What Causes A Hard Lump At The Site Of Puncture Post Treatment?

About a month or two ago, I stepped on a wall plug and punctured the bottom of my toe at the base with one of the metal prongs. I was put on 3 antibiotics as a result as received a tetanus shot. The wound closed up no problem. Recently, I noticed that there is a quite noticeable, raised lump where the injury was that is hard. Is this anything to be concerned about?