If I could go back 6 years and refuse my 1st left TKR I would. I ended up fracturing the 1st 3 prosthesis'. I was told the 1st 2 were due to me being allergic to bone cement. Never have been able to find out why #3 failed. But it also fractured. I had a fractured tibia when all this started and a delay in a proper diagnosis caused me to hobble around on the fracture which destroyed the cartilage. I am told each of the 3 new joints were 'top of the line' and they shouldn't have broken. Now, after 3 new knee joints and 4 operations (incl 1 antibiotic spacer) ended up with the bone ends being "trimmed" and now my left leg is about 3" shorter than my right. I was told by my surgeons (4 over the 3 new knees) and each said this was a operation performed thousands of times/year. I believe I used the top of the local surgeons around here and do not doubt their experience and qualifications. But something isn't right! I hope no one else has to go through what I have. As far as knowing when it's time, the docs all said the patient knows when it's time and the meds and procedures no longer give relief. Good luck!