Coupling device for coupling a rod to a bone anchoring element

A method of coupling a rod to bone using a bone anchoring device comprising an anchoring element comprising a shank for anchoring to bone and a head, and a coupling device comprising a monolithic receiving part having a first end and a second end, a central axis extending through the first and second ends, a channel at the first end for receiving the rod, an accommodation space for accommodating the head, and an opening at the second end sized to facilitate insertion of the head into the accommodation space, wherein an inner surface of the receiving part that defines part of the accommodation space forms a first seat portion for the head, a retainer element positionable in the accommodation space and having an inner surface that forms a second seat portion for the head, and a locking element, the method comprising:

• anchoring the shank of the anchoring element to bone;
• pivoting the receiving part relative to the head when the head is held in the receiving part, wherein the first seat portion of the receiving part and the second seat portion of the retainer element together form a seat for the head, such that the head is configured to be seated in both the first and second seat portions at the same time while remaining pivotable relative to both the first and second seat portions to hold the head in the receiving part in a pivotable manner;
• inserting the rod into the channel of the receiving part;
• and
• advancing the locking element in the channel to lock respective positions of the head and the rod relative to the receiving part.

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

• a bone anchoring element comprising a shank for anchoring to bone and a head;
• a monolithic receiving part having a first end and a second end, a central axis extending through the first and second ends, a channel at the first end for receiving the rod, 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 first engagement surface;
• and
• a retainer element positionable in the accommodation space and having an inner surface that forms at least part of a seat for the head and a second engagement surface;
• wherein one of the first or second engagement surfaces is formed by a projection that is engageable with a recess formed at the other one of the first or second engagement surfaces to define an axis of rotation that extends through the projection and that is perpendicular to the central axis, and wherein the retainer element is rotatable relative to the receiving part around the axis of rotation from a first position where the head is insertable through the opening into the receiving part to a second position where the retainer element at least partially blocks the opening to prevent removal of the head from the receiving part.