Abstract: A catheter-based delivery device is disclosed for delivering and deploying a prosthesis at a treatment site. The delivery device includes a sheath having a segment with a plurality of ribs, a plurality of slots and a helical spine that extends along the segment. The helical spine has a non-uniform width that provides torsional stiffness that varies along a length of the segment, wherein the torsional stiffness permits a rotational force or torque to be transferred from a proximal end to a distal end of the segment. A prosthesis may be disposed in a delivery state within the segment and may be radially aligned with a treatment site by rotating the sheath about a longitudinal axis thereof, such that torque applied to the sheath is transferred through the segment to permit the segment, and the prosthesis disposed therein, to be rotated substantially in unison with a remainder of the sheath.