I have ostearthritis in both knees, had a cartilage (meniscus) removed 50 years ago, when that was the treatment for a torn cartilage. 3 months ago when moving house, my right knee finally gave up the ghost & the joint clicks with every step. I am know scheduled for a replacement knee. Last week I got a sudden pain in my left calf when walking but managed to get back to the car & home. Didn't go to the docs & the pain is gradually subsiding, suspect a ligament or torn muscle. When my knee finally went we were due to go on holiday, so to ensure some mobility I bought a mobility scooter & took it with us. What concerned me using it was my weight increase & the exercises I was supposed to do before the knee op'. So after much prevaricating, decided to swap it for a Triad Tracer semi recumbent trike. Went for a spin on it yesterday & was pleasantly surprised how easy it was to use with no clicking in my right knee. I'm in the process now of trying to convert it from fixed gear to 6 gears & there is a thread on the mobility forum.