Pivotal bone anchor assembly having threaded receiver lower opening and shank head

Abstract

A pivotal bone screw assembly includes a head member with a pair of upstanding arms extending upward from a base to define a channel for receiving a rod, with the base including a cavity communicating with both the open channel and with a bottom of the head member through a lower opening having at least a partial thread cut therein. The assembly also includes a shank with a capture structure and an anchor portion opposite the capture structure for fixation to the bone of a patient, with the capture structure having a partially spherical shape configured for positioning within the cavity to provide for pivotal motion between the head member and the shank prior to locking the rod in the channel with a closure top. The assembly further includes a second thread configured for threaded engagement with the threaded lower opening as part of an assembly process by which the capture structure is retained in the cavity of the head member.

What is claimed is: 
     
         1 . A pivotal bone screw assembly for securing an elongate rod to a bone of a patient via a closure top, the pivotal bone screw assembly comprising:
 a head member including a base defining a cavity centered about a vertical centerline axis and communicating with a bottom of the head member through a lower opening, and a pair of upstanding arms extending upward from the base to define an upwardly-open channel extending perpendicular to the vertical centerline axis and configured to receive the elongate rod, the upwardly-open channel communicating with the cavity and including opposed interior surfaces with a discontinuous inner thread formed therein, the lower opening including an at least partial thread cut into the lower opening;   a shank including a longitudinal axis, a capture structure at a proximal end, and a body extending distally from the capture structure with an anchor portion configured to fix to the bone, the capture structure including a partially spherical shape and a top end with a tool engagement structure formed therein, the capture structure configured for positioning within the cavity so as to provide for pivotal motion between the head member and the shank prior to locking of the elongate rod in the upwardly-open channel via the closure top; and   a second thread configured for threaded engagement with the at least partial thread cut into the lower opening as part of an assembly process by which the capture structure is retained in the cavity of the head member.   
     
     
         2 . The pivotal bone screw assembly of  claim 1 , wherein the tool engagement structure further comprises a drive socket extending inward from an upper surface of the capture structure and configured to receive a tool to drive the shank into the bone. 
     
     
         3 . The pivotal bone screw assembly of  claim 2 , wherein the socket is defined by a plurality of planar tool engagement faces centered about and aligned parallel with the longitudinal axis. 
     
     
         4 . The pivotal bone screw assembly of  claim 1 , wherein the second thread is part of the capture structure of the shank and the capture structure was threaded through the lower opening as part of the assembly process by which the capture structure is retained in the cavity of the head. 
     
     
         5 . The pivotal bone screw assembly of  claim 1 , further comprising the closure top, wherein the closure top is configured to threadably engage the discontinuous inner thread of the upwardly-open channel to apply a downward force to the elongate rod to lock the elongate rod within the upwardly-open channel. 
     
     
         6 . The pivotal bone screw assembly of  claim 5 , wherein the discontinuous inner thread of the upwardly-open channel and a thread of the closure top are each configured to interface with each other such that splay of the pair of upstanding arms extending upward from the base is substantially eliminated when the closure top is used to lock the elongate rod within the upwardly-open channel. 
     
     
         7 . The pivotal bone screw assembly of  claim 1 , wherein the inner surface of the cavity of the head member includes a partially spherical surface adjacent to the lower opening. 
     
     
         8 . The pivotal bone screw assembly of  claim 1 , wherein the lower opening of the head member includes a downwardly-opening beveled surface adjacent to the bottom of the head member and defining a partial conical-shaped structure. 
     
     
         9 . The pivotal bone screw assembly of  claim 1 , wherein the shank further includes a cannulation extending along at least a portion of longitudinal axis. 
     
     
         10 . A method of assembling a pivotal bone screw assembly for securing an elongate rod to a bone of a patient via a closure top, the method comprising:
 providing a shank including a longitudinal axis, a capture structure at a proximal end, and a body extending distally from the capture structure with an anchor portion configured to fix to the bone, the capture structure including a partially spherical shape and a top end with a tool engagement structure formed therein;   providing a head member including a base defining a cavity centered about a vertical centerline axis and communicating with a bottom of the head member through a lower opening, and a pair of upstanding arms extending upward from the base to define an upwardly-open channel extending perpendicular to the vertical centerline axis and configured to receive the elongate rod, the upwardly-open channel communicating with the cavity and including opposed interior surfaces with a discontinuous inner thread formed therein, the lower opening including an at least partial thread cut into the lower opening; and   threading a second thread into the at least partial thread cut into the lower opening as part of a process by which the capture structure is retained in the cavity of the head member.   
     
     
         11 . The method of  claim 10 , further comprising positioning the capture structure in the cavity. 
     
     
         12 . The method of  claim 11 , wherein the capture structure is uploaded into the cavity. 
     
     
         13 . The method of  claim 11 , wherein once the capture structure is retained in the cavity of the head member, the capture structure is positionable within the cavity so as to provide for pivotal motion between the head member and the shank prior to a locking of the elongate rod in the upwardly-open channel via the closure top. 
     
     
         14 . The method of  claim 11 , wherein the capture structure is positioned in the cavity subsequent to the second thread being threaded into the at least partial thread cut into the lower opening. 
     
     
         15 . The method of  claim 10 , wherein the second thread is part of the capture structure of the shank, and the capture structure is threaded through the lower opening to position the capture structure in the cavity of the head member. 
     
     
         16 . The method of  claim 15 , wherein once the capture structure is retained in the cavity of the head member, the capture structure is positionable within the cavity so as to provide for pivotal motion between the head member and the shank prior to a locking of the elongate rod in the upwardly-open channel via the closure top. 
     
     
         17 . The method of  claim 10 , wherein the tool engagement structure further comprises a drive socket extending inward from an upper surface of the capture structure and configured to receive a tool to drive the shank into the bone. 
     
     
         18 . The method of  claim 10 , wherein the inner surface of the cavity of the head member includes a partially spherical surface adjacent to the lower opening. 
     
     
         19 . The method of  claim 10 , wherein the lower opening of the head member includes a downwardly-opening beveled surface adjacent to the bottom of the head member and defining a partial conical-shaped structure. 
     
     
         20 . The method of  claim 10 , wherein the shank further includes a cannulation extending along at least a portion of the longitudinal axis.