Pivotal bone anchor assembly with insert configured for forced downward displacement by tooling

Abstract

A medical implant assembly includes a shank having a head and an anchor portion, and a receiver having a base defining a central bore for receiving the shank head through a bottom opening and an upper portion defining a channel for receiving an elongate rod. The central bore extends upwardly to a closer mating structure adjacent the top of the receiver and an inwardly-protruding horizontal ridge below the closure mating structure. The assembly also includes an insert having a saddle surfacing for receiving the elongate rod, a lower surface for engaging the shank head, and outward-facing side surfaces adjacent upward-facing top edge surfaces. The insert is initially positionable into the central bore with the outward facing side surfaces in an overlapping arrangement with the horizontal ridge to maintain the position of the insert within the receiver prior to uploading the shank head.

What is claimed is: 
     
         1 . A medical implant assembly for securing an elongate rod to a bone of a patient via tooling and a closure top, the medical implant assembly comprising:
 a shank comprising a longitudinal axis, a head at a proximal end, and a body extending distally from the head with an anchor portion configured for anchoring to the bone;   a receiver comprising a base defining a lower portion of a central bore centered about a vertical centerline axis and configured to receive the head of the shank uploadable through a bottom opening in the base, and an upper portion defining a channel configured to receive the elongate rod, the central bore communicating with a bottom of the receiver through the bottom opening and extending upward through the channel to a top of the receiver and including a closure mating structure adjacent the top of the receiver configured to mate with the closure top, an expansion chamber above the bottom opening, and a discontinuous horizontal ridge protruding inwardly and extending at least partially circumferentially around the central bore between the expansion chamber and the closure mating structure;   an insert positionable into the central bore of the receiver prior to the head of the shank, the insert having an upward-facing saddle surface configured to engage the elongate rod, a downward-facing surface configured to engage the head of the shank, and outward-facing side surfaces adjacent upward-facing top edge surfaces, the outward-facing side surfaces configured for a first overlapping arrangement with the horizontal ridge so as to at least partially hold the insert in the channel of the receiver;   a retainer uploadable through the bottom opening of the receiver and at least partially positionable within the lower portion of the central bore below the insert,   wherein after the head of the shank is uploaded into the lower portion of the central bore and captured by a resilient expansion of the retainer within the expansion chamber, the insert is configured for forced downward displacement within the central bore via direct engagement from the tooling so as to move the downward-facing surface of the insert into engagement with the head of the shank and the upward-facing top edge surfaces into a second overlapping arrangement with the horizontal ridge so as to inhibit the insert from moving back up within the central bore of the receiver.   
     
     
         2 . The medical implant assembly of  claim 1 , wherein the second overlapping arrangement between the discontinuous horizontal ridge and the upward-facing top edge surfaces of the insert is an overlapping interference engagement configured to bias the downward-facing surface of the insert against the head of the shank to establish a non-floppy friction fit between the shank and the receiver prior to securing the elongate rod within the channel with the closure top. 
     
     
         3 . The medical implant assembly of  claim 1 , wherein when the head of the shank is captured by the retainer, the shank and the retainer are pivotal with respect to the receiver. 
     
     
         4 . The medical implant assembly of  claim 1 , wherein the first overlapping arrangement between outward-facing side surfaces of the insert and the horizontal ridge is configured to inhibit downward displacement of the insert prior to the forced downward displacement by the tooling. 
     
     
         5 . The medical implant assembly of  claim 1 , wherein the receiver further includes a discontinuous downward-facing stop surface formed into the central bore between the horizontal ridge and the closure mating structure and configured for overlapping arrangement with the upward-facing top edge surfaces of the insert to prevent the insert from moving upwards within the central bore. 
     
     
         6 . The medical implant assembly of  claim 1 , wherein the insert is uploadable through the bottom opening into the central bore of the receiver. 
     
     
         7 . The medical implant assembly of  claim 6 , wherein the receiver further includes guide surfaces formed into the central bore between the expansion chamber and the closure mating structure and configured to slidably engage with cut-out portions of the insert upon the uploading of the insert into the central bore to prevent rotation of the insert relative to the receiver. 
     
     
         8 . The medical implant assembly of  claim 1 , wherein the outward-facing side surfaces of the insert further comprises a groove configured to receive the horizontal ridge prior to the forced downward displacement of the insert within the central bore of the receiver. 
     
     
         9 . The medical implant assembly of  claim 1 , wherein the insert further comprises a cylindrical base portion having a central aperture and a pair of insert arms extending upwardly from the cylindrical base portion to define the upward-facing saddle surface therebetween. 
     
     
         10 . The medical implant assembly of  claim 1  and further comprising the elongate rod and the closure top, wherein the closure top is configured for positioning entirely within the central bore of the receiver above the elongate rod and in engagement with the closure mating structure to apply a downward pressure to a top of the elongate rod, so as to secure the elongate rod to the bone of the patient. 
     
