Nerve blocks are often performed as therapeutic or palliative interventions for pain relief. However, they are often performed for diagnostic or prognostic purposes. When considering nerve blocks for chronic pain, clinicians must always consider the indications, risks, benefits, and proper technique. Nerve blocks encompass a wide variety of interventional procedures. The most common nerve blocks for chronic pain and that may be applicable to the neurosurgical patient population are reviewed in this article. This article is an introduction and brief synopsis of the different available blocks that can be offered to a patient.
Key points
- •
Nerve blocks can be performed for a variety of conditions, providing diagnostic and therapeutic modalities.
- •
Whenever considering nerve blocks, risks and benefits must be considered before intervention.
Introduction
Nerve blocks are often performed as therapeutic or palliative interventions for pain relief. However, they are often performed for diagnostic or prognostic purposes. When considering nerve blocks for chronic pain, clinicians must always consider the indications, risks, benefits, and proper technique, in order to provide maximal benefit for the patients. Nerve blocks encompass a wide variety of interventional procedures. The most common nerve blocks for chronic pain and that may be applicable to the neurosurgical patient population are reviewed in this article. This article is an introduction and brief synopsis of the different available blocks that can be offered to a patient.
Introduction
Nerve blocks are often performed as therapeutic or palliative interventions for pain relief. However, they are often performed for diagnostic or prognostic purposes. When considering nerve blocks for chronic pain, clinicians must always consider the indications, risks, benefits, and proper technique, in order to provide maximal benefit for the patients. Nerve blocks encompass a wide variety of interventional procedures. The most common nerve blocks for chronic pain and that may be applicable to the neurosurgical patient population are reviewed in this article. This article is an introduction and brief synopsis of the different available blocks that can be offered to a patient.
Diagnostic versus therapeutic nerve blocks
In general, nerve blocks may be divided into diagnostic and therapeutic interventions. Pain is a subjective unpleasant sensation, the exact pathophysiology of which is uncertain or multifactorial in most clinical situations. In human beings, chronic pain is a complex process that is compounded by psychosocial, financial, and sometimes legal matters. When the cause of pain is unclear despite appropriate history taking, physical examination, and imaging or electrodiagnostic studies, diagnostic or prognostic nerve blocks may be in order. For instance, pain originating in the zygapophyseal joints or the sacroiliac joint cannot reliably be diagnosed by clinical examination or imaging studies and diagnostic local anesthetic blocks are frequently called on to confirm the diagnosis. However, there are significant limitations to nerve blocks in making the leap from pain relief to establishing that pain is mediated by the targeted nerve, because performance of a nerve block takes into consideration many assumptions:
- 1.
The nerve being blocked is responsible for generation, conduction, or maintenance of the painful stimulus
- 2.
The operator performing the procedure is skilled in the performance of the block
- 3.
The needle is placed in the exact and correct anatomic location
- 4.
The patient does not have anatomic variations or aberrant physiologic or pharmacologic responses to the medication used
- 5.
The volume of the medication injected is appropriate for the nerve/space
- 6.
The medication injected will remain in place and anesthetize only the targeted nerve and no other nerves or structures or act systemically
- 7.
The patient is able to understand and interpret the response to the block appropriately
Nonetheless, when properly performed in the appropriate clinical setting, nerve blocks can provide valuable adjunct information that, when taken together with the patient’s complete clinical picture, may help in decision making about the cause of pain.
The most commonly performed diagnostic nerve blocks include:
- 1.
Selective nerve blocks. These may be indicated in the presence of radicular symptoms and questionable or multiple levels of abnormalities on imaging studies. Assessing selective nerve root blocks is challenging given that no loss of cutaneous sensation occurs following surgical division of a single nerve root. Multiple studies attest to the high positive predictive value of selective nerve root blocks and their accuracy is superior to that of imaging and electrodiagnostic testing. Nonetheless, accuracy of these blocks awaits authentication in controlled blinded trials.
- 2.
Joint injections. Controlled diagnostic blocks have been used successfully to identify the sacroiliac joint and other joints as a source of pain and represent the most reliable way of diagnosing painful joint syndromes. Sacroiliac joint pain accounts for between 15% and 20% of patients presenting with axial low back pain. Even though their validity has yet to be proved, small-volume local anesthetic blocks are still the most used method for diagnosing sacroiliac joint pain.
- 3.
Medial branch blocks. Medial branches of posterior rami supply zygapophyseal (facet) joints at the same level and the level below. Hence, blocking a single facet joint requires blockade of 2 medial branches. Diagnostic medial nerve branch blocks are the gold standard to establish facet-mediated pain. Lumbar zygapophyseal pain accounts for up to 15% of patients with axial low back pain.
- 4.
