An epidural steroid injection puts anti-inflammatory medication into the epidural space — the layer just outside the covering of the spinal cord — next to a nerve root that is inflamed and irritated.
It is one of the most common procedures in pain medicine and one of the most misunderstood, mostly because of what people assume it will do.
What it treats, and what it does not
The strongest evidence is for radicular pain: pain that starts in the spine and travels down a limb along the path of a nerve. Sciatica is the familiar example.
When a disc presses on or chemically irritates a nerve root, the root becomes inflamed, and inflammation is what steroid is good at reducing. Take the inflammation down and the pain travelling down the leg often settles considerably.
What it does not do is change the anatomy. The disc is still where it was. A narrowed spinal canal is still narrow. This is why the effect is real but time-limited, and why an injection is not an alternative to surgery in someone who genuinely needs surgery.
For back pain sitting only in the back, with nothing radiating, the evidence is considerably weaker. A clinic offering an epidural for that should be able to explain why.
What the appointment is like
You are awake. You lie face down, the skin is cleaned and numbed with local anaesthetic, and the physician uses fluoroscopy — live X-ray — to guide the needle. Contrast dye is usually injected first to confirm the medication will spread where it is intended.
The injection itself takes a few minutes. Most of the appointment is preparation and the observation period afterwards.
The local anaesthetic that goes in with the steroid often produces several hours of noticeable relief. That is the anaesthetic, not the steroid, and it wearing off by the evening is expected. The steroid takes longer — commonly two to seven days — to do its work.
A sore back at the injection site for a day or two is common. Some people get a temporary flare before the improvement.
How long it lasts
Weeks to a few months is the usual honest answer, and it varies widely between people.
That window is the point. The most useful thing an epidural does is make physical therapy possible for someone who could not tolerate it before. Used that way, the benefit can outlast the injection. Used on its own, the pain generally returns as the steroid wears off and nothing else has changed.
There are limits on how often they are repeated, largely because of the cumulative effects of steroid. If you are being offered a fourth or fifth in a year, it is reasonable to ask what the longer plan is.
What to tell the clinic beforehand
Some of this changes whether the procedure can go ahead safely:
- Blood thinners or antiplatelet medication, including over-the-counter ones. Many need to be paused, and the timing differs by drug — do not stop anything on your own.
- Diabetes. Steroid raises blood sugar, often for several days, and insulin users may need a plan.
- Any current infection, or fever.
- Allergies to contrast dye or local anaesthetic.
- Possible pregnancy, because the procedure uses X-ray guidance.
When to call afterwards
Most people have nothing worse than a sore back. Call promptly for fever, worsening or spreading weakness in the leg, new problems controlling your bladder or bowels, or a severe headache that is clearly worse when you sit or stand up.
These are uncommon. They are worth knowing about so you act rather than wait.
What to ask
Is my pain radicular, and which nerve root are you targeting? What are we hoping the injection makes possible? How long should I expect relief to last? What is the plan if it works, and the plan if it does not?