Polyaxial pedicle screw assembly with cannulated screw shank having an internal drive socket surrounded by a planar top end surface

Abstract

A polyaxial pedicle screw assembly includes a receiver having a channel for receiving a rod and a central bore with a seating surface proximate a bottom opening. The assembly also includes a screw shank having a shank head at a proximal end and an anchor portion at a distal end configured for fixation to the bone, with the shank head having an outer spherical surface with a single common radius and an annular planar top end surface entirely surrounding an internal drive socket formed into a top end of the shank head. The assembly further includes a pressure insert having an upper surface for receiving the rod and a lower surface for engaging the outer spherical surface of the shank head to direct a downwardly-directed force from the rod to the screw shank in a locked configuration. The annular planar top end surface on the shank head remains spaced apart from the lower surface of the insert so as to not directly receive the downwardly-directed force therefrom in the locked configuration.