     
         11 . A medical implant assembly for securing an elongate rod to a bone of a patient via tooling and a closure top, the medical implant assembly comprising:
 a shank comprising a longitudinal axis, a head portion at a proximal end, and a body extending distally from the head with an anchor portion configured for anchoring to the bone;   a receiver comprising a base defining a lower portion of central bore with a bottom opening centered about a vertical centerline axis and configured to receive the head portion of the shank positionable therein through the bottom opening, and an upper portion above the base defining a channel configured to receive the elongate rod, the central bore communicating with a bottom of the base through the bottom opening and extending upward through the channel to a top of the receiver and including a closure mating structure adjacent the top of the receiver configured to mate with the closure top and a horizontal ridge protruding inwardly and extending at least partially circumferentially around the central bore between the bottom opening and the closure mating structure;   an insert uploadable through the bottom opening into the central bore of the receiver prior to the head portion of the shank, the insert having an upper saddle surface engageable with the elongate rod positionable in the channel, a downward-facing surface configured to engage the head of the shank, and outward-facing side surfaces adjacent upward-facing top edge surfaces, the outward-facing side surfaces configured for a first overlapping engagement with the horizontal ridge so as to at least partially hold the insert in the channel of the receiver in a first position,   wherein the insert is configured for downward displacement within the central bore via direct force from the tooling so as to be moved into a second position lower than the first position in which the upward-facing top edge surfaces of the insert are in a second overlapping engagement with the horizontal ridge of the central bore to inhibit the insert from moving back up therein, and the downward-facing surface of the insert is in engagement with the head portion of the shank.   
     
     
         12 . The medical implant assembly of  claim 11 , wherein the second overlapping engagement between the horizontal ridge and the upward-facing top edge surfaces of the insert is an overlapping frictional engagement configured to bias the downward-facing surface of the insert against the head portion of the shank to establish a non-floppy friction fit between the shank and the receiver prior to securing the elongate rod within the channel with the closure top. 
     
     
         13 . The medical implant assembly of  claim 11 , wherein the receiver further includes a discontinuous downward-facing stop surface formed into the central bore between the horizontal ridge and the closure mating structure and configured for overlapping engagement with the upward-facing top edge surfaces of the insert to prevent the insert from moving upwards within the central bore. 
     
     
         14 . The medical implant assembly of  claim 11 , wherein receiver further includes guide surfaces formed into the central bore between the expansion chamber and the closure mating structure and configured to slidably engage with cut-out portions of the insert upon the uploading of the insert into the central bore to prevent rotation of the insert relative to the receiver. 
     
     
         15 . The medical implant assembly of  claim 11 , wherein the outward-facing side surfaces of the insert include a groove configured to receive the horizontal ridge prior to the forced downward displacement of the insert within the central bore of the receiver. 
     
     
         16 . The medical implant assembly of  claim 11  and further comprising a retainer uploadable through the bottom opening prior to the head portion of the shank and configured to capture and hold the head portion of the shank within the lower portion of the central bore, wherein when the head portion of the shank is captured by the retainer, the shank and the retainer are pivotal with respect to the receiver. 
     
     
         17 . The medical implant assembly of  claim 11  and further comprising the elongate rod and the closure top, wherein the closure top is configured for positioning entirely within the central bore of the receiver above the elongate rod and in engagement with the closure mating structure to apply a downward pressure to a top of the elongate rod, so as to secure the elongate rod to the bone of the patient. 
     
     
         18 . A method of assembling a medical implant assembly configured for securing an elongate rod to a bone of a patient via tooling and a closure top, the method comprising:
 positioning an insert into a central bore of a receiver prior to a head of a shank, the insert including an upward-facing saddle surface configured to engage the elongate rod and outward-facing side surfaces adjacent upward-facing top edge surfaces, the receiver including a base defining a lower portion of the central bore centered about a vertical centerline axis and configured to receive the head of the shank uploadable into the central bore through a bottom opening in the base, and an upper portion defining a channel configured to receive the elongate rod;   establishing a first overlapping arrangement between the outward-facing side surfaces of the insert and a discontinuous horizontal ridge of the central bore of the receive so as to maintain the insert in the channel of the receiver, the central bore communicating with a bottom of the receiver through the bottom opening and extending upward through the channel to a top of the receiver and including a closure mating structure adjacent the top of the receiver configured to mate with the closure top, an expansion chamber above the bottom opening, and the discontinuous horizontal ridge protruding inwardly and extending at least partially circumferentially around the central bore between the expansion chamber and the closure mating structure;   uploading a retainer into the bottom opening of the receiver; and   positioning the retainer at least partially within the central bore below the insert.   
     
     
         19 . The method of  claim 18 , wherein positioning the insert into the central bore of the receiver further comprises uploading the insert through the bottom opening in the base of the receiver. 
     
     
         20 . The method of  claim 18 , further comprising uploading the head of the shank into the central bore through the bottom opening of the receiver, wherein the shank includes a longitudinal axis, the head at a proximal end, and a body extending distally from the head with an anchor portion configured for anchoring to the bone. 
     
     
         21 . The method of  claim 18 , wherein after the head of the shank is uploaded into the bottom opening of the receiver and captured by a resilient expansion of the retainer within the expansion chamber, the insert is configured for forced downward displacement within the central bore via direct engagement from the tooling so as to come into engagement with the head of the shank, and with the upward-facing top edge surfaces of the insert entering into a second overlapping arrangement with the horizontal ridge so as to inhibit the insert from moving back up within the central bore of the receiver.