Disclosed is a polyaxial screw including a friction element (12) positioned between the head (3) of the threaded bone anchoring portion (2) and the head (9) of the mechanical thread anchoring portion (4) on the one hand, and a retaining element (13, 18) ensuring that the anchoring portions (2, 4) cannot separate from each other while guaranteeing that the anchoring portion with the mechanical thread (4) is free to move in vertical translation and angular pivoting with respect to the threaded bone anchoring portion (2) so as to be able to axially preposition the mechanical thread anchoring portion (4) with respect to the axial anchoring position of the threaded bone anchoring portion (2).