Pivotal bone anchor assembly with centrally open screw shank

A cannulated pivotal bone anchor assembly for implantation in a bone of a patient, the cannulated pivotal bone anchor assembly comprising:

• a shank comprising a capture portion at an upper end, an anchor portion opposite the capture portion configured for implantation in the bone, and an axial bore extending entirely through the shank along a longitudinal axis to a top opening at a top end of the capture portion and a bottom opening at a bottom end of the anchor portion, the axial bore being closed laterally along an entire length thereof and having a constant diameter at least along the anchor portion of the shank through to the bottom opening, the capture portion including a central drive structure and a circumferentially extending upward-facing planar surface surrounding and entirely peripheral to the central drive structure;
• and
• a head member comprising a base defining an internal cavity centered about a vertical centerline axis and in communication with a bottom of the head member through a lower opening, and an upper portion defining a channel communicating with the internal cavity and including a first guide and advancement structure proximate a top of the head member, the internal cavity including a seating surface proximate the lower opening configured to support the capture portion of the shank with the shank extending downward through the lower opening with the longitudinal axis of the shank being orientable coaxially with the vertical centerline axis of the head member and at any of a plurality of angles relative to the vertical centerline axis;
• an elongate rod sized and shaped for insertion into the channel of the head member;
• and
• a closure top configured for positioning within the channel of the head member above the elongate rod and having a second guide and advancement structure rotatably engageable with the first guide and advancement structure to apply a downward pressure to a top of the elongate rod, so as to frictionally lock the shank in a fixed position relative to the head member,
• wherein when the shank and head member are coupled together and prior to the elongate rod and closure top being received within the channel of the head member, the cannulated pivotal bone anchor assembly is configured for insertion along a guide wire positioned in the axial bore of the shank and for implantation into the bone of the patient as a fully assembled unit, with only the elongate rod and closure top remaining to be inserted into the channel of the head member.