condition (e.g. radiculopathy). This may result in new-onset pain, which can become chronic. This pain may also result from the accumulation of scar tissue resulting from surgery, if this is near enough to a spinal nerve root.
Epidural steroid injections may result in pain relief for patients affected by the conditions listed above. Epidural steroid injection procedures may also be applied to the diagnosis of these conditions, e.g. an experimental injection into a certain area may help to confirm or deny the presence of damaged nerve roots. This may contribute to an accurate diagnosis, and to the possible role of epidural steroid injections in further treatment.
If the symptoms or conditions as described above are relevant to you, arranging a consultation with your physician or a pain specialist to discuss your case and its effect on your life is recommended. These health professionals can provide any further information and options for treatment. You may also be able to acquire more extensive educational material on your condition. Cases in which pain is not perceived as particularly severe or detrimental may respond to recommendations of reducing everyday activity and then gradually building up to an average former level of this over time. Research into spinal pain and its management indicates that approximately 90% of all patients may respond significantly in terms of pain rating scale scores to conservative first-line options, including physical therapy. However, a physician with a patient in severe or chronic pain that is not reduced by these treatments may decide that they are a candidate for epidural steroid injections.
The results of some recent studies suggest that epidural steroid injections may prevent unnecessary surgeries or delay the need for a valid surgical procedure. This prospective, multicenter trial compared the outcomes of patients with pain related to a herniated disc with a history of epidural steroid injection treatment to those of patients with the same condition but who never underwent injections. This study demonstrated that 56% of those treated with injections found surgery was not needed, compared to 19% of the patients who never underwent a course of epidural steroid injection therapy.
Persistent or chronic pain continues to be a prominent healthcare and economic issue. Some estimates indicate that approximately 90% of people are likely to encounter some type of pain that affects their ability to function normally at some point. Back pain is a major component of the total incidence of all pain. It is associated with an annual economic burden of $100 billion or more. Chronic pain may be treated using several well-recognized therapies and applications. These include epidural steroid injection treatment, which is associated with effective relief from back and neck pain.
This treatment option is a safe, minimally-invasive procedure that may be an alternative to more extensive surgery. Many patients experience decreases in pain immediately after one of these procedures. The process of epidural steroid injection and the resulting effects on neck and back pain are well-documented in scientific and clinical literature.
Epidural steroid injections may treat pain associated with disorders of the spinal cord or of the spinal nerves that branch out from this to travel into the body. They are thought to reduce pain based on the anti-inflammatory properties of steroids and the beneficial effects of the injections themselves on epidural blood flow and nerve cells. However, epidural steroid injections may be associated with some adverse effects. Side effects include the increased risk of gastric disorders and arthritis, increases in bodyweight, and emotional changes.
Many patients react positively to a single injection. Others, however, may need multiple injections to achieve expected pain relief. In these cases, a physician or pain specialist may design a treatment schedule tailored to the individual’s needs. Epidural steroid injections have been associated with the reduced need for surgery in conditions such as radiculopathy. Their success may depend on many factors, however, including the time elapsed before adequate diagnosis and treatment of the pain type in question. Contact your doctor or pain specialist if you feel epidural steroid injections may be the right treatment for you.
- Bicket MC, Gupta A, Brown CH, Cohen SP. Epidural injections for spinal pain: A systematic review and meta-analysis evaluating the “control” injections in randomized controlled trials. 2013;119(4):907-31.
- Boswell M, Hansen H, Trescot A, Hirsch J. Epidural Steroids in the management of chronic spinal pain. Pain Physician. 2003;6:319-
- Boswell MV, Trescot AM, Datta S, et al. Interventional techniques: evidence-based practice guidelines in the management of chronic spinal pain. American Society of Interventional Pain Physicians. Pain Physician. 2007;10(1):7-111.
- Cohen SP, Bicket MC, Jamison D, Wilkinson I, Rathmell JP. Epidural Steroids: A comprehensive, evidence-based review. Reg Anesth Pain Med. 2013;38:175-200.
- Colimon F, Villalobos F. Epidural steroid injections: Evidence and technical aspects. Techniques in Regional Anesthesia and Pain Management. 2010;14:113-119.
- Collighan N, Gupta S. Epidural steroids. Brit J Anaesth. 2010;10(1):1-5.
- Fish D, Kobayashi H, Chang T, Pham Q. MRI prediction of therapeutic response to epidural steroid injection in patients with cervical radiculopathy. Am J Phys Med Rehabil. 2009;3:239-246.
- Ghai B, Vadajae KS, Wig J, Dhillon MS. Lateral parasagittal verses midline interlaminar lumbar epidural steroid injection for management of low back pain with lumbosacral radicular pain: A double-blind randomized study. Anesth Analg 2013;117(1):219-227.
- Huston CW. Cervical epidural steroid injections in the management of cervical radiculitis: Interlaminar versus transforaminal. A review. Curr Rev Musculoskelet Med. 2009;2(1):30-42.
- Kwon JW, Lee JW, Kim SH, Choi JY, Yeom JS, Kim HJ, Kwack KS, Moon SG, Jun WS, Kang HS. Cervical interlaminar epidural steroid injection for neck pain and cervical radiculopathy: effect and prognostic factors. Skeletal Radiol. 2007;36(5):431-6.
- Livingston, E, Lynn C. Steroid injections to treat pain. JAMA. 2012;308(19):2047.
- Manchikanti L, Buenaventura R, Manhcikanti K, et al. Effectiveness of therapeutic lumbar transforaminal epidural steroid injections in managing lumbar spinal pain. Pain Physician. 2012;15:E199-E245.
- Pasqualucci A, Varrassi G, Braschi A, et al. Epidural local anesthetic plus corticosteroid for the treatment of cervical brachial radicular pain: Single injection versus continuous Infusion. Clin J Pain. 2007;23(7):551-7.