Method of assembling a bone anchor assembly with a threaded universal shank head

A method of assembling a bone anchor assembly configured for securing a fixation rod to a bone of a patient with a closure, the method comprising:

• positioning one of a rod-engaging insert or a capture portion-engaging retainer into the central bore of a receiver to form a pivoting receiver sub-assembly or a non-pivoting receiver sub-assembly, respectively, the receiver having a vertical centerline axis, an upper portion defining a channel configured to receive the fixation rod, and a base defining a lower portion of the central bore formed around the vertical centerline axis and communicating with a bottom surface of the receiver through a bottom opening, the central bore extending upwardly from the bottom opening through the channel to a top of the receiver and including a guide and advancement structure mateable with the closure proximate the top of the receiver;
• and
• uploading a capture portion of one of a plurality of bone anchors through the bottom opening and into a lower portion of the central bore of the pivoting receiver sub-assembly or the non-pivoting receiver sub-assembly, each of the plurality of bone anchors comprising a longitudinal axis, a capture portion at a proximal end, an anchor portion at a distal end configured for fixation to the bone, and an integral neck portion extending between the capture portion and the anchor portion,
• wherein the capture portion of the each of the plurality of bone anchors comprises a partial spherical outer surface extending outward and upward from the neck portion to an annular planar top surface and including a discontinuous central portion defined by combined crest surfaces of a pair of helically wound upper threadforms formed into the partial spherical outer surface.