Bone anchoring device
A polyaxial bone anchoring device includes a bone anchoring element having a head and a shaft, a receiving part having a head receiving portion, a rod receiving portion, and a bore having a bore axis, and a pressure member movable in the bore and having a first surface for engaging the head, wherein the pressure member is movable to a first position where friction between the first surface and the head generates a preload on the head to maintain the shaft at a temporary angular position relative to the receiving part, and wherein the pressure member is configured to engage the receiving part to generate a holding force for holding the pressure member at the first position without a positive lock, and wherein the pressure member is movable in and out of the first position by applying an axial force on the pressure member greater than the holding force.
1. A polyaxial bone anchoring device comprising:
a bone anchoring element having a head with a spherical-segment shaped portion and a shaft for anchoring to a bone;
a receiving part for coupling the bone anchoring element to a rod, the receiving part having a head receiving portion with an accommodation space for accommodating the head, and a rod receiving portion with a bore in communication with the accommodation space;
a pressure member movable in the bore and comprising a first surface for engaging the head, a second surface for engaging the rod, and two radially outwardly extending projections configured to latch into annular grooves in the receiving part to restrict axial movement of the pressure member in the receiving part; and
a sleeve-like insert piece comprising an endless ring separable from the pressure member and insertable into the receiving part;
wherein when the head of the bone anchoring element, the insert piece, and the pressure member are in the receiving part, the insert piece is positionable around and forms a seat for the spherical-segment shaped portion of the head, and the pressure member is movable to a position where the first surface of the pressure member directly contacts the head to lock the head relative to the receiving part.
2. The polyaxial bone anchoring device of claim 1 , wherein the pressure member is substantially cylindrical.
3. The polyaxial bone anchoring device of claim 1 , wherein the pressure member has a first end and a second end, and a recess at the second end with a spherical-segment shape corresponding to the spherical-segment shaped portion of the head of the bone anchoring element.
4. The polyaxial bone anchoring device of claim 1 , wherein the insert piece is configured to pivot in the accommodation space of the receiving part.
5. The polyaxial bone anchoring device of claim 4 , wherein when the insert piece is seated in the receiving part and has a central axis coaxial with a central axis of the receiving part, a lower edge of the insert piece extends out of a lower opening of the receiving part.
6. The polyaxial bone anchoring device of claim 1 , wherein when the head, the insert piece, and the pressure member are in the receiving part, the pressure member is configured to contact the head while being spaced apart from the insert piece.
7. The polyaxial bone anchoring device of claim 1 , wherein the accommodation space has a spherical-segment shape.
8. The polyaxial bone anchoring device of claim 1 , wherein the rod receiving portion is at a first end of the receiving part, and wherein the pressure member is insertable into the receiving part from the first end towards the head receiving portion.
9. The polyaxial bone anchoring device of claim 1 , wherein the pressure member is movable to a first position where friction between the first surface and the head generates a preload on the head to maintain the shaft at a temporary angular position relative to the receiving part, and to a second position different from the first position where the head is locked relative to the receiving part.
10. A method for coupling a rod to a bone via a polyaxial bone anchoring device comprising a bone anchoring element having a head with a spherical-segment shaped portion and a shaft for anchoring to a bone, a receiving part for coupling the bone anchoring element to a rod, the receiving part having a head receiving portion with an accommodation space for accommodating the head, and a rod receiving portion with a bore in communication with the accommodation space, a pressure member movable in the bore and comprising a first surface for engaging the head, a second surface for engaging the rod, and two radially outwardly extending projections configured to latch into annular grooves in the receiving part to restrict axial movement of the pressure member in the receiving part, a sleeve-like insert piece comprising an endless ring separable from the pressure member and insertable into the receiving part, and a fixation element, the method comprising:
inserting the bone anchoring element into a bone when the head, the insert piece, and the pressure member are in the receiving part, with the insert piece around and forming a seat for the spherical-segment shaped portion of the head;
adjusting an angular position of the shaft relative to the receiving part;
inserting a rod into the rod receiving portion of the receiving part; and
advancing the fixation element in the receiving part to advance the rod towards the head receiving portion, and to exert an axial force on the pressure member to advance the pressure member to a position where the first surface of the pressure member directly contacts the head to lock the head relative to the receiving part and to lock a position of the rod relative to the receiving part.
11. The method of claim 10 , further comprising:
inserting the head of the bone anchoring element into the accommodation space of the receiving part when the insert piece is in the receiving part; and
inserting the pressure member into the receiving part.
12. A polyaxial bone anchoring device comprising:
a bone anchoring element having a shaft for anchoring to a bone and a head with a spherical-segment shaped portion defining a widest part of the head, wherein at least part of the spherical-segment shaped portion is directed towards the shaft;
a receiving part for coupling the bone anchoring element to a rod, the receiving part having a head receiving portion with an accommodation space for accommodating the head, and a rod receiving portion with a bore in communication with the accommodation space;
a pressure member movable in the bore and comprising a first surface for engaging the head, a second surface for engaging the rod, and two radially outwardly extending projections configured to latch into annular grooves in the receiving part to restrict axial movement of the pressure member in the receiving part; and
a sleeve-like insert piece comprising an endless ring separable from the pressure member and insertable into the receiving part;
wherein when the head of the bone anchoring element, the insert piece, and the pressure member are in the receiving part, the insert piece is positionable around the widest part of the head defined by the spherical-segment shaped portion, and the pressure member is movable to a position where the first surface of the pressure member directly contacts the head to lock the head relative to the receiving part.
13. The polyaxial bone anchoring device of claim 12 , wherein the pressure member is substantially cylindrical.
14. The polyaxial bone anchoring device of claim 12 , wherein the pressure member has a first end and a second end, and a recess at the second end with a spherical-segment shape corresponding to the spherical-segment shaped portion of the head of the bone anchoring element.
15. The polyaxial bone anchoring device of claim 12 , wherein the insert piece is configured to pivot in the accommodation space of the receiving part.
16. The polyaxial bone anchoring device of claim 15 , wherein when the insert piece is seated in the receiving part and has a central axis coaxial with a central axis of the receiving part, a lower edge of the insert piece extends out of a lower opening of the receiving part.
17. The polyaxial bone anchoring device of claim 12 , wherein when the head, the insert piece, and the pressure member are in the receiving part, the pressure member is configured to contact the head while being spaced apart from the insert piece.
18. The polyaxial bone anchoring device of claim 12 , wherein the accommodation space has a spherical-segment shape.
19. The polyaxial bone anchoring device of claim 12 , wherein the rod receiving portion is at a first end of the receiving part, and wherein the pressure member is insertable into the receiving part from the first end towards the head receiving portion.
20. The polyaxial bone anchoring device of claim 12 , wherein the pressure member is movable to a first position where friction between the first surface and the head generates a preload on the head to maintain the shaft at a temporary angular position relative to the receiving part, and to a second position different from the first position where the head is locked relative to the receiving part.