A note on the uniqueness of minimal length carrier graphs
  We show that minimal length carrier graphs are not unique, but if M is in a large class of hyperbolic 3-manifolds, including the geometrically finite ones, then M has only finitely many minimal length carrier graphs and no two of them are homotopic. As a corollary, we obtain a new proof that the isometry group of a geometrically finite 3-manifold is finite. 
Michael Siler
math.GT