Abstract:
The invention relates to a device ( 3 ) that is used to fit a nucleus prosthesis comprising: a deformable elastic nucleus prosthesis ( 1 ) which can adapt to the shape of intervertebral cavities, said prosthesis consisting of two parts, namely a male part ( 11 ) and a female part ( 12 ); and an insertion assembly ( 2 ) which is connected to the nucleus prosthesis ( 1 ). The elastic deformation of the inventive nucleus prosthesis ( 1 ) makes it possible for the prosthesis to be inserted into the intervertebral cavity. According to the invention, said prosthesis is inserted using the elasticity thereof and the insertion means ( 2 ) which form part of the device ( 3 ) before insertion but which can be subsequently removed. The invention also relates to different forms of prosthesis and insertion devices.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention concerns an intervertebral disk prosthesis and means for its insertion as well as an insertion procedure. This prosthesis, after insertion and removal of the means of insertion, replaces the nucleus of the existing cavity after partial or total ablation of the latter by preserving the ring of the intervertebral disk concerned.  
       PRIOR ART  
       [0002]     We would like to briefly bring to mind the construction of an intervertebral disk linking to vertebral bodies and whose functioning is complex. This disk is comprised of a centrally located nucleus pulposus and of an annulus fibrosus—peripherical structure containing the nucleus and solidly bringing together the vertebral plates. As all the elastic links of the human body, the intervertebral disks are subject to degeneration, particularly those of the lumbar vertebral column which are most often subjected to stress.  
         [0003]     Most of the pathologies of the disk come from the fissure of the annulus which lets part of the nucleus escape, the latter then forms a flange which is often in contact with the nervous system, where the most sensitive area of the annulus is. This disk hernia will press the nervous roots or the dura mater and causes intense pains and can even lead to paralysis.  
         [0004]     However, a degenerated disk can be treated by replacing the whole or part of the nucleus and the damaged annulus. Many invasive systems replace the totality of the nucleus as well as the major part of the annulus. However, even if these reproduce the adequate mechanic responses, they all have the inconvenience of being very difficult to anchor, forcing the operator to add external elements to the prosthesis which are fixed to the vertebras. These metallic pieces cause the organism to react, which will tend to block movements and the prosthesis becomes inoperable.  
         [0005]     Patent EP 0919209 describes a nucleus prosthesis comprised of dry hydrogel, which after implantation will take on water and swell by at least one millimetre in height. The incision of the annulus must be in this case larger in order to let the block pass, thus diminishing its function as a barrier wall, the inventors then proposed to place two smaller blocks, each block entering one another by a small opening, in this case the blocks don&#39;t have any mechanic link and there remain empty spaces inside the cavity which cannot be filled in any way. With so many constraints appearing on the already damaged annulus, this places in doubt the lifespan of the implant and the viability of the annulus.  
         [0006]     Patent application No. 0,100,127 solves the problem by means of an elastic envelope, by an opening in the annulus which will adjust to the cavity by elastic expansion. A viscose filling material must be then injected which by being polymerised will fill the prosthesis and thus fill the cavity. This operation requires a supplementary injection step which, in certain cases can be constraining in that it increases operation time.  
         [0007]     Patent EP0621 020 A is essentially based on the insertion means which in this case are specifically adapted to ball-type spherical materials and which do not resemble the elastic, form-adjustable materials which are the core of the present invention, the former not at all making unpatentable the latter.  
         [0008]     The U.S. Pat. No. 5,800,549A is a force generator for the injection of a vertebral-column implant, the means put into operation are different from those of the present invention which uses extremely simple means based on readily available materials.  
         [0009]     U.S. Pat. No. 5,645,597A describes a method enabling the withdrawal of the nucleus, then a prosthesis comprised of an elastic ring covered by two membranes, the ring having a hole for the passage of a gel introduced with a syringe which will fill the centre of the prosthetic cavity. In the present invention, the prosthesis is comprised of two parts out of which each part is perfectly polymerised before being separately introduced and precisely guided in relation to one another.  
         [0010]     Patent EP 1132031 A solves a different problem from that solved in the present patent application, in that in this prior art the question is to make a graft grow on a damaged bone, the injected particles are of the non-malleable bone, which has nothing to do with the problem that the present application wishes to resolve.  
         [0011]     The present invention does not require any product injection, it solves the posed problem by means which are completely different from this prior art, the latter not taking away from the novelty and the inventive activity of the present invention in any way.  
         [0012]     None of the documents examined so far have attempted to connect the characteristics of the nucleus prosthesis to the means of insertion used.  
     