Differential nerve blocks. These blocks are often performed in the setting of abdominal or pelvic pain of unknown cause. An anatomic (nerve-by-nerve block) or pharmacologic approach may be used. The pharmacologic approach is preferred and involves epidural blockade of all innervation to the target area (typically T4 level) and evaluation of the pain response as the epidural block resolves. It is most useful to differentiate organic peripheral pain that would be amenable to further interventions from central pain.
False-positive responses occur with blocks even with the use of imaging. For instance, a placebo response rate of 38% (false-positives) has been shown for uncontrolled lumbar facet joint blocks and a low positive predictive value of 31%. To curtail the rate of false-positive responses, repeat blocks or comparative local anesthetic blocks have been performed, resulting in refinement of diagnostic accuracy.
Diagnostic blocks typically provide a patient with relief limited to the duration of action of the local anesthetic used, although longer-lasting responses are occasionally noted.
Therapeutic nerve blocks
Therapeutic interventions allow longer-term pain relief. The many common therapeutic nerve interventions include epidural steroid injections, radiofrequency ablations, and sympathetic nerve neurolysis.
Epidural Steroid Injection
Introduction
Epidural steroid injections have been used for chronic spinal pain relief for decades. Depositing steroids in the epidural space helps reduce inflammation around nerve roots contributing to pain. Epidural steroids can be delivered by several approaches, including the interlaminar, transforaminal, and caudal approaches.
Epidural steroid injection can be performed as a more conservative approach than surgery, when surgery is not indicated or as a palliative bridge to surgery. Epidural injections can benefit a patient when the pain is secondary to disc herniation, discogenic pain, or spinal stenosis. Benefits involve predominantly short-term pain relief, although occasionally long-term pain relief occurs. A series of 3 injections can be done in a 6-month span; however, this standard relates to limiting steroid toxicity. The main concern with repeated epidural steroid injections centers on the amount of total steroid injected and the possibility of causing adrenal suppression and affecting bone reabsorption.
Indications
Indications for epidural steroid injection include radiculopathy secondary to disc herniation, isolated spondylotic spurring of the foramina, or neurogenic claudication associated with spinal stenosis.
Efficacy
Moderate to strong evidence exists for interlaminar and transforaminal epidural steroid injections, at least in the short-term relief of radicular pain.
Multiple studies of transforaminal epidural steroid injections in patients with herniated discs, radiculopathy, and stenosis reported significant benefit in pain scores, walking tolerance, and standing.
In 2010, the American Society of Anesthesiologist Task Force on Chronic Pain Management published a practice guideline that stated, “Epidural Steroid injections with or without local anesthetics may be used as part of a multimodal treatment regimen to provide pain relief in selected patients with radicular pain or radiculopathy. Shared decision making regarding epidural steroid injections should include a specific discussion of potential complications, particularly with regard to the transforaminal approach.”
Procedure
There are multiple approaches to delivering steroid into the epidural space. The interlaminar epidural steroid injection uses a midline approach and delivers medications centrally with some spread to surrounding nerve roots. It is useful in central canal stenosis and in patients with diffuse disorder. The transforaminal approach is a directed injection, either right or left sided, and delivers medication that surrounds the affected nerve root with spread into the anterior epidural space. The caudal approach uses the opening at the sacral hiatus to deliver medication to the lower lumbar spine area. These procedures are done under fluoroscopic guidance and confirmation is obtained with contrast dye before injection of steroid ( Fig. 1 ).
Complications
When considering an epidural steroid injection, the risks versus benefits must be assessed. Potential risks of the procedure include, but are not limited to, dural puncture, postdural headache, bleeding, infection, nerve damage, epidural hematoma, epidural abscess, and paralysis. Transforaminal injections of particulate steroids carry a small but significant risk of embolization of large steroid particles into radicular arteries and from there into arterial spinal cord artery or vertebral arteries. Catastrophic events have occurred, in particular with cervical transforaminal injection of particulate steroids. Nonparticulate steroids are now advocated in transforaminal epidural steroid injections in the cervical region. Even though the risks are low, all patients must be well informed and consented before the procedure.
Facet Joint Nerve Blocks
Introduction
Zygapophyseal or facet joints are a source of pain for many patients. A common cause of this joint pain is degeneration and arthritis of the spine and joint.
Pain that is caused by facet joints typically presents with axial pain that increases with movement. Pain is worse with bending, extending, and rotational movements. Radiation of pain toward the extremity is an uncommon presentation but pain is often referred to the buttocks or shoulders.
Patients typically have insidious onset of pain over time; however, a subgroup of patients has sudden onset of facet pain that occurs after some sort of trauma or deceleration (whiplash) injury.
Though facet arthropathy is a common finding on imaging, correlation must be made with history and physical examination. When suspicion of facet-related pain is high, a diagnostic medial branch block must be performed to confirm the diagnosis. A unilateral or bilateral approach can be performed, depending on the patient’s character of pain. The facet joint is provided with sensory innervation by the medial branch of the posterior primary ramus.
