Last week I tripped and landed on one knee replacement and then the other one hit. It was on my concrete basement floor. They feel like they did when I first got them four years ago. Just tight and not good at all. My left one is a little swollen and walking is hard. I went to my os and he xrayed them and said they looked okay. I just can't help feeling that my left one really took a hit and just doesn't feel right. Like something is out of place with it. Maybe I'm over reacting. I'm 54 and got my knee replacements at 50. I would like them to last as long as possible. Is there a possibility of damage that would not show up on an x-ray? Just wondering if anyone has had this experience. It is unsettling to say the least.