    
     DESCRIPTION  
       [0013]     The drawings, serving to understand the invention, are:  
         [0014]      FIG. 1  of sheet  1 / 8  is a cross-section of the complete device (prosthesis and means of insertion).  
         [0015]      FIG. 2  of sheet  2 / 8  is an exploded view of the means which make up the invention.  
         [0016]      FIG. 3  of sheet  3 / 8  is a perspective view of the prosthesis comprised of two distinct parts.  
         [0017]      FIG. 4  of sheet  3 / 8  is a perspective view of the prosthesis after the joining of the two parts.  
         [0018]      FIG. 5   a  of sheet  4 / 8  is a horizontal cross-section of the prosthesis comprised of 2 parties before assembly.  
         [0019]      FIG. 5   b  of sheet  4 / 8  is a horizontal cross-section of the prosthesis comprised of 2 joint parties.  
         [0020]      FIG. 6   a  of sheet  4 / 8  is a perspective view of a prosthesis of a different form from the original one.  
         [0021]      FIG. 6   b  of sheet  4 / 8  is the same prosthesis assembled, the male part having been introduced into the female part.  
         [0022]      FIGS. 7   a  and  7   b  of sheet  4 / 8  present the same situations as  FIGS. 6   a  and  b , the female part being in this case a ring split from one part to another in sectors.  
         [0023]      FIG. 8  of sheet  5 / 8  shows an assembly of components that take part in the invention before the introduction into the intervertebral disc.  
         [0024]      FIG. 9  of sheet  5 / 8  shows the assembly of means after the introduction of the female part into the intervertebral disc.  
         [0025]      FIG. 10  of sheet  5 / 8  is the same prosthesis as that of  FIG. 9 , but after the introduction of the male part into the female part.  
         [0026]      FIG. 11  of sheet  5 / 8  represents the same prosthesis once certain means used for insertion are withdrawn.  
         [0027]      FIG. 12  of sheet  5 / 8  shows the prosthesis once in place, the guidance stems having been cut.  
         [0028]      FIG. 13  of sheet  5 / 8  shows a longitudinal cross-section of the prosthesis placed in the intervertebral disc.  
         [0029]      FIGS. 14, 15  and  16  of sheet  6 / 8  show a prosthesis in which the male part is a variant which allows for fixing on the bone.  
         [0030]      FIG. 17  of sheet  7 / 8  show the steps of the installation method.  
         [0031]      FIGS. 18 and 19  of sheet  8 / 8  are perspective views for the assembly of another embodiment of the prosthesis showing components before insertion.  
         [0032]      FIG. 20  of sheet  8 / 8  is a cross-section (in the shape of a champagne cork) of a male and female prosthesis in place.  
         [0033]      FIG. 21  of sheet  8 / 8  shows the same prosthesis once the guidance stems are removed.  
         [0034]      FIG. 22  of sheet  8 / 8  is a vertical cross-section of the prosthesis.  
         [0035]      FIG. 23  of sheet  8 / 8  is a vertical cross-section of the installed prosthesis. 
     
    
       [0036]     Device  3  for the installation of a nucleus prosthesis together with its insertion means includes, in a first embodiment, 
        nucleus prosthesis  1      an insertion assembly  2         
 
         [0039]     Means  1  is itself formed of means  12  referred to as the female part, made out of elastically deformable material whose form may be a hollow sphere with flattened poles, formed: 
        of a central cavity  121  connected to a rigid stem  21 ,     of an introduction opening  122 , of a means  11  male part which comprises a full, deformable sphere  111  whose main functions are:     to draw aside the female part  12  in order to introduce itself and perfectly fit the shape of cavity  121  after its introduction, to be ready to support the imposed mechanical strains.        
 
         [0043]     This means  11  has in its rearward part a flange  113  whose form is determined so as to be embedded in the opening  122  which elastically deforms during the introduction. Once this operation is carried out, the male part  11  takes its definitive place and cannot be expelled from the female part  12 .  
         [0044]     The nucleus prosthesis  1  is introduced into the intervertebral cavity by an insertion assembly  2  allowing its introduction, namely: 
        the rigid stem  21  connected to means  12  through the intermediary of a flexible connection  124      some tubes  23 ,  24  and  25  being used to introduce means  1  into the cavity. The tube  23  contains the female part  12  of the prosthesis  1  compressed with its guidance stem  21 ; it also contains the tube  24 .        
 
