Pivotal bone anchor assembly with resilient tensioning members stabilized by pins

A spinal stabilization assembly intended for securing an elongate rod to a bone of a patient, the spinal stabilization assembly comprising:

• a shank having a shank head with an at least partially spherical upper surface and an anchor portion opposite the shank head implantable into the bone of the patient;
• a receiver having vertical centerline axis, a base portion with a bottom opening, a pair of upright arms extending upward from the base portion to define a channel configured to receive the elongate rod, and a central bore extending upwards along the vertical centerline axis from the bottom opening through the channel to tops of the upright arms and including a spherical seating surface adjacent the bottom opening, an internal mating structure adjacent the tops of the uprights arms configured to cooperate with a closure mechanism, and a chamber between the internal mating structure and the spherical seating surface;
• the receiver having opposing side holes extending into the chamber configured to receive a pair of pins;
• a resiliently-expandable retainer positionable in the central bore of the receiver prior to the shank head and configured to capture and hold the shank head in the receiver, the retainer having an at least partially spherical outer surface engageable with the spherical seating surface;
• a pair of opposing resilient tensioning members positionable in the chamber and retained therein by the pair of pins extending through the opposing side holes in the receiver and openings in the tensioning members, the opposing tensioning members having inwardly-facing surfaces below downwardly-facing surfaces;
• and
• a pressure insert at least partially positionable in the opposing tensioning members below the downwardly-facing surfaces,
• wherein the pressure insert includes an upper surface configured to engage the elongate rod and a lower surface configured to engage the at least partially spherical upper surface of the shank head when the spinal stabilization assembly is in a locked orientation with the closure mechanism.