A medical implant assembly includes a polyaxial bone anchor having a shank with an upper portion, a receiver, a retainer for holding the shank upper portion in the receiver, a lower compression insert with surfaces for closely receiving an elongate connecting member and a closure structure that may independently engage the lower compression insert to lock the shank with respect to the receiver while selectively not locking the elongate member. Projections or splines of the shank upper portion mate with holding pockets on the retainer. The bone anchor includes a shank upper surface exclusively engaging the lower compression insert that is spaced from the retainer, the retainer and shank being configured for polyaxial motion with respect to the receiver prior to locking.
