Sore knees is one of the symptoms that helped me get diagnosed with Crohns back in 1998.. Suddenly I had arthritis in both knees (at the backs if I recall), and also my wrists. Once I had to start crawling up the stairs I knew something was wrong and went to the emergency department. Prednisone cleared it all up in a couple hours when I started it, I was so thrilled I was running up the stairs. When you cut back on your prednisone your symptoms can rebound a little since the inflammation in your body increases, as the other poster mentioned, but your own body's cortisol production will increase eventually and you'll feel good again.
Whenever I tapered on prednisone, I had symptoms that almost felt like a relapse for 3 or 3 days after each taper. For me it was usually headaches, nausea, extreme fatigue, and a wierd lightheadedness- I would see stars if I got up too quickly etc. Quite unpleasant but it always goes away.