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Selective Nerve Root Block (SNRB)

What is a selective nerve root block?

SNRB is a common interventional procedure for diagnosis or managing leg pain resulting from spinal derangement. In some patients, SNRB is the last nonsurgical treatment attempted prior to surgery. SNRB injection targets the anterior epidural space and the spinal nerve as it exits the neural foramen. SNRB can be used to define the source of pain and is especially useful when clinical findings and results of electrodiagnostic and imaging studies are equivocal. In addition, SNRB may be particularly useful to identify the symptomatic level in patients with multilevel pathology. Several studies show favorable short-term outcomes with SNRB. 

How is a SNRB performed?
Aspirin-based products and platelet inhibitors are discontinued 7 to 10 days prior to injection. The setting for SNRB injection is a hospital operating room. We use real-time fluoroscopic guidance during the injection. The spinal needle is inserted and advanced under fluoroscopic guidance. A contrast dye is injected to confirm the suspected symptomatic nerve root. A mixture solution of steroid and anesthetic agent are injected into the symptomatic nerve root. Procedure time is about 10 minutes. After the procedure, the patient will be observed in the recovery room for 10-20 minutes.
For your safety, the patient needs to transport by accompany from the hospital to home. With some patients, steroids require a couple days to be effective. 
What are the indications for SNRB?
1. Spinal stenosis—especially in symptomatic foraminal stenosis 
2. The patient may describe low back pain with radiation into the buttocks and down the leg, typically in a unilateral distribution.    
3. The patients who have high risks for operation                                                                
4. Prior spine surgery and ongoing radicular and/or axial pain                             
5. Radicular pain of postoperative scarring 
6. To identify nerve root responsible for pain when clinical or radiographic findings are equivocal                                                                                                                       
7  For diagnosis of atypical extremity pain                                                                             
8. To confirm the pain generator in failed back surgery syndrome with atypical extremity pain 
What are the contraindications for SNRB?                                                           
1. Allergy to medications                                                                               
2. Pregnancy                                                                                                          
3. Coagulopathy                                                                                                                                      
4. Anticoagulation (aspirin, warfarin and antiplatelet agent therapy should be stopped 7-10 days before SNRB)                                                                                                        
5. Skin infection at the injection site 
What are the benefits and risks of SNRB?
Benefits of SNRB: 
1. To relieve pain and to increase the quality of life
2. Allowing participation in recreation activities
3. Less invasive, with short recovery time 
Performed as outpatient clinic
The patients who received SNRB showed significant improvement in function at 6 days and showed significant improvement in pain at both 30 days and 6 months. If the initial response to SNRB is favorable but short-lived, a series of injections (3-6 times per year) is recommended. The interval for sequential block varies from days to weeks for a series of injections.
Risks of SNRB:
1. Postinjection exacerbation of pain (1% of cases) 
2. Increase in blood glucose level from steroid injection
3. Neurologic complications due to direct nerve trauma 
4. The procedure may need to be repeated in 3-6 months
5. Infection (very rare)
6. Bleeding (very rare)
Dr.Chaiyot Chaichankul
Orthopedic Sugeon-Spine Specialist
You may find our specialist here at Orthopedic Institute, Phyathai 2 Hospital
Phyathai 2 Hospital
International Correspondence Center
Tel:  +66-2617-2444 ext. 2020 or 2047  E mail:

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