Artificial Joints

I am wonderingif there are any other people with artificial knees or hips. After 12 knee surgery's and finally replacment of both my knees I am at a stage where I can get back into the gym and lose some of the weight I put on. Due to my age (young for typical TKR's) I am only 49yrs old. I was 47 when the doc when I had the first TKR. The surgeon used a knee for an active lifestyle. (The Binford 6100 series LOL)
I guess I am looking for anyone else that has had some success in the gym with TKR's. High Impact activities are definately out. I have hired a Personal Trainer and she is very good.