Method of assembling a pivotal bone anchor assembly with snap-in-place bushing

Abstract

A method of assembling a pivotal bone anchor assembly includes positioning a bushing into a body member having an axial bore with a lower interior surface adjacent a bottom opening, a channel for receiving a fixation rod, and hollow spaces formed into sidewalls of the axial bore. The bushing includes a curved upper surface for receiving the fixation rod and outwardly protruding structures that resiliently snap into the hollow spaces to inhibit the bushing from moving upward in the axial bore. The method also includes positioning the head of a bone anchor into the axial bore with the bone anchor extending downward through the bottom opening and with the lower interior surface supporting head of the bone anchor to provide for pivotal movement between the bone anchor and the body member prior to locking the pivotal bone anchor assembly via the fixation rod and a closure.

What is claimed is: 
     
         1 . A method of assembling a pivotal bone anchor assembly configured to secure a fixation rod to a bone of a patient with a closure, the method comprising:
 positioning a bushing into an axial bore of a body member,
 the body member comprising a base defining a lower portion of the axial bore centered about a vertical centerline axis and communicating with a bottom of the base through a bottom opening, and a pair of upright arms extending upward from the base to define a channel configured to receive the fixation rod, the axial bore extending upwardly from the bottom opening through the channel to tops of the upright arms and including a lower interior surface disposed about the bottom opening, an internal closure mating structure adjacent the tops of the upright arms, and at least one hollow space with a downwardly facing surface formed into sidewalls of the axial bore between the lower interior surface and the tops of the upright arms, 
 the bushing comprising a curved upper surface configured to receive the fixation rod, a central opening, and at least one outwardly protruding structure that resiliently snaps into the at least one hollow space upon positioning of the bushing into the axial bore to inhibit the bushing from moving upward in the axial bore; and 
   positioning a partial spherical head of a bone anchor into the lower portion of the axial bore of the body member, the bone anchor comprising a shank body having a longitudinal axis, the partial spherical head at a proximal end of the shank body, and an anchor portion opposite the partial spherical head configured for attachment to the bone,   wherein the lower interior surface of the axial bore supports the partial spherical head of the bone anchor to provide for pivotal movement between the shank body and the body member prior to locking the pivotal bone anchor assembly with the fixation rod via the closure.   
     
     
         2 . The method of  claim 1 , wherein the at least one outward protruding structure of the bushing positioned within the at least one hollow space of the body member inhibits the bushing from rotating relative to the body member about the vertical centerline axis. 
     
     
         3 . The method of  claim 1 , wherein the central opening of the bushing is configured to provide access to the partial spherical head of the bone anchor. 
     
     
         4 . The method of  claim 1 , wherein a lower surface of the bushing engages the partial spherical head of the bone anchor. 
     
     
         5 . The method of  claim 4 , wherein positioning the at least one outward protruding structure of the bushing within the at least one hollow space of the body member establishes a pre-lock press fitment between the lower surface of the bushing and the partial spherical head of the bone anchor so that the bone anchor and the body member do not move freely with respect to each other prior to insertion and securement of the fixation rod with the closure. 
     
     
         6 . The method of  claim 1 , wherein the lower interior surface of the axial bore further comprises an upward facing rounded surface that directly engages the partial spherical head of the shank to form a modified ball joint. 
     
     
         7 . The method of  claim 1 , wherein positioning the partial spherical head of the shank into the lower portion of the axial bore further comprises downloading the shank through the channel of the body member with the anchor portion passing downward through the bottom opening. 
     
     
         8 . The method of  claim 1 , wherein positioning the partial spherical head of the shank into the lower portion of the axial bore further comprises uploading the partial spherical head of the shank through the bottom opening. 
     
     
         9 . The method of  claim 8 ,
 wherein the partial spherical head of the shank and the bottom opening of the body member further comprise complementary threads formed therein, and   wherein uploading the partial spherical head of the shank through the bottom opening further comprises threading the partial spherical head of the shank upward through the bottom opening.   
     
     
         10 . A method of assembling a pivotal bone anchor assembly configured to secure a fixation rod to a bone of a patient with a closure, the method comprising:
 positioning a partial spherical head of a shank into a lower portion of an axial bore of a body member,
 the shank comprising a shank body having a longitudinal axis, the partial spherical head at a proximal end of the shank body, and an anchor portion opposite the partial spherical head configured for attachment to the bone, 
 the body member comprising a base defining the lower portion of the axial bore centered about a vertical centerline axis and communicating with a bottom of the base through a bottom opening, and a pair of upright arms extending upward from the base to define a channel configured to receive the fixation rod, the axial bore extending upwardly from the bottom opening through the channel to tops of the upright arms and including a lower interior surface disposed about the bottom opening, an internal closure mating structure adjacent the tops of the upright arms, and at least one downwardly facing surface formed into sidewalls of the axial bore between the lower interior surface and the tops of the upright arms; and 
   positioning a compression bushing into the axial bore until at least one outer surface of the compression bushing snaps under the at least one downwardly facing surface of the axial bore to inhibit the compression bushing from moving upward in the axial bore, the compression bushing comprising a central opening configured to provide access to the partial spherical head and a curved upper surface configured to receive the fixation rod,   wherein the lower interior surface of the axial bore supports of the partial spherical head of the shank within the body member with the shank extending downwardly through the bottom opening.   
     
     
         11 . The method of  claim 10 , wherein the compression bushing cooperates with the body member to exert a distal force towards the head to frictionally hold the head down within the body member prior to a locking of the assembly via the closure, so as to provide a friction fit articulatable relationship between the shank and the body member. 
     
     
         12 . The method of  claim 10 , wherein the lower interior surface of the axial bore further comprises an upward facing rounded surface that directly engages the partial spherical head of the shank to form a modified ball joint. 
     
