Locking element for a polyaxial bone anchor, bone plate assembly and tool

1. A locking element configured to be used with a polyaxial bone anchor having a head with a portion, the locking element including a central axis, a bottom side, a top side opposite to the bottom side, and a peripheral surface portion that extending completely around the locking element that has an external thread, wherein

the bottom side defines a first recess facing toward the bottom side for accommodating and applying a force in a direction toward the bottom side to at least the portion of the head of the polyaxial bone anchor, and

the top side defines a second recess off the central axis and having a non-circular cross-section in a plane perpendicular to the central axis for torqueable engagement with a driver, the second recess includes an outer wall and an inner wall and a groove defined therebetween, and the outer wall and the inner wall continuously curve without sharp angles along the second recess.

2. The locking element of claim 1 , wherein the first recess does not extend completely through the locking element.

3. The locking element of claim 2 , wherein the outer and inner walls extend parallel to each other, and no portion of the outer and inner walls extends radially to the central axis.

4. The locking element of claim 1 , wherein the first recess has a conical shaped region.

5. The locking element of claim 1 , wherein the first recess has a spherically curved portion.

6. The locking element of claim 5 , wherein the spherically curved portion either,

(i) opens directly to the bottom side of the locking element, or

(ii) opens directly to a tapering portion that opens directly to the bottom side of the locking element, the tapering portion tapering to meet a largest opening of the spherically curved portion.

7. The locking element of claim 6 , wherein a first level (L1) is defined by the highest point of a circle drawn along the spherically curved portion of the first recess in a cross-sectional plane including the central axis, and (L1) is at a level at least as high as a second level (L2) that is defined by a bottom of the second recess.

8. The locking element of claim 1 , wherein the second recess does not extend completely through the locking element.

9. The locking element of claim 1 , wherein the second recess is located substantially in a radially outer area of the top side.

10. The locking element of claim 1 , wherein the second recess comprises a continuous groove.

11. The locking element of claim 10 , wherein the groove is one of ring-shaped, star-shaped, and wavy.

12. The locking element of claim 1 , wherein the locking element does not include any recess extending from the top side completely through the locking element to the bottom side.

13. The locking element of claim 1 , wherein the peripheral surface portion with the external thread spans a height of the entire locking element, making the locking element fully threaded.

14. The locking element of claim 1 , wherein the peripheral surface portion with the external thread does not span the entire locking element, thereby defining a non-threaded section adjacent the bottom side.

15. The locking element of claim 14 , wherein an axial length of the non-threaded section is equal to or smaller than the axial length of a threaded section of the portion with the external thread.

16. The locking element of claim 1 , wherein a shape of the second recess consists of a repeating pattern about the central axis.

17. The locking element of claim 1 , wherein a shape of the second recess is rotationally symmetrical about the central axis.

18. A bone plate assembly, comprising:

an elongate plate member with a top side and a bottom side, and at least two holes extending from the top side to the bottom side,

at least two bone anchors, each bone anchor comprising a shank configured to anchor into a bone, and a head having a top and a portion with a largest outer diameter (d), wherein the shank is extendable through a hole of the at least two holes;

wherein at least one of the holes is configured to define a seat at the bottom side adapted to pivotably receive the head and wherein the at least one of the holes includes a bore at the top side with a bore axis and an inner diameter (D) which is at least as large as the largest diameter (d) of the head; and

a locking element configured to be inserted into the bore and having a central axis coaxial with the bore axis, the locking element including a bottom side configured to face the head when the head is pivotably received in the seat and the locking element is inserted into the bore, a top side configured to face away from the head when the head is pivotably received in the seat and the locking element is inserted into the bore, and a peripheral surface portion extending completely around the locking element between the top and bottom sides, the peripheral surface portion having an external thread, wherein

the bottom side defines a first recess facing toward the bottom side for accommodating and applying a force in a direction toward the bottom side to at least a portion of the head, the first recess not extending completely through the locking element,

the top side defines a second recess having a non-circular cross-section in a plane perpendicular to the central axis configured for engagement with a driver, the second recess includes an outer wall and an inner wall and a groove defined therebetween, and the outer wall and the inner wall continuously curve without sharp angles along the second recess,

wherein, when the head is pivotably received in the seat, the locking element is inserted into the bore to apply a force on the head to compress the head directly against the seat to resist movement of the bone anchor relative to the plate member.

