Selective Nerve Block
Another common injection, a selective nerve root block (SNRB), is primarily used to diagnose the specific source of nerve
root pain and/ or for therapeutic relief of low back pain and/or leg pain.

When a nerve root becomes compressed and inflamed, it can produce back and/or leg pain. Occasionally, an imaging study (e.g. MRI) may not clearly show which nerve is causing the pain and an SNRB injection is performed to assist in isolating the source of pain. In addition to its diagnostic function, this type of injection for pain management can also be used as a treatment for a far lateral disc herniation (a disc that ruptures outside the spinal canal).

In an SNRB, the nerve is approached at the level where it exits the foramen (the hole between the vertebral bodies). The injection is done with lidocaine (a numbing agent). Flouroscopy (live x-ray) is used to ensure the medication is delivered to the correct location. If the patient’s pain goes away after the injection, it can be inferred that the back pain generator is the specific nerve root that has just been injected.

Success rates vary depending on the primary diagnosis and whether or not the injections are being used primarily for diagnosis. While there is no definitive research to dictate the frequency of SNRB’s, it is generally considered reasonable to limit SNRB’s to three-four times per year.

Technically, SNRB injections are more difficult to perform than epidural steroid injections and should be performed by experienced physicians. Since the injection is outside the spine, there is no risk of a wet tap (cerebrospinal fluid leak). However, since the injection is right next to the nerve root, sometimes an SNRB will temporarily worsen the patient’s leg pain.


A block that is performed to determine if a specific spinal nerve root is the source of pain and reduce inflammation around the nerve root thus decreasing or relieving the pain.


The patient is given a local anesthetic. The physician then locates, under fluoroscopy, a specific spinal nerve root. A needle is introduced through the skin into the area adjacent to the nerve root. Medication is then injected into the area bathing the nerve root.


Relief of back and leg pain for approximately 24-48 hours.


The procedure itself should only take about twenty-thirty minutes. You need to plan on being at the facility for approximately two hours.

Possible Effects;

During the injection pain may be increased temporarily. Following the procedure you may experience some initial discomfort. Once the medication reaches the inflamed area your pain should hopefully be relieved.

  • You may experience an aggravation of your usual pain after the injection for 24 to 48 hours, during which the local anesthetics effect have subsided.
  • Should you have increased pain after the injection, you may apply ice to the area for duration of no more than 10-15 minutes each time, 4-5 times per day, as needed for pain.
  • Provided that you do not have allergic reaction to the medication and you do not have liver problems, you may take Tylenol as needed for pain, no more than 3 grams per day, for the first 24-48 hours.
  • Please resume all your previous medications immediately following the procedure, on the normal schedule or as indicated by your primary care/managing physician.
  • Please seek immediate medical attention for fever, chills, weakness, or bladder and bowel loss of function.
  • Please follow up with the referring physician 1-2 weeks following the procedure.