"...knees were giving out, and it took a LOT of stress off of them..."

I think that is the whole thing. You see people hiking along on flat level ground, and a pair of hiking poles look pretty silly, they often don't even touch the ground. But once you hit rougher country they really help, 'specially on the downhill. I think that a solid method of adjusting the length is important. I just don't trust those twist lock things, if they are to suppord me and my load going downhill. I prefer the spring button type of lock. Not quite as adjustable for length, but a nice solid lockup...