Coupling assembly for coupling a rod to a bone anchoring element, and polyaxial bone anchoring device
A coupling assembly for coupling a rod to a bone anchoring element, including a receiving part having first and second ends, a recess at the first end for the rod, and an accommodation space for a head of the bone anchoring element, the accommodation space having an opening at the second end to permit insertion of the head into the receiving part, a retainer element configured to be arranged at least partially in the accommodation space and to hold at least part of the head, and a spring element configured to be arranged at least partially in the accommodation space and to be compressed in an axial direction. The retainer element and the spring element are separate parts. When the retainer element and the spring element are in the accommodation space of the receiving part in a first position, the spring element extends into the recess of the receiving part.
1. A bone anchoring device for coupling a rod to a bone, the bone anchoring device comprising:
a bone anchoring element comprising a shank for anchoring to the bone and a head;
a receiving part having a first end, a second end below the first end, a central axis extending through the first end and the second end, a recess at the first end for receiving the rod, and an accommodation space at the second end for accommodating the head of the bone anchoring element;
a retainer element positionable at least partially in the accommodation space, the retainer element comprising an upwardly facing surface configured to contact and exert an upwardly directed pressure on the head; and
a spring separate from the retainer element, the spring comprising a lower surface configured to contact and exert a downwardly directed pressure on the retainer element;
wherein when the head, the retainer element, and the spring are held in the receiving part with the head in contact with the upwardly facing surface of the retainer element, the retainer element is configured to remain spaced apart from all portions of the head above a greatest diameter of the head measured in a direction perpendicular to the central axis, and the spring is configured to be blocked from contacting the head by another part of the bone anchoring device.
2. The bone anchoring device of claim 1 , wherein the spring is ring-shaped and positionable to extend circumferentially around the central axis in the receiving part.
3. The bone anchoring device of claim 2 , wherein the spring is configured to extend uninterruptedly for the entire circumference around the central axis.
4. The bone anchoring device of claim 1 , wherein the accommodation space forms an opening at the second end of the receiving part sized to permit insertion of the head of the bone anchoring element therethrough, and the retainer element is radially expandable to facilitate passing of the greatest diameter of the head therethrough.
5. The bone anchoring device of claim 1 , wherein the head and/or spring are movable in the receiving part to a position where at least the lower surface of the spring is configured to extend to an axial position lower than the greatest diameter of the head.
6. The bone anchoring device of claim 1 , wherein at least part of the spring is movable axially in the receiving part.
7. The bone anchoring device of claim 1 , wherein the entire spring is positionable axially higher than the entire retainer element in the receiving part.
8. The bone anchoring device of claim 1 , wherein an upper surface of the spring is configured to abut against an inner surface of the receiving part.
9. The bone anchoring device of claim 1 , further comprising a pressure element positionable at least partially in the accommodation space and separable from the retainer element and the spring, wherein the pressure element comprises a downwardly facing surface configured to contact and exert a downwardly directed pressure on the head for locking the head in the receiving part.
10. The bone anchoring device of claim 9 , wherein an upper surface of the spring is configured to abut against the pressure element in the receiving part.
11. The bone anchoring device of claim 9 , wherein the spring is positionable axially between at least part of the retainer element and at least part of the pressure element.
12. The bone anchoring device of claim 9 , wherein the spring is configured to be blocked from contacting the head by the pressure element.
13. A bone anchoring device for coupling a rod to a bone, the bone anchoring device comprising:
a bone anchoring element comprising a shank for anchoring to the bone and a head;
a receiving part having a first end, a second end below the first end, a central axis extending through the first end and the second end, a recess at the first end for receiving the rod, and an accommodation space at the second end for accommodating the head of the bone anchoring element;
a pressure element positionable at least partially in the accommodation space, the pressure element comprising a downwardly facing surface configured to contact and exert a downwardly directed pressure on the head for locking the head in the receiving part; and
a spring separate from the pressure element, wherein the spring is configured to extend uninterruptedly around a majority of a circumference around the central axis;
wherein when the head, the pressure element, and the spring are held in the receiving part, the spring is configured to be spaced apart from all portions of the head below a greatest diameter of the head measured in a direction perpendicular to the central axis, at least an upper region of the spring is configured to extend to an axial position higher than a bottom of the pressure element, and at least a lower region of the spring is configured to extend to an axial position lower than the bottom of the pressure element.
14. The bone anchoring device of claim 13 , wherein the spring is configured to extend uninterruptedly for the entire circumference around the central axis.
15. The bone anchoring device of claim 13 , wherein the accommodation space forms an opening at the second end of the receiving part sized to permit insertion of the head of the bone anchoring element therethrough.
16. The bone anchoring device of claim 13 , further comprising a retainer element positionable at least partially in the accommodation space, the retainer element comprising an upwardly facing surface configured to contact and exert an upwardly directed pressure on the head.
17. A bone anchoring device for coupling a rod to a bone, the bone anchoring device comprising:
a bone anchoring element comprising a shank for anchoring to the bone and a head;
a receiving part having a first end, a second end below the first end, a central axis extending through the first end and the second end, a recess at the first end for receiving the rod, and an accommodation space at the second end for accommodating the head of the bone anchoring element;
a pressure element positionable at least partially in the accommodation space, the pressure element comprising a downwardly facing surface configured to contact and exert a downwardly directed pressure on the head for locking the head in the receiving part; and
a radially expandable element that is separate from the pressure element and that is movable axially in the receiving part;
wherein when the head, the pressure element, and the radially expandable element are held in the receiving part, at least part of the radially expandable element is positionable around the pressure element and configured to surround a majority of a circumference around the pressure element in a manner such that the pressure element remains movable axially downwardly relative to both the receiving part and the radially expandable element, while the radially expandable element avoids obstructing the axially downward movement of the pressure element.
18. The bone anchoring device of claim 17 , wherein the pressure element is configured to remain spaced apart from all portions of the head below a greatest diameter of the head measured in a direction perpendicular to the central axis.
19. The bone anchoring device of claim 17 , wherein the radially expandable element comprises an upwardly facing surface configured to contact and exert an upwardly directed pressure on the head.
20. The bone anchoring device of claim 17 , further comprising a spring separate from the pressure element and the radially expandable element, wherein the spring comprises a lower surface configured to contact and exert a downwardly directed pressure on the radially expandable element.