Knee replacement pain could be caused by a part of your prosthesis that has broken off! This past month I evaluated a woman who had her knee replaced about 4 years ago. Things went well until she had a fall a few months ago and then her knee became swollen and very painful. She went back to the surgeon who implanted the device and according to her, she was blown off. He in fact wanted to sign her up to replace the other knee. I do know for sure that he refused to order a knee MRI. On ultrasound exam things didn’t look quite right so I ordered the MRI that you see above. What did it show? Regrettably, she’s knocked a piece of her prosthesis off and what’s left of the knee is quite aggravated.
First, the white stuff on the MRI above is extensive swelling likely from irritation of the soft-tissues by the broken plastic part. In addition, it could also be due to a reaction to the prostheses, which could be why this one failed so early. Second, to understand what you’re seeing, note the type of knee replacement device used to the left. It has a “Tibial Baseplate” that extends all across the bottom knee bone (tibia). On top of that is plastic that extends as far as the metal baseplate. On the MRI you can see the baseplate (yellow arrows) on both the front view (middle picture) and side view (right picture). Now look at the plastic piece above the baseplate. The red arrows clearly point to a gap seen on both the front and side views. So her plastic “articular insert” is missing a large chunk and that marble sized piece is floating around somewhere in what’s left of her knee.
The upshot? Knee replacement is big surgery. I always tell patients that big surgeries=big potential complications. This woman can tell you about those right now, as she’s looking at a sub-5 year failure on her new knee!