Selective nerve root block

Selective Nerve Root Block (SNRB) is practiced as a part of the management of radicular pain due to a particular affected nerve root in both cervical and lumbar regions 1) 2) 3).

A Systematic review aimed to examine the diagnostic accuracy of selective nerve root blocks (SNRBs) to identify patients most likely to benefit from lumbar decompression surgery.

INFORMATION SOURCES: MEDLINE (Ovid), MEDLINE In-Process & Other Non-Indexed Citations, EMBASE, Science Citation Index, Biosis, LILACS, Dissertation abstracts and National Technical Information Service from inception to 2018.

Risk of bias and applicability was assessed using the QUADAS-2 tool. Beynon et al., performed random-effects logistic regression to meta-analyse studies grouped by reference standard.

6 studies (341 patients) were included in this review. All studies were judged at high risk of bias. There was substantial heterogeneity across studies in sensitivity (range 57%-100%) and specificity (10%-86%) estimates. Four studies were diagnostic cohort studies that used either intraoperative findings during surgery (pooled sensitivity: 93.5% [95% CI 84.0 to 97.6]; specificity: 50.0% [16.8 to 83.2]) or 'outcome following surgery' as the reference standard (pooled sensitivity: 90.9% [83.1 to 95.3]; specificity 22.0% [7.4 to 49.9]). Two studies had a within-patient case-control study design, but results were not pooled because different types of control injections were used.

They found limited evidence which was of low methodological quality indicating that the diagnostic accuracy of SNRB is uncertain and that specificity in particular may be low. SNRB is a safe test with a low risk of clinically significant complications, but it remains unclear whether the additional diagnostic information it provides justifies the cost of the test 4).

Guyot, studied a series of 298 patients who received a selective nerve root injection and made a comparative study dividing them into 2 groups according to the drugs used. In group A, they used betamethasone 6 mg and lidocaine, while in group B, triamcinolone 60 mg and bupivacaine were used for the procedure. They evaluated the patients for a period of at least 8 months, assuming the need for surgical therapy as the failure of the procedure.

Both groups had 149 patients with similar etiological characteristics. Forty-seven patients (16%) required surgery to relieve pain with a similar distribution between groups (24 from group A and 23 from group B). Time between nerve root injection and surgery was 86.79 (14-360) days on average in group A and 75.76 (2-180) days in group B with no statistical difference (P = .67). Only one complication was documented, an anaphylactic shock in a patient in group B.

Based on these results, they found no difference in the type of steroid or local anesthetic used for selective nerve root injections 5).

In a case series of 40 patients the effect of SNRB was typically short acting in majority of patients and recurrence is expected. It creates a window period with reduced pain but of varied intervals depending on the pathology. It did not alter the prognosis in those with severe disease where surgery is well indicated. Level of Evidence - Level 4 6).

A total of 105 block anesthetics were performed under fluoroscopic guidance in 47 consecutive patients with pure radiculopathy from a single confirmed level: 47 blocks were performed at the symptomatic level, and 58 were performed at the adjacent asymptomatic “control” level. Contrast and local anesthetics were injected, and spot radiographs were taken in all cases. We calculated the diagnostic value of the block anesthetics using concordance with the injected level. We analyzed the potential causes of false results using spot radiographs.

On the basis of a definition of a positive block as 70% pain relief, determined by receiver-operator characteristic (ROC) analysis, diagnostic lumbar selective nerve root block anesthetics had a sensitivity of 57%, a specificity of 86%, an accuracy of 73%, a positive predictive value of 77%, and a negative predictive value of 71%. False-negatives were due to the following causes identifiable on spot radiographs: insufficient infiltration, insufficient passage of the injectate, and intraepineural injections. On the other hand, false-positives resulted from overflow of the injectate from the injected asymptomatic level into either the epidural space or symptomatic level.

The accuracy of diagnostic lumbar selective nerve root blocks is only moderate. To improve the accuracy, great care should be taken to avoid inadequate blocks and overflow, and to precisely interpret spot radiographs 7).

Chung JY, Yim JH, Seo HY, Kim SK, Cho KJ. The Efficacy and Persistence of Selective Nerve Root Block under Fluoroscopic Guidance for Cervical Radiculopathy. Asian Spine J. 2012;6:227–32.
Anderberg L, Annertz M, Persson L, Brandt L, Saveland H. Transforaminal steroid injections for the treatment of cervical radiculopathy: a prospective and randomised study. Eur Spine J. 2007;16:321–8.
Narozny M, Zanetti M, Boos N. Therapeutic efficacy of selective nerveroot blocks in the treatment of lumbar radicular leg pain. Swiss Med Weekly. 2001;131:75–80.
Beynon R, Elwenspoek MMC, Sheppard A, Higgins JN, Kolias AG, Laing RJ, Whiting P, Hollingworth W. The utility of diagnostic selective nerve root blocks in the management of patients with lumbar radiculopathy: a systematic review. BMJ Open. 2019 Apr 20;9(4):e025790. doi: 10.1136/bmjopen-2018-025790. PubMed PMID: 31005925.
Guyot JP. Lumbar Selective Nerve Root Block: Comparative Study Using Two Pharmacological Formulae. Global Spine J. 2018 Jun;8(4):374-377. doi: 10.1177/2192568217728724. Epub 2017 Sep 1. PubMed PMID: 29977722; PubMed Central PMCID: PMC6022957.
Arun-Kumar K, Jayaprasad S, Senthil K, Lohith H, Jayaprakash KV. The Outcomes of Selective Nerve Root Block for Disc Induced Lumbar Radiculopathy. Malays Orthop J. 2015 Nov;9(3):17-22. doi: 10.5704/MOJ.1511.002. PubMed PMID: 28611904; PubMed Central PMCID: PMC5393129.
Yeom JS, Lee JW, Park KW, Chang BS, Lee CK, Buchowski JM, Riew KD. Value of diagnostic lumbar selective nerve root block: a prospective controlled study. AJNR Am J Neuroradiol. 2008 May;29(5):1017-23. doi: 10.3174/ajnr.A0955. Epub 2008 Feb 13. PubMed PMID: 18272560.
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