         [0047]     The tube  24  contains the male part  11  guided by stem  21 , this mean  24  will be used as a push rod for the female part  12  compressed inside the tube  23 .  
         [0048]     Tube  25  threaded on stem  21  is used as a push rod for the male part  11  towards the female part  12 .  
         [0049]     The method of insertion  5  includes 7 steps; 
        step 1: introduction into the tube  24  of the male part  11  threaded on the stem  21 ;     step 2: sliding of the tube  23  around the tube  24 , the female part  12  is introduced into the tube  23 ;     step 3: presentation of the insertion device  1  before the opening of the cavity to fill;     step 4: pushing of the female part  12  by the tube  24  ( FIG. 9 ); step 5: introduction of tube  25  threaded on stem  21  to bring the male part  11  into the opening  122  of the female part  121 ;     step 6: pushing using tube  25  of the male part  11  into the opening  122  to embed means  11  in means  12 ;     step 7: tubes  23 ,  24 ,  25  are withdrawn, stem  21  being removed, for example by a cut at the level of the flexible connection  124 , which releases prosthesis  1  of the insertion device  2 . The shapes of the nucleus prostheses&#39;  1  male parts  11  and female parts  12  can have several alternatives, always compatible with the same insertion procedure  5 .        
 
         [0056]     The female part  12  can have an opening  122  which can be either a circular form or the shape of a slit traversing through the prosthesis  12  in sectors, which is presented in the form of a split ring.  
         [0057]     There always exists in this opening  122  a constriction  123 , which will prohibit the male part  11  from being expelled once positioned in the female part  12 . The external forms of the envelope, when not under strain, can vary, the essential function being to adapt to the cavity, intervertebrally, to fill without risk of slip or expulsion.  
         [0058]     The male part  11  ( FIGS. 14 and 15 ) can comprise at its end a flange  115  which comprises a fixing  116  on the bones, for example: holes allowing fastening screws to pass, in order to better guarantee in certain cases the non-expulsion of the prosthesis. The female part, due to its adaptation of form coming from its nature as an elastic material, may have a capacity of deformation which enables it to pass through tubes and openings of insertion which have more reduced sections, one can appreciate the ratio reduction or compression (relationship R between the diameters D and d before and after installation in the tube) R is greater than 2  
         [0059]     In another embodiment (see  FIGS. 18, 19 ,  20 ,  21  and  22 ) the elastically deformable nucleus prosthesis  1  includes two parts; 
        a means  12 , referred to as a female part, having the shape of an open ring in order to let in a male part  11 , the means  12  comprises a threading  127   f  receiving a guidance stem  21  whose end is threaded (male threading  127   m  corresponding to  127   f ), the aforementioned rigid stem  21  makes it possible to freely guide the male part  11  of the prosthesis  1  until its insertion and also to withdraw stem  21  by simple unscrewing, once prosthesis  1  is in place.        
 
         [0061]     Means  12  includes an opening  122  allowing the introduction of means  11  (male part  127   a ). Means  11  preferably has the shape of a one way cork, it comprises a full deformable spherical head  111  as well as, if necessary, a slightly extending cylindrical body, and is placed at the periphery of the ring.  
         [0062]     In this solution, the anchoring of the male part  11  in the female part is ensured by a one way system of overlapping of the male parts  128   m  and female parts  128   f , a system integrated into the shape of the parts during manufacture.  
         [0063]     Upon the introduction, the male part  11  draws aside opening  122  of the ring, the latter, due to elasticity, afterwards comes to be closed again on the male part  11 . Moreover, (see  FIG. 22 ) the spherical head of the male part slightly exceeds the thickness of the ring. When the prosthesis is subjected to the dynamic stresses, this spherical part is compressed first, thus it increases the one way function making impossible the expulsion of the male part.  
         [0064]     The female part can have a metal insert receiving the threaded rod  127   m , which is visible under X rays. Once prosthesis  1  is in place, the position of the insert makes it possible to check the stability of the prosthesis over time, it also allows easy disassembly of the stem  21  once the prosthesis is installed.  
         [0065]     All the embodiments which consist in introducing a nucleus prosthesis with its means of insertion in an osseous cavity, then to withdraw these insertion means, are a part of the invention and are claimed as such. They can comprise either the means described in the present invention, or equivalent means as soon as they make apparent possible cuts or removable means or provisional fixings.