Method of assembling a pivotal bone anchor assembly with non-pivoting pre-lock friction fit shank head retainer

A method of assembling a pivotal bone anchor assembly intended for securing an elongate rod to a bone of a patient, the method comprising:

• providing a retaining structure positionable into a receiver,
• the receiver comprising a proximal end, a distal end, a vertical centerline axis extending between the proximal end and the distal end, an open channel extending downward from the proximal end of the receiver configured to receive the elongate rod, and a central bore comprising a lower interior recess communicating with a bottom surface at the distal end of the receiver through a lower opening, an internal support surface adjacent to and above the lower opening, and a guide and advancement structure adjacent the proximal end of the receiver configured to mate with a closure, and
• the retaining structure comprising a body with a center opening, a discontinuous inner support surface, and an outer surface;
• positioning a spherical head of a shank into the receiver;
• positioning the retaining structure into the lower interior recess in the receiver with the outer surface of the retaining structure spaced apart from the internal support surface of the central bore;
• and
• positioning the spherical head of the shank against the inner support surface of the retaining structure, with the shank extending distally from the retaining structure and the lower opening at the distal end of the receiver, such that a maximum diameter of the spherical head of the shank is frictionally engaged by the inner support surface to provide a pre-lock friction fit therebetween,
• wherein the outer surface of the retaining structure is downwardly engageable with the internal support surface in the lower interior recess of the receiver so as to have a non-pivoting configuration with respect to the receiver, and
• wherein the retaining structure is spaced apart with respect to the elongate rod when the assembly is in a locked configuration with the closure.