I'm new here, but hope someone has an idea of what this could be. I am in my mid 50's and have had both my knees replaced. The right one was done about 14 years ago, the left one was about 7 years ago. I have had little problem with either knee since surgery. When I got up this morning I almost fell when I put weight on my left leg. The pain in my left knee was horrible. I tried working through it thinking it was just stiff from sleeping, but it has not improved. It doesn't hurt unless I put weight on it, and then it's an excruciating sharp pain on the right side of the knee only. I have never had anything like this before, even before it was replaced. Any suggestions as to what it may be?