Agree a good PT is in order, and the suggestions offered here are all consistent with the advice I received from mine. I did the Norte/Primitivo last spring, and I think the combo of poles (I think two are best for this purpose), bent knees and smaller steps worked for me. I still had some swelling after some of the longer descents, but with some ibuprofen and an application of Bio Freeze to aid recovery it was manageable.
For what it's worth, I will add that as part of my recovery from an earler knee injury, my PT recommended including backwards walking in my training - the idea being if you're only walking forward, you only develop part of your leg muscles; walking backwards helps develop the whole muscle (and that to prevent knee injuries you also need to strengthen the muscles above and below the knee).
The advice was to alternate 1-2 minutes of backwards with 3-6 minutes of forward throughout the walk. Although the injury healed before I began my Camino, I found that it was so helpful that I continue to try to do it 2-3 times/week - I found it really works leg muscles in ways that forward walking doesn't - I seem to be able to walk for miles going forward feeling almost nothing in my legs, but after a few minutes walking backward, I feel the fatigue in the muscles and particularly on uphills/downhills feel a different stretch in the psoas, which makes me think it's doing something and must be helpful, so I've kept it as part of weekly routine. Your foot also strikes the ground in a different fashion, toe to heel instead of heel to toe.
It's probably safest to do this on a local school track, but I live in a relatively low-traffic area and found a nice 4 mile loop with relatively smooth roads, crossing to the other side of the road for the backwards portions so that while walking backwards I can see cars coming. I know where the smooth parts of the road are, so that's where I turn around to walk backwards, using the side of the road and the middle lane marker to stay centered; I've been doing it long enough now that I barely turn my head to keep on track or avoid bumps/holes. It's slow going at first until you get used to it, and obstructions in the road can be a real hazard. At the time my PT recommended this strategy, I remember reading several articles on it (mostly about backwards running - some claim that you burn more calories backwards, even if it is slower - who knows, that's not why I do it ). It's also an interesting conversation starter! I've had runners, cyclists, even people in cars stop to ask me about it, hahaha!