You responses have not only made me chuckle but confirmed to me that there aren't many surgeons who have a definitive idea about what to do and when to do it! It's all from the 'grab it out of the air' school of philosophy!
It actually puts me in the mind of the time, back in 1963, when we had a group of American surgeons visit our hospital and all gather in the operating theatre to watch Ken McKee (designer of the very first modern hip replacements) do a surgery. During this procedure, one surgeon actually asked McKee how long he though these artificial hip replacements would last. McKee looked up from his surgery and gazed into space for about 4 minutes and then said "Well, I reckon if we get 10 years out of them we'll be doing well".
But that statement has echoed down over the years as a statement of absolute fact! How many times, in this forum alone, do people report that their surgeons have told them with a considerable degree of confidence, that "hips won't last more then 10-15 years"! Yet I was there when this statement was made and know it to have been a casual, unconsidered, throw-away comment made on the spur of the moment! And people STILL believe it!