Pivotal bone anchor assembly with a bottom loaded cannulated shank having a planar top surface

Abstract

A pivotal bone anchor assembly includes a receiver having a lower portion defining a cavity with a retention structure proximate a lower opening and an upper portion defining a channel, and a shank having a capture portion with a spherical outer surface, an anchor portion opposite the capture portion for fixation to the bone, an internal drive structure opening onto a top end, an upward-facing planar surface surrounding the internal drive structure above the spherical outer surface, and a central bore extending from the internal drive structure down to the bottom of the anchor portion. The assembly also includes a retainer having an outer surface engageable with the retention structure and an inner surface engageable with the spherical outer surface, upon an uploading of the capture portion through the lower opening, so as to capture and hold the capture portion within the cavity with the shank being pivotal with respect to the receiver prior to securing a fixation rod within the channel with a closure.

What is claimed is: 
     
         1 . A pivotal bone anchor assembly configured for implantation in a bone of a patient about a guide wire with a drive tool, and for securing a fixation rod to the bone with a closure, the pivotal bone anchor assembly comprising:
 a receiver comprising a lower portion defining a cavity centered about a vertical centerline axis and communicating with a bottom of the receiver through a lower opening, and an upper portion integral with the lower portion defining a channel communicating with the cavity and configured to receive the fixation rod, the receiver further including an integrally-formed closure mating structure at an upper end of the upper portion configured to receive the closure and an integrally-formed internal retention structure at a lower end of the cavity proximate the lower opening;   a shank comprising a longitudinal axis, a capture portion at an upper end having a rounded shape with an at least partially spherical outer surface extending above and below a midline plane defined at a maximum width of the capture portion perpendicular to the longitudinal axis, an internal drive structure configured to mate with the drive tool formed into the capture portion and opening onto a top end of the capture portion, an anchor portion opposite the capture portion configured for fixation to the bone, and a central bore extending from the internal drive structure down to a bottom end of the anchor portion and configured to receive the guide wire, the capture portion including a circumferentially-extending upward-facing planar surface surrounding the internal drive structure above the at least partially spherical outer surface, the capture portion configured for uploading into the cavity of the receiver through the lower opening with the shank extending downward through the lower opening; and   a retainer configured for positioning within the cavity with an outer surface of the retainer engaging the retention structure of the receiver and an inner surface of the retainer configured to engage the capture portion of the shank when the capture portion is uploaded into the cavity, so as to capture and hold the capture portion of the shank within the cavity of the receiver, and with the shank being pivotal with respect to the receiver prior to securing the fixation rod within the channel with the closure.   
     
     
         2 . The pivotal bone anchor assembly of  claim 1 , wherein the anchor portion of the shank is configured for implantation in the bone about the guide wire with the drive tool prior to the capture portion of the shank being captured within the cavity of the receiver by the retainer. 
     
     
         3 . The pivotal bone anchor assembly of  claim 1 , wherein the anchor portion of the shank is configured for implantation in the bone about the guide wire with the drive tool subsequent to the capture portion of the shank being captured within the cavity of the receiver by the retainer. 
     
     
         4 . The pivotal bone anchor assembly of  claim 1 , wherein the anchor portion of the shank is configured for implantation in the bone about the guide wire with the drive tool prior to the closure being positionable within the upper portion of the receiver. 
     
     
         5 . The pivotal bone anchor assembly of  claim 1 , wherein the upward-facing planar surface is perpendicular to the longitudinal axis. 
     
     
         6 . The pivotal bone anchor assembly of  claim 1 , wherein the upward-facing planar surface is annular. 
     
     
         7 . The pivotal bone anchor assembly of  claim 1 , wherein the at least partially spherical outer surface of the capture portion extends upwards from the midline plane to an outer edge of the upward-facing planar surface. 
     
     
         8 . The pivotal bone anchor assembly of  claim 1 , wherein the at least partially spherical outer surface of the capture portion extends downwards from the midline plane to a neck of the shank extending between the capture portion and the anchor portion and having a substantially smooth outer surface. 
     
     
         9 . The pivotal bone anchor assembly of  claim 8 , wherein the outer surface of the neck further comprises a circumferentially-extending curvate surface having a minimal radius that is less than a radius of the anchor portion immediately adjacent the neck. 
     
