Selective nerve root block: what the injection involves, risks and aftercare

A spinal nerve can become irritated where it leaves the spine, for example by a disc bulge or narrowing of the exit hole. The result is pain, tingling or weakness that travels down the leg, as in sciatica, or down the arm. A selective nerve root block places medicine next to the nerve involved. Cambridge describes injecting local anaesthetic and steroid around one of the nerves as they exit the spine to find out whether a specific nerve is causing the symptoms and potentially to relieve pain.

It is not needed for every episode of sciatica, many of which settle with time, activity and simple measures. It is usually considered when pain is persistent or severe, the cause is not clear from scans, or a decision about surgery depends on which nerve is responsible. The diagnostic use is important: if the pain eases while the anaesthetic is working, that supports the nerve being the source.

The injection treats symptoms rather than the structural cause. Relief can be complete, temporary or absent, so it is best viewed as one step in a plan rather than a cure.

Alternatives include staying active with physiotherapy, medicines for nerve pain, an epidural steroid injection and, in selected cases, spinal surgery. Which suits you depends on the cause of the nerve irritation, how long it has lasted and how much it affects daily life.

A nerve root block differs from a general epidural because it is aimed at one nerve level, which makes it more useful when the team needs to know exactly which nerve to blame. If you are unsure why this injection rather than another is suggested, ask what each would tell the team.

You will be asked about medicines that affect bleeding. North Bristol says people taking warfarin, clopidogrel, rivaroxaban, dipyridamole or dabigatran must tell the clinic beforehand, and Cambridge lists stopping times, for example clopidogrel, prasugrel or ticagrelor five days before, and rivaroxaban, apixaban, edoxaban or dabigatran 48 hours before, while aspirin continues. Always follow the instructions in your own appointment letter and do not stop anything on your own initiative.

Tell the team if you are or might be pregnant, because X-rays or CT are used. Tell them if you are diabetic, because steroids can raise blood sugar. Bring someone with you to take you home, as most leaflets ask.

• Tell staff about allergies, particularly to contrast dye.

• Arrange an escort and avoid planning to use public transport alone afterwards.

• Wear clothing that is easy to move in for lying face-down.

You lie face down on the X-ray or CT table. The skin is cleaned and numbed with local anaesthetic. A fine needle is then guided by the imaging to the exit hole of the nerve root, and contrast dye is used to confirm that it is in the right place before the medicine is injected. North Bristol says you may feel a brief sharp pain down the leg if the needle touches the nerve.

North Bristol gives 15 to 30 minutes and says you stay awake. Cambridge describes about 20 minutes in the CT department. After the injection you rest for observation, which North Bristol puts at 30 to 60 minutes, before going home.

Newcastle says to allow up to two hours at the hospital in total. Because the leg can feel numb or heavy for a while, staff check that you can stand and walk safely before you leave.

Common effects are temporary numbness or heaviness in the leg for up to 24 hours, bruising or soreness at the site, and a flare of pain for two to three days, which North Bristol attributes to steroid irritation. Plymouth describes temporary effects of the steroid including a rise in blood pressure and blood sugar in people with diabetes, and notes that repeated steroid use can have prolonged effects on bone density, the gut and immunity.

Less common problems named in the leaflets include bleeding or bruising, infection, which shows as redness or tenderness, and allergic reaction to the contrast dye. Newcastle also lists no pain relief and radiation exposure. North Bristol says an overnight stay is needed if the leg stays persistently numb. Cambridge states that the CT dose is equivalent to a few months or years of natural background radiation and that the risk from it is considered low.

The timing of relief varies. Newcastle says pain may ease immediately, within 12 to 24 hours, or not change for days and then improve slowly over weeks. North Bristol notes that the steroid begins working in two to three days. Cambridge arranges a review of the response at one to two weeks, so keep a record of how your pain behaves.

Driving advice varies: North Bristol says not for the rest of the day, Plymouth and Newcastle say 24 hours, and Cambridge says driving may resume the next day. Plymouth advises increasing movement gradually over the following weeks. If you have diabetes, Plymouth advises monitoring blood glucose for several days.

Plymouth lists new leg weakness, bowel or bladder problems, new back pain and fever as reasons to seek urgent help through your GP, NHS 111, the pain clinic or the emergency department. North Bristol adds redness or tenderness at the injection site as a possible infection sign.

Call 999 or go to A&E for sudden weakness, loss of control of the bladder or bowel, or numbness between the legs. These can signal pressure on spinal nerves and need same-day assessment.

• Is this block meant mainly to diagnose or to treat in my case?

• Will it be done under X-ray or CT, and why?

• What would a good response look like and when will we review it?

• Which of my medicines need to change beforehand?

• What happens next if it helps, and if it does not?

The technique is the same either way. On the NHS you are usually referred through a spinal or pain service and the wait depends on local capacity, while a private provider may offer an earlier slot. Ask who reviews the response afterwards and what follow-up is included, because the result guides the next decision.