I had a total knee replacement over 6 years ago. Although I have a good range of motion and can walk OK, when I am in one place for an extended time, my knee locks up and is painful. When sleeping, I am woken up with knee pain after about 2 hours. If I sit in one place for 1/2 to 1 hour, my knee starts hurting & I have to stand up and stretch. I am told that my knee cap is not a perfect fit and has some lateral movement which leads to the pain I experience. Doesn't make sense to me. Have also been told by 3 doctors that this is a common complaint and does not justify surgery to repair it.