Medial branch blocks provide diagnostic value, indicating whether the joint is the pain generator for a patient. Patients are asked to perform movements that normally cause them pain after the procedure and their pain is reassessed. Significant pain relief, 50% or greater, is considered a positive response and a patient can return for a radiofrequency ablation at a later date. Radiofrequency ablation provides a much longer duration of pain relief, averaging about 6 to 9 months in duration.
Procedure
A diagnostic medial branch block is conducted with local anesthetic only. Using fluoroscopic guidance, the needles are positioned along the posterior spine at a consistent location where the medial branch is known to travel.
In the cervical region, the needles are advanced toward the middle of the articular pillars. After correct location has been verified, 0.25 mL of local anesthetic is injected. In the thoracic and lumbar regions, after correct location has been verified, 0.5 mL of local anesthetic is injected.
Radiofrequency ablation is performed in a similar manner to medial branch blocks; however, sensory and motor testing is typically performed before the ablation ( Fig. 2 ).
Efficacy
Good evidence exists in support of radiofrequency lesioning of the medial branch nerves given that properly performed diagnostic tests have provided significant temporary relief.
Numerous placebo-controlled trials have examined lumbar facet pain and shown that radiofrequency ablation yielded positive results in lumbar pain in selected patients.
Complications
Complications include pain at the injection site, injury to spinal nerves, uncomfortable dysesthesia, and sensory loss. Use of fluoroscopic guidance, proper testing before ablation, and performance of the procedure in an awake or minimally sedated patient results in near elimination of major risks.
Sympathetic Blocks
Introduction
These are multiple neural pathways that are involved in the perception and maintenance of pain. Following neuronal injury, the sympathetic nervous system is involved in pain perception and maintenance of chronic pain.
The sympathetic chain extends from the first thoracic level to the second or third lumbar level. Its target area covers the cervical to the sacral region, providing sympathetic stimulation throughout the body. Targeting different sympathetic ganglia allows blockade of sympathetic fibers in various regions throughout the body that may be contributing to or maintaining a patient’s chronic pain.
Efficacy
Limited evidence exists in support of the use of sympathetic blocks in pain relief of extremity pain. There is stronger evidence for efficacy in neurolytic celiac plexus blocks in patients with pancreatic cancer pain. There are multiple studies investigating the use of neurolysis in patients with cancer. One study comparing celiac plexus neurolysis versus sham showed significant pain relief at follow-up at 6 weeks. A meta-analysis of 21 retrospective studies in patients undergoing celiac plexus neurolysis reported that 89% of patients received excellent pain relief in the follow-up visit at 2 weeks and 90% of patients received pain relief at the 3-month visit. When investigating superior hypogastric plexus blocks, it has been reported that 70% of patients with pelvic pain associated with cancer received significant pain relief in terms of visual analog scores.
Stellate Ganglion Block
Introduction
The cervical sympathetic trunk contains 3 ganglia: the superior, middle, and inferior cervical ganglia. In 80% of people the lowest cervical ganglia is fused with the upper thoracic ganglion to form the cervicothoracic ganglion, also known as the stellate ganglion. The cervicothoracic ganglion is on or just lateral to the longus colli muscle between the base of the seventh cervical transverse process and the neck of the first rib. The cervicothoracic ganglion receives preganglionic fibers from the lateral gray column of the spinal cord. The preganglionic fibers for the head and neck emerge from the upper 5 thoracic spinal nerves, ascending in the sympathetic trunk to synapse in the cervical ganglia. The preganglionic fibers supplying the upper extremity originate from the upper thoracic segments between T2 and T6 and in turn synapse in the cervicothoracic ganglion.
Procedure
The block is generally conducted at the sixth or seventh cervical vertebra using ultrasonography or fluoroscopic guidance. Ultrasonography allows a physician to visualize the soft tissue, artery, vein, and neural bundle. Fluoroscopy allows better visualization of bony structures.
Regardless of the technique, after appropriate positioning of the needle is confirmed, approximately 2 to 5 mL of 0.25% bupivacaine or ropivacaine are injected. Injection is done slowly, in increments, being aware of any signs of local anesthetic toxicity. Signs of appropriate spread include increased temperature in the affected upper extremity, venodilatation in the ipsilateral arm, nasal congestion, anhidrosis, and Horner syndrome. For a successful sympathetic block, a temperature increase in the hand to at least 34°C is recommended to achieve meaningful interruption of the postganglionic sympathetic supply. The many indications for the blockade of the stellate ganglion include, but are not limited to, complex regional pain syndrome of the upper extremity, vascular insufficiency of the upper extremity, hyperhydrosis, acute pain of herpes zoster, postherpetic neuralgia, congenital prolonged QT syndrome (left cervicothoracic ganglion blockade), migraines, tension and cluster headaches, cerebral angiospasm, and cerebral thrombosis ( Fig. 3 ).
