User blog comment:Doomlurker/After Arkham City/@comment-4505582-20111009081153

Plus this the Joker has sustained many injures from his mutation. When someone transforms into a Titan monster, his spinal cord and bone structure bursts through his skin. In some early concepts (one is added by me, check the Titan monster page) a metal pieces are bursting through it's skin. In the final models, the metal was replaced by bones.