I had my free session a week ago at Osteo Strong and that night my neck and knee hurt. Here I am a week later and knee is still giving me problems. I had total knee replacement on the knee last winter and am really worried that I have serious damage to it. I made them aware at Osteostrong of the replacement surgery and they never voiced any concerns about possible consequences to my knee from trying the machines. Tomorrow I'm seeing the surgeon for x-rays to see if I damaged it on their machines. I wish I'd never heard of Osteostrong!