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 coupling assembly for coupling a rod to a 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 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 a head of the bone anchoring element;
a seat positionable at least partially in the accommodation space, the seat comprising an upwardly facing surface configured to contact and exert an upwardly directed pressure on the head;
a pressure element separable from the seat and positionable at least partially in the accommodation space, the pressure element comprising a downwardly facing surface configured to contact and to exert a downwardly directed pressure on the head for locking the head in the receiving part; and
a spring separable from the seat and the pressure element, wherein the spring is configured to extend uninterruptedly around a majority of a circumference around the central axis and to contact the seat in the receiving part;
wherein when the pressure element, the seat, and the spring are in the receiving part, the spring is configured to extend to an axial position above a bottom of the pressure element, and to have an outer width that is as wide as maximum outer widths of the pressure element and the seat, respectively.
2 . The coupling assembly of claim 1 , wherein the spring is configured to extend uninterruptedly for the entire circumference around the central axis.
3 . The coupling assembly 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 wherein the seat is radially expandable to facilitate passing of a greatest diameter of the head therethrough.
4 . The coupling assembly of claim 1 , wherein at least part of the spring is movable axially in the receiving part.
5 . The coupling assembly of claim 1 , wherein an upper surface of the spring is configured to abut against the pressure element in the receiving part.
6 . The coupling assembly of claim 1 , wherein the spring is configured to extend to an axial position below the bottom of the pressure element.
7 . The coupling assembly of claim 1 , wherein an inner width of the spring is as wide as an outer width of the pressure element, to facilitate positioning of the spring around at least part of the pressure element.
8 . The coupling assembly of claim 1 , wherein the seat comprises an expandable portion, and wherein an inner width of the spring is as wide as an outer width of the expandable portion of the seat.
9 . 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, an accommodation space for accommodating the head of the bone anchoring element, and an opening at the second end sized to facilitate insertion of the head therethrough into the accommodation space;
a seat positionable at least partially in the accommodation space, the seat comprising an upwardly facing surface engageable with the head to hold the head in the receiving part;
a rod contacting element separable from the seat, the rod contacting element comprising a rod contacting surface configured to extend into the recess of the receiving part to engage the rod; and
a third element separable from the seat and the rod contacting element;
wherein each of the seat, the rod contacting element, and the third element is insertable from the first end of the receiving part into the receiving part to a configuration where the third element is directly engageable with both the seat and the rod contacting element, and wherein when the seat, the rod contacting element, and the third element are assembled to the receiving part, the head is insertable through the opening at the second end of the receiving part into the accommodation space.
10 . The bone anchoring device of claim 9 , wherein the third element comprises a spring configured to extend uninterruptedly around a majority of a circumference around the central axis.
11 . The bone anchoring device of claim 9 , wherein the rod contacting element further 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.
12 . The bone anchoring device of claim 9 , wherein the rod contacting element is insertable downwardly from the first end of the receiving part past an abutment of the receiving part, and is configured to be restricted from being removed from the first end of the receiving part by the abutment.