I was about to say the patella is removed during knee replacement surgery often and the back cleaned up, but if this is the opposite knee, it is not due to the replacement. It could simply have to do with arthritis. That causes stiffness alone. If it's bothering you a lot, start with the orthopedist. FYI, wish me luck: I just had my right knee replacement about 14 days or so ago and am in the thick of it. I get the staples taken out in a couple of days.Forgot to say pain is now in my left leg duh. Quad pain was in right TKR!