How Epidural Steroid Injections Work

Understanding Epidural Injections

An epidural steroid injection delivers steroids directly into the epidural space in the spine. Sometimes additional fluid (local anesthetic and/or a normal saline solution) is used to help ‘flush out’ inflammatory mediators from around the area that may be a source of pain.

The epidural space encircles the dural sac and is filled with fat and small blood vessels. The dural sac surrounds the spinal cord, nerve roots, and cerebrospinal fluid (the fluid that the nerve roots are bathed in).

Typically, a solution containing cortisone (steroid) with local anesthetic (lidocaine or bupivacaine), and/or saline is used.

• A steroid, or cortisone, is usually injected as an anti-inflammatory agent. Inflammation is a common component of many low back conditions and reducing inflammation helps reduce pain. Triamcinolone acetonide, Dexamethasone, and Methylprednisolone acetate are commonly used steroids.

• Lidocaine (also referred to as Xylocaine) is a fast-acting local anesthetic used for temporary pain relief. Bupivacaine, a longer lasting medication, may also be used. Although primarily used for pain relief, these local anesthetics also act as ‘flushing’ agents to dilute the chemical or immunologic agents that promote inflammation.

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• Saline is used to dilute the local anesthetic or as a ‘flushing’ agent to dilute the chemical or immunologic agents that promote inflammation.

See Epidural steroid injections for a clear step-by-step illustration of how and where an injection is done.

Epidural steroid injections control inflammation

Epidural injections are often used to treat radicular pain, also called sciatica, which is pain that radiates from the site of a pinched nerve in the low back to the area of the body aligned with that nerve, such as the back of the leg or into the foot. Inflammatory chemicals (e.g. substance P, PLA2, arachidonic acid, TNF-α, IL-1, and prostaglandin E2) and immunologic mediators can generate pain and are associated with common back problems such as lumbar disc herniation or facet joint arthritis. These conditions, as well as many others, provoke inflammation that in turn can cause significant nerve root irritation and swelling.

Steroids inhibit the inflammatory response caused by chemical and mechanical sources of pain. Steroids also work by reducing the activity of the immune system to react to inflammation associated with nerve or tissue damage. A typical immune response is the body generating white blood cells and chemicals to protect it against infection and foreign substances such as bacteria and viruses. Inhibiting the immune response with an epidural steroid injection can reduce the pain associated with inflammation.