Polyaxial bone screw assembly

1. A polyaxial bone screw assembly for fixation to a bone, the assembly including a shank with a threaded body and an upwardly extending head portion, a retainer structure sized and shaped to join and polyaxially rotate with the shank, and a receiver that operably receives the head portion and retainer, the assembly further wherein:

a) the head portion comprising a retainer engagement portion including a partially circumferential curvate groove with contoured upper and lower mating surfaces and a pair of spaced recesses;

b) the retainer structure being sized and shaped to matingly engage the retainer engagement portion so as to form a substantially spherical ball-shaped pivoting surface with the head portion, the retainer structure comprising

i) top and bottom mating surfaces complementary contoured for mating with the head portion upper and lower mating surfaces; and

ii) a pair of spaced prongs sized and shaped to matingly engage the head portion recesses;

c) the 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 upper head portion, 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, where the upper head portion mates with the retainer within the cavity.

2. The assembly according to claim 1 including a pressure insert that pivotably engages the shank head portion comprising:

i) a lower body with a pair of spaced opposed partially cylindrical surfaces and a pair of spaced vertical faces; and

ii) a pair of opposed upwardly extending arm structures, each arm structure having a radially extending protrusion with a centrally located locking slot, the cavity of the receiver having an interior wall having a protrusion that mates with locking slot.

3. A polyaxial bone screw assembly for fixation to a bone, the assembly including a shank with a threaded body and an upwardly extending head portion, a retainer structure sized and shaped to matingly engage the head portion, a receiver pivotally engaging the head portion, and an upper pressure insert receivable in the receiver and pivotably engaging the head portion, the improvement comprising:

a) the head portion having a retainer engagement portion including a partially circumferential curvate groove with contoured upper and lower mating surfaces and a pair of spaced locking recesses;

b) the retainer structure being sized and shaped to matingly engage the retainer engagement portion so as to form a substantially spherical ball-shaped pivoting surface with the head portion, the retainer structure comprising

i) top and bottom mating surfaces complementary contoured for mating with the head portion upper and lower mating surfaces; and

ii) a pair of spaced prongs sized and shaped to matingly engage the head portion locking recesses;

c) the upper pressure insert comprising

i) a lower body with a pair of spaced opposed partially cylindrical surfaces and a pair of spaced vertical faces; and

ii) a pair of opposed upwardly extending arm structures, each arm structure having a radially exteding protrusion with a centrally located locking slot; and

d) a receiver having

i) two spaced apart arms each being inwardly threaded and defining a gap therebetween,

ii) a U-shaped channel extending along a second axis transverse to the first axis adapted to receive a rod member,

iii) a first opening and a second opening extending along the first axis,

iv) a cavity within the first opening and the second opening, the second opening being sized and shaped to provide for uploading the shank upper head portion therethrough, the shank upper head portion mating with the retainer within the cavity;

v) a shaped wall, the wall being sized and shaped to slidingly at least partially engage the spherical ball member during positioning, and

vi) below the threads of the two spaced apart arms are formed two protrusions that operatively connect with the locking slot of the pressure insert.

4. The assembly of claim 3 , wherein the retainer further includes an external surfaces angled inwardly toward the top of the receiver located on the edge of the arms along the U-shaped channel.

5. The assembly of claim 3 , wherein the

retainer further includes an exterior surface, along the exterior surface is an aperture defining an interior surface.

6. A polyaxial bone screw assembly for fixation to a bone, the assembly including a shank with a threaded body and an upwardly extending head portion, a retainer structure sized and shaped to matingly engage the head portion, a receiver pivotally engaging the head portion, and an upper pressure insert receivable in the receiver and pivotably engaging the head portion, the improvement comprising:

a) the head portion comprising a retainer engagement portion including a partially circumferential curvate groove with contoured upper and lower mating surfaces and a pair of spaced locking recesses;

b) the retainer structure being sized and shaped to matingly engage the retainer engagement portion so as to form a substantially spherical ball-shaped pivoting surface of the head portion, the retainer structure comprising:

i) top and bottom mating surfaces complementary contoured for mating with the head portion upper and lower mating surfaces; and

ii) a pair of spaced prongs sized and shaped to matingly engage the head portion locking recesses;

c) the upper pressure insert comprising:

i) a lower body with a pair of spaced opposed partially cylindrical surfaces and a pair of spaced vertical faces; and

ii) a pair of opposed upwardly extending arm structures, each arm structure having a radially extending protrusion with a centrally located locking slot; and

d) the receiver having an upper portion, an intermediate portion, and a lower portion and defining a first axis extending between the upper and lower portions, the receiver having a first opening at the upper portion and a second opening at the lower portion, the upper portion comprising two spaced apart arms each being inwardly threaded and defining a gap therebetween, the upper portion further comprising a U-shaped channel extending along a second axis transverse to the first axis and adapted to receive a rod member, the lower portion of the receiver having a lower restrictive neck below a cavity formed therein, and the intermediate portion comprising a substantially cylindrical inner wall with a protrusion that mates with the locking slot of the pressure insert, located below the two spaced apart arms and above the lower restrictive neck.

7. A shank and retainer assembly for a bone screw wherein:

a) the shank has a lower threaded portion for implantation in a bone of a patient and an upper portion; the shank upper portion includes a first partial sphere; and

b) the retainer compress a second partial sphere whereby mating of the first and second partial sphere during mating forms a combined substantially ball shaped pivot structure.

8. The assembly according to claim 7 , wherein the first partial sphere includes a concave region and the second partial sphere includes a convex region that mates with the concave region.