Intervertebral Disc Prosthesis

Abstract

The present invention relates to an intervertebral disc prosthesis preferably comprising at least three pieces including an upper plate ( 1 ), a lower plate ( 2 ) and a mobile core ( 3 ) at least in relation to the lower plate ( 2 ), co-operation means ( 23, 33 ) allowing to limit or eliminate the movements of the core ( 3 ) in relation to the lower plate ( 2 ), in translation and in rotation, respectively, about an axis substantially parallel to the lower plate ( 2 ) and about an axis substantially perpendicular to the lower plate ( 2 ), at least one part of the surface of at least one plate being concave and complementary with a convex surface ( 30 ) of the core ( 3 ), with which it is in contact, wherein the tip ( 31 ) of the convex surface ( 30 ) of the core ( 3 ) is off centre, in at least one direction, in relation to the centre ( 32 ) of this convex surface ( 30 ).

1 . An intervertebral disc prosthesis comprising at least three pieces including a first plate, ( 1 ), a second plate, ( 2 ) and a mobile core ( 3 ), at least in rotation, at least in relation to one of the plates ( 1 ,  2 ), the core ( 3 ) having a curved surface in contact with at least a part of a complementary curved surface of the first plate ( 1 ), and a substantially flat surface in contact with at least a part of a substantially flat of the second, male and female co-operation means ( 23 ,  33 ) situated near the periphery of the second plate ( 2 ) and of the core ( 3 ) allowing, to limit or prevent, the movements in translation of the core in relation to the second plate to along an axis substantially parallel to the substantially flat surfaces, and allowing to limit or prevent the movements in rotation of the core in relation to the second plate, about an axis substantially perpendicular to the substantially flat surfaces, at least one part of the surface of at least one plate being concave and complementary with a is convex surface ( 30 ) of the core ( 3 ), with which it is in contact, wherein the tip ( 31 ) of the convex surface ( 30 ) of the core ( 3 ) is off centre, in at least one direction, in relation to the geometric centre ( 32 ) of this convex surface ( 30 ) of the core ( 3 ). 
     
     
         2 . Intervertebral disc prosthesis set forth in  claim 1 , wherein the rest position of the core ( 3 ), that being when the patient is motionless, is shifted in the opposite direction to that of the off centre of the tip ( 31 ) of the convex surface ( 30 ) of the core ( 3 ), thanks to the fact that the axes of symmetry of the first ( 1 ) and second ( 2 ) plates are aligned when the plates are anchored on the vertebrae and that the concave surface ( 10 ) of at least one plate ( 1 ), complementary with the convex surface ( 30 ) of the core ( 3 ), induces the aligning of the off-centre tip ( 31 ) of this convex surface ( 30 ) of the core ( 3 ) with the axes of symmetry of the plates ( 1 ,  2 ) and therefore a shifting of the core ( 3 ) in the opposite direction to that of the off centre of the tip ( 31 ) of its convex surface ( 30 ), which provokes a bringing together of the co-operation means ( 33 ) present on the core ( 3 ) and those ( 23 ) present on at least one plate ( 2 ), this bringing together consequently limits the displacement of the core ( 3 ) in the opposite direction to that of the off centre of the tip ( 31 ) of its convex surface ( 30 ). 
     
     
         3 . Intervertebral disc prosthesis set forth in  claim 1 , wherein the same plates ( 1 ,  2 ) can be assembled with different cores ( 3 ), the difference between the cores ( 3 ) consisting in the position of the tip ( 31 ) of their convex surface ( 30 ) in relation to the centre ( 32 ) of this convex surface ( 30 ) of the core ( 3 ). 
     
     
         4 . Intervertebral disc prosthesis set forth in  claim 1 , wherein the same cores is ( 3 ) can be assembled with different plates ( 1 ,  2 ), the difference between the plates consisting in the angle between the median planes representing the upper and lower surfaces of the plates. 
     
