What Causes A Non Healing Wound?

my father in law had gone through by pass surgery many years back and 7 years back he meet with an accident in which his leg was wounded and till now wound has not healed in fact got ulcer and lots of swelling in leg, his age must be around 60 is skin grafting solution to it and are there chances that skin grafting might lead to pralysis and he is not dieabitic patient