19. The bone plate assembly of claim 18 , wherein the second recess does not extend completely through the locking element.

20. The bone plate assembly of claim 19 , wherein the locking element is without any recess passing from the top side to the bottom side.

21. The bone plate assembly of claim 18 , wherein the first recess has a conical shaped region.

22. The bone plate assembly of claim 18 , wherein the first recess has a spherical segment-shaped region.

23. The bone plate assembly of claim 22 , wherein a first level (L1) is defined by the highest point of a circle drawn along the spherical segment-shaped region of the first recess in a cross-sectional plane including the central axis, and (L1) is at a level at least as high as a second level (L2) that is defined by a bottom of the second recess.

24. The bone plate assembly of claim 18 , wherein the second recess comprises a continuous groove extending completely around the top side with a contour configured to have form-fitting engagement with the driver.

25. The bone plate assembly of claim 24 , wherein the continuous groove has a star-like shape.

26. The bone plate assembly of claim 18 , further comprising another locking element, wherein the locking element and the another locking element have different axial lengths.

27. The bone plate assembly of claim 18 , further comprising a plug member adapted to close a hole of the at least two holes if a bone anchor of the at least two bone anchors is not used in the hole.

28. The locking element of claim 18 , wherein a shape of the second recess consists of a repeating pattern about the central axis.

29. The bone plate assembly of claim 18 , wherein the outer and inner walls of the second recess extend parallel to each other, and no portion of the outer and inner walls extends radially to the central axis.

30. A bone plate assembly, comprising:

an elongate plate member with a top side and a bottom side, and at least two holes extending from the top side to the bottom side,

at least two bone anchors, each bone anchor comprising a shank configured to anchor into a bone, and a head having a top and a portion with a largest outer diameter (d), wherein the shank is extendable through a hole of the at least two holes;

wherein at least one of the holes is configured to define a seat at the bottom side adapted to pivotably receive the head of one of the bone anchors and wherein the at least one of the holes includes a bore at the top side with a bore axis and an inner diameter (D) which is at least as large as the largest diameter (d) of the head; and

a locking element including a central axis, a bottom side, a top side opposite to the bottom side, and a peripheral surface portion extending completely around the locking element and which has an external thread, wherein the top side defines a recess with a non-circular cross-section in a plane perpendicular to the central axis for torqueable engagement with a driver, the recess includes an outer wall and an inner wall and a groove defined therebetween, and the outer wall and the inner wall continuously curve without sharp angles along the recess,

wherein when the head is pivotably received in the seat, the locking element is rotatably driven into the bore at the recess to apply a force on the head to compress the head directly against the seat to resist movement of the one of the bone anchors relative to the plate member.

31. The bone plate assembly of claim 30 , wherein the recess defines a star-like contour, polygonal shape, wavy shape, or flower-like contour.

32. The bone plate assembly of claim 30 , wherein the recess does not extend completely through the locking element.

33. The bone plate assembly of claim 30 , wherein the locking element at the central axis is closed.

34. The bone plate assembly of claim 30 , wherein the locking element includes a lower second recess facing toward the bottom side for accommodating at least a portion of the head of the bone anchor, the second recess having at least one of a spherical segment-shaped region and a conical shaped region for applying a force in a direction toward the bottom side to at least the portion of the head of the bone anchor.

35. The bone plate assembly of claim 34 , wherein the locking element at the central axis is closed.

36. The locking element of claim 30 , wherein a shape of the recess consists of a repeating pattern about the central axis.

37. The bone plate assembly of claim 30 , wherein the outer and inner walls of the recess extend parallel to each other, and no portion of the outer and inner walls extends radially to the central axis.

38. A locking element configured to be used with a polyaxial bone anchor having a head with a portion, the locking element including a central axis, a bottom side, a top side opposite to the bottom side, and a peripheral surface portion that extending completely around the locking element that has an external thread, wherein

the bottom side defines a first recess facing toward the bottom side for accommodating and applying a force in a direction toward the bottom side to at least the portion of the head of the polyaxial bone anchor, and

the top side defines a second recess off the central axis and having a non-circular cross-section in a plane perpendicular to the central axis for torqueable engagement with a driver, the second recess includes an outer wall and an inner wall and a groove defined therebetween, and the outer wall and inner wall extend parallel to each other, and no portion of the outer wall and the inner wall extends radially to the central axis.