Nerve Root Block

Selective nerve root blocks are based on the assumption that delivering a small amount of medication to a specific target can accurately identify the source of pain and provide information that could affect or predict their surgical outcome.


Nerve Root Block Summary

Nerve root block can provide pain relief in patients experiencing pain in the upper or lower limbs and in the thoracic area secondary to nerve root irritation at the spinal level. Nerve root blocks can also provide important diagnostic information that may formulate further management plan. However it is important to note that in some cases injection treatment may not provide the desired results or the pain relief may not be sustained. At Pain Spa Dr. Krishna always performs nerve root blocks under real time fluoroscopy guidance, using state of the art equipment. This ensures 100% accuracy and our complication rates are extremely low.

At Pain Spa we offer cervical, thoracic and lumbar nerve root blocks under fluoroscopy guidance. Dr Krishna is very experienced in these procedures and has a very meticulous approach and safety record.

Information Sheet

Therapeutic Indications

  • Sciatica
  • Disc prolapse in the neck or lumbar spine causing pain in upper limbs or leg pain
  • Spinal stenosis
  • Degenerative spine disease
  • Failed back surgery syndrome

Determining a single structure within the spine as the source of pain can prove to be a diagnostic challenge due to the complexity and interrelation of the structures involved in the spinal column. Additionally, distinct anatomical structures can clinically present with similar symptom patterns and no physical examination finding can be specifically attributed to any one structure. To further complicate this dilemma, multiple structural abnormalities noted on imaging studies are frequently found to be painless.


The spinal cord gives rise to 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. Spinal nerves exit the spinal cord and course outward to the peripheral body through intervertebral foramina, which begin at C2/3. The first intervertebral neural foramen is formed at C2/3 and transmits the C3 nerve root. There are no neural foramina above C2/3 and the spinal nerve roots of C1 and C2 lie posterior to the atlanto-occipital and atlanto-axial joints respectively. Spinal nerve roots from C3 to L5 exit anterior to the facet joints through the neural foramina.

Each spinal nerve consists of a dorsal and a ventral root, which come together to create a short, unified segment within the intervertebral neural foramen. This short, intraforaminal segment is the spinal nerve proper although it is sometimes imprecisely referred to as the spinal nerve root. Once the spinal nerve is formed, it quickly bifurcates into a dorsal and ventral ramus as it exits the spinal column.


Pain from disc herniation can arise from nerve root compression and stimulation of nociceptors in the annulus or posterior longitudinal ligament. Nerve root edema can result from microvascular injury inside the nerve roots, and has also been noted to produce pain in nerve roots. In patients with stenotic nerve root canals there can also be mechanical compression of an exiting nerve root. The nerve roots, as they exit the intervertebral foramina, have a poorly developed epineurium, rendering them particularly vulnerable to mechanical and chemical injury. Painful spinal stenosis may result from disc bulging, protrusion, and herniation combined with osteophytes and arthritic changes of facet joints that cause narrowing of the spinal canal or neural foramina. Thus, various proposed mechanisms for radicular pain include partial axonal damage, neuroma formation, focal demyelination, intraneural edema and impaired microcirculation.

The other explanation surrounds the theory of chemical irritation and inflammation around the discs and nerve roots, which is considered a pain generator in conjunction with or without mechanical factors

Transforaminal Epidural Injection Vs Selective Nerve Root Block (snrb)

Various terms have been used to describe what a number of practitioners consider to be the same procedure- transforaminal, paraforaminal, nerve root block, SNRB and periradicular injections. The basic difference between a transforaminal injection and a selective nerve root block is probably just semantic and may be technically limited to only a few millimeters of the final needle tip position (in the medial to lateral plane). In a transforaminal injection, considered by some to be more of a therapeutic procedure, the injectate is delivered more medially and therefore more proximally to the anterior epidural space. It is spread on to adjacent nerves inside the spinal canal and is considered to limit the validity due to the lack of control of the spread of the injectate. By contrast, SNRBs could possibly permit greater specificity. The fact that this injection is extraforaminal and that the delivery of drugs would be distal to the convergence of the ventral and dorsal rami, a more confined spread could be achieved and therefore have improved legitimacy as a diagnostic tool.


MRI scan of the spine is considered the gold standard for investigating radicular pain or sciatica. CT Scan can be considered if MRI scan is contraindicated due to presence of pace maker, metal clips in the brain or other neural implants. Scans can accurately show the nerve root compression but it is important to note that the clinical presentation may not always match the pathology evident on the scan. Radiographic changes are equally common in non- symptomatic individuals. In addition, compression of the nerve roots in some patients may only be evident in standing position and standing MRIs are not widely available as yet. Good history taking and examination, in conjunction with imaging can improve the accuracy of diagnosis and interpretation of pathology seen on the scans.

Clinical Presentation

Sciatica classically presents with leg pain in a dermatomal distribution, with or without back pain. Other symptoms include:

  • Pain in the buttock or leg up to the foot
  • Burning or tingling
  • Sharp, shooting pain
  • Weakness and numbness in the leg
  • Pain worse with bending and walking
  • Pain exacerbated by coughing and sneezing

Radicular pain in the arms from cervical pathology can present with similar symptoms including:

  • Pain in the arm, forearm and/or hand
  • Burning or tingling
  • Sharp, shooting pain
  • Weakness and numbness in the upper limb
  • Weak grip, clumsiness

Indications For Selective Nerve Root Blocks

Nerve root blocks can be performed at cervical, thoracic or lumbar levels.

