In October last year I had a total knee replacement, at age 66, on a knee that had no kneecap since I was 18, having played “blood sports” (rugby!) when a well aimed size 12 boot ended my rugby days.
After 45 years of not cycling and getting bigger (18stone) I bought a KTM Macina with the “halfway” cross bar and loved it but had problems with my stability, getting my leg over, so changed to to a “Dutch style” Cube. I found both these bikes fabulous to ride but as I’m not supposed to lift anything heavy I found attaching the rack to the tow bar, attaching the bike to the rack etc etc a real pain, literally!
The result was to sell the Cube ebike and go for a Brompton folder to see how I managed... I find it so light to store and transport and a great ride with 6 gears and lowered gearing. It’s doing my knee the power of good but living where I do, which is very hilly, I miss the electric assistance. So I have an electric Brompton on order, which I will comment on when it arrives.
My advice is to try to cycle whatever it takes.. the non weight bearing exercise will be great for your knee and improve both muscles and knee flection.
I now have full flection and can bend my knee as far as the “good” one.
Oops.... I’ve just remembered why I started this posting... I have heard great reports for the “swing cranks”. Ok they aren’t cheap, as TimEbike says, but compared to the cost a a gym membership for physio, general exercise and the fact you are getting out into the open, they are worth the investment.
Good luck with the TKR.