3. The improvement of claim 1 wherein the insert has an outer surface releasably frictionally locked against the receiver.
1. In a bone anchor, the improvement comprising: a) a shank having a body for fixation to a bone and an integral upper substantially spherical head; b) a receiver having a top portion and a receiver base and an outer surface, the receiver top portion defining a first open channel, the base defining a chamber and a lower opening, the chamber communicating with both the channel and the lower opening, the top portion having a pair of opposed through apertures formed therein; c) an insert disposed within the receiver, the insert having a curved surface sized and shaped for frictional mating cooperation with the shank head and having a second open channel, the insert further having a pair of outwardly extending arm portions, each arm portion having an interior surface and each arm portion partially extending through one of the apertures of the receiver, an arm portion interior surface having a groove, the groove being engageable a first manipulation tool for movement of the insert both downwardly into contact with the shank head, upwardly away from the shank head, and rotational movement of the insert; and d) a resilient open retainer having a retainer base, the retainer captured within the chamber and expandable about at least a portion of the shank head and wherein expansion-only locking engagement occurs between the shank upper portion and the retainer base and between the retainer base and the receiver.