I Have Had Both Knees Replaced In 2011 And 2012.

I have had both knees replaced in 2011 and 2012. My recovery has gone well though I have hip and back arthritis. I have stopped running but still have some interest in restarting running. I was a heel pounder and am considering working on leg muscle strengthening and changing my stride to a greater effort to run more on my forefoot, what risks should I consider in this decision.