Patent ID: 7572279

Claim:
A polyaxial bone screw assembly comprising: (a) a shank having a body for fixation to a bone and a capture structure extending from the body, the capture structure having an outer surface with a first helically wound guide and advancement structure; (b) a head having a top portion and a base, the head top portion defining an open channel, the base having a seating surface partially defining a cavity, the channel 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) an open discontinuous retainer structure having an external surface and a central channel with an internal surface having a discontinuous 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 shank and retainer structure mating in the head so as to allow polyaxial rotation thereof relative to the head and with the shank extending above the retainer structure, the shank having an external tool engagement formation thereon to engage a driving tool with the tool engagement structure being accessible to the tool when the shank and retainer structure are mated.