Bone anchor assembly with twist-in-place pressure insert
A polyaxial bone screw assembly includes a threaded shank body having an upper portion, a receiver member or head, a retaining and articulating structure, and a pressure insert disposed between the shank upper portion and a rod. The receiver has a U-shaped cradle defining a channel for receiving a spinal fixation rod and a receiver cavity. The retaining and articulating structure attaches to the shank and rotates with the shank in the cavity during positioning. The pressure insert presses upon the shank upper portion and not the retaining and articulating structure.
1. A bone anchor assembly for securing an elongate rod to a bone, the bone anchor assembly comprising:
a shank having a proximal capture portion and an anchor portion extending distally from the proximal capture portion for fixation to the bone;
a receiver having a longitudinal axis, an upper portion defining a U-shaped channel with inner sidewall surfaces configured to receive the elongate rod, and a lower portion defining a cavity communicating with the U-shaped channel and a receiver bottom opening, the inner sidewall surfaces including a guide and advancement structure and a discontinuous downward-facing shoulder pre-formed therein between the guide and advancement structure and the bottom opening; and
a pressure insert sized and shaped to be positioned downwardly within the receiver into a first position, the pressure insert having upward-facing contact surfaces and being rotatable into a second position that locates the upward-facing contact surfaces at least partially under the receiver discontinuous downward-facing shoulder to prevent the pressure insert from moving back up within the receiver.
2. The bone anchor assembly of claim 1 , wherein the pressure insert further comprises a central body having radially-extending portions that are operable to rotate underneath opposing portions of the receiver discontinuous downward-facing shoulder when the pressure insert is rotated about the receiver longitudinal axis, the radially-extending portions having the upward-facing contact surfaces formed thereon.
3. The bone anchor assembly of claim 2 , wherein the upward-facing contact surfaces of the radially-extending portions include a pair of sloped portions operable to engage the opposing portions of the receiver discontinuous downward-facing shoulder as the pressure insert is rotated about the receiver longitudinal axis to provide a cam action that converts the rotatory motion of the pressure insert into linear downward movement of the pressure insert.
4. The bone anchor assembly of claim 3 , wherein the upward-facing contact surfaces of the radially-extending portions further include substantially horizontal portions adjacent the sloped portions and operable to frictionally engage the receiver discontinuous downward-facing shoulder when the pressure insert is fully rotated to the second position.
5. The bone anchor assembly of claim 4 , wherein the pressure insert continues to rotate toward the second position after the linear downward movement of the pressure insert is complete.
6. The bone anchor assembly of claim 2 , wherein the central body of the pressure insert further includes a rod-engaging U-shaped cradle formed therein that aligns with the U-shaped channel of the receiver when the pressure insert is fully rotated to the second position.
7. The bone anchor assembly of claim 1 , wherein the pressure insert engages the shank.
8. The bone anchor assembly of claim 1 , wherein the pressure insert is rotatable into the second position with a tool.
9. The bone anchor assembly of claim 8 , wherein an upper surface of the pressure insert includes at least one tool engagement structure complementary with an engagement portion of the tool.
10. The bone anchor assembly of claim 1 , wherein the proximal capture portion of the shank is uploaded through the receiver bottom opening.
11. The bone anchor assembly of claim 1 , further comprising a retainer sized and shaped for loading into the receiver cavity to engage and hold the shank proximal capture portion in spaced relation with respect to the receiver while an outer surface of the retainer engages an interior surface of the receiver cavity to allow a pivotal motion between the receiver and the shank.
