Polyaxial bone anchor with compound articulation and pop-on shank

In a bone anchor, the improvement comprising:

• a) a shank having a body for fixation to a bone and an integral head having at least one curved surface;
• b) a receiver having a top portion and a base, the receiver top portion defining an open channel, the base having a first surface partially defining a cavity, the channel communicating with the cavity, the receiver having at least one tool receiving through aperture;
• c) at least one insert disposed within the receiver, the insert sized and shaped to directly engage with the shank head curved surface and to cooperate with lock and release tools that extend through the receiver tool receiving aperture for pressing the insert downwardly against the shank head into one of non-floppy sliding engagement and temporary locking engagement with the shank head;
• and
• d) a resilient open retainer captured within the cavity and expandable within the cavity about at least a portion of the shank head, the retainer having a first polyaxial articulation with the shank head and a second polyaxial articulation with the receiver when in an unlocked position, and wherein expansion-only locking engagement occurs between the shank head and the retainer and between the retainer and the receiver when in a locked position.

In a bone anchor, the improvement comprising:

• a) a shank having a body for fixation to a bone and an integral head having a first spherical surface;
• b) a receiver having a top portion and a base, the receiver top portion having first and second opposed arms defining an open channel, the base having a lower opening and a second spherical surface partially defining a base cavity, the channel communicating with the cavity and the lower opening, each receiver arm having a tool receiving sloping surface and a through aperture;
• c) at least one top loaded insert disposed within the receiver, the insert having a third spherical surface sized and shaped to directly engage with the shank head first spherical surface, the insert having third and fourth opposed arms, each arm having a recessed surface aligned with one of the receiver sloping surfaces and sized and shaped for receiving lock and release tools that extend through the receiver tool receiving apertures for pressing the insert downwardly into engagement with the shank head;
• and
• d) a resilient open retainer captured within the cavity and expandable within the cavity about at least a portion of the shank head first spherical surface, the retainer having a first polyaxial articulation with the shank head first spherical surface and a second polyaxial articulation with the receiver second spherical surface when in an unlocked position, and wherein the retainer is in expansion-only locking engagement between the shank head and the receiver when the shank is in a locked position with respect to the receiver.