Another thought...my foot seems to roll heel-to-toe better as I increase the strength in my atrophied calf and ankle muscles. Is there any chance that you've lost strength in your calf and ankle during your knee ordeal? If so, you could try strengthening those muscles to see if it helps your foot to roll better. One of the things that I've learned in PT is to not ignore the muscles in the front of my calf. I had never considered working the front of my calf before my muscles atrophied but it turns out that those muscles are as important to walking properly as are the muscles in the back of the calf.