12. A bone anchor assembly for securing an elongate rod to a bone, the bone anchor assembly comprising:
a shank having a proximal capture portion with an outer spherical surface and an anchor portion extending distally from the proximal capture portion for fixation to the bone;
a receiver having a longitudinal axis, an upper portion defining a U-shaped channel with inner sidewall surfaces configured to receive the elongate rod, and a lower portion defining a cavity communicating with the U-shaped channel and a receiver bottom opening, the shank positionable within the receiver with the shank anchor portion extending through the bottom opening, the inner sidewall surfaces including a guide and advancement structure formed therein, the receiver having an internal downward-facing surface located between the guide and advancement structure and the receiver bottom opening; and
a pressure insert sized and shaped to be disposed downwardly into a first position within the receiver adjacent the receiver downward-facing surface, after the shank has been positioned within the receiver, with the shank proximal capture portion outer spherical surface frictionally engageable with the pressure insert for directly receiving downward pressure from the pressure insert, the pressure insert having an upward-facing surface configured to engage the receiver downward-facing surface,
wherein the pressure insert is rotatable with a tool about the receiver longitudinal axis into a second position within the receiver, with the insert upward-facing surface entering into frictional engagement with the receiver downward-facing surface, so as to apply downward pressure to the shank proximal capture portion outer spherical surface by biased overlapping engagement therebetween so as to provide a frictionally articulatable relationship for the shank with respect to the receiver prior to the elongate rod being received within the receiver.
13. The bone anchor assembly of claim 12 , wherein at least one of the insert upward-facing surface and the receiver downward-facing surface includes a sloped portion operable to provide a cam action that converts the rotatory motion of the pressure insert into linear downward movement of the pressure insert.
14. The bone anchor assembly of claim 13 , wherein the pressure insert continues to rotate toward the second position after the linear downward movement of the pressure insert is complete.
15. The bone anchor assembly of claim 12 , wherein the receiver downward-facing surface further comprises a discontinuous upper shoulder of a rigid recess machined into the inner sidewall surfaces between the guide and advancement structure and the receiver bottom opening.
16. The bone anchor assembly of claim 15 , wherein the insert upward-facing surface further comprises at least one sloped portion operable to provide a cam action that converts the rotatory motion of the pressure insert into linear downward movement of the pressure insert upon engagement with the discontinuous upper shoulder of the recess.
17. The bone anchor assembly of claim 16 , wherein the at least one sloped portion of the upper surface further comprises a pair of sloped portions formed into the insert upward-facing surface and operable to engage opposing portions of the discontinuous upper shoulder as the pressure insert is rotated about the receiver longitudinal axis.
18. The bone anchor assembly of claim 17 , wherein the insert upward-facing surface further includes substantially horizontal portions adjacent the sloped portions and operable to frictionally engage the discontinuous upper shoulder of the recess when the pressure insert is fully rotated to the second angular orientation.
19. The bone anchor assembly of claim 12 , wherein the pressure insert further includes a U-shaped cradle formed therein for engaging the elongate rod that aligns with the U-shaped channel of the receiver when the pressure insert is fully rotated into the second position.
20. The bone anchor assembly of claim 12 , wherein the pressure insert is rotated about 90 degrees around the receiver longitudinal axis from the first position to the second position.
21. The bone anchor assembly of claim 12 , wherein the pressure insert has a non-round shape, as viewed from above, with a width that is smaller than a length thereof.
22. The bone anchor assembly of claim 21 , wherein the insert upward facing surface further comprises a U-shaped cradle extending across the width of the pressure insert.
23. The bone anchor assembly of claim 12 , wherein an upper surface of the pressure insert includes at least one tool engagement structure complementary with an engagement portion of the tool.
24. The bone anchor assembly of claim 23 , wherein the at least one tool engagement structure further comprises a plurality of such tool engagement structures formed into the upper surface of the pressure insert.
25. The bone anchor assembly of claim 12 , further comprising a retainer sized and shaped for loading into the receiver cavity to engage and hold the shank proximal capture portion within the receiver while an outer surface of the retainer engages an interior surface of the receiver cavity to allow for pivoting motion between the receiver and the shank to provide for a pivotal orientation therebetween.
