| 主权项 |
1. A polyaxial bone anchoring device comprising:
an anchoring element having a shaft for anchoring to a bone, a head having a curved outer surface portion, and a longitudinal axis extending through the shaft and the head; a receiving part having a top end and a bottom end, a channel for receiving a rod therein, a coaxial bore extending from the top end in a direction of the bottom end, a seat portion for receiving the head at the bottom end, and a recess at an inner wall of the receiving part; and a pressure element configured to be arranged within the bore between the head of the anchoring element and the top end of the receiving part, the pressure element having a head contacting surface portion configured to contact the curved outer surface portion of the head, and comprising a projection, wherein, when the head is seated in the seat portion, the recess is entirely between a plane of the receiving part and the bottom end of the receiving part, the plane being defined by the curved outer surface portion of the head having a greatest width or diameter of the head in a direction perpendicular to the longitudinal axis, wherein, when the head engages the head contacting surface portion and the pressure element is in the receiving part, the head is pivotable with respect to the receiving part and the projection engages a surface of the recess facing toward the bottom end of the receiving part such that the head is prevented from moving toward the top end of the receiving part, and wherein the head is configured to be locked at an angle by exerting pressure via the pressure element onto the head. |
