A polyaxial bone anchoring system comprising: - a bone anchoring member provided with a hemispherical head, - a tubular barrel for coupling a stabilizing element to the bone anchoring member, with said tubular barrel comprising a base traversed by an axial channel, the cross section of which is greater than the cross section of the hemispherical head, with said axial channel having, in the lower part, a frustoconical housing which widens in the direction opposite the hemispherical head and, upstream from the frustoconical housing, a transverse shoulder, the internal cross-section of which is substantially equal to the cross-section of the hemispherical head, - means for locking the bone anchoring member in the tubular barrel, with said locking means being positioned in the axial channel of the base, upstream from the housing, and - a conical split ring the outer surface of which matches the inner surface of the frustoconical housing and the minimum cross-section of which, when idle, is smaller than the nominal cross-section of the hemispherical head, with said ring being made of a deformable material between an expanded position allowing the passage of the hemispherical head through the split ring and a retracted position, having a cross section smaller than the minimum cross-section, when idle, to be inserted into the frustoconical housing, with the frustoconical housing having a height greater than the height of the split ring and, close to the shoulder, a cross section greater than the outer cross section of the ring, characterized in that the frustoconical housing has a radial groove, close to the shoulder, which delimits the upper part of the frustoconical housing. - a bone anchoring member provided with a hemispherical head, - a tubular barrel for coupling a stabilizing element to the bone anchoring member, with said tubular barrel comprising a base traversed by an axial channel, the cross section of which is greater than the cross section of the hemispherical head, with said axial channel having, in the lower part, a frustoconical housing which widens in the direction opposite the hemispherical head and, upstream from the frustoconical housing, a transverse shoulder, the internal cross-section of which is substantially equal to the cross-section of the hemispherical head, - means for locking the bone anchoring member in the tubular barrel, with said locking means being positioned in the axial channel of the base, upstream from the housing, and - a conical split ring the outer surface of which matches the inner surface of the frustoconical housing and the minimum cross-section of which, when idle, is smaller than the nominal cross-section of the hemispherical head, with said ring being made of a deformable material between an expanded position allowing the passage of the hemispherical head through the split ring and a retracted position, having a cross section smaller than the minimum cross-section, when idle, to be inserted into the frustoconical housing, with the frustoconical housing having a height greater than the height of the split ring and, close to the shoulder, a cross section greater than the outer cross section of the ring, characterized in that the frustoconical housing has a radial groove, close to the shoulder, which delimits the upper part of the frustoconical housing.