Spinal fixation system

Abstract

A clamp assembly for securing a bone anchor to a generally cylindrical rod. The clamp assembly includes a first portion, a second portion and a compressible ball carried by the second portion, the ball having a through hole for receiving the generally cylindrical rod. The first portion includes first and second flanges, each of the first and second flanges defining an aperture for receiving a portion of the bone anchor. The first and second flanges are movable from a first position in which the first and second flanges are separated by a gap to a second position in which the first and second flanges are drawn toward each other. The first and second flanges include first and second opposing surfaces, respectively, the first and second opposing surfaces being angled relative to one another in the first position.

1 . A clamp assembly for securing a bone anchor to a generally cylindrical rod, the clamp assembly comprising: 
 a first portion including first and second spaced apart flanges, the first and second spaced apart flanges both defining apertures for receiving a portion of the bone anchor, wherein the first and second flanges include first and second opposing surfaces, respectively, the first and second opposing surfaces being angled relative to one another before the first and second flanges are drawn toward one another;    a second portion; and    a compressible ball carried by the second portion, the ball having a through hole for receiving the generally cylindrical rod.    
     
     
         2 . The clamp assembly of  claim 1 , wherein the through hole defined by a generally cylindrical inner surface has at least one relieved channel.  
     
     
         3 . The clamp assembly of  claim 1  in combination with the bone anchor, the bone anchor having an upper threaded portion extendable through the apertures of the first and second flanges and engaging a nut such that tightening of nut draws the first and second flanges toward one another and the second portion compresses the ball.  
     
     
         4 . The clamp assembly of  claim 3 , wherein the first and second opposing surfaces are generally parallel to one another when the nut is tightened.  
     
     
         5 . The clamp assembly of  claim 4 , wherein the second portion circumferentially surrounds the ball substantially completely when the first and second flanges are drawn together.  
     
     
         6 . The clamp assembly of  claim 1 , wherein the generally cylindrical surface includes a plurality of relieved channels.  
     
     
         7 . The clamp assembly of  claim 6 , wherein the plurality of relieved channels extend generally parallel to an elongated axis of the rod.  
     
     
         8 . The clamp assembly of  claim 1 , wherein the compressible ball and the second portion of the clamp assembly define a ball and socket joint such that the rod is permitted to pivot relative to the clamp assembly about a center of the ball.  
     
     
         9 . A clamp assembly for securing a bone anchor to a generally cylindrical rod, the clamp assembly comprising: 
 a first portion including first and second flanges, each of the first and second flanges defining an aperture for receiving a portion of the bone anchor, the first and second flanges movable from a first position in which the first and second flanges are separated by a gap to a second position in which the first and second flanges are drawn toward each other, the first and second flanges including first and second opposing surfaces, respectively, the first and second opposing surfaces being angled relative to one another in the first position;    a second portion; and    a compressible ball carried by the second portion, the ball having a through hole for receiving the generally cylindrical rod.    
     
     
         10 . The clamp assembly of  claim 9 , in which the first and second opposing surfaces are generally parallel to one another in the second position.  
     
     
         11 . The clamp assembly of  claim 10 , wherein the second portion circumferentially surrounds the ball substantially completely when the first and second flanges are in the second position.