Polyaxial bone screw assembly

Abstract

A polyaxial bone screw assembly for capturing a rod includes a receiver, a threaded shank body having an upper capture portion mated with a retaining and articulating structure, a compression insert and a closure having a domed bottom. The closure captures and fixes the rod within the receiver between the domed bottom and the compression insert, the insert pressing on the retaining and articulating structure to fix such structure against the receiver.

1 . A closure for a bone screw assembly including a shank for implanting in a bone and a receiver joined with the shank and having an upper channel formed between a pair of arms each having a first inwardly facing helically wound flange form; the closure comprising:
 a) a generally cylindrical body with a bottom;   b) a driving structure for rotating the body;   c) a second outwardly facing helically wound flange form on the body sized and shaped to rotatably mate with the first flange forms on the receiver; and   d) the bottom of the closure having a downwardly projecting dome.   
     
     
         2 . The closure according to  claim 1  wherein the dome extends across the entire closure bottom. 
     
     
         3 . The closure according to  claim 1  in combination with the shank, receiver and rod. 
     
     
         4 . The closure according to  claim 3  wherein the shank and receiver are separate and polyaxially joined during positioning and thereafter locked by downward advancement of the closure relative to the receiver. 
     
     
         5 . A polyaxial bone screw assembly adapted to hold a rod and comprising:
 a) a shank having a lower threaded portion for implantation in a bone and an upper capture portion;   b) a receiver having an inner cavity operably and polyaxially receiving the shank upper portion during positioning; the receiver also having a pair of upstanding arms that have inwardly facing and helically wound first flange form guide and advancement structure forming a channel therebetween adapted to receive the rod; and   c) a closure having a cylindrical body with a helically wound second flange form guide and advancement structure thereon that is sized and shaped to operably mate with the first flange form guide and advancement structure upon rotation and to advance the closure downwardly through the channel so as to be adapted to apply downward pressure to the rod, the closure including a drive mechanism for operably rotating the closure, the closure body having a bottom that has a downwardly facing dome adapted for engaging the rod.   
     
     
         6 . The assembly according to  claim 5  including a retainer for joining with and polyaxially rotating with the shank upper portion in the cavity during positioning and holding the shank in the receiver; and a pressure insert positioned between the rod and the shank upper portion and transferring downward force from the rod to the shank so as to lock a position of the shank relative to the receiver when the closure is fully advanced. 
     
     
         7 . A polyaxial bone screw adapted to receive a rod and comprising:
 a) a shank having a lower threaded portion for implanting in a bone of a patient and an upper capture portion;   b) a receiver having an internal cavity that operably receives the shank capture portion; the receiver also having a pair of spaced upstanding arms forming a rod receiving channel therebetween and having inwardly facing first guide and advancement structures thereon;   c) a compression structure operably positioned above the shank and including a cradle having a U-shaped seating surface sized and shaped to receive the rod; the seating surface having a lowest rod receiving linear portion that remains perpendicular to a central vertical axis of the receiver as the compression structure moves vertically relative to the receiver, whereby the rod is received in the receiver so as to be perpendicular to the central axis of the receiver; and   d) a closure having a generally cylindrical body and a bottom with a second guide and advancement structure thereon that rotatably mates with the first guide and advancement structure on the receiver arms; the closure bottom having a downwardly facing and rod engaging dome.   
     
     
         8 . The bone screw assembly according to  claim 7  including a retainer that joins with the shank capture portion in the receiver to polyaxially rotate with the shank in the receiver during positioning and that holds the shank in the receiver, the compression structure engaging and applying downward locking force directly to the retainer and not directly to the shank as the closure is advanced downwardly between the arms and against the rod. 
     
     
         9 . The bone screw according to  claim 8  wherein the shank and the retainer both polyaxially rotate together relative to both the compression structure and the receiver during positioning. 
     
