As others have said, slow down and take shorter steps down hill.
On moderate uphill, or downhill, where there's a temptation to go quickly, "place" your feet down, don't stomp! This requires effort at first, but will become habit after a while.
I was practically crippled by knee pain half way through a section, but stopping early and resting - and taking 2 ibuprofen that afternoon, that evening, and the next morning, I was able to continue the next day - and did 19 miles up and out of Hot Springs!