Coupling device for coupling a rod to a bone anchor

A bone anchoring device comprising:

• a bone anchor comprising a head and a shank configured to be anchored in bone or in a vertebra;
• and
• a coupling device for coupling a rod to the bone anchor, the coupling device comprising:
• a receiving part configured to receive the head of the bone anchor, the receiving part having a first end and a second end, a central axis that extends between the first end and the second end, two legs at the first end that define a recess for receiving the rod, wherein the recess extends in a longitudinal direction transverse to the central axis, and an opening at the second end sized to facilitate insertion of the head from the second end into the receiving part;
• and
• a monolithic pressure member positionable at least partially in the receiving part to exert pressure on the head, the pressure member comprising a body that defines a rod support surface for supporting the rod and four arms, wherein each of the four arms extends circumferentially around the central axis from a first end that is connected axially to another portion of the pressure member to a free second end that is positioned laterally away from the body;
• wherein when the head and the pressure member are assembled with the receiving part, the pressure member is movable to a pre-locking position where the head is restricted from removal from the receiving part and each of the four arms is configured to engage a corresponding abutting surface portion on the bone anchoring device to hold the pressure member at the pre-locking position.

A coupling device for coupling a rod to a bone anchor, the coupling device comprising:

• a receiving part configured to receive a head of the bone anchor, the receiving part having a first end and a second end, a central axis that extends between the first end and the second end, and two legs at the first end that define a recess for receiving the rod, wherein the recess extends along a longitudinal axis that is transverse to the central axis, and wherein sides of the legs are recessed relative to an envelope defined by an outer surface of the receiving part such that the width of the legs is narrowed in a circumferential direction around the central axis;
• and
• a monolithic pressure member positionable at least partially in the receiving part to exert pressure on an inserted head, the pressure member comprising a rod support surface for supporting the rod and an arm having a free end that is configured to be located at a different axial position than the entire rod support surface;
• wherein when the pressure member is assembled with the receiving part, at least part of the arm of the pressure member is positioned outside a corresponding one of the legs of the receiving part and extends at least partially into the recessed region on the side of the corresponding one of the legs, while being aligned with the corresponding one of the legs in a direction parallel to the longitudinal axis and located substantially within the envelope defined by the outer surface of the receiving part.