Anchoring device for anchoring a rod in bones or vertebrae

1. An anchoring assembly for anchoring a rod to a bone or a vertebra, the anchoring assembly comprising:

a bone anchoring device comprising:

a shaft; and

a head connected to said shaft and having a recess with a base having a contact surface, the head further comprising two substantially vertically extending legs spaced apart by a first distance and defining a channel;

a fixation element having a contact surface facing the contact surface of the base of the head, the fixation element secured to the legs and configured to move sufficiently into and out of the channel; and

at least a first rod and a second rod having different diameters and configured to be interchangeably received in the channel and to be clamped by the fixation element;

wherein when any one of the rods is received in the channel, the contact surface of the fixation element and the contact surface of the base contact the rod to clamp the rod in the channel;

wherein the first rod and the second rod each have diameters within a range that is smaller than the first distance and sufficiently sized so as to be spaced apart from a bottom of the contact surface of the base when clamped in the channel; and

wherein for all rods having a diameter within the range, the rod contacts the contact surface of the base only along two contact lines.

2. The anchoring assembly of claim 1 , wherein said contact surfaces are shaped such that when the first rod or the second rod is clamped, the clamped rod contacts the contact surface of the fixation element along a third contact line.

3. The anchoring assembly of claim 1 , wherein the fixation element has a projection on its side facing the rod, the projection being configured so as to be able to contact rods of different diameters.

4. The anchoring assembly of claim 1 , wherein the cross section of the base is substantially V-shaped.

5. The anchoring assembly of claim 4 , wherein side walls of the base which form the V-shape are curved.

6. The anchoring assembly of claim 1 , wherein the contact surfaces are configured to clamp a plurality of rods with different diameters in a stepless manner.

7. The anchoring assembly of claim 1 , wherein the head and the shaft are connected monoaxially.

8. The anchoring assembly of claim 1 , wherein the shaft is pivotably connected to the head and wherein a pressure element is provided to lock the angular position of the shaft relative to the head and wherein the pressure element comprises the base for the rod.

9. The anchoring assembly of claim 1 , wherein the rod has a substantially circular cross section.

10. The anchoring assembly of claim 1 , wherein the shaft, the head and the fixation element are made of a biocompatible material.

11. The anchoring assembly of claim 1 , wherein the base comprises an internal hole for providing a contact surface in two areas located on both sides of the legs, respectively.

12. The anchoring assembly of claim 1 , wherein the diameter of the first rod is larger than the diameter of the second rod by about 14%.

13. The anchoring assembly of claim 1 , further comprising a third rod having a diameter different than the diameters of the first rod and the second rod.

14. An anchoring assembly for anchoring a rod to a bone or a vertebra, the anchoring assembly comprising:

a bone anchoring device comprising a shaft and a head pivotably connected to said shaft and having two substantially vertically extending legs spaced apart by a first distance and defining a channel;

a pressure element having a recess including a base with a contact surface, the pressure element configured to lock the angular position of the shaft relative to the head;

a fixation element having a contact surface facing the contact surface of the base of the pressure element, the fixation element secured to the legs and configured to move sufficiently into and out of the channel; and

at least a first rod and a second rod having different diameters and configured to be interchangeably received in the channel when the head of the bone anchoring device and the pressure element are assembled, and to be clamped by the fixation element;

wherein when any one of the rods is received in the channel, the contact surface of the fixation element and the contact surface of the base of the pressure element contact the rod to clamp the rod in the channel;

wherein the first rod and the second rod each have diameters within a range that is smaller than the first distance and sufficiently sized so as to be spaced apart from a bottom of the contact surface of the base of the pressure element when claimed in the channel; and

wherein for all rods having a diameter within the range and that are configured to be received in the channel when the head of the bone anchoring device and the pressure element are assembled, the rod contacts the contact surface of the base of the pressure element only along two contact lines.

15. The anchoring assembly of claim 14 , wherein the contact surface of the fixation element is defined by a projection facing the contact surface of the base of the pressure element.

16. The anchoring assembly of claim 14 , wherein the fixation element comprises an outer fixation member configured to lock the angular position of the shaft relative to the head, and an inner fixation member comprising the contact surface facing the contact surface of the base of the pressure element and configured to move sufficiently into and out of the outer fixation member to clamp the first rod or the second rod in the channel.

17. The anchoring assembly of claim 16 , wherein the contact surface of the inner fixation member is defined by a projection facing the contact surface of the base of the pressure element.

18. The anchoring assembly of claim 14 , wherein the diameter of the first rod is larger than the diameter of the second rod by about 14%.

19. A method of attaching a bone anchoring assembly to a bone or a vertebra, the anchoring assembly comprising a bone anchoring device comprising a shaft and a head connected to said shaft and having a recess with a base having a contact surface, the head further comprising two substantially vertically extending legs spaced apart by a first distance and defining a channel, a fixation element having a contact surface facing the contact surface of the base of the head, the fixation element secured to the legs and configured to move sufficiently into and out of the channel, and at least a first rod and a second rod having different diameters and configured to be interchangeably received in the channel and to be clamped by the fixation element, wherein when any one of the rods is received in the channel, the contact surface of the fixation element and the contact surface of the base contact the rod to clamp the rod in the channel, wherein the first rod and the second rod each have diameters within a range that is smaller than the first distance and sufficiently sized so as to be spaced apart from a bottom of the contact surface of the base when clamped in the channel, and wherein for all rods having a diameter within the range the rod contacts the contact surface of the base only along two contact lines, the method comprising:

attaching the bone anchoring device to a bone or vertebra;

inserting the first rod or the second rod in the channel; and

clamping the inserted rod in the channel with the fixation element.

20. The method of claim 19 , wherein the diameter of the first rod is larger than the diameter of the second rod by about 14%.

21. An anchoring assembly for anchoring a rod to a bone or a vertebra, the anchoring assembly comprising:

at least a first rod and a second rod having different diameters;

a bone anchoring device comprising:

a shaft; and

a head connected to the shaft and having a recess with a base having a contact surface, the head further comprising two substantially vertically extending legs defining a channel for interchangeably receiving each one of the rods in the channel; and

a fixation element having a contact surface facing the contact surface of the base of the head, the fixation element secured to the legs and configured to move sufficiently into and out of the channel to interchangeably clamp each of the rods in the channel;

wherein the contact surface of the base has a substantially V-shaped cross-section and comprises a first side wall comprising a flat surface lying along a first plane extending from one of the legs towards a bottom of the base and a second side wall comprising a flat surface lying along a second plane extending from the other one of the legs towards the bottom of the base, wherein the second plane intersects the first plane; and

wherein when one of the rods is received in the channel, the contact surface of the fixation element and the contact surface of the base contact the rod to clamp the rod in the channel.