Selective nerve root blocks
Section snippets
Anatomy
The nerve root morphology and course vary slightly depending on the location. In the thoracic and lumbar spine, spinal nerve roots exit through their respectively numbered vertebral neural foramina. As each lumbar nerve root exits through the lateral recess, it courses inferolaterally under the pedicle (Fig 1). Lateral to the neural foramen, the nerve root expands slightly at the dorsal root ganglion; more peripherally, it returns to its previous size. In the thoracic spine, the nerve root
Rationale
Low back pain is one of the most common health problems in the United States and is the leading cause of disability for persons younger than 45 years of age. The lifetime prevalence of low back pain is 80%. It is estimated that the evaluation and treatment of low back pain costs billions of dollars annually.10
Most patients obtain relief from conservative therapy, typically consisting of various combinations of rest, medications, and physical therapy. Chiropractic manipulation is also commonly
Mechanism of action
Previous studies on the pathophysiology of radiculopathy suggested the concept that pain and neurologic dysfunction result from mechanical compression of the nerve root.18 It is now thought that mechanical factors alone do not provide a sufficient explanation. Although mechanical compression can lead to inflammation and therefore radiculopathy,11 many authors have proposed that inflammation around the nerve roots is caused by chemical irritation from a herniated disc.18, 19 Inflammation around
Indications
Selective nerve root blocks are used both as therapeutic and diagnostic procedures. Most patients who are selected for nerve root blocks have had previous diagnostic imaging studies, usually a recent CT or MRI. The patients are referred to us for SNRBs by our clinical colleagues who want to determine the cause and exact site of the pain as well as to exclude other causes for the radicular symptoms. The patients that are usually selected include the following: postsurgical patients with
Contraindications
There are few absolute contraindications for a selective nerve root block: (1) systemic infection or superficial infection along the needle path; (2) uncorrectable coagulopathy, international normalized ratio > 1.5 or platelets < 50,000/mm3; (3) allergy to the steroid or local anesthetic (relative contraindication if allergic to iodinated contrast as gadolinium can be used); and (4) pregnancy.3, 25
Theoretical risks
Complications from an SNRB are very low. There is the remote possibility of nerve root laceration, spinal fluid leak, or production of a spinal block.4 Before the procedure each patient is assessed and informed of the risk for infection, bleeding, nerve injury, allergic reaction to contrast, and the medication side effects. Pneumothorax is an additional risk with thoracic nerve root blocks. For the cervical nerve root block, there is an additional risk of inadvertent vascular puncture.
Expectations
Selective nerve root blocks are generally performed on an outpatient basis. Before the procedure, patients are told to bring a driver, expect to take the rest of the day off as needed, and provide an MRI or CT that is less than a year old. The MRI/CT is not technically necessary, but it assists with the location selection. Thus, we will often perform these procedures without the MRI/CT, if the referring clinician has determined a specific root to be injected. If anticoagulation medication is
Medications
Lidocaine hydrochloride 1% buffered with sodium bicarbonate is administered for local skin anesthesia. The nerve root block injection consists of a combination of a 1:1 mixture of steroid and a long acting local anesthetic. The steroids used at our institution are either Kenalog (Bristol-Myers Squibb Co, Princeton, NJ) 40 mg/mL (triamcinolone acetonide injectable suspension) or Celestone Soluspan (Schering Corporation, Kenilworth, NJ) 6 mg/mL (betamethasone sodium phosphate and betamethasone
Technique
Selective nerve root blocks are minimally invasive procedures and do not require admission. At our institution, we do not sedate our patients. The procedure can be done with either CT or fluoroscopic guidance. We choose to perform all of our nerve root blocks under fluoroscopy because the technique is easier to execute and results in a cost savings. Although many authors describe performing cervical nerve toot blocks using CT guidance,3, 5, 25 we and many others will only perform this procedure
Lumbosacral
Informed consent is obtained before the procedure. The patient is asked to describe the location and level of pain using a ten point pain scoring system. The patient is placed prone on the fluoroscopy table. The appropriate location is marked under fluoroscopic guidance. The fluoroscopic unit is rotated ipsilaterally until the corresponding facet is moved medially away from the lateral margin of the vertebral body. Additionally, a small amount of craniocaudal angulation is applied to profile
Cervical
In the cervical spine, there are 8 cervical nerve roots. For example, if the symptoms correlate with the seventh cervical root, the C6/7 foramen is the injection target. Before the procedure the patient’s MRI of the cervical spine is reviewed to evaluate for an anomalous location of the vertebral artery, which may alter the decision to perform the SNRB. After informed consent, the patient is placed supine on the fluoroscopy table and the head is turned contralaterally. The patient is made as
Thoracic
Thoracic nerve root blocks are not routinely requested at our institution. The procedure is not significantly different from that of lumbar nerve root blocks. The main concern with the thoracic nerve root block is the close proximity of the pleura and the potential for a pneumothorax during needle placement. It is beneficial to review the patient’s CT or MRI to determine the location of the adjacent lung relative to the needle path.
The patient is placed prone on the fluoroscopy table.
Side effects/complications
The side effects from this procedure can include insomnia the night of the procedure, transient nonpositional headaches that resolve within 24 hours, increased post-procedure back pain at the injection site, facial flushing, vasovagal reaction, allergic reactions to the medications, nausea, and increased leg pain with radicular symptoms.3, 4 Pneumothorax is a risk with thoracic nerve root blocks.
Summary
Selective nerve root blocks are valuable diagnostic and therapeutic procedures in patients with radicular symptoms. Understanding the anatomy, benefits, and risks, as well as precise needle placement, are important factors in performing successful nerve root blocks. The techniques we describe come from our training and ongoing experience. There are other acceptable methods as well.
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Cited by (8)
Selective nerve root blocks as predictors of surgical outcome: Fact or fiction?
2011, Techniques in Regional Anesthesia and Pain ManagementCitation Excerpt :The dura continues on as perineurium. The epineurium is then a continuation of the epidural connective tissue and surrounds the nerve, forming a sheath that retrogradely connects to the epidural space.26 The nerve root exits the foramen from the posterior aspect of the neural foramen.
Transforaminal Epidural Block and Selective Nerve Root Block
2010, Minimally Invasive Percutaneous Spinal TechniquesSpinal CT-guided interventional procedures for management of chronic back pain
2005, Journal of Vascular and Interventional RadiologyTransforaminal epidural block and selective nerve root block
2010, Minimally Invasive Percutaneous Spinal Techniques: Expert Consult: Online and Print with DVDPercutaneous dorsal root ganglion block for treating lumbar compression fracture-related pain
2018, Acta NeurochirurgicaInterventional management of Chronic pain
2009, Annals of the Academy of Medicine Singapore