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 and release an inserted head, to a second position, in which radial expansion of the retainer element is hindered to prevent release of an inserted head. When the locking element is in the second position, a head of an anchoring element can be locked by exertion of a pressure force directly onto the head to press the head against the retainer element.
