Polyaxial bone anchoring device with enlarged pivot angle

1. A polyaxial bone anchoring device comprising:

a receiving part for coupling a rod to a bone anchoring element, the receiving part comprising a top end, a bottom end, a longitudinal axis that opens that extends from the top end toward the bottom end, two arms defining a channel open to the top end for receiving the rod, an opening at the bottom end through which the longitudinal axis extends for accommodating at least part of the bone anchoring element, an inner surface, and an internal groove that is formed in and recessed from respective portions of the inner surface above and below the internal groove; and

an inner member positionable at least partially in the internal groove, the inner member configured to maintain a connection between the receiving part and the bone anchoring element;

wherein the internal groove extends circumferentially around a central axis that is oriented at a first angle oblique to the longitudinal axis, and wherein a central axis of the inner member is configured to be oriented at a second angle oblique to the longitudinal axis that is smaller than a maximum angle of angulation between the receiving part and a connected bone anchoring element.

2. The polyaxial bone anchoring device of claim 1 , wherein the internal groove is substantially symmetrical with respect to the central axis of the internal groove.

3. The polyaxial bone anchoring device of claim 1 , wherein a first passage extends coaxially with the central axis of the internal groove from the bottom end toward the top end, and a second passage extends coaxially with the longitudinal axis from the top end toward the bottom end.

4. The polyaxial bone anchoring device of claim 1 , wherein the inner member forms a seat for a head of the bone anchoring element.

5. The polyaxial bone anchoring device of claim 1 , wherein the inner member is movable axially in the receiving part.

6. The polyaxial bone anchoring device of claim 1 , wherein the opening at the bottom end of the receiving part has a diameter that is greater than a greatest diameter of a head of the bone anchoring element, such that the head is insertable into the receiving part from the bottom end.

7. The polyaxial bone anchoring device of claim 1 , wherein the receiving part is configured to allow pivoting of the bone anchoring element in a symmetrical manner relative to the central axis of the internal groove.

8. The polyaxial bone anchoring device of claim 1 , wherein the channel for the rod extends perpendicularly to the longitudinal axis.

9. The polyaxial bone anchoring device of claim 1 , wherein the inner member is expandable.

10. The polyaxial bone anchoring device of claim 1 , wherein the first and second angles are substantially the same.

11. A polyaxial bone anchoring device comprising:

a receiving part for coupling a rod to a bone anchoring element, the receiving part comprising a top end, a bottom end, a longitudinal axis that extends from the top end toward the bottom end, two arms defining a channel open to the top end for receiving the rod, an opening at the bottom end through which the longitudinal axis extends for accommodating at least part of the bone anchoring element, an inner surface, and an internal groove that is formed in and recessed from respective portions of the inner surface above and below the internal groove; and

an inner member configured to exert pressure on a head of the bone anchoring element in the receiving part;

wherein the internal groove extends circumferentially around a central axis that is oriented at a first angle oblique to the longitudinal axis such that the internal groove is angled relative to the longitudinal axis with a high side and a low side, and wherein an axial distance between the top end of the receiving part and at least part of a downward facing surface at the bottom end that is circumferentially aligned with the high side of the internal groove is less than an axial distance between the top end and another part of the downward facing surface that is oriented in a different circumferential direction.

12. The polyaxial bone anchoring device of claim 11 , wherein the internal groove is substantially symmetrical with respect to the central axis.

13. The polyaxial bone anchoring device of claim 11 , wherein the opening at the bottom end of the receiving part is substantially symmetrical with respect to the central axis.

14. The polyaxial bone anchoring device of claim 11 , wherein the inner member is positionable at least partially in the internal groove.

15. The polyaxial bone anchoring device of claim 11 , wherein the inner member forms a seat for a head of the bone anchoring element.

16. The polyaxial bone anchoring device of claim 11 , wherein the inner member is expandable.

17. The polyaxial bone anchoring device of claim 11 , wherein the receiving part is configured to allow pivoting of the bone anchoring element in a symmetrical manner relative to the central axis.

18. The polyaxial bone anchoring device of claim 11 , wherein the channel for the rod extends perpendicularly to the longitudinal axis.

19. A polyaxial bone anchoring device comprising:

a bone anchoring element comprising a shank for anchoring to bone and a head;

a receiving part for coupling a rod to the bone anchoring element, the receiving part comprising a top end, a bottom end, a longitudinal axis that extends from the top end toward the bottom end, two arms defining a channel that is open to the top end and that extends perpendicularly to the longitudinal axis for receiving the rod, and an opening at the bottom end for accommodating at least part of the bone anchoring element; and

an expandable inner member configured to exert pressure on the head of the bone anchoring element in the receiving part;

wherein when the bone anchoring element is assembled to the receiving part, both the receiving part and the inner member are configured to facilitate pivoting of the bone anchoring element to a larger maximum angle in a first radial direction relative to the longitudinal axis than in a second radial direction relative to the longitudinal axis.

20. The polyaxial bone anchoring device of claim 19 , wherein the longitudinal axis extends through the opening at the bottom end of the receiving part.

21. The polyaxial bone anchoring device of claim 19 , wherein the opening at the bottom end of the receiving part is substantially rotationally symmetrical.

22. The polyaxial bone anchoring device of claim 19 , wherein the opening at the bottom end of the receiving part extends circumferentially around a central axis that is oriented at an angle oblique to the longitudinal axis.

23. The polyaxial bone anchoring device of claim 19 , wherein a central axis of the inner member is configured to be oriented at an angle oblique to the longitudinal axis.

24. The polyaxial bone anchoring device of claim 19 , wherein the opening at the bottom end of the receiving part has a diameter that is greater than a greatest diameter of the head of the bone anchoring element, such that the head is insertable into the receiving part from the bottom end.

25. The polyaxial bone anchoring device of claim 19 , wherein the inner member is configured to cover at least a portion of the head of the bone anchoring element from an upper side of the head.