26. A bone anchor assembly for securing an elongate rod to a bone, the bone anchor assembly comprising:
a shank having a proximal portion with a partial spherical shape and an anchor portion extending distally from the proximal portion for fixation to the bone;
a receiver having a first longitudinal axis, an upper portion defining a U-shaped channel with inner sidewall surfaces configured to receive the elongate rod, and a lower portion defining a cavity communicating with the U-shaped channel and a receiver bottom opening with the shank anchor portion extending therethrough, the inner sidewall surfaces including a guide and advancement structure formed therein, the receiver having a non-threaded internal downward-facing surface radially spaced from the first longitudinal axis and located between the guide and advancement structure and the receiver bottom opening;
a closure configured to made with the receiver guide and advancement structure; and
a pressure insert having a second longitudinal axis and being sized and shaped to be disposed downwardly into a first position within the receiver adjacent the receiver downward-facing surface, the pressure insert having a non-threaded upward-facing surface radially spaced from the second longitudinal axis and configured to overlap with the receiver downward-facing surface,
wherein the pressure insert is rotatable with a removable tool about the first and second longitudinal axes into a second final rotational position within the receiver, with the insert upward-facing surface coming into an overlapping relationship with the receiver downward-facing surface, so as to prevent the insert from moving back up within the receiver, the insert being rotating into the second final position by direct engagement with the tool which is removed from within the receiver prior to the closure being positioned therein.
27. The bone anchor assembly of claim 26 , wherein the pressure insert includes at least one tool engaging structure formed therein.
28. The bone anchor assembly of claim 26 , wherein the receiver downward-facing surface further comprises a discontinuous upper ledge of a recess formed into the receiver between the guide and advancement structure and the receiver bottom opening.
29. The bone anchor assembly of claim 26 , wherein the pressure insert further includes a U-shaped cradle formed therein for engaging the elongate rod that aligns with the U-shaped channel of the receiver when the pressure insert is fully rotated into the second final position.
30. The bone anchor assembly of claim 26 , wherein the pressure insert is rotated about 90 degrees around the first and second longitudinal axes from the first position to the second final position.
31. The bone anchor assembly of claim 26 , wherein a portion of the pressure insert has a non-round shape with a width that is smaller than a length thereof.
32. The bone anchor assembly of claim 26 , wherein an upper surface of the pressure insert includes at least one off-axis tool engagement structure complementary with an engagement portion of the tool.
33. The bone anchor assembly of claim 32 , wherein the at least one off-axis tool engagement structure further comprises a plurality of such tool engagement structures formed into the upper surface of the pressure insert.
34. The bone anchor assembly of claim 26 , further comprising a retainer sized and shaped for loading into the receiver cavity to engage and hold the shank proximal capture portion within the receiver while an outer surface of the retainer engages an interior surface of the receiver cavity to allow for pivoting motion between the receiver and the shank to provide for a pivotal orientation therebetween.
35. A bone anchor assembly for securing an elongate rod to a bone via a closure, the bone anchor assembly comprising:
a shank having a proximal portion and an anchor portion extending distally from the proximal portion for fixation to the bone;
a receiver having a longitudinal axis, an upper portion defining a U-shaped channel with inner sidewall surfaces configured to receive the elongate rod, and a lower portion defining a cavity communicating with the U-shaped channel and a receiver bottom opening for receiving the proximal portion of the shank therethrough, the inner sidewall surfaces including a guide and advancement structure and opposed discontinuous non-threaded downward-facing surfaces formed therein between the guide and advancement structure and the receiver cavity;
a retainer sized and shaped for loading into the receiver cavity to engage and hold the shank proximal portion in spaced relation with respect to the receiver while an outer surface of the retainer engages an interior surface of the receiver cavity to allow a pivotal motion between the receiver and the shank; and
a pressure insert sized and shaped to be positioned downwardly within the receiver into a first position, the pressure insert having non-threaded upward-facing surfaces and being rotatable with a tool into a second final position that locates the insert upward-facing surfaces under the receiver downward-facing surfaces to prevent the pressure insert from moving back up within the receiver prior to the elongate rod and the closure being placed within the receiver channel.
36. The bone anchor assembly of claim 35 , wherein the pressure insert further comprises a central body having radially-extending portions with the insert upward-facing surfaces that are operable to rotate underneath the receiver downward-facing surfaces when the pressure insert is rotated about the receiver longitudinal axis into the second final position.
37. The bone anchor assembly of claim 35 ,
wherein the pressure insert is rotated about 90 degrees around the receiver longitudinal axis from the first position to the second final position with the tool, and wherein the tool directly engages the insert and is removed from within the receiver prior to the elongate rod and the closure being placed within the receiver channel.
38. The bone anchor assembly of claim 35 , wherein an upper surface of the pressure insert includes at least one tool engagement structure complementary with an engagement portion of the tool.