Ask Health Experts and Get Answers to Your Health Question ASAP
The only way that it would effect it is if some of the swelling goes down. It works over several days, so I doubt even a lot of swelling would be down by that time. But even if the swelling has gone down, that wouldn't change anything on the reading.
Here is a web site that discusses the injection of cortisone into a joint in case you are interested in learning a little bit more about that procedure.
If you have any other concern don't hesitate to ask.