Pivotal bone anchor assembly and method for use thereof

A pivotal bone anchor assembly for securing a longitudinal connecting member to a bone of a patient via a fastener, the pivotal bone anchor assembly comprising:

• a receiver having a central bore centered about a vertical centerline axis and in communication with a bottom surface of the receiver through a lower opening, and an upper portion defining a channel configured to receive the longitudinal connecting member and including a helically wound thread form threadably engageable with the fastener, the channel communicating with the central bore, the central bore including at least one non-threaded downward facing surface below the helically wound thread form and a lower spherical seating surface adjacent the lower opening;
• a shank having a head portion with a lower spherical surface and an upper spherical engagement surface and an anchor portion opposite the head portion configured for attachment to the bone, the head portion configured for being positioned within a lower portion of the central bore with the shank extending downwardly through the lower opening and the lower spherical surface pivotally engageable with the lower spherical seating surface;
• and
• a compression insert having a central opening, an upwardly facing surface configured to receive the longitudinal connecting member, and at least one notch with an engagement surface extending about the notch, the engagement surface being resiliently downwardly compressible;
• wherein the compression insert is configured for axially biased overlapping engagement between the downward facing surface of the central bore and the engagement surface extending about the notch of the compression insert, so as to apply a downward frictional force on the head portion of the shank prior to locking the assembly with the fastener.

A method of using a bone anchor assembly configured to secure a longitudinal connecting member to a bone of a patient, the method comprising:

• providing:
• a receiver having an upper portion with a channel configured to receive the longitudinal connecting member, a shank holding lower portion including a lower opening, and a receiver central bore communicating with the lower opening and being centered on a receiver longitudinal axis and including a downward facing engagement surface,
• a shank having a head portion and an anchor portion opposite the head portion configured for attachment to the bone, and
• a compression insert having a lower portion with a downwardly facing surface, and an upper portion including at least one notch formed in an outer surface of the upper portion of the compression insert and defining at least one resiliently compressible upward facing surface integral with the upper portion of the compression insert and extending over the at least one notch;
• loading the head portion of shank into the shank holding lower portion of the receiver, and positioning the compression insert in the receiver central bore;
• and
• engaging the at least one resiliently compressible upward facing surface of the compression insert with the downward facing engagement surface of the receiver central bore to provide an axially directed force for a pre-lock friction prior to securing the longitudinal connecting member in the channel.