Selective Nerve Root Block

A selective nerve root block is an injection of local anaesthetic placed precisely around a single spinal nerve root as it leaves the spine. Its main purpose is diagnostic: to test whether one particular nerve is responsible for pain travelling into an arm or leg. It is especially useful when a scan shows more than one nerve that could be pinched, and it is not clear which one is actually causing symptoms.

Each nerve root supplies a fairly predictable area of the arm or leg. If numbing one specific root temporarily abolishes the pain in that distribution, it strongly suggests that this nerve is the source. Using X-ray guidance, and often a small amount of contrast dye to confirm correct needle position, the anaesthetic is delivered around the chosen root. The response is then observed: meaningful, temporary relief points to that nerve; little change points away from it.

The skin over the injection site is numbed, and you lie still — usually face down — while imaging guides the needle. You may briefly feel a tingle or a reproduction of your familiar pain as the needle nears the nerve, which actually helps confirm the target. The injection itself takes only a few minutes. Afterwards the limb may feel numb or heavy for a few hours as the anaesthetic works. You will usually be asked to record your pain over the following hours and to arrange to be taken home.

When imaging shows several possible sites of nerve compression, choosing the right one to treat is critical — surgery or other treatment aimed at the wrong level is unlikely to help. By isolating and testing a single nerve, a selective nerve root block can identify the true pain generator, making any subsequent treatment far more targeted. It can also provide a period of pain relief, though its central role here is diagnostic.

• —NICE — Low Back Pain and Sciatica in Over 16s (NG59)
• —Faculty of Pain Medicine, Royal College of Anaesthetists — Standards
• —British Association of Spine Surgeons (BASS)

This information is for general patient education and is not a substitute for an individual consultation. Always seek personalised advice from a qualified spinal specialist.