An interspinous implant, for implantation between two adjacent dorsal spines (EI,ES) each including an upper edge, a lower edge and two opposed lateral faces (E4, E5), wherein the implant is designed to be implanted from only one lateral face (E4, E5) of the spines, by including: - at least one body with dimensions arranged so as to maintain or restore a distance between the adjacent edges (E2, E3) of the two spinous processes (EI, ES) and including at least two wings (11, 12) extending on the same lateral face of the body so that at least a part of each wing (11, 12) lies along at least a part of one lateral face (E4, E5) of one of the two spinous processes (EI, ES) and, additionally, - at least one retainer (2, 4, 24, L) independent of the body, designed to retain the body of the implant between the two spines, and including at least one insert having a folded position and a deployed position, said body comprises at least one passage extending through at least one part of the body, by opening into at least one lateral face of the interspinous implant and splitting into two in the direction of the upper and lower spines, and allowing the insertion of the said insert when it is in its folded position, from the same lateral face (E4, E5) as the one from which the body is inserted between the spines, characterized in that: - said insert including at least two curved plates articulated about an articulation axis to pivot between, the folded position and the deployed position, - said passage has a shape, dimensions and orientation complementary to the shape, dimensions and orientation of the at least two curved plates, such that they slide through said passage without deformation when said insert is in the folded position and inserted into said passage, which spreads said insert into its deployed position, so that at least a part of these at least two curved plates projects outside said passage, towards the upper and lower spines, along at least a part of the lateral face of the body opposite to the one comprising the wings (11, 12). - at least one body with dimensions arranged so as to maintain or restore a distance between the adjacent edges (E2, E3) of the two spinous processes (EI, ES) and including at least two wings (11, 12) extending on the same lateral face of the body so that at least a part of each wing (11, 12) lies along at least a part of one lateral face (E4, E5) of one of the two spinous processes (EI, ES) and, additionally, - at least one retainer (2, 4, 24, L) independent of the body, designed to retain the body of the implant between the two spines, and including at least one insert having a folded position and a deployed position, - said insert including at least two curved plates articulated about an articulation axis to pivot between, the folded position and the deployed position, - said passage has a shape, dimensions and orientation complementary to the shape, dimensions and orientation of the at least two curved plates, such that they slide through said passage without deformation when said insert is in the folded position and inserted into said passage, which spreads said insert into its deployed position, so that at least a part of these at least two curved plates projects outside said passage, towards the upper and lower spines, along at least a part of the lateral face of the body opposite to the one comprising the wings (11, 12).