US Patent 9456853 Polyaxial bone screw with shank articulation pressure insert and method

A polyaxial bone screw assembly includes a threaded shank body having an upper portion, a receiver member or head, a retaining and articulating structure, and a pressure insert disposed between the shank upper portion and a rod. The receiver has a U-shaped cradle defining a channel for receiving a spinal fixation rod and a receiver cavity. The retaining and articulating structure attaches to the shank and rotates with the shank in the cavity during positioning. The pressure insert presses upon the shank upper portion and not the retaining and articulating structure.