I am glad that your OS was able to reassure you about things. I honestly believe that there is nothing wrong with your implant. They are really strong, but the soft tissue around it is most likely very inflamed and will take some time to "calm down"----in the mean time, take it easy, ice, rest and elevate and let the soft tissue around the knee calm down and heal.
I am not sure why PT's treat TKR folks this way. I do know that at the PT center that I went to, there were two sets of PT's---one for the "athletic injuries" and one for the "joint replacement" folks like me. The two groups never crossed patients.
I think that some of the PT's (yours, especially) treats all surgeries the same---which is definitely not the case. This TKR recovery is dealing with a knee that has had two bones sawed off and the knee joint has obviously sustained major surgical trauma, so it it imperative to take things gently and slowly.
Using a stationary bike can be helpful--but right now, I would ease very slowly onto it and simply let that surgical knee of yours calm down.
I wonder how long it will be for all of this to heal.
Your ROM is great, and it is imperative to keep in mind that recovery from a TKR can take upwards to a year to be complete. My BTKR recovery took about eight months, so please be patient. One of the most frustrating aspects of a TKR recovery is how slowly things can progress---glaciers may move faster!
Patience, Grasshopper, Patience!!!
Hang in there----you just have to be patient---this is a setback that is truly temporary. Ice, elevate, rest, and do not worry about things---once the soft tissue around the knee calms down, you will be able to move slowly and gently forward---and keep in mind that recovery is not linear---it is indeed more like a roller coaster.