     
         10 . A spinal bone anchor assembly for cooperation with a rod having a radius, the assembly comprising:
 a) a shank having a lower portion for implanting into bone and an upper portion;   b) a receiver communicating with the shank, the receiver having an inner cavity operably and polyaxially receiving the shank upper portion during positioning, the receiver also having a pair of upstanding arms, each arm having a partial inwardly facing first helical guide and advancement structure thereon, the arms forming a rod receiving channel;   c) a compression structure located within the receiver cavity and movable therein during positioning, the compression structure having a seating surface with a second radius sized and shaped for receiving the rod at the first radius; and   d) a closure having an outer second helically wound guide and advancement structure thereon sized and shaped for operably mating with the first guide and advancement structure upon rotation of the closure between the receiver arms and into the rod receiving channel, the closure having a downwardly directed domed rod engaging surface, the closure rod engaging surface operatively pressing downwardly on the rod and fixing the rod between the closure and the compression structure seating surface.   
     
     
         11 . In a bone anchor assembly having a shank pivotal with respect to a head defining a cavity and a lower opening, the shank further having a bone implanting portion integral with an upper portion, the bone implanting portion extending through the head lower opening, the upper portion located within the head cavity and moveable with respect to the head during positioning of the shank with respect to the head prior to fixing an angle of orientation of the shank with respect to the head, the head further having opposed upright arms defining a channel for receiving a length of a rod, the channel communicating with the cavity, the upright arms having an inner first helically wound guide and advancement structure thereon, the assembly further having a compression structure located within the cavity and a closure structure having a second guide and advancement structure thereon for rotating mating engagement with the first guide and advancement structure, the improvement wherein:
 a) the closure structure has a base with a downwardly directed domed surface; and   b) the compression structure has an outer cylindrical surface defined by an outer diameter, the compression structure further comprising a rod seating surface, the seating surface having a width substantially equal to the outer diameter, the seating surface width extending in a direction along the length of the rod, the compression structure being movable within the head cavity during positioning of the shank with respect to the head prior to fixing of the angle of the shank with respect to the head, the closure structure domed surface pressing downwardly on the rod and fixing the rod against the compression structure seating surface when the angle of the shank is fixed with respect to the head.   
     
     
         12 . In a bone anchor assembly having a shank connected to a head defining a cavity and a lower opening, the shank further having a bone implanting portion integral with an upper portion, the bone implanting portion extending through the head lower opening, the upper portion located within the head cavity, the head further having opposed upright arms defining a channel for receiving a length of a rod, the channel communicating with the cavity, the upright arms having an inner first helically wound guide and advancement structure thereon, the assembly further having a compression structure located within the cavity and a closure structure having a second guide and advancement structure thereon for rotating mating engagement with the first guide and advancement structure, the improvement wherein:
 a) the closure structure has a base with a downwardly directed domed surface; and   b) the compression structure has opposed outer peripheral surfaces defined by a width in the direction of the length of the rod, the compression structure further comprising a rod seating surface, the seating surface having a width substantially equal to the width between the outer peripheral surfaces, the seating surface width thereby more fully supporting the length of the rod, the compression structure being movable within the head cavity during positioning of the shank with respect to the head prior to fixing of the rod with respect to the head, the closure structure domed surface pressing downwardly on the rod and fixing the rod against the entire width of the compression structure seating surface when the rod is fixed with respect to the head.   
     
     
         13 . In a polyaxial bone screw having a shank for implanting in a bone, a receiver with a cavity that operably receives an upper portion of the shank and upward extending first arms forming a channel therebetween adapted to receive a connecting member, the first arms having top surfaces, a compression insert operably positioned above and in direct contact with an upper end of the shank and including upward extending second arms that extend around and above the connecting member when the connecting member is in the channel, the improvement wherein the closure comprises:
 a) an outer fastener having a through bore with an internal surface guide and advancement thread;   b) an inner set screw having an outer surface guide and advancement thread and a bore with a central axis opening onto a top surface of the inner set screw, the bore terminating at a bottom tool engagement abutment surface, said abutment surface having a central axis secondary bore communicating with the exterior terminating on a bottom surface of the inner set screw, the inner set screw being threadedly received in the outer fastener;   c) the inner set screw in a final position located beneath the top surfaces of the receiver arms.   
     
     
         14 . The improvement according to  claim 13 , wherein the outer fastener engages the compression insert second arms to provide for downward application of force to the shank from the insert to allow independent locking of the shank relative to the receiver without locking the position of the connecting member relative to the receiver. 
     
