Difficult prognoses

I am a very active 46 and have severe early osteoarthritis of the knee arising (viewed arthroscopically) from a sports injury, although little pain. My (well respected) orthopaedic surgeon tells me that I will need a replacement knee within 2 to 15 years, probably about 10, depending how much I am prepared to give up in terms of activities. Others, including another orthopaedic surgeon and several exeprienced physiotherapists tell me that such a prognosis is an excessively bold one to make. I realise that no-one has a crystal ball, that predicitions are very difficult to make but is there evidence, anecdotal or otherwise, to show that such a prognosis may be very wrong?