Diagnostic Indications

Selective nerve root blocks are used to clarify challenging clinical situations, in order to determine the pathophysiology of clinical pain, the site of nociception and the pathway of afferent neural signals. This may provide valuable information to the surgeons in determining the exact level of pathology and thereby the surgical procedure offered to the patient.


Injections are generally avoided in patients with systemic infection or skin infection over puncture site, bleeding disorders or coagulopathy, allergy to local anaesthetics or any of the medications to be administered.


The procedure is usually done on an outpatient basis. The procedure is performed under fluoroscopic guidance to ensure accuracy of needle placement. Patients need to be aware that the outcome of the procedure is variable and they may not receive the desired benefits. Similarly, they must be aware of the transient nature of the therapeutic benefits and that there may need repeated injections.

Generally a mixture of local anaesthetic and steroid is injected. The local anaesthetic agent within the injectate may act on the nerve root to prevent abnormal firing , whereas corticosteroids may reduce inflammation of around the nerve root. The anaesthetic is probably responsible for immediate pain relief, whereas steroids are believed to be responsible for pain relief 2–6 days after their administration. For a diagnostic block, a short-acting anaesthetic alone is sufficient.


Complications are rare, particularly if injections are performed using a precise needle-positioning technique. Severe allergic reactions to local anaesthetics are uncommon. Steroid injections may produce local reactions, occurring most often immediately after injection. These local reactions last for 24 to 48 hours, and are relieved by application of ice packs. Post-procedural pain flare-up may occasionally occur, and may be treated with painkillers. Neurological complications including paraesthesias, numbness and paralysis have been described but are rare. Infections including epidural abscess and chemical meningitis can occur but the incidence is very low as the procedure is performed under strict aseptic conditions.

In recent years, embolic events have been reported after transforaminal epidural steroid injections with particulate steroids. These embolic phenomena can result in serious complications including spinal cord injury, stroke and death. Undetected vascular injections of the vertebral artery or spinal radicular arteries with particulate steroids are postulated to have caused embolic infarctions. Complications can be minimized with meticulous technique, injecting contrast under live fluoroscopy and using non-particulate steroids.

Particulate Vs Non-particulate Steroids

Very little data compare the clinical efficacy of particulate versus non-particulate steroids. In 2006, Dreyfuss compared the efficacy of dexamethasone to triamcinalone in cervical transforaminal epidural injections. Both groups exhibited statistically and clinically significant improvements in pain at four weeks. The triamcinolone group demonstrated a non–statistically significant trend toward more improvement.

In 2008, O’Donnell compared the efficacy of triamcinolone to dexamethasone transforaminal ESI in the treatment of low back and/or radicular pain. Both groups showed statistically significant improvement but more so in the triamcinolone group. This study is limited by its inclusion of patients with both low back pain and lumbar radiculitis.

Particulate steroids appear to be slightly more efficacious than non-particulate steroids but further studies need to be done. It is probably wise to use a non-particulate steroid like dexamethasone in cervical and thoracic transforaminal injections. The choice in lumbosacral transforaminal injections is debatable, especially if appropriate safety measures are used. The risk with particulate steroid injections has not been associated with
inter laminar epidural steroid injections nor with intra-articular injections.

Clinical Outcome

The principle behind diagnostic nerve root injections forms the premise that the local anesthetic used in these injections will act only at the desired site and therefore provides the practitioner an indisputable etiology of the pain-generating source. The lack of clinical-radiological correlation, the presence of multilevel spine disease, the conflicting correspondence between electromyography and clinical findings, as well as the presence of atypical pain patterns have prompted pain clinicians to collaborate in searching for a definite etiology of pain to limit spine interventions, and possibly, improve surgical outcomes.

A patient’s subjective report of 50% pain relief or greater after local anesthetic infiltration is what currently exclusively defines a technically successful diagnostic or therapeutic nerve root injection. The criterion of success is not particularly rigorous since it is based on a patient’s subjective interpretation; hence, the predictability of the information provided by the diagnostic injection has to be modest at best. The lack of an indisputable measurable objective finding leads to an unacceptable number of false-positive results.

The combination of clinical findings (history and physical examination), radiological evidence, and interventional diagnostic procedural information is what should be weighed together to reach the final assessment of the causative source. The lack of response to blocks suggests either lack of delivery of the medication to the desired target, severe at-level pathology that prohibits the injectate from reaching the desired target, or pain signals possibly generated more centrally. A technically successful selective nerve root block that does not provide post procedural pain relief gives strong and truly valuable negative prognostic information (negative-predictive value). Thus, since the lack of pain relief post block correlates with poor surgical outcome, the information obtained should be used to explore other forms of minimally invasive treatment modalities and defer surgery as a ‘permanent fix’.

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Dr Murli Krishna

Consultant Pain Medicine