I Had Major Knee Surgery In 2012. A Year Or

I had major knee surgery in 2012. A year or so ago when I walk on a hard surface such as Walmart or mall, my right foot which is also the side I had the surgery becomes numb. The sensation then rides up my leg into my right buttock it feels numb and is very painful. I constantly have to rest my leg by lifting it up and resting it on the grocery cart. What could be causing this? It happens every time I go into that type of store with a hard service. Thanks in advance