Polyaxial bone anchor with retainer with notch for mono-axial motion
A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in an integral receiver, the receiver having an upper channel for receiving a longitudinal connecting member and a lower cavity cooperating with a lower opening. A down-loadable compression insert having a sub-structure, a down-loadable friction fit split retaining ring having inner and outer tangs and an up-loadable shank upper portion cooperate to provide for pop- or snap-on assembly of the shank with the receiver either prior to or after implantation of the shank into a vertebra. The shank and receiver once assembled cannot be disassembled.
1. A polyaxial bone anchor assembly comprising:
a) a shank having a body for fixation to a bone and an integral upper portion,
b) an U-shaped receiver having a top portion and an integral base, the receiver top portion defining an open rod-receiving channel, the integral base defining a cavity communicating with a bottom opening, the bottom opening having at least one concave curved bottom surface, the integral upper portion of the shank positionable within the cavity, and the channel communicating with the cavity;
c) a retainer positioned within the cavity prior to the shank being loaded and capturing the shank upper portion once loaded, the retainer being in a non-pivotal relationship with respect to the receiver; and wherein the retainer having a cut-out surface being sized and shaped to cooperate with the concave curved bottom surface of the receiver to provide for increased polyaxial motion in at least one direction for the shank with respect to the receiver.
2. The polyaxial bone anchor assembly of claim 1 , wherein the receiver further comprises a receiver chamber, partially defined by a ceiling surface disposed substantially perpendicular to the central axis and an inner wall adjacent and substantially perpendicular to the ceiling surface, the inner wall located between a pair of receiver arms and a first planar loading surface and a second planar loading surface, the ceiling surface and the inner wall partially defining an expansion chamber for receiving an expandable open retainer about the shank upper portion.
3. The polyaxial bone anchor assembly of claim 2 , wherein the retainer has an outer tapered surface located below and spaced from the receiver first and second planar loading surfaces when in a final locked position.
4. The polyaxial bone anchor assembly of claim 2 , further comprising an insert located within the receiver, the insert having an inner lower surface in a friction fit with the shank upper portion during temporary manipulation of the shank with respect to the receiver, the shank upper portion being movable with respect to the insert with some resistance when a force is applied to the shank to pivot the shank with respect to the receiver, the insert being in locked frictional engagement with the shank upper portion when a force is applied on the insert that in turn presses the retainer into the expansion only locked position.
5. The polyaxial bone anchor assembly of claim 4 , wherein the insert is spaced from the retainer.
6. The polyaxial bone anchor assembly of claim 4 , wherein the receiver has a frusto-conical surface in contact with an outer surface of the insert that presses the insert inner lower surface toward the shank upper portion to create the temporary friction fit.
7. The polyaxial bone anchor assembly of claim 6 , wherein the insert has a pair of opposed lower slots.
8. The polyaxial bone anchor assembly of claim 4 , wherein the insert has a pair of opposed outer projections and each receiver arm has an aperture for receiving one of the outer projections.
9. The polyaxial bone anchor assembly of claim 8 , wherein a receiver wall partially defining one of the apertures for receiving one of the insert outer projections further comprises a lip, the lip engaging one of the insert outer projections.
10. The polyaxial bone anchor assembly of claim 2 , wherein the shank is bottom loaded.
11. The polyaxial bone anchor assembly of claim 1 further comprising a longitudinal connecting member, the member comprising:
a) a cord held in tension at either end of the connecting member;
b) a first hard sleeve having a body and opposed flanges sized and shaped for placement outside of the receiver, the body further having opposed protruding portions, the tensioned cord received by the sleeve, the sleeve body located within the receiver and seated on an insert;
c) a closure top rotatably mated with the guide and advancement structure, the sleeve protruding portions engaging both the closure top and the insert; and
d) a spacer, the spacer receiving the cord therethrough, the spacer located between the first sleeve and one of a second sleeve and an end blocker and set screw combination, the cord being held in tension at one of the second sleeve and the end blocker.
12. The polyaxial bone anchor assembly of claim 11 , further comprising a compressible bumper located adjacent the blocker.
13. The polyaxial bone anchor assembly of claim 11 , wherein each flange has a planar top surface and the spacer has an extended portion with a planar bottom surface in contact with the flange planar top surface.
14. The polyaxial bone anchor assembly of claim 13 , wherein the spacer is engaged with both the first and second sleeves.