Patent ID: 8398682

Claim:
A polyaxial bone screw assembly comprising: (a) a shank having a body for fixation to a bone and an upper head portion, the upper head portion having a mating segment and a first partial spherical surface; (b) a retainer structure being mateable with the mating segment of the upper head portion, the retainer structure having a second partial spherical surface such that when mated, the first and second partial spherical surfaces form at least a partial spherical ball member; (c) a receiver defining an open channel and having a base with a lower seating surface partially defining a cavity, the seating surface being sized and shaped to engage at least a portion of the spherical ball member, the open channel communicating with the cavity, the cavity communicating with an exterior of the base through an opening sized and shaped to receive the shank upper head portion by uploading the upper head portion through the opening; the upper head portion mating with the retainer within the cavity; and (d) a bushing sized and shaped to fit at least partially within the open channel and cavity, the bushing having a lower rounded surface engageable with at least a portion of the spherical ball member; wherein (e) the shank mating segment and the retainer structure cam together so as to form the spherical ball member.