I have had two knee replacements, both successful, the last 18 months ago. Range of motion, flexion, etc. are all excellent. But both knees have persistently felt stiff, like an ace bandage is wrapped around them. Today a physical therapist examined them and said that I have fluid on both of the knees. I will go to an orthopedic doctor, but how might that have happened, what are the dangers, and what course of action might be expected?