Patent ID: 11426208

Abstract:
A pivotal bone anchor assembly includes a receiver with an axial bore communicating with a bottom of the receiver through a bottom opening, a circumferential locking groove adjacent the bottom opening, a circumferential expansion groove above the locking groove with a diameter that is greater than the diameter of the locking groove, and a transition surface between the locking groove and the expansion groove. The assembly also includes an insert uploadable through the bottom opening, an open retainer ring uploadable through the bottom opening after the insert and positionable within the locking groove, and a shank having a shank head. An upward loading motion of the shank head through the bottom opening urges the open retainer ring up into expansion around the shank head within the expansion groove, after which the open retainer ring resiliently returns to the locking groove, with a bottom surface of the open retainer ring seated against an upwardly-facing seating surface and a top surface extending above the level of the transition surface into the expansion groove, so as to capture the shank head of the shank within the axial bore of the receiver.