     
         13 . The method of  claim 10 , wherein positioning the partial spherical head of the shank into the lower portion of the axial bore further comprises downloading the shank through the channel of the body member with the anchor portion passing downward through the bottom opening. 
     
     
         14 . The method of  claim 10 , wherein positioning the partial spherical head of the shank into the lower portion of the axial bore further comprises uploading the head of the shank through the bottom opening. 
     
     
         15 . The method of  claim 14 ,
 wherein the partial spherical head of the shank and the bottom opening of the body member further comprise complementary threads formed therein, and   wherein uploading the partial spherical head through the bottom opening further comprises threading the partial spherical head upward through the bottom opening.   
     
     
         16 . The method of  claim 10 ,
 wherein the at least one downwardly facing surface of the axial bore further comprise a pair of opposing downwardly facing surfaces on opposite sides of the axial bore, and   wherein the at least one outer surface of the compression bushing further comprises upper surfaces of a pair of opposite engagement structures protruding laterally outward from the bushing.   
     
     
         17 . The method of  claim 16 , wherein the opposing downwardly facing surfaces further comprise the upper surfaces of opposed apertures extending through the sidewalls of the bushing. 
     
     
         18 . The method of  claim 16 , wherein the pair of opposite engagement structures further comprise opposite resilient tabs at the upper ends of the compression bushing. 
     
     
         19 . A method of assembling a pivotal bone anchor assembly configured to secure a fixation rod to a bone of a patient with a closure, the method comprising:
 loading a head of a shank into an axial bore of a body member so the head is located in the axial bore while the shank extends distally through a bottom opening of the body member, the bottom opening extending between the axial bore and a bottom surface of the body member, the head being at least partially spherical and formed on a proximal end of the shank, the axial bore formed along a longitudinal axis of the body member and intersecting a channel of the body member adapted to receive the fixation rod, the axial bore including a proximal closure mating structure adapted to receive the closure, an inwardly protruding structure between the proximal closure mating structure and the bottom opening, and a distal interior surface adjacent the bottom opening supporting the head while allowing for pivotal movement of the shank relative to the body member; and   loading a compression bushing into the axial bore so the compression bushing is pressed at least partially past the inwardly protruding structure with an interference surface engagement between the compression bushing and the inwardly protruding structure to inhibit the head and the compression bushing from moving upward within the axial bore.   
     
     
         20 . The method of  claim 19 , wherein the compression bushing cooperates with the body member to exert a distal force towards the head to frictionally hold the head down within the body member prior to a locking of the assembly via the closure, so as to provide a friction fit articulatable relationship between the shank and the body member. 
     
     
         21 . The method of  claim 19 , wherein the distal interior surface of the axial bore further comprises an upward facing rounded surface that directly engages the head of the shank to form a modified ball joint. 
     
     
         22 . The method of  claim 19 , wherein loading the head of the shank into the axial bore of the body member further comprises downloading the shank through the channel of the body member with an anchor portion of the shank passing downward through the bottom opening. 
     
     
         23 . The method of  claim 19 , wherein loading the head of the shank into the axial bore of the body member further comprises uploading the head of the shank through the bottom opening. 
     
     
         24 . The method of  claim 23 ,
 wherein the head of the shank and the bottom opening of the body member further comprise complementary threads formed therein, and   wherein uploading the head of the shank through the bottom opening further comprises threading the head of the shank upward through the bottom opening.   
     
     
         25 . A method of assembling a pivotal bone anchor assembly configured to secure a fixation rod to a bone of a patient with a closure, the method comprising:
 loading a head of a shank into an axial bore of a body member so the head is located in the axial bore while the shank extends distally through a bottom opening of the body member, the bottom opening extending between the axial bore and a bottom surface of the body member, the head being at least partially spherical and formed on a proximal end of the shank, the axial bore formed along a longitudinal axis of the body member and intersecting a channel of the body member adapted to receive the fixation rod, the axial bore including a proximal closure mating structure adapted to receive the closure, a distal interior surface adjacent the bottom opening supporting the head while allowing for pivotal movement of the shank relative to the body member, and opposing hollow spaces with downwardly facing surfaces formed into sidewalls of the axial bore between the proximal closure mating structure and the bottom opening; and   loading a compression bushing into the axial bore until opposite engagement structures projecting outward from first and second arms of the compression bushing are respectively received in the opposed hollow spaces to inhibit the head and the compression bushing from moving upward within the axial bore, the first and second arms defining a curved upper surface therebetween adapted to receive the fixation rod.   
     
     
         26 . The method of  claim 25 , wherein the opposite engagement structures resiliently snap into the opposed hollow spaces during the loading of the compression bushing into the axial bore. 
     
     
         27 . The method of  claim 25 , wherein upper surfaces of the opposite engagement structures resiliently engage the downwardly facing surfaces of the hollow spaces to establish a pre-lock press fitment between a lower surface of the compression bushing and the head of the shank so that the shank and the body member do not move freely with respect to each other prior to insertion and securement of the fixation rod with the closure. 
     
     
         28 . The method of  claim 25 , wherein the lower interior surface of the axial bore further comprises an upward facing rounded surface that directly engages the head of the shank to form a modified ball joint. 
     
     
         29 . The method of  claim 25 , wherein loading the head of the shank into the axial bore of the body member further comprises downloading the shank through the channel of the body member with an anchor portion of the shank passing downward through the bottom opening. 
     
     
         30 . The method of  claim 25 ,
 wherein the head of the shank and the bottom opening of the body member further comprise complementary threads formed therein, and   wherein loading the head of the shank into the axial bore of the body member further comprises threading the head of the shank upward through the bottom opening.