The Collaborative International Dictionary of English v.0.48:

Impacted \Im*pact"ed\, a.
   1. Driven together or close.
      [1913 Webster]

   2. Specifically: (Dentistry) Grown in an abnormal direction
      so that it is wedged against another tooth and cannot
      erupt normally; -- of teeth, especially the third molar;
      as, to extract an impacted third molar.
      [PJC]

   Impacted fracture (Surg.), a fracture in which the
      fragments are driven into each other so as to be
      immovable.
      [1913 Webster]

WordNet (r) 3.0 (2006):

impacted fracture
    n 1: fracture in which one broken end is wedged into the other
         broken end