Regarding Canada's "18 weeks" wait time... it's not accurate, depending on what they really mean, though; at least not in my experience. My wife destroyed both meniscuses (menisci?) jumping out of a tractor and needs knee replacements. All told it's closer to 18 months to get the knees replaced. Not sure, but if she couldn't have walked after the accident I expect she would have gotten surgery sooner. Still, the way I look at it, 18 months is not a long time to wait, if you have acceptable and bearable mobility, to get "free" knees.
What if you don't have 18 months to wait? I had several co-workers in Toronto whose children had injuries playing sports. The wait time for MRI plus knee surgery, etc. was longer than 18 months in Ontario. They went to the U.S. and paid out of pocket to have the MRI and surgery -- usually in under a week. This is a very common story in Canada.