We use injections for two main reasons. One is to help us work out what is wrong and the other is to help treat the pain. It is important you understand the difference because we will often ask you about the effect of the injection for both these reasons.
Diagnosis – work out what is wrong
Sometimes we find it difficult to be sure which spinal nerve (or facet joint) is causing the pain, or even if the pain is coming from the spine at all. Spinal injections can help us work this out and make the diagnosis. When we perform a spinal injection, a mixture of steroid and local anaesthetic is injected. The local anaesthetic numbs the nerve, similar to a dentist injection. For the first 6-24 hours any pain from the nerve (or joint) should be relieved at least 80%. We call this a positive test. We will usually ask you what happened during this period and it is important that you make a note of it. Even if the pain comes back after this, it is still a positive test and provides us with useful information.
Treatment – help improve the pain
The other benefit of the injection is that the steroid can reduce the inflammation, and it is inflammation that causes pain. It is not masking the pain; it is actually taking the cause of the pain away. The steroid usually starts working a day or two after the injection. Its effect may last a few days, a few weeks, a few months or even permanently.
We can repeat the injection but in a different place to help us make the diagnosis. We can repeat the injection in the same place if it helped with the pain first time, and lasted long enough to justify another injection (in other words, longer than a few days). It is commonly believed that you can only have a maximum of three or so injections. This is partly true, because we usually find the effect of the injections becomes less after two or three, not because multiple injections are particularly dangerous.