Using a type of x-ray guidance called a fluoroscope, a needle is placed into your spine next to the nerve that is causing the pain in your arm or leg. The medicine is injected so it can surround the nerve and lower the inflammation and pain. The injection can be used to relieve pain.
This type of injection can also be used to diagnose pain: if there is an injection next to the nerve the doctor things is causing the pain, but the pain does not improve, then the pain must be coming from another place.