18. In a bone anchor, the improvement comprising: a) a shank having a body for fixation to a bone and an integral upper portion having a convex substantially spherical first surface with a first radius; b) a receiver having a base and a pair of upright arms forming an open channel, the base defining a chamber and having a lower opening, the channel communicating with the chamber; c) at least one insert disposed within the receiver chamber having structure that directly engages lock and release tools; d) a resilient open retainer captured within the chamber and expandable about at least a portion of the shank upper portion, the retainer having a concave surface with a radius smaller than the radius of the shank upper portion first surface, the retainer concave surface terminating at upper and lower edges, the edges frictionally mating with the shank first spherical surface, providing a friction fit between the retainer and the shank during non-locking angular manipulation of the shank with respect to the receiver; and e) wherein expansion-only locking engagement occurs between the shank upper portion and the retainer and between the retainer and the receiver.
18. In a bone anchor, the improvement comprising: a) a shank having a body for fixation to a bone and an integral upper portion having a convex substantially spherical first surface with a first radius; b) a receiver having a base and a pair of upright arms forming an open channel, the base defining a chamber and having a lower opening, the channel communicating with the chamber; c) at least one insert disposed within the receiver chamber having structure that directly engages lock and release tools; d) a resilient open retainer captured within the chamber and expandable about at least a portion of the shank upper portion, the retainer having a concave surface with a radius smaller than the radius of the shank upper portion first surface, the retainer concave surface terminating at upper and lower edges, the edges frictionally mating with the shank first spherical surface, providing a friction fit between the retainer and the shank during non-locking angular manipulation of the shank with respect to the receiver; and e) wherein expansion-only locking engagement occurs between the shank upper portion and the retainer and between the retainer and the receiver. 21. The improvement of claim 18 wherein the retainer further comprises a pair of opposed outwardly extending resilient tabs and the retainer having a base with at least a first planar surface and the receiver having a second planar surface partially defining the receiver chamber and a second pair of opposed apertures and wherein after the shank upper portion is received through the retainer base, the retainer base first planar surface is seated on the receiver second surface and the resilient tabs expand to a neutral state and are captured within the second pair of receiver apertures.