Polyaxial bone anchoring device

摘要

A polyaxial bone anchoring device includes an anchoring element having a shank and a head having an outer surface portion shaped as a segment of a sphere, a receiving part having a seat portion for receiving the head, and a pressure element having a head contacting surface portion having at least two circumferentially distinct projections and defining a recess for holding the head, the recess having a first region configured to receive the head and a second region defined by at least part of one of the projections and having an undersize compared to the shape of the head, such that when the head is held in the recess, the projections extend over a portion of the head with the largest outer diameter, and the head contacting surface portion corresponding to the second region is expanded from a neutral position to clamp the head by friction.

主权项

1. A polyaxial bone anchoring device comprising:
an anchoring element having a shank for anchoring to a bone and a head having an outer surface portion shaped as a segment of a sphere including a largest outer diameter of the sphere; a receiving part having a first end and a second end, a channel for receiving a rod therein, a bore extending from the first end in a direction of the second end along a bore axis, a seat portion at the second end configured to contact the head, and at least one accommodation space in the seat portion; and a pressure element having a head contacting surface portion comprising a plurality of circumferentially distinct projections and defining a recess having a first region configured to receive the head and a second region defined by portions of the projections and having a diameter smaller than the largest outer diameter of the sphere such that, when the head is held in the recess, the projections extend over a portion of the head with the largest outer diameter of the sphere, wherein when the head contacts the seat portion, the pressure element is movable from a first position, wherein free ends of the projections are located at the largest diameter of the sphere and project radially into the at least one accommodation space, to a second position, wherein the free ends of the projections extend past the largest diameter of the sphere and project radially to a less degree toward or into the at least one accommodation space than in the first position and the second region of the head contacting surface portion is expanded from a neutral position to clamp the head by friction such that the clamped head remains pivotable with respect to the receiving part prior to being fixed.