Coupling device for coupling a bone anchor to a rod and bone anchoring device with such a coupling device

1 . A polyaxial bone anchoring device comprising:

a bone anchoring element comprising a shank for anchoring to bone and a head;

a receiving part having a first end, a second end below the first end, a longitudinal axis extending through the first and second ends, a channel at the first end for receiving a rod, an accommodation space for pivotably holding the head of the bone anchoring element, and an opening at the second end sized to facilitate insertion of the head therethrough to a seat in the accommodation space;

a pressure member positionable in the receiving part and comprising an upwardly facing surface having at least a portion configured to extend into the channel to engage the rod and a downwardly facing surface having at least a portion configured to exert pressure on the head to lock the head relative to the receiving part; and

a pair of expandable members, wherein when the pressure member is in the receiving part, each of the expandable members is configured to extend from the upwardly facing surface of the pressure member towards the first end of the receiving part to a free end surface that is configured to directly engage the receiving part, and wherein the expandable members are configured to be positioned on opposite sides of the channel for the rod, respectively, and are directly accessible from the first end;

wherein when the head and the pressure member are in the receiving part, the expandable members are axially expandable in a direction of the longitudinal axis to urge the pressure member away from the first end of the receiving part to increase the pressure exerted on the head.

2 . The polyaxial bone anchoring device of claim 1 , wherein the expandable members are expandable axially to a configuration where the pressure member exerts a force on the head that is sufficient to lock the head relative to the receiving part.

3 . The polyaxial bone anchoring device of claim 1 , wherein the pressure member is configured to assume an insertion position where the head is insertable through the opening at the second end of the receiving part to the seat.

4 . The polyaxial bone anchoring device of claim 1 wherein the pressure member is configured to assume a pre-locking position where the head is restricted from being removed from the receiving part.

5 . The polyaxial bone anchoring device of claim 1 , wherein the expandable members are elastically deformable.

6 . The polyaxial bone anchoring device of claim 1 , further comprising a locking member insertable into the channel and comprising an engagement surface that is engageable with the receiving part to lock the rod in the channel, wherein the expandable members are configured to protrude radially into a path of the locking member when the locking member is advanced into the channel.

7 . The polyaxial bone anchoring device of claim 1 , wherein the expandable members form arms that extend upwardly from the upwardly facing surface of the pressure member.

8 . The polyaxial bone anchoring device of claim 1 , wherein the expandable members are separable from and connectable to the pressure member.

9 . The polyaxial bone anchoring device of claim 8 , wherein each of the expandable members extends axially into the upwardly facing surface of the pressure member.

10 . The polyaxial bone anchoring device of claim 1 , wherein the pressure member is prevented from extending to an axial position that is higher than the free end surfaces of the expandable members.

11 . The polyaxial bone anchoring device of claim 1 , wherein at least part of each of the expandable members is movable radially relative to the longitudinal axis.

12 . The polyaxial bone anchoring device of claim 11 , wherein the at least part of each of the expand members is movable radially relative to the longitudinal axis while a radial position of the free end surface of the expandable member remains constant.

13 . A polyaxial bone anchoring device comprising:

a bone anchoring element comprising a shank for anchoring to bone and a head;

a receiving part having a first end, a second end below the first end, a longitudinal axis extending through the first and second ends, a channel at the first end for receiving a rod, an engagement surface at the first end for engaging a locking member to lock the rod in the channel, first and second abutments positioned axially higher than a bottom of the engagement surface, and an accommodation space at the second end for pivotably holding the head of the bone anchoring element;

a pressure member positionable in the receiving part and comprising a downwardly facing surface having at least a portion configured to exert pressure on the head to lock the head relative to the receiving part; and

at least one flexible member, wherein when the pressure member is in the receiving part the flexible member is configured to extend from the pressure member towards the first end of the receiving part to a free end surface that is configured to directly engage the receiving part;

wherein when the pressure member is in the receiving part, the free end surface of the flexible member is configured to engage the first abutment of the receiving part to hold the pressure member at an insertion position where the head is insertable from the second end of the receiving part into the accommodation space; and

wherein when the head and the pressure member are in the receiving part, the free end surface of the flexible member is movable axially downwardly to engage the second abutment positioned axially lower than the first abutment to hold the pressure member at a pre-locking position to restrict removal of the head from the receiving part.

14 . The polyaxial bone anchoring device of claim 13 , wherein the engagement surface at the first end of the receiving part comprises a thread, and wherein the first and second abutments are positioned higher axially than the bottom of the thread.

15 . The polyaxial bone anchoring device of claim 13 , wherein the first and second abutments is each configured to restrict upward movement of the pressure member relative to the receiving part.

16 . The polyaxial bone anchoring device of claim 13 , wherein the flexible member is formed as part of the pressure member and forms an arm that extends upwardly from other portions of the pressure member in the receiving part.

17 . A polyaxial bone anchoring device comprising:

a bone anchoring element comprising a shank for anchoring to bone and a head;

a rod;

a receiving part having a first end, a second end below the first end, a longitudinal axis extending through the first and second ends, a channel at the first end for receiving the rod, an accommodation space for pivotably holding 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; and

a monolithic pressure member positionable in the receiving part and comprising a downwardly facing surface having at least a portion configured to exert pressure on the head to lock the head relative to the receiving part and a rod retention surface;

wherein when the pressure member is held in the receiving part at an insertion position, the head is insertable through the opening at the second end into the accommodation space, while the rod is insertable into the channel and configured to be clamped relative to at least the pressure member by the rod retention surface.

18 . The polyaxial bone anchoring device of claim 17 , wherein when the head is held in the accommodation space, the rod is insertable into the channel and configured to be clamped by the rod retention surface while a pressure exerted by the pressure member on the head remains substantially constant.