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 lower opening, a bottom surface, a receiver central bore centered about a vertical centerline axis and in communication with the bottom surface of the receiver through the lower opening, and an upper portion defining a channel configured to receive the longitudinal connecting member and including a mating structure engageable with the fastener, the channel communicating with the receiver central bore, and the receiver central bore including at least one non-threaded downwardly-facing surface below the mating structure and a lower at least partially spherical seating surface adjacent the lower opening;
• a shank having a head portion with a lower spherical engagement 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 positionable within a lower portion of the receiver central bore with the shank extending downwardly below the bottom surface and the lower spherical engagement surface pivotally engageable with the lower at least partially spherical seating surface;
• and
• a compression insert having a central opening centered on an insert longitudinal axis, an upwardly-facing surface configured to receive the longitudinal connecting member, at least one notch at least partially formed in an outer surface of the compression insert and extending at least in part in a traverse direction relative to the insert longitudinal axis, and an engagement surface extending above the notch, the engagement surface being resiliently downwardly deflectable in an axial direction relative to the insert longitudinal axis;
• wherein the compression insert is configured for axially biased overlapping engagement between the downwardly-facing surface of the receiver central bore and the engagement surface extending above 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 downwardly-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 central opening centered on an insert longitudinal axis, a lower portion with a downwardly-facing surface, and an upper portion including at least one notch at least partially formed in an outer surface of the upper portion of the compression insert and extending at least in part transversely relative to the insert longitudinal axis, and defining at least one resiliently deflectable upwardly-facing surface integral with the upper portion of the compression insert and extending over the at least one notch, the at least one resiliently deflectable upwardly-facing surface being deflectable in an axial direction relative to the insert longitudinal axis;
• positioning the compression insert in the receiver central bore, and loading the head portion of the shank into the shank holding lower portion of the receiver;
• and
• engaging the at least one resiliently deflectable upwardly-facing surface of the compression insert with the downwardly-facing engagement surface of the receiver central bore to provide an axially directed force for a pre-lock friction fit prior to securing the longitudinal connecting member in the channel.