Diagnostic Injections

A diagnostic injection is a precisely placed injection of local anaesthetic used not primarily to treat pain but to identify its source. When scans show several possible culprits, or when the origin of pain is unclear, numbing one specific structure — a particular joint, nerve or disc level — and seeing whether the pain temporarily disappears can reveal whether that structure is responsible. It is a test that provides information, often used to guide later treatment decisions.

The principle is simple: if numbing a specific structure reliably takes the pain away for the duration the anaesthetic lasts, that structure is likely part of the problem; if the pain is unchanged, it probably is not. To place the injection accurately, imaging guidance — usually X-ray screening (fluoroscopy), sometimes ultrasound or CT — is used to direct the needle to the exact target. A small amount of local anaesthetic (sometimes with a steroid) is injected, and the response over the following hours is recorded, often with a pain diary.

The procedure is done in a clean, controlled setting with imaging equipment. The skin is numbed first, and you may feel pressure or a brief ache as the needle reaches the target. It usually takes only a few minutes. Because the diagnostic value comes from what happens afterwards, you will typically be asked to note how your pain behaves over the next hours and days. You may need someone to accompany you home, and the team will give specific after-care advice.

Scans show structure, not pain, and many changes they reveal are painless. A diagnostic injection adds the missing piece by testing directly whether a specific structure generates a person's symptoms. This can turn an uncertain picture into a clear target, helping to avoid treatment aimed at the wrong level. The pages in this section describe the main types of spinal diagnostic injection and how each is used.

• —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.