     
         10 . The pivotal bone anchor assembly of  claim 1 , wherein the shank is configured to pivot with respect to the retainer. 
     
     
         11 . The pivotal bone anchor assembly of  claim 1 , wherein the retainer is configured to be non-pivotable with respect to the receiver. 
     
     
         12 . The pivotal bone anchor assembly of  claim 1 , wherein the retainer further comprises a top surface, a bottom surface, at least one through slot extending from the top surface to the bottom surface, and an at least partially spherical inner surface configured to engage the at least partially spherical outer surface of the capture portion of the shank. 
     
     
         13 . The pivotal bone anchor assembly of  claim 1 , wherein the retainer is configured to be uploaded into the cavity of the receiver through the lower opening. 
     
     
         14 . The pivotal bone anchor assembly of  claim 13 , wherein the retainer is configured to form a smaller diameter to pass through the lower opening. 
     
     
         15 . The pivotal bone anchor assembly of  claim 1 , wherein the retention structure of the cavity of the receiver further comprises a circumferential groove surrounding the lower opening and spaced from the bottom of the receiver, the circumferential groove having a downward-facing upper surface and an upward-facing lower surface. 
     
     
         16 . The pivotal bone anchor assembly of  claim 15 , wherein the outer surface of the retainer further comprises a top surface and a bottom surface configured to engage the downward-facing upper surface and the upward-facing lower surface of the circumferential groove, respectively. 
     
     
         17 . The pivotal bone anchor assembly of  claim 15 , wherein the cavity of the receiver further comprises a substantially cylindrical surface extending upward from the circumferential groove and configured to receive the capture portion of the shank. 
     
     
         18 . The pivotal bone anchor assembly of  claim 1 , wherein the inner surface of the retainer further comprises:
 an upper at least partially spherical surface extending downward and inward from a top surface of the retainer and configured to engage the at least partially spherical outer surface of the capture portion to provide for pivotal movement of the shank with respect to the receiver; and   a lower conical surface extending upward and inward from a bottom surface of the retainer.   
     
     
         19 . The pivotal bone anchor assembly of  claim 18 , wherein the lower opening of the receiver further comprises a conical surface configured to align with the lower conical surface of the retainer to provide for increase articulation of the shank with respect to the receiver. 
     
     
         20 . The pivotal bone anchor assembly of  claim 1 ,
 wherein the internal drive structure further comprises an internal drive aperture with internal sidewalls extending downward from the opening onto the top end of the capture portion to a bottom seating surface, and   wherein the central bore of the shank further comprises an upper opening at the bottom seating surface of the drive aperture.   
     
     
         21 . The pivotal bone anchor assembly of  claim 1 , wherein the channel of the receiver further comprises an upwardly-open channel defined by interior surfaces of a pair of upright arms extending upwardly from the lower portion. 
     
     
         22 . The pivotal bone anchor assembly of  claim 1 , wherein the closure mating structure of the upper portion of the receiver further comprises a helically wound guide and advancement structure. 
     
     
         23 . The pivotal bone anchor assembly of  claim 1  and further comprising the fixation rod and the closure, wherein the closure is configured for positioning within the channel of the receiver above the fixation rod and in engagement with the closure mating structure to apply a downward pressure towards a top of the fixation rod, so as to frictionally lock the shank in a fixed position relative to the receiver. 
     
     
         24 . The pivotal bone anchor assembly of  claim 23 , wherein the at least partially spherical outer surface of the capture portion is configured to receive the downward pressure applied towards the top of the rod by the closure top to frictionally lock the shank in the fixed position relative to the receiver. 
     
     
         25 . The pivotal bone anchor assembly of  claim 23  and further comprising an insert positionable within the receiver prior to the fixation rod,
 wherein an upper surface of the insert is configured to engage the fixation rod, and 
 wherein a lower surface of the insert is configured to engage the capture portion of the shank while spaced from the upward-facing planar surface of the capture portion. 
 
     
     
         26 . The pivotal bone anchor assembly of  claim 25 , wherein the insert is configured to be top loaded into the receiver.