Bone anchoring device

1. A bone anchoring device comprising

an anchoring element comprising a shank to be anchored in a bone or a vertebrae;

a connection element having a longitudinal axis for connecting at least two anchoring elements, the connection element being made of an elastic material;

a receiving part being connected to the shank for receiving the connection element and for connecting the connection element to the shank;

a seat for the connection element, the seat being provided in the receiving part;

a one piece monolithic locking element being rotatably engageable with the receiving part for fixation of the connection element in the seat;

wherein at least a portion of the connection element that is to be received in the seat has a constant cross-section along the longitudinal axis and wherein the locking element has an engagement structure that is configured to contact the portion of the connection element when the portion of the connection element is seated in the seat and the locking element is rotatably engaged with the receiving part, and

wherein when the portion of the connection element is fixed in the seat upon tightening of the locking element, the elastic material is configured to flow for a form-fit connection between the connection element and the engagement structure of the locking element;

wherein the seat comprises an engagement structure that is configured to contact the portion of the connection element when the portion of the connection element is seated in the seat and the locking element is rotatably engaged with the receiving part;

wherein the engagement structure of the seat comprises an elongate projection which length extends in a direction transverse to the longitudinal axis of the connection element;

wherein the receiving part has a substantially U-shaped recess forming two open legs with an inner thread provided on the legs and wherein the locking element is an inner screw to be screwed-in between the legs;

wherein the engagement structure of the locking element is a ring-shaped projection; and,

wherein a diameter of the ring-shaped projection equals a distance between two elongate projections of the seat.

2. The bone anchoring device of claim 1 , wherein the seat is provided at the bottom of the recess.

3. The bone anchoring device of claim 1 , wherein the bone anchoring element is pivotably connected to the receiving part and wherein the seat is provided in a pressure element which is movable in the receiving part and locks the angular position of the bone anchoring element if pressure is exerted on the pressure element.

4. The bone anchoring device according to claim 1 , wherein the connection element is made of an elastomer material.

5. The bone anchoring device according to claim 1 , wherein the connection element is a rod.

6. The bone anchoring device according to claim 1 , wherein the surface of the portion of the connection element is a substantially smooth surface without any one of projections and depressions.

7. The bone anchoring device according to claim 1 , wherein the engagement structure of the locking element engages the surface of the connection element to create an indirect form-fit connection.

8. The bone anchoring device according to claim 1 , wherein the engagement structure of the seat engages the surface of the connection element to create an indirect form-fit connection.

9. The bone anchoring device according to claim 1 , wherein the locking of the connection element in the receiving part is achieved by a frictional connection with a portion of an indirect form-fit connection of the locking element with the connection element.

10. The bone anchoring device of claim 1 , wherein the connection between the locking element and the receiving part is a threaded connection.

11. The bone anchoring device of claim 1 , wherein the rod is clamped between the seat and the locking element and wherein a contour of the seat and a contour of the locking element deviate from the contour of the rod.

12. The bone anchoring device of claim 1 , wherein the elongate projection of the engagement structure of the seat substantially forms a U-shape.

13. The bone anchoring device of claim 1 , wherein the form-fit connection between the connection element and the engagement structure of the locking element occurs without harming the integrity of a surface of the connection element.