Expandable Osteosynthesis Cage

Abstract

An expandable osteosynthesis implant has branches ( 5 ) each connected at one end to a seat ( 7 ) which is pierced by an orifice ( 8 ), suitable for being slid from a posterior direction between the facing faces of two consecutive vertebrae in order to hold them a given distance apart and restore stability of the spinal column. According to the invention, said branches ( 5 ) and said seat ( 7 ) define a hollow cage ( 1 ) which, in a “rest” position, has an outside general shape that is a cylinder of circular section, and a portion at least of the inside volume ( 9 ) of the cage ( 1 ) towards the distal ends of said branches ( 5 ) is in the form of a circular truncated cone whose large base is towards said seat ( 7 ) which implant has at least three branches ( 5 ) and, inside said inside volume ( 9 ) at least one spacer ( 2 ) suitable for passing through said orifice ( 8 ) and the large base of the truncated cone.

What is claimed is: 
     
         1 . An intervertebral spacing implant comprising:
 a seat having a proximal end, a distal end, and a plurality of flat planar surfaces between the proximal and distal ends;   a plurality of branches coupled to the distal end of the seat and extending in a distal direction away from the seat, the seat and the branches forming a cage defining an internal volume, each branch having an inward side and an outward side;   one or more spacers, each having a perimeter and a connector to removably couple to a spacer-advancing instrument, the one or more spacers configured to fit within the cage and move in the distal direction upon the urging of the spacer-advancing instrument, the one or more spacers and cage configured such that one or more branches will move from an unextended position to an extended position when the one or more spacers are urged in the distal direction; and   one or more shoulders formed on the inward side of one or more branches, the one or more shoulders configured to secure at least one of the one or more spacers near the distal end of the plurality of branches by resisting proximal movement of the at least one of the one or more spacers;   wherein (a) the internal volume between the distal end of the seat and at least one of the one or more spacers is unoccupied by a link member when the at least one of the one or more spacers is secured by the one or more shoulders and the spacer-advancing instrument is removed, (b) the cage is configured to allow insertion of graft material into the internal volume, (c) at least one of the one or more shoulders includes a portion non-collinear with the inward side of at least one of the one or more branches the one or more shoulders are formed on, and (d) at least one of the plurality of flat planar surfaces is coupled to, but not included within, a planar surface.