What Causes A Hard Lump At The Centre Of The Shin?

Hi, I had a fall a few weeks ago and hit the centre of my shin against the lip of my bed frame with considerable force. The area bruised instantly and hurt for a few days but the majority of the bruising has now gone away. However, I have since developed a lump there under the skin (which is hard and feels like it is actually on the bone). It is slightly tender to the touch but otherwise not problematic. Is this something I should be concerned about or will it go away with time? -Thanks!