A screw (1) polyaxial bone comprising a head (7), a rod (6, 106), a retaining ring (8, 88, 107) spaced from said shaft and received in said head said retaining ring in engagement with and being secured to a portion (25) upper stem, the polyaxial bone screw characterized in that: a) the head (7) has a channel (38) adapted to receive a member (3) elongated rod having an orifice (52) partially defining a restrictive neck (54) b) the stem (6) has a bottom (15, 110) adapted to be implanted in a bone (2) of a patient and the top being sized and shaped to be positioned within the head and including a keyway (24 , 120) projecting radially outwardly c) the retaining ring includes a recess (62, 94, 120) receiving a keyway that receives the key to secure the ring to said upper shaft for rotation polyaxially with the stem relative to the head before locking an angular position of the rod with respect to the head, being a radius of the outer surface of the larger retaining ring restrictive to maintain said shaft in said head while allowing polyaxial movement of said stem neck and retaining ring with respect to said head during placement d) said upper dimensioned rod being shaped and positioned to receive a pressure force downwardly from said rod member after the rod member is received in the channel (38) and then the rod transfers the pressing force the retaining ring to lock the position of the rod and retaining ring with respect to the head.Un tornillo (1) óseo poliaxial que comprende una cabeza (7), un vástago (6, 106), un anillo de retención (8, 88, 107) separado de dicho vástago y recibido en dicha cabeza dicho anillo de retención en acoplamiento con y estando asegurado a una parte (25) superior de vástago, el tornillo óseo poliaxial caracterizado por que: a) la cabeza (7) tiene un canal (38) adaptado para recibir un miembro (3) de varilla alargado y que tiene un orificio (52) que define parcialmente un cuello restrictivo (54) b) el vástago (6) tiene una parte inferior (15,