     
         15 . The improvement according to  claim 13 , wherein the closure outer fastener has a top surface that is substantially flush with a top surface of the upright arms of the receiver. 
     
     
         16 . The improvement according to  claim 13 , wherein the inner set screw in the final position is positioned extends below a bottom surface of the outer fastener. 
     
     
         17 . In a polyaxial bone screw having a shank for implanting in a bone, a receiver with a cavity that operably receives an upper portion of the shank and upward extending first arms forming a channel therebetween adapted to receive a connecting member, the first arms having top surfaces, a compression insert operably positioned above and in direct contact with an upper end of the shank and including upward extending second arms that extend around and above the connecting member when the connecting member is in the channel, the improvement wherein the closure comprises:
 a) an outer fastener having a through bore with an internal surface guide and advancement thread and being positioned entirely within the arms of the receiver such that a top surface of the outer fastener is flush with the top surfaces of the receiver first pair of arms;   b) an inner set screw having an outer surface guide and advancement thread and a bore with a central axis opening onto a top surface of the inner set screw, the bore terminating at a bottom tool engagement abutment surface, said abutment surface having a central axis secondary bore communicating with the exterior terminating on a bottom surface of the inner set screw, the inner set screw being threadedly received in the outer fastener;   c) the inner set screw in a final position located beneath the top surfaces of the receiver arms.   
     
     
         18 . The improvement according to  claim 17 , wherein the outer fastener engages the compression insert second arms to provide for downward application of force to the shank from the insert to allow independent locking of the shank relative to the receiver without locking the position of the connecting member relative to the receiver. 
     
     
         19 . The improvement according to  claim 17 , wherein the inner set screw further comprises a bottom surface, and wherein in the final position, the inner set screw bottom surface extends below a bottom surface of the outer fastener. 
     
     
         20 . The improvement according to  claim 19 , wherein the bottom surface of the inner set screw is flat. 
     
     
         21 . In a polyaxial bone screw having a shank for implanting in a bone, a receiver with a cavity that operably receives an upper portion of the shank and upward extending first arms forming a channel therebetween adapted to receive a connecting member, the first arms having top surfaces, a compression insert operably positioned above and in direct contact with an upper end of the shank and including upward extending second arms that extend around and above the connecting member when the connecting member is in the channel, the improvement wherein the closure comprises:
 a) an outer fastener having a through bore with an internal surface guide and advancement thread and being positioned entirely within the arms of the receiver such that a top surface of the outer fastener is flush with the top surfaces of the receiver first pair of arms;   b) an inner set screw having an outer surface guide and advancement thread, the inner set screw being threadedly received in the outer fastener;   c) the inner set screw in a final position located beneath the top surfaces of the receiver arms and the top surface of the outer fastener.   
     
     
         22 . The closure according to  claim 21 , wherein the outer fastener engages the compression insert second arms to provide for downward application of force to the shank from the insert to allow independent locking of the shank relative to the receiver without locking the position of the connecting member relative to the receiver. 
     
     
         23 . The closure according to  claim 21 , wherein the inner set screw further comprises a bottom surface, and wherein in the final position, the inner set screw bottom surface extends below a bottom surface of the outer fastener. 
     
     
         24 . The closure according to  claim 23 , wherein the bottom surface of the inner set screw is flat. 
     
     
         25 . The closure according to  claim 23 , wherein the bottom surface of the inner set screw is dome shaped. 
     
     
         26 . A medical implant bone screw including:
 a) a shank adapted to be implanted in a bone at a lower end and having an upper end;   b) a receiver structure located at the shank upper end; the receiver having a first pair of upright arms forming a channel therebetween adapted to receive a connecting member, the upright arms having a top surface;   c) a lower compression member positioned below and around the connecting member and having a second pair of upright arms that are sized and shaped to extend above the connection member; the lower compression member engaging the shank; and   d) a closure having an outer ring that is positioned entirely within and threadably securable to an inner side of the receiver first pair of upright arms; the closure having an inner set screw threadably secured and advanced in the outer ring and relative to the receiver, wherein the inner set screw is positioned beneath the top surface of the receiver.