Knee replacement and that really scares me

I can't advise re the embollism and blood thinners, and this is something you'll need to discuss with your GP and ortho surgeon. My experience of hip replacement is that they will put you on blood thinners for a while anyway post op to avoid embollisms assocaited with the surgery.

As for the surgery for your knees, my sister has two and my brother in law just the one. All 3 ops were successful, and both regained a good degree of pain free mobility after. Do strengthening exercises as much as your pain levels allow pre-op (my hip was so bad it was impossible) as it does aid recovery if you can. And do what your physio says post op - this also makes an enormous difference to how much flexion you'll recover. And not just for a few weeks, keep it up for as long as it takes to get your knee back to where you need it.

Try not to over-think the surgery - it sounds brutal, but it's very routine now and they all know what they're doing. I decided not to research what they do in hip replacement and went into surgery in a state of blissful oblivion (bordering on denial), placing my full trust in the medical team. I thoroughly recommend this as a way of managing anxiety levels. I had a minor wobble when the anaesthetists got stuck in, but it was all so quick and they were so nice and clearly knew exactly what they were doing, that I just let them get on with it and raised my trust levels to "Defcon 5".

As for the pain? It will only get worse if you don't have the operation, but will be very much better after. There will be some post op pain, as it's quite an invasive procedure, but they'll send you home with pain relief, (although I found I didn't need much, after a year of ingesting handfuls of prescription painkillers) and it does improve. It's very different to the awful grinding pain you're experiencing now. The only way is up!