The clinician will do certain tests moving the arm in specific directions and have an indication of what the problem in the shoulder may be. If the fluid is then injected into the appropriate space the effect of the local anaesthetic may be apparent after a few minutes. If the tests are repeated the diagnosis can often be confirmed immediately. Such a positive response would also prove that the cortisone (which may be mixed with the local anaesthetic) is in the correct space and may have a beneficial effect in the longer term.
It has to be realised that the effect of cortisone in this instance is mainly anti-inflammatory – it reduces pain and swelling in the tissues where it is injected. In the case of an acute inflammatory condition the effect of the cortisone will therefore mostly be seen after about 2 days. Another important feature is that the longer term effect of the cortisone would also indicate the diagnosis. If it is merely an acute inflammatory condition the cortisone could be virtually curative, if it is a long term condition (e.g. osteoarthritis) the cortisone may have a temporary beneficial affect which will wear off. In a mechanical condition e.g. a tear of the tendon the effect of the cortisone may be short lived.
It can be seen that the effect of the injection gives the clinician the following information:
- The effect of the local anaesthetic suggests where the problem is located in the joint (which anatomical space).
- The effect of the cortisone is a further aid in diagnosing the problem in the joint: generally speaking the less serious the problem the more beneficial the cortisone will be.
It is important to note that these injections have to be done accurately to ensure that they are put in the correct space. Some clinicians might be experienced enough to do this without any help.
In our unit we often use ultrasound guidance to ensure that the needle is in the exact space to be able to reach the correct conclusion. Some clinicians, especially radiologists, may use x-rays to aid them in injecting accurately.
Ultrasound guidance improves accuracy of injection placement in the correct anatomic space.