@saeternes Prior to my last TKR I asked the surgeon about "pre-hab". He asked me if I was exercising at all and I told him I did water aerobics and water jogging and my recumbent bike. He said "perfect!". That was exactly what he would have suggested. It really did serve me well.
I was supposed to have a TKR in February of 2015 but due to low platelet counts I was turned away by the doctor as I lay on the bed, IV in, waiting to be brought into surgery, From that point I worked hard at these exercises and by the time I had the TKR, in October 2017, my leg was feeling much better but I still chose to have it done since I knew I would eventually have to.
I would imagine the elliptical would be good also, and for me, I get better cardio out of the elliptical, but you could check that with your surgeon.
JK