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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).