Abstract:
A implant for a cervical vertebra comprises two branches adapted to extend respectively substantially along the two cervical laminae of a given cervical vertebra that have been spaced apart from each other after osteotomy of the laminae, and a rigid body interconnecting the two branches.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to cases of compression syndrome in the spine of the neck. 
     Compression syndrome in the cervical vertebrae can arise because of injury or of malformation. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a device for responding to cases of compression syndrome. 
     In order to achieve this object, the invention provides an implant for a cervical vertebra, the implant comprising two branches adapted to extend respectively substantially along the two cervical laminae of a given cervical vertebra that have been spaced apart from each other after osteotomy of the laminae, and a rigid body interconnection the two branches. 
     Thus, after osteotomy of the cervical laminae and after they have been spread rearwards, the branches of the implant can be fixed to the respective laminae to hold them apart, thereby putting an end to compression on the cavity. 
     Advantageously, the implant has a deformable link between the body and at least one of the branches. 
     Thus, the implant adapts appropriately to the morphology of the vertebra. 
     Advantageously, the link is elastically flexible. 
     Advantageously, the body has a zone of thickness that is reduced compared with the thickness of the remainder of the body and that defines the link. 
     Advantageously, the body is generally curved in shape, having a center of curvature situated on the same side as the branches. 
     Thus, the size of the implant is matched to the shape of the cavity. 
     Advantageously, the body has a curved inner face situated facing the branches and an outer face opposite from the branches, the inner face having curvature with a center of curvature that is situated on the same side as the branches and a radius of curvature that is smaller than the radius of curvature of the outer face. 
     Here again, the shape of the implant leaves the necessary volume for the cavity. 
     Advantageously, at least one of the branches has portions in relief. 
     Advantageously, the portions in relief form abutments preventing link elements that extend substantially perpendicularly to the longitudinal direction of the branch from moving along the branch. 
     This facilitates fixing the branches to the laminae and increases the lifetime of the fixings. 
     Advantageously, the portions in relief comprise notches. 
     Advantageously, the branches are suitable for being engaged in holes formed in the cervical laminae, and the portions in relief comprise barb-forming teeth. 
     Advantageously, the branch is of a width measured between the tips of the teeth that tapers towards the free end of the branch. 
     Advantageously, the portions in relief extend over two opposite longitudinal faces of the branch. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages of the invention will appear further on reading the following description of two preferred embodiments given as non-limiting examples. In the accompanying drawings: 
     FIGS. 1 and 2 are an elevation view and a side view of an implant constituting a first embodiment of the invention; 
     FIG. 3 is a view of the FIG. 1 implant installed on a vertebrae; and 
     FIGS. 4 and 5 are two views analogous to FIGS. 1 and 2 of an implant constituting a second embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIGS. 1 and 2, in a first embodiment, the implant  2  is generally in the form of a flat elongate bar having two plane faces  4  and  6  that are opposite each other, the bar being bent to give it a U-shape that comprises two branches  10  and a body  8  interconnecting the two branches. The bar is bent about two axes, corresponding to the bends, and parallel to the plane faces  4  and  6  which can thus be referred to respectively as the inner face and as an outer face. The implant has an axis of symmetry  12  passing through the middle of the body  8 . The two branches  10  slope outwards, each away from said axis  12 . The body  8  and the two branches  10  are of about the same length. 
     The shape of the body  8  is generally curved, having a center of curvature situated on the axis  12  and on the same side as the branches  10 . An inside face  14  of the body has a radius of curvature that is smaller than the radius of curvature of an outside face  16  of the body opposite therefrom. The body  8  has two link zones  18  at its respective ends which are contiguous with the branches  10 . The two zones  18  are of reduced thickness, i.e. they present thickness that is less than the thickness of the remainder of the body. Each of them provides an elastically flexible deformable link between the body  8  and a respective branch  10 . These zones  18  of reduced thickness are defined by depressions in the inner face  4  serving to provide spaces for receiving the ends of the laminae of the vertebra. 
     Each branch  10  has two longitudinal edge faces  20 , in which pairs of notches  22  are formed, the notches in each pair extending into the respective faces  20  at the same levels along the branch. By way of example, there are three pairs of notches  22  along each branch. Between them the notches  22  define flat-topped teeth  23 . 
     To use the implant, osteotomy is performed in the two cervical laminae  24  of a cervical vertebra  26  so as to open up the cervical cavity  28  defined by the laminae. The laminae  24  are then spread apart from each other towards the back of the patient&#39;s body, e.g. until they slope towards each other only slightly, thereby eliminating the compression on the cavity  28 . 
     The implant  2  is put into place. For this purpose, each branch  10  is pressed against a respective lamina  24  on an outside face of the lamina remote from other lamina. Each branch  10  is attached to the associate lamina  24  by binding means  30  which can be threads or tows of implantable material. These means are received in the respective pairs of notches  22 , which prevent them from sliding along the associate branch  10 . The implant  2  is thus secured at its implantation site in a manner that prevents it from moving. The implant serves to keep the laminae  24  spaced apart from each other. 
     With reference to FIGS. 4 and 5, in a second embodiment of the implant, the body  8  is of a length that is about three times the length of the branches  10 . In addition, the body  8  is of a constant thickness over its entire length, which thickness is identical to the thickness of the branches  10 . It is defined by the two faces  4  and  6  which are curved, concentrically and with the same radius of curvature. 
     Each branch  10  has notches  122  in its edge faces  20  defining pairs of teeth  123  that have sharp tops. Each tooth  123  has, on its side adjacent to the free end of the branch  10 , a face  124  that slopes at an angle relative to the direction perpendicular to the longitudinal direction of the branch. The angle a is equal to 60°, for example. On its side adjacent to the body  8 , each tooth  123  present a face  126  that is perpendicular to the longitudinal direction of the branch. At the bottom of each notch  122 , the junction  125  between two faces  124  and  126  of adjacent teeth  123  is curved. In addition, the width l of the branch  10  corresponding to the distance between the tips of the teeth  123  in each pair decreases linearly from the end of the branch connected to the body towards the free end of the branch. The aligned tips of the three teeth  123  on each face  20  define a line which forms an angle b relative to the longitudinal direction of the branch  10 . This angle b can be 3 °, for example. The embodiment shown in FIGS. 2 and 4 is advantageously applied to cases where the two branches  10  are engaged in holes formed slantwise in the cervical laminae, the teeth  123  forming barbed plungers that serve to prevent said branches from escaping from the laminae by coming out of said holes. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.