Low profile spinal prosthesis incorporating a bone anchor having a deflectable post and a compound spinal rod

Abstract

A spine stabilization prosthesis which supports the spine while providing for the preservation of spinal motion. The spine stabilization prosthesis incorporates a bone anchor having a deflectable post and a compound spinal rod which provide for load sharing while preserving range of motion and reducing stress exerted upon the bone anchors and spinal anatomy. The bone anchor includes a deflectable post connected by a ball-joint to a bone screw. The compound spinal rod includes a coupling mounted to the deflectable post and connected by a pivoting joint to a rod. The combined motions of the ball-joint and the pivoting joint support a range of motion of adjacent vertebrae which closely approximates the natural range of motion of the spine.

1 . A dynamic spine stabilization device comprising:
 a bone screw having a longitudinal axis, a proximal end and a distal end;   the distal end of the bone screw being adapted to engage a vertebra;   the proximal end of the bone screw having a housing;   a bore in the housing, the bore having an open end and a closed end and the closed end of the bore terminating in a pocket;   an elongated deflectable post;   a retainer at a first end of the deflectable post,   wherein the deflectable post is received in the bore such that the retainer is positioned within the pocket and a second end of the deflectable post extends through the open end of the bore;   the bore having a limit surface arranged at a first angle relative to the longitudinal axis of the bone screw and positioned to contact the deflectable post over an area when the deflectable post pivots through said first angle from alignment with the longitudinal axis of the bone screw; and wherein the limit surface is frusto-conical in shape; and   the housing securing the retainer of the deflectable post in the pocket of the housing such that the retainer can pivot within the pocket.   
     
     
         2 . The spine stabilization device of  claim 1 , wherein deflection of said deflectable post beyond said first angle requires a significantly larger load per unit of deflection than deflection of said post up to said first angle. 
     
     
         3 . The spine stabilization device of  claim 1 , wherein:
 said deflectable post and said retainer are made in one piece; and   said housing and bone screw are made in one piece.   
     
     
         4 . The spine stabilization device of  claim 1 , wherein said deflectable post and said retainer are made of cobalt chrome alloy. 
     
     
         5 . The spine stabilization device of  claim 1 , further comprising a compound spinal rod mounted to the second end of the deflectable post wherein the compound spinal rod comprises a coupling connected by a pivoting joint to a rod; and
 wherein the deflectable post retains the ability to pivot relative to the bone screw with the compound spinal rod mounted to the second end of the deflectable post.   
     
     
         6 . The spine stabilization device of  claim 5 , wherein:
 a first end of the coupling is mounted in fixed relationship to the second end of the deflectable post; and   a second end of the coupling is connected by the pivoting joint to the rod.   
     
     
         7 . The spine stabilization device of  claim 6 , wherein the coupling comprises a dogleg connector positioned between the first end of the coupling and the second end of the coupling. 
     
     
         8 . The spine stabilization device of  claim 7 , wherein:
 the coupling has, at the first end, a bore adapted to mounting the coupling in fixed relationship to the post; and   the coupling has, at the second end, a clevis adapted to receive the rod; and   wherein a pin passes through the clevis and the rod to form the pivoting joint.   
     
     
         9 . The spine stabilization device of  claim 8 , wherein the pivoting joint has an axis which is perpendicular to a longitudinal axis of the deflectable post and offset from the longitudinal axis of the deflectable post. 
     
     
         10 . A spine stabilization device comprising:
 a bone screw having a longitudinal axis, a distal end adapted to engage a bone and a proximal end;   a deflectable post having a distal end and a proximal end;   the distal end of the deflectable post being connected by a joint to the proximal end of the bone screw;   the proximal end of the deflectable post being connected to a first end of a coupling;   a second end of the coupling being connected by a pivoting joint to a rod; and   wherein the joint allows the deflectable post to pivot relative to the bone screw including after attachment of the rod to the deflectable post by the coupling.   
     
     
         11 . The spine stabilization device of  claim 10 ,
 wherein said bone screw has a housing that includes said joint; and   wherein said housing has a frusto-conically shaped limit surface arranged at a first angle relative to the longitudinal axis of the bone screw and positioned to contact the deflection post over an area when the deflection post pivots through said first angle from alignment with the longitudinal axis of the bone screw.   
     
     
         12 . The spine stabilization device of  claim 11 , wherein the coupling comprises a dogleg connector positioned between the first end and the second end. 
     
     
         13 . The spine stabilization device of  claim 12 , wherein the pivoting joint permits the rod to pivot about an axis perpendicular to a longitudinal axis of the deflectable post and offset from the longitudinal axis of the deflectable post. 
     
     
         14 . The spine stabilization device of  claim 13 , further comprising a limit surface associated with the bone screw and arranged at a first angle relative to the longitudinal axis of the bone screw and positioned to contact the deflectable post over an area after a first angle of pivoting of the deflectable post away from alignment with the longitudinal axis of the bone screw. 
     
     
         15 . A dynamic spine stabilization device comprising:
 an elongated bone anchor having a longitudinal axis, a distal end and a proximal end;   a post having a distal end and a proximal end;   a joint which secures the distal end of the post to the proximal end of the bone anchor such that the post can pivot relative to the bone anchor;   a tubular extension of the bone anchor which extends over a distal portion of the post;   a limit surface associated with the tubular extension and arranged at a first angle relative to the longitudinal axis of the bone anchor and positioned to contact the post over an area when the post pivots through a first angle from alignment with the bone anchor, wherein the limit surface is frusto-conical in shape; and   wherein the limit surface resists pivoting of said post beyond said first angle.   
     
     
         16 . The spine stabilization device of  claim 15 , further comprising a compound spinal rod mounted to the proximal end of the post wherein the compound spinal rod having a coupling connected by a pivoting joint to a rod, and
 wherein the post retains the ability to pivot relative to the elongated bone anchor with the compound spinal rod mounted to the proximal end of the deflectable post.   
     
     
         17 . The spine stabilization device of  claim 16 , wherein:
 a first end of the coupling is mounted in fixed relation ship to the post; and   a second end of the coupling is connected by the pivoting joint to the rod.   
     
     
         18 . The spine stabilization device of  claim 17 , wherein the coupling comprises a dogleg connector between the first end of the coupling and the second end of the coupling. 
     
     
         19 . The spine stabilization device of  claim 16 , wherein:
 the coupling has, at the first end, a bore adapted to mount the coupling in fixed relationship to the post; and   the coupling has, at the second end, a clevis adapted to receive the rod; and   wherein a pin passes through the clevis and the rod to form the pivoting joint.   
     
     
         20 . The spine stabilization device of  claim 15 , wherein:
 said tubular extension comprises a cap securely mounted to the proximal end of the bone anchor; and   the cap having a bore therethrough.