A selective nerve root injection, also called a selective nerve root block injection, is a procedure in which a doctor injects a steroid called cortisone around a nerve root. Cortisone reduces inflammation around the nerve, which lessens pressure on the nerve and reduces pain.
This type of injection is commonly used for herniated discs.
Selective nerve root injections take approximately three to seven days to take effect and last for approximately four months or more. Having more than three injections in one year can increase your risk of side effects.