The source of musculoskeletal (MSK) pain can sometimes be very difficult to identify. In MSK medicine we use the term “pain generator” which describes the injured or inflamed tissue(s) that are causing the pain. Sometimes an image like an x-ray, ultrasound, CT or MRI can identify the injured or inflamed tissue and locate the pain generator. Very often, however, the pain generator is not where the image shows pathology, or there is no pathology to be seen.
In these cases, the use of a diagnostic injection can be very helpful. Say, for example, you have pain around your hip area. There are many possible causes of the hip pain and if testing and imaging doesn’t clearly suggest where the pain is coming from I’ll use a diagnostic injection to help guide me. Depending on the symptoms, I might start by injecting the main bursa of the hip called the greater trochanteric bursa with a local anesthetic.
If that fails to ease the pain I might try injecting a local into the tendon attachments of the gluteus muscles. Where the pain persists I might then inject the joint or one of the muscle layers or into the joint itself. This process of injecting different possible pain generators until one area gives some relief is the first step in doing a diagnostic injection. Once an injected area gives relief I know that we have put the medicine where the pain originates.
At this point I will usually suggest injecting a corticosteroid into the same area. The value of adding cortisone to the solution injected is that it has a much longer lasting anti-inflammatory and pain-relieving effect. Where the local anesthetic will give a few minutes or a few hours of relief, cortisone will give a few days to weeks of relief. Having days to weeks of less pain gives the time and space to make a much clearer assessment of the effect of treating that area.
Once the area treated gives reliable relief we can then consider other treatment options.