I am 17 weeks post surgery on bilateral partial knee replacements. I tackle long flights of stairs by turning myself around and going down backwards. I hang on to the rail at all times. I make a note of the # of stairs, I descend with the leg that isn't the one closest to the rail, 1 step at a time until I reach the bottom. I stop occasionally to do knee bends to keep my stretches going. I can descend quite quickly. It may not work for everyone to try this method, but it works great for me. 🙂