Locking element for a polyaxial bone anchor, bone plate assembly and tool

摘要

A locking element is configured to be used with a polyaxial bone anchor, and is substantially cylindrical with a bottom side facing a head of the bone anchor, a top side opposite to the bottom side, and a surface portion with an external thread. The locking element has a first recess at the bottom side for accommodating at least a portion of the head, and a second recess at the top side for engagement with a driver. The second recess is located outside the center of the top side. The head has a portion with a largest diameter, and a first level L1 is defined by the highest point of a circle with the largest diameter drawn around the head, and a second level L2 is defined by the bottom of the second recess, L2 being at a level not higher than L1.