An articulatable member for an instrument (141; 142) for use in a surgical procedure, the articulatable member comprising: a plurality of links (311, 312, 313, 314. 315) extending in a series from a proximal end link to a distal end link, adjacent links (312, 313, 314, 315) of the plurality of links being pivotably coupled to form joints between adjacent links; a first cable extending between the proximal end link and the distal end link, wherein the first cable is configured to actuate articulation of the articulate member in response to a tensible force applied to the first cable; and a second cable extending between and fixed to the proximal end link and the distal end link, wherein the second cable is configured to passively constrain the articulatable member during articulation; wherein each link of the plurality of links comprises a ring shape defining a central aperture and an outer perimeter; wherein the first cable extends through a first aperture in each link of the plurality of links, the first aperture located between the central aperture and the outer perimeter radially inward a first distance from an outer perimeter of each link of the plurality of links; wherein the second cable follows a helical path along at least a portion of the articulatable member from the proximal end link to the distal end link; wherein the second cable extends through a second aperture in each link of the plurality of links; characterized by the second aperture being located between the central aperture and the outer perimeter and radially inward a second distance greater than the first distance from the outer perimeter of each link of the plurality of links. a plurality of links (311, 312, 313, 314. 315) extending in a series from a proximal end link to a distal end link, adjacent links (312, 313, 314, 315) of the plurality of links being pivotably coupled to form joints between adjacent links; a first cable extending between the proximal end link and the distal end link, wherein the first cable is configured to actuate articulation of the articulate member in response to a tensible force applied to the first cable; and a second cable extending between and fixed to the proximal end link and the distal end link, wherein the second cable is configured to passively constrain the articulatable member during articulation; wherein each link of the plurality of links comprises a ring shape defining a central aperture and an outer perimeter; wherein the first cable extends through a first aperture in each link of the plurality of links, the first aperture located between the central aperture and the outer perimeter radially inward a first distance from an outer perimeter of each link of the plurality of links; wherein the second cable follows a helical path along at least a portion of the articulatable member from the proximal end link to the distal end link; wherein the second cable extends through a second aperture in each link of the plurality of links; characterized by the second aperture being located between the central aperture and the outer perimeter and radially inward a second distance greater than the first distance from the outer perimeter of each link of the plurality of links.