A radially expandable stent (10, 20) having longitudinal and circumferential axes, the stent comprising: a plurality of rings arranged longitudinally to form a tubular body assembly, each ring comprising a circumferential sequence of cells (14, 21), wherein: each cell is longitudinally defined by a first pair of deformable struts (12, 22) on a first longitudinal side and a second pair of deformable struts (12, 22) on a second longitudinal side, the struts of the first pair set at an angle to one another and the struts of the second pair set at an angle to one another, the angle between each pair increasing as the stent is expanded from a compact configuration towards an expanded configuration; and at least one cell is circumferentially defined by a first cross member and a second cross member, the first cross member fixedly supporting a distal end of a rail member, the second cross member slidingly engaging a medial portion of the rail member; wherein the rail member is configured to slide circumferentially in a first direction with respect to the second cross member as the stent is expanded towards an expanded configuration; and wherein the medial portion of the rail member includes at least one tooth element configured to engage the second cross member so as to permit sliding in the first direction, and to engage the second cross member so as to resist sliding in an opposite second direction, so as to inhibit the stent from radially contracting. a plurality of rings arranged longitudinally to form a tubular body assembly, each ring comprising a circumferential sequence of cells (14, 21), wherein: each cell is longitudinally defined by a first pair of deformable struts (12, 22) on a first longitudinal side and a second pair of deformable struts (12, 22) on a second longitudinal side, the struts of the first pair set at an angle to one another and the struts of the second pair set at an angle to one another, the angle between each pair increasing as the stent is expanded from a compact configuration towards an expanded configuration; and at least one cell is circumferentially defined by a first cross member and a second cross member, the first cross member fixedly supporting a distal end of a rail member, the second cross member slidingly engaging a medial portion of the rail member; each cell is longitudinally defined by a first pair of deformable struts (12, 22) on a first longitudinal side and a second pair of deformable struts (12, 22) on a second longitudinal side, the struts of the first pair set at an angle to one another and the struts of the second pair set at an angle to one another, the angle between each pair increasing as the stent is expanded from a compact configuration towards an expanded configuration; and at least one cell is circumferentially defined by a first cross member and a second cross member, the first cross member fixedly supporting a distal end of a rail member, the second cross member slidingly engaging a medial portion of the rail member; wherein the rail member is configured to slide circumferentially in a first direction with respect to the second cross member as the stent is expanded towards an expanded configuration; and wherein the medial portion of the rail member includes at least one tooth element configured to engage the second cross member so as to permit sliding in the first direction, and to engage the second cross member so as to resist sliding in an opposite second direction, so as to inhibit the stent from radially contracting.