If you have walked into and out of the Grand Canyon twice with your artificial knees, you should be able to walk the Camino. That is one steep descent! And if you have any trouble with a particular type of terrain, you can always use a taxi or bus for a short way. I've done this to avoid steep descents into Zubiri and El Acebo/Molinaseca (due to life-long knee problems).
I'm going to add another voice to the general discussion on trekking pole suggestions. If you have knee problems, do not attempt the Camino without trekking poles...TWO of them. One trekking pole or a walking stick is insufficient if you have knee problems (tried it, ended up on the bus, a lot). There are some very steep descents on the Camino, and your trekking poles could make the difference between arriving in Santiago or not.
Then even more important, learn how to use them correctly. I use Leki poles, have on all but one Camino, and I swear by them. The Pacer poles are fancier (and more expensive?), I think. But here are my minimum requirements for trekking poles:
1. Collapsible / adjustable so you can make them longer on descents and shorter on ascents and flat terrain. Also makes it possible to put them in a checked bag and hang them from your pack when you don't need them.
2. If not Pacers, be sure they have wrist straps, and be sure you know how to use them.
3. Rubber tips that go over the metal tips for walking on paved surfaces. Critical for gripping the pavement and so the tap-tap-tapping doesn't annoy everyone else around.
If you are in the US you can pick up a DVD on how to use trekking poles correctly -
http://adventurebuddies.net/03-03-dvd.htm You might check your public library for an early version of this, but that might be VHS and not DVD. Or we can meet up on the trail in April/May and I'll show you some tricks
Nancy