Why Is my knee still numb after 4 years of surgery?

I tore my Tibia bone four years ago from when I was a competitive skier. They took X rays and gave me surgery. They tried to do microscopic surgery but then they had to do surgery normally where they cut the skin to get to the bone because the bone i tore was too big. They Got A wire stuck in my leg during the surgery and left it there because they didnt want to injure my leg anymore. They put a screw where it was torn.It's been four years but to this day my leg is still numb can some one tell me why?