     
         5 . Intervertebral disc prosthesis set forth in  claim 1 , wherein an angle between the upper surface of the upper plate ( 1 ) and the lower surface of the second plate ( 2 ) can be imposed either by the fact that the median planes representing the upper and lower surfaces of the second plate ( 2 ) and/or the first plate ( 1 ) create an angle, or by restricting, thanks to the co-operation means ( 23 ,  33 ), movements of the core ( 3 ) about a position imposing an inclination of at least one of the plates ( 1 ,  2 ). 
     
     
         6 . Intervertebral disc prosthesis set forth in  claim 1 , wherein the same plates ( 1 ,  2 ) can be assembled with cores ( 3 ) of different thicknesses and/or sizes. 
     
     
         7 . Intervertebral disc prosthesis set forth in  claim 1 , wherein at least the lower surface of the core ( 3 ) and the upper surface of the second plate ( 2 ) are plane. 
     
     
         8 . Intervertebral disc prosthesis set forth in  claim 1 , wherein the dimensions of each male co-operation means ( 33 ) are slightly less than those of each female co-operation means ( 23 ) so as to allow slight clearance between the core ( 3 ) and the second plate ( 2 ). 
     
     
         9 . Intervertebral disc prosthesis set forth in  claim 1 , wherein the dimensions is of each male means ( 33 ) are substantially the same as those of each female means ( 23 ) so as to prevent any clearance between the core ( 3 ) and the second plate ( 2 ). 
     
     
         10 . Intervertebral disc prosthesis set forth in  claim 1 , wherein the core ( 3 ) is made of polyethylene. 
     
     
         11 . Intervertebral disc prosthesis set forth in  claim 1 , wherein first ( 1 ) and second ( 2 ) plates are made of metal. 
     
     
         12 . Intervertebral disc prosthesis set forth in  claim 1 , wherein the second plate ( 2 ) comprises female means ( 23 ) co-operating with male means ( 33 ) of the core ( 3 ). 
     
     
         13 . Intervertebral disc prosthesis set forth in  claim 12 , wherein the male means ( 33 ) of the core ( 3 ) are two contact plates situated on the two side edges of the core ( 3 ) and the female means ( 23 ) of the second plate ( 2 ) are four walls situated, in pairs, on each of the two lateral edges of the second plate ( 2 ). 
     
     
         14 . Intervertebral disc prosthesis set forth in  claim 13 , wherein the walls forming the female co-operation means ( 23 ) of the second plate ( 2 ) are curved toward the centre of the prosthesis, so as to cover at least a part of the male means ( 33 ) of the core ( 3 ) and to prevent it from lifting. 
     
     
         15 . Intervertebral disc prosthesis set forth in  claim 1 , wherein the second plate ( 2 ) comprises male means co-operating with female means of the core ( 3 ). 
     
     
         16 . Intervertebral disc prosthesis set forth in  claim 15 , wherein the male means of the second plate ( 2 ) are two contact plates facing one another on two edges of the prosthesis, and the female means of the core ( 3 ) are two recesses. 
     
     
         17 . Intervertebral disc prosthesis set forth in  claim 15 , wherein the male means of the second plate ( 2 ) are two walls facing one another in the vicinity of two edges of the prosthesis, and the female means of the core ( 3 ) are recesses. 
     
     
         18 . Intervertebral disc prosthesis set forth in  claim 15 , wherein the male means of the second plate ( 2 ) are two nibs curved toward the interior of the prosthesis and facing one another on two edges of the prosthesis, and the female means of the core ( 3 ) are two recesses. 
     
     
         19 . Intervertebral disc prosthesis set forth in  claim 18 , wherein at least one of the nibs is replaced by a contact plate fitted with a bore on which is fixed a lug by way of a pin penetrating the bore. 
     
     
         20 . Intervertebral disc prosthesis set forth  claim 1 , wherein the first plate ( 1 ) is bulged on at least a part of its upper surface to adapt to the form of the vertebrae.