I have RA, I have had both my knees replaced, why do they still give me problems?

There could be several reasons why your knees are still bothering you. If it has been less than 1 year since your surgery, be patient - this may yet improve. If the surgery was several years ago, you could be experiencing a regrowth of inflamed joint tissue (synovium) around the replaced joint, you may be experiencing loosening of the implanted hardware in the knees, or you could have soft tissue pain around the knees (bursitis, e.g.). I would encourage you to discuss these concerns with the orthopedist who performed your surgery if you have not already done so, then if everything checks out from his/her standpoint, discuss your problems with your rheumatologist to see if there is a way your symptoms can be better managed medically.