I think if your X-ray or MRI shows bone-on-bone, then TKR will be done! My daughter-in-law is only in her 50, she had both knees totally replaced because of bone-on-bone. I am 78 with knee pain but the doctor only recommend PT, Cortisone shots and Advil. He said my knee only shows narrow gap but not bone-on-bone. Also, he won't do TKR if I was 85 or over even with bone-on-bone condition!!! Don't know if this is because Medicare policy or only his own policy!