A polyaxial bone anchor 1 comprising a receiver 10 defining a chamber 76 communicating with a channel 62, the channel 62 being sized and shaped for receiving a portion of a longitudinal connecting member 21, the chamber 76 communicating with a lower opening 95 and the chamber 76 having a sidewall surface, a shank 4 having a threaded body 24 integral with an upper portion and a first axis A being located centrally and parallel to the body, the shank body extending out of and downwardly from the receiver lower opening. A retainer 12 located in the chamber prior to upward loading of the shank 4 and a top load insert 14, the anchor 1 characterised in that the upper portion 8 has a first convex surface with a first radius with respect to the first axis, the shank having a second curved surface near the bottom of the upper portion, the second curved surface having a second radius with respect to the first axis that is the same as the first radios. The first convex surface 44 located at substantially a top of the upper portion 8, the retainer 12 being resilient and open and having a third convex outer surface with a third radius with respect to the first axis, the third radius being substantially equal to the first radius when the retainer 12 is in a substantially neutral, non-expanded state, the retainer 12 being expandable in the chamber 76 about the shank upper portion 8 and receiving the first convex surface there through to capture the shank upper portion 8 in the chamber 76. The retainer 12 being joined to the shank 4 at an interface located along the shank upper portion 8 between the first convex surface and the shank body. The interface being at least one of cylindrical, frusto-conical and curved geometry. The retainer 12 and shank 4 being joined in relationship to one another and in pivotal relationship with the receiver sidewall surface prior to locking the retainer 12 against the receiver 10. The inset 14 having a lower surface radiused to mate with the shank up
