K-homology and index theory on contact manifolds
  Let X be a closed connected contact manifold. On X there is a naturally arising class of hypoelliptic (but not elliptic) operators which are Fredholm. In this paper we solve the index problem for this class of operators. The solution is achieved by combining Van Erp's earlier partial result with the Baum-Douglas isomorphism of analytic and geometric K-homology. 
Paul F. Baum, Erik van Erp
math.OA math.DG