The selective nerve root block (SNRB), is a procedure that is used to diagnose the specific nerve that is the source of chronic pain. The procedure is also used for the treatment of chronic lumbar (low back) and leg and buttock pain (sciatica). Sciatica is pain associated with lumbar disc degeneration that impinges the sciatic nerve and causes pain through the buttock extending down the back of the leg.
This pain is the result of a nerve trunk becoming impinged (compressed, also referred to as pinched) between the vertebral bodies due to deterioration of the intervertebral discs. A bulging or herniated disc may be the cause of the impingement by one of several ways.
A bulging disc may extend beyond its normal position and come into contact with the nerve trunk pressing it against the vertebral body. A herniated disc also extends beyond its normal position and comes into contact with the nerve but is more severe than a bulging disc, the resulting pain is often more severe.
A deteriorated disc may become thinned to the point that the foramen narrows and the vertebral body itself comes into contact with the nerve root. The worst case scenario is a herniated disc that contacts the nerve root which is also thinned so that the foramen narrows and the vertebral body comes into contact with the nerve root.
In some of these cases surgery may be required to either remove bone to enlarge the foramen or to replace the disc with an artificial disc, or to perform a fusion where a small piece of bone graft is placed between the vertebrae restoring the natural spacing.
For any of these conditions the patient may benefit from a selective nerve block to reduce their pain levels by the numbing of the nerve root. The selective nerve block is performed by injecting a mixture of local anesthetics and a corticosteroid precisely into the area where the nerve exits the foramen (hole between the vertebrae through which the nerve trunk passes) in order to numb the nerve.
The procedure is performed by placing the patient face down on an exam table; the intended injection area is cleansed with an antiseptic solution to prevent infection. The skin at the injection site is then numbed with a topical anesthetic and then a thin needle is inserted into the area using fluoroscope guidance.
A fluoroscope is a type of x-ray machine that allows the doctor to see a real time image of the needle to ensure that a nerve is not struck with the needle. When the needle is in place a contrast dye is injected to ensure the correct nerve is being treated and then a mixture of local anesthetic and corticosteroid is injected into the area.
The patient usually has nearly immediate relief due to the local anesthetic but this wears off in a few hours. The steroid medication may take a day or two to become effective but then it will last from several days to several weeks. It usually requires several treatments before the maximum benefit is achieved but afterwards the effects may last for several months to a year. All of this is assuming the nerve root injected around is the one causing symptoms.