I agree with @heyjoe415 - some people may be able to put off surgery for a few years by losing weight, obviously the more poundage (pun intended) the knee has to endure the faster it wears out. Imagine carting an extra 20 lb bag of potatoes every time you walk up and down the stairs. But at some point whether it's due to genetics or old age overuse, if your cartilage wears out and you are bone on bone, your options are surgery or a wheelchair when cortisone or synthetic gel injections quit working. Having a TKR involves your commitment to regularly and fully do the assigned rehab exercises. Just having the surgery and then sitting back and doing nothing will not bring good results. Get in shape before surgery if possible, but for sure, plan to be very serious about rehab exercising.