Hi all, I've been a physical therapist for forty+ years and have helped hundreds of people rehab after TKR surgery. My mother, older brother and older sister have all had both knees replaced, so my genetics point toward a knee replacement or two in my future. I see no inherent problem with cycling after surgery as long as you have gained sufficient ROM to accommodate the full revolution of the crank with some extra ROM for a cushion. As far as falling, your more likely to injure some other body part than the mechanical knee. They are extremely durable. However, be aware that infection after an injury where there is a break in the skin, represents an additional hazard when there is a foreign implant. All this said, and I am going to have to blaspheme here, I find rowing to be much easier on my 64 year old knees than cycling - especially hills. I continue to do both, and several of my crew teammates have had one or both knees replaced. My knees ache after cycling, never after rowing As a disclaimer, I am a certified indoor rowing instructor and have completed all the requirements to be a USRowing level II rowing coach.