The amalgamated free product of hyperfinite von Neumann algebras over   finite dimensional subalgebras
  In this paper we describe the amalgamated free product of two hyperfinite von Neumann algebras over a finite dimensional subalgebra. In general the free product is a finite direct sum of interpolated free group factors and a hyperfinite von Neumann algebra. We then show that the class of von Neumann algebras of this form is closed under taking amalgamated free products over finite dimensional subalgebras. 
Ken Dykema and Daniel Redelmeier
math.OA