I just had what may be an allergic reaction to Synvisc. This is my third time getting the injections. The second shots in a series of 3 for my knees. About 9 hours after my injections, one in each knee, my left knee swelled up causing extreme pain and discomfort. After calling my doc. and starting on steroids the swelling quickly came down. Here's what I don't understand why only one knee reacted? And I am willing to suffer some discomfort for the relief I got from the other series. Any thoughts.