An implantable device for fixation of spinous processes, comprising: a first plate having a first surface and defining an aperture, wherein the first plate further comprises a split ring collar positioned at least partially within the aperture; a second plate, spaced from the first plate having a second surface facing the first surface, the second plate defining an aperture, wherein the second plate further comprises a second split ring collar positioned at least partially within the aperture; and a single post having a first end portion configured to selectively pass through the split ring collar positioned within the aperture in the first plate and connectable to the first plate and a second end portion configured to selectively pass through the second split ring collar positioned within the aperture in the second plate and connectable to the second plate, to connect the first plate to the second plate, wherein the connections of the first plate and the second plate to the single post permit the first and second plates (100, 200) to move polyaxially with respect to one another and to translate along a longitudinal length of the single post; wherein the first and second plates (100, 200) each comprise a set screw (150, 250), the set screw configured to interface the respective split ring collar (140, 240) thereto the respective single post, thereby affixing the first and second plate (100, 200) onto the single post, and wherein the first and second split ring collars (140, 240) each comprise on an outer surface a protrusion element configured to engage into a circumferential groove in the apertures (130, 230) of the first and second plates (100, 200). a first plate having a first surface and defining an aperture, wherein the first plate further comprises a split ring collar positioned at least partially within the aperture; a second plate, spaced from the first plate having a second surface facing the first surface, the second plate defining an aperture, wherein the second plate further comprises a second split ring collar positioned at least partially within the aperture; and a single post having a first end portion configured to selectively pass through the split ring collar positioned within the aperture in the first plate and connectable to the first plate and a second end portion configured to selectively pass through the second split ring collar positioned within the aperture in the second plate and connectable to the second plate, to connect the first plate to the second plate, wherein the connections of the first plate and the second plate to the single post permit the first and second plates (100, 200) to move polyaxially with respect to one another and to translate along a longitudinal length of the single post; wherein the first and second plates (100, 200) each comprise a set screw (150, 250), the set screw configured to interface the respective split ring collar (140, 240) thereto the respective single post, thereby affixing the first and second plate (100, 200) onto the single post, and wherein the first and second split ring collars (140, 240) each comprise on an outer surface a protrusion element configured to engage into a circumferential groove in the apertures (130, 230) of the first and second plates (100, 200).