Patent ID: 7833250

Claim:
A polyaxial bone screw assembly comprising: (a) a shank having a body for fixation to a bone and a capture structure extending upward from the body, the capture structure having an outer surface with a first helically wound guide and advancement structure, the shank extending above the capture structure so as to have an upper surface spaced from the capture structure; (b) a head having a top portion and a base, the head top portion defining an open channel sized and shaped to receive a rod, the base having a seating surface partially defining a cavity, the channel being located directly above and communicating with the cavity, the cavity communicating with an exterior of the base through an opening sized and shaped to receive the capture structure therethrough; and (c) a retainer structure having an external surface and a central bore with an internal surface having a second helically wound guide and advancement structure thereon, the first helically wound guide and advancement structure configured to rotatably mate with the second helically wound guide and advancement structure to secure the retainer structure to the capture structure within the head cavity, the external surface configured to be in slidable mating engagement with the seating surface of the head so as to enable selective angular positioning of the shank body with respect to the head, the retainer structure being positioned in spaced relationship from and beneath the shank upper surface and the shank upper surface adapted to receive locking pressure from a pressure structure located above the shank upper surface such that, between the shank upper surface and the retainer, only the shank upper surface engages the pressure structure.