If you're a likely candidate for knee replacement, what nonsurgical processes will you have to go through first?

Well the surgeon said I will have to lose a 100lbs first.

I have overused and injured my knees via sports over the years. Volleyball, Racquetball, Hiking, Ultimate Frisbee, etc.
Annual or as needed visit to my Orthopedic Dr.
Having any fluid drained
Annual Cortisone Shot
Cartlidge regeneration therapy (if the reason)
Support sleeve or Braces during specific activity
PT to resolve/strengthen areas of concern.
Adjusting your activities.

They may go straight to surgery for many reasons above my pay grade. Pain and complete lack of mobility may be one reason.

Cardiologist – will check you heart to make sure it will be able to take the stresses of anesthesia, surgery, and rehab.

It really depends on where you live, your personal circumstance, and your medical condition.

As @Caravanfan says, it would depend on all those factors and also the recommendations of the orthopedist or orthopedic surgeon you go to. No one size fits all.

My surgeon would have done it right away since it was bone on bone and nothing was going to help it. But I chose to get shots for over a year just to put off the surgery. Then I did aquatherapy for 8 weeks to help strengthen the surrounding muscles before surgery. I wish I hadn’t bothered with the shots – they were unpredictable as to whether they worked or not.

If your cartilage is gone. Cortizone is really a bandaid at that point. I actually went to a class last week with a relative who has surgery scheduled. Some places do it as day surgery now with no overnight stay if you can meet PT standard for discharge (like climb a few stair to get into your house).