1. In a medical implant assembly having at least one polyaxial bone screw attached to a longitudinal connecting member, the bone screw having a receiver with a channel, the improvement wherein: a) at least a portion of the longitudinal connecting member is sized and shaped to be received in the receiver channel; and further comprising: b) a compression insert directly engaging both the longitudinal connecting member and a shank of the polyaxial bone screw, the insert having a base, a pair of opposed arms with outer receiver engaging portions, and the opposed arms defining a through channel with a lower connecting member seating surface; wherein c) the compression insert is top-loadable in the receiver in a first orientation, wherein, when in the first orientation, the compression insert through channel is substantially perpendicular to the receiver channel, and then rotated to a second orientation, such that the compression insert through channel is substantially parallel to the receiver channel and cooperating receiver portions snap into the receiver engaging portions.
21. The improvement of claim 1 wherein a) the receiver engaging portions are a pair of opposed outwardly extending portions.