What can cause severe pain 1yr after total knee replacement surgery? My mother has numbness in foot and knee. Sometimes swelling. Thanks

Varies. There are multiple possibilities, but one general way to look at it is either there is something wrong with the knee replacement surgery outcome, or your mother has another condition causing pain in that area. The most common "other" cause is a condition calked spinal stenosis, which is essentially a pinched nerve in the back that can cause leg pain and numbness.