Pivotal bone anchor assembly with retainer pre-positioned in expansion chamber and tool-deployable insert

Abstract

A pivotal bone anchor assembly includes a receiver defining a central bore with a circumferentially-extending horizontal interference structure located above an upper expansion region and a lower locking region, and a shank having an upper end portion up-loadable into the central bore through a bottom opening. The assembly also includes a retainer having an upper portion and a lower expansion portion pre-positioned within the upper expansion region and being operable to capture the upper end portion of the shank, and a compression insert postionable within the central bore having an upwardly-facing surface for engaging a rod, an exterior side surface for engaging the horizontal interference structure, and a lower recess for receiving the upper portion of the retaining structure in a side-to-side overlapping engagement. The compression insert is restrained from moving downwardly within the central bore until forcible downward displacement by direct engagement with tooling to drive the exterior side surface of the compression insert at least partially through the horizontal interference structure.