Patent ID: 8262704

Claim:
A bone anchoring device comprising a bone anchoring element having a shank, a receiving part for connecting the shank of the bone anchoring element to a rod, and a securing element having an outer thread, the receiving part comprising: a first end and a second end and a central axis extending from the first end in a direction of the second end, a recess having a substantially U-shaped cross section, the recess extending from the first end in the direction of the second end and forming two legs open at the first end and coming together at a bottom of the recess, the recess defining a channel to receive the rod, the channel having a longitudinal axis, the two legs having an inner thread to receive the securing element, the outer thread configured to cooperate with the inner thread to secure the rod, wherein the receiving part is polyaxially connectable to the bone anchoring element and the two legs are provided with stiffening structures to reduce splaying caused by a torque acting on the two legs at the time of final tightening of the rod by the securing element, the stiffening structures comprising a first envelope of the receiving part located above the bottom of the recess along a plane perpendicular to the central axis, the first envelope extending a greater distance from the central axis than every envelope of the receiving part that is parallel to the first envelope and located below the bottom of the recess.