There are two principal forms of injections:
These aim to reduce inflammation. So if the pain is either in the spine or in the limb and generated by inflammation, and the steroid is locally strong enough, the pain will go. The steroid, when injected, only works locally. Often, the steroid will be injected in a solution with local anaesthetic to cover the pain of the injection. The injection is usually given under sedation or local anaesthetic via a fine needle and can be delivered into the facet joints, around the nerves in the back of the discs, the epidural space or around the nerve root sheaths.
If the injection occurs remote from the pain generator site, it will not work and similarly it will fail if the steroid is not strong enough or if the pain is not mediated primarily though inflammation – when it is more mechanical pain.
Heat is used to take away the nerve supply from the painful structure. If heat is principally applied to the fine nerves supplying the facet joint, it is called a rhizotomy. If heat injections are applied to the disc, then it is called intradiscal electro-therapy (IDET). This is an example of a needle-based treatment. This will work if the correct target is located – whatever the mechanism of pain generation.
If steroid injected into the facet joints produces only a temporary reduction in pain, then sometimes it is worth trying injecting a lubricating-type substance called hyaluronase (Ostenil). This sometimes produces a more long lasting benefit.