US Patent 9924975 Bone anchor having a snap-fit assembly

A pivotal bone anchor assembly includes a shank sub-assembly comprising a shank and a coupler, and a receiver sub-assembly comprising a receiver having a bore with a bottom opening and a snap-fit assembly proximate the bottom opening comprising an insert, a retainer ring positioned within an expansion chamber, and a positioner configured to hold the retainer ring in position. The shank sub-assembly is uploaded through the receiver bottom opening such that the positioner is pushed up into a holder chamber and the retainer rings engages a circumferential locking groove of the coupler to secure the shank sub-assembly with the receiver sub-assembly with a snap-fit connection.