Blood thinners. I have ITP, which means that I have an abnormally low platelet count. The surgeon talked with my oncologist ( my ITP is non cancerous but mimics cancer in certain ways) and decided no blood thinners but it seemed like an appropriate amount of doctors thinking it through was going on.
Predisposition for knee weakness. Although I have been a runner for over 40 years, my knees had always been pretty good. My injury was a slip while running where the surface switched from snow to black ice and was downhill to boot. I don't think preexisting condition had much, if anything, to do with it.