Semirigid linking piece for stabilizing the spine

Abstract

The invention concerns a linking piece designed to maintain a spacing between at least two anchoring elements screwed into vertebrae. The piece comprises at least: a flexible part ( 10 ) divided into two branches ( 12, 14 ), the ends of said branches being interconnected in pairs and defining a first neutral plane (Pm), and, two rigid parts ( 20, 22 ) forming rods, having a first fixing C portion ( 20′, 22′ ) and a second fixing portion ( 20″, 22″ ), each said second portion ( 20″, 22″ ) of said rigid parts ( 20, 22 ) extending respectively in two opposite directions said ends of said branches interconnected in pairs, such that said linking piece, whereof the fixing portions ( 20′, 22′ ) are respectively fixed on each of the anchoring elements is designed to bend elastically perpendicularly to said neutral plane (Pm).

1 . A connecting member for maintaining the spacing between at least two anchor members screwed into vertebrae, the connecting member being characterized in that it comprises: 
 a flexible part divided into two spaced continuous branches that are substantially symmetrical about a longitudinal axis of said member, the ends of said branches being interconnected in pairs and defining a first median plane, and    two rigid rod-forming parts each having a fixing first portion and a second portion, each of said second portions of said two rigid parts respectively extending said ends of said branches interconnected in pairs in opposite directions, the cross-section of each of said branches being less than the cross-section of said rigid parts so that said connecting member, said fixing portions of which are fixed to respective anchor members, is able to bend elastically about an axis that is perpendicular to the longitudinal axis, said perpendicular axis being contained in said median plane of the connecting member on relative movement of the vertebrae, whereby the vertebrae, which are held spaced relative to each other, are movable relative to each other.    
     
     
         2 . A connecting member according to  claim 1 , adapted to interconnect n anchor members, the connecting member being characterized in that it comprises n rigid parts between which there are disposed n−1 flexible parts along the longitudinal axis of said member, each rigid part situated between two flexible parts having a first or fixing portion and two second portions, each of said second portions being situated at a respective end of said first or fixing portion, said second portions extending respective ends of the branches of said two flexible parts so that the median planes of all the flexible parts are substantially the same, and in that the rigid parts situated at the ends of said member have respective single second portions extending the ends of the branches of the flexible parts.  
     
     
         3 . A connecting member according to  claim 1  or  claim 2 , characterized in that the sum of the surface areas of the sections of said two branches is less than the surface area of the section of said rigid rod-forming parts.  
     
     
         4 . A connecting member according to any one of  claims 1  to  3 , characterized in that said branches have portions parallel to each other and to the longitudinal axis of said member and in that the distance between said branches is at least equal to the length of said portions.  
     
     
         5 . A connecting member according to  claim 4 , characterized in that the distance between the ends of said branches connected in pairs lies in the range 1.5 times to 2.5 times the distance between said branches.  
     
     
         6 . A connecting member according to any one of  claims 1  to  5 , characterized in that the section of said rigid rod-forming parts is circular.  
     
     
         7 . A connecting member according to any one of  claims 1  to  6 , characterized in that it is made of titanium alloy.  
     
     
         8 . A vertebral stabilization system for fastening together at least two vertebrae each having a median plane substantially perpendicular to the axis of the spine of which they are part and a posterior wall defining a posterior median plane of said spine, said system comprising at least two anchor members each adapted to be fixed into the posterior wall of a vertebra so that a line which intersects said two anchor members is substantially parallel to said axis of the spine, 
 the system being characterized in that it further comprises a connecting member according to any one of  claims 1  to  7  whose two rigid parts are adapted to interconnect said two anchor members so that said median plane defined by said two branches is substantially parallel to said posterior median plane of said spine, whereby said vertebrae, which are interconnected in their posterior portions, are relatively movable along said axis of said spine.