Polyaxial bone anchors include a retainer for holding a shank within a receiver, the retainer being in at least two discrete pieces and cooperating with a variety of inserts, some of which independently lock the polyaxial mechanism. Polyaxial and mono-axial bone anchor assemblies include pivot and/or pressure inserts or pads that cooperate with longitudinal connecting members to provide a desired degree of continued control of angulation of the longitudinal connecting member in the sagittal plane or to hold the connecting member in place. Pressure pads for deformable rods may also be made from a deformable plastic material.
