Coupling assembly and polyaxial bone anchoring device comprising the same
A coupling assembly for coupling a rod to a bone anchoring element is provided, wherein the coupling assembly includes a receiving part having a first end, a second end, a central axis extending through the first end and second end, an accommodation space for accommodating a head of an anchoring element, a bore extending from the accommodation space to the first end, and a recess for receiving a rod. The accommodation space has an opening at the second end sized to permit insertion of a head of the bone anchoring element. The coupling assembly further includes a retainer element configured to be positioned at least partially in the accommodation space and being radially expandable and/or compressible to allow retaining a head inserted through the opening. The retainer element is held in position adjacent the opening by an engagement structure provided at or in the accommodation space. The coupling assembly further includes a locking element configured to be arranged at least partially in the accommodation space. The locking element is movable from a first position, in which the retainer element is allowed to expand acid release an inserted head, to a second position, in which radial expansion of the retainer element is hindered to present release of an inserted head. When the locking element is in the second position, a head of an liming element can be locked by exertion of a pressure force directly onto the head to press the head against the retainer element.
1 . A bone anchoring device comprising:
a bone anchoring element having a shank for anchoring to bone and a head; and
a coupling assembly for coupling a rod to the bone anchoring element, the coupling assembly comprising:
a receiving part having a first end, a second end below the first end, a central axis extending through the first and second ends, an accommodation space for accommodating the head, an opening at the second end sized to facilitate insertion of the head into the accommodation space, and a recess at the first end for receiving the rod; and
a retainer element and a separate locking element that are both positionable at least partially in the accommodation space;
wherein when the retainer element and the locking element are in the receiving part and the locking element is at an inserting position, an abutting surface of the locking element engages another surface of the coupling assembly to restrict upward movement of the locking element, while the retainer element is configured to remain spaced apart from the locking element and is expandable for inserting the head; and
wherein the locking element is movable axially from the inserting position to a pre-locking position where radial expansion of the retainer element is restricted to prevent removal of the head from the receiving part, while the head is configured to extend upwards to an axial position that is closer to the first end of the receiving part than the abutting surface of the locking element is to the first end of the receiving part.
2 . The bone anchoring device of claim 1 , wherein the locking element further comprises a rod receiving surface configured to extend into the recess of the receiving part to engage the rod.
3 . The bone anchoring device of claim 1 , wherein the entire retainer element is radially expandable to facilitate inserting the head.
4 . The bone anchoring device of claim 1 , wherein when the locking element is at the pre-locking position and when the shank of the bone anchoring element is coaxial with the central axis of the receiving part, the head is configured to extend upwards to an axial position that is closer to the first end of the receiving part than the abutting surface of the locking element is to the first end of the receiving part.
5 . The bone anchoring device of claim 1 , wherein the locking element abuts against the receiving part at the inserting position.
6 . The bone anchoring device of claim 1 , wherein another portion of the locking element extends upwards from the abutting surface towards the first end of the receiving part.
7 . The bone anchoring device of claim 1 , wherein an axial length of the locking element is substantially the same at the inserting and pre-locking positions.
8 . The bone anchoring device of claim 1 , wherein the locking element directly restricts the radial expansion of the retainer element at the pre-locking position.
9 . A bone anchoring device comprising:
a bone anchoring element having a shank for anchoring to bone and a head; and
a coupling assembly for coupling a rod to the bone anchoring element, the coupling assembly comprising:
a receiving part having a first end, a second end, a central axis extending through the first and second ends, an accommodation space for accommodating the head, an opening at the second end sized to facilitate insertion of the head into the accommodation space, and a recess at the first end for receiving the rod;
a retainer element positionable at least partially in the accommodation space; and
a locking element separable from the retainer element and positionable at least partially in the accommodation space, the locking element having an inner surface that extends axially with a substantially constant inner width, such that when the retainer element and the locking element are in the receiving part, another portion of the coupling assembly is movable along the inner surface in the locking element;
wherein when the head, the retainer element, and the locking element are in the receiving part, the head and the locking element are capable of contacting one another, and the locking element is movable from an inserting position where the retainer element is expandable for inserting the head, to a pre-locking position where radial expansion of the retainer element is restricted to prevent removal of the head from the receiving part.
10 . The bone anchoring device of claim 9 , wherein the entire retainer element is radially expandable to facilitate inserting the head.
11 . The bone anchoring device of claim 9 , wherein at the pre-locking position, the retainer element is configured to remain spaced apart from a region of the head above a greatest diameter of the head.
12 . The bone anchoring device of claim 9 , wherein part of the retainer element is configured to extend into the locking element and to move along the inner surface.
13 . The bone anchoring device of claim 12 , wherein the locking element directly restricts the radial expansion of the part of the retainer element that extends into the locking element at the pre-locking position.
14 . The bone anchoring device of claim 9 , wherein the locking element directly restricts the radial expansion of the retainer element at the pre-locking position.
15 . The bone anchoring device of claim 9 , wherein the locking element is configured to remain spaced apart from a region of the head above a greatest diameter of the head at the pre-locking position.
16 . A bone anchoring device comprising:
a bone anchoring element having a shank for anchoring to bone and a head; and
a coupling assembly for coupling a rod to the bone anchoring element, the coupling assembly comprising:
a receiving part having a first end, a second end below the first end, a central axis extending through the first and second ends, an accommodation space for accommodating the head, an opening at the second end sized to facilitate insertion of the head into the accommodation space, and a recess at the first end for receiving the rod; and
a retainer element and a separate locking element that are both positionable at least partially in the accommodation space;
wherein when the head, the retainer element, and the locking element are in the receiving part, the locking element is movable axially from an inserting position where the entire retainer element is radially expandable to have an outer width that is wider than an outer width of the locking element to facilitate insertion of the head, to a pre-locking position where radial expansion of the retainer element is restricted to prevent removal of the head from the receiving part while the locking element is configured to remain spaced apart from a region of the head above a greatest diameter of the head.
17 . The bone anchoring device of claim 16 , wherein the locking element directly restricts the radial expansion of the retainer element at the pre-locking position.
18 . The bone anchoring device of claim 16 , wherein when the retainer element and the locking element are in the receiving part, a lowermost end of the locking element is positionable closer axially to the first end of the receiving part than an uppermost end of the retainer element is to the first end of the receiving part.
19 . The bone anchoring device of claim 16 , wherein the retainer element and the locking element are configured to contact one another at the pre-locking position.
20 . The bone anchoring device of claim 16 , wherein an axial length of the locking element is substantially the same at the inserting and pre-locking positions.