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A polyaxial bone anchor including a housing, a bone screw, and a retainer for pivotably coupling the head of the bone screw to the housing. The retainer is positioned into the bore of the housing and includes a plurality of alternating tabs and slots circumferentially arranged to define a cavity for

A polyaxial bone anchor including a housing, a bone screw, and a retainer for pivotably coupling the head of the bone screw to the housing. The retainer is positioned into the bore of the housing and includes a plurality of alternating tabs and slots circumferentially arranged to define a cavity for receiving the head portion of the bone screw therein. The retainer is axially moveable in the housing from a first position in which the head portion is not passable through the lower opening of the retainer to a second position in which the head portion is passable through the lower opening of the retainer.

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1. A retainer for a pedicle screw, the retainer comprising: a cylindrical-like body comprising: an outer wall extending along an axis; andan internal spherically concave cavity adapted to receive a head portion of a pedicle screw;an upper portion;a helical portion connecting the upper portion and th

1. A retainer for a pedicle screw, the retainer comprising: a cylindrical-like body comprising: an outer wall extending along an axis; andan internal spherically concave cavity adapted to receive a head portion of a pedicle screw;an upper portion;a helical portion connecting the upper portion and the cylindrical-like body, the helical portion allowing the retainer to be resiliently compressed by an axially compressive force to reduce an axial length of the retainer and resiliently lengthened when the compressive force is removed; anda lower face connected to the cylindrical-like body at an opposite end as the helical portion. 2. The retainer of claim 1, wherein the upper portion includes a planar superior surface. 3. The retainer of claim 1, wherein the upper portion has a U-shape. 4. The retainer of claim 1, wherein the upper portion includes an axial throughbore. 5. The retainer of claim 4, wherein the axial through-bore penetrates the lower face at an opening to the internal spherically concave cavity. 6. The retainer of claim 5, wherein the axial through-bore at the upper portion is smaller than the opening at the lower face. 7. The retainer of claim 1, wherein the retainer is made from a resilient material. 8. The retainer of claim 7, wherein the resilient material comprises a pliable polymeric material or a malleable metallic material. 9. The retainer of claim 8, wherein the cylindrical-like body, the upper portion, the lower face and the helical portion are monolithic. 10. The retainer of claim 1, wherein the cylindrical-like body includes a plurality of tabs. 11. The retainer of claim 10, wherein the cylindrical-like body includes a plurality of slots interposed with the plurality of tabs. 12. The retainer of claim 1, wherein the lower face includes a bevel. 13. The retainer of claim 1, wherein the helical portion comprises a slot extending spirally around the cylindrical-like body to allow resilient axial compression of the upper portion. 14. A retainer for a bone anchor, the retainer comprising: a body comprising: an upper surface and a lower surface;a concavity disposed within the body between the upper and lower surfaces, the concavity configured to receive a head portion of a pedicle screw; andan axial bore extending from the upper surface, through the spherical concavity, and to the lower surface; andresilient spring means within the body such that the upper surface and the lower surface are axially movable relative to each other upon application and removal of an axial compressive force. 15. The retainer of claim 14, wherein the resilient spring means comprises a helical spring. 16. The retainer of claim 15, wherein the resilient spring means comprises a slot extending transverse to the axial bore and that winds spirally along the body. 17. The retainer of claim 14, further comprising: a plurality of interposed tabs and slots within the body such that the tabs are radially flexible relative to a longitudinal axis of the axial bore. 18. The retainer of claim 14, wherein the body is formed of a resilient material. 19. The retainer of claim 14, further comprising a bevel around an inferior-most outer edge of the body. 20. The retainer of claim 14, wherein the axial bore has an upper opening on the upper surface that is smaller than a lower opening on the lower surface. 21. The retainer of claim 20, further comprising a fastener comprising: a spherical head sized to mate with the spherical concavity within the body;an elongate shaft extending from the spherical head and sized to fit through the lower opening; anda driver socket on the spherical head positioned to be accessible through the upper opening.