FR2819714A1 - Intervertebral disc prosthesis comprises closed casing, inlet tube, packing material and venting tube or opening - Google Patents

Abstract

Intervertebral disc prosthesis comprises a closed casing (2), an inlet tube (4), a packing material (5) and a venting tube or opening (6). An independent claim is also included for a device for inserting the prosthesis, comprising a tube for maintaining the casing in a reduced volume and a pushrod for introducing the casing into the intervertebral cavity.

Description

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INTERVERTEBRAL DISC PROSTHESIS AND ITS IMPLEMENTATION METHOD ----------------------------- --------
Field of the Invention: The present invention relates to an intervertebral disc prosthesis as well as to its method of implementation. This prosthesis thanks to its associated devices aims to replace the cavity left by a partial or total ablation of the nucleus while preserving as much as possible the annulus of the intervertebral disc concerned.

 PRIOR ART: we will briefly recall the constitution of an intervertebral disc linking two vertebral bodies and which has a complex functioning. This disc is composed of a pulposus nucleus located in the center and an annulus fibrosus, a fibrous peripheral structure containing the nucleus and firmly connecting the vertebral plates. Like all the elastic connections of the human body, the intervertebral discs are subject to degeneration, in particular those of the lumbar spine which are most often used.

 Most pathologies of the disc come from a cracking of the annulus which lets out part of the nucleus, the latter then forms a protuberance which is often in contact with the nervous system, the most sensitive area of the annulus being this side. This herniated disc presses on the nerve roots or the dura mater and causes intense pain that can go as far as paralysis.

 However, a degenerate disc can be treated by replacing all or part of the damaged nucleus and annulus. Many invasive systems replace the entire nucleus as well as most of the annulus. However, even if they reproduce the appropriate mechanical responses, they all have the disadvantage of being very difficult to anchor, forcing the operator to add

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 metallic elements external to the prosthesis which are fixed to the vertebrae. These metal parts cause the body's defense reactions which will tend to block the movements of the prosthesis which becomes inoperative.

 Patent WO 99/02108 describes the replacement of the nucleus by a permeable membrane which the operator deploys using an instrument and into which a hydrogel is injected. The annulus is partly preserved and is used to hold the prosthesis in place. However, it does not solve the entire problem posed.

 The hydrogels have poor mechanical strength and the mechanical stresses they undergo are too great for the prosthesis to be able to resist and replace the annulus which, despite its partial preservation, remains damaged. In addition, the installation is not simple; the membrane must be deployed by a metal instrument which could tear it off; the closure is ensured by a valve and a plug made of a hard material which could, in the event of expulsion, cause irreparable damage to the nervous system.

 Patent EP 091 9209A1 describes a nucleus prosthesis formed of a hydrogel block which after implantation will take up water and swell by at least one millimeter in height. The incision of the annulus must in this case be wider to be able to pass the block, its role of bulwark is therefore reduced; the inventors then proposed to put 2 smaller blocks, each block being returned one after the other by a reduced orifice, in this case the blocks have no mechanical connection and there are empty spaces inside the cavity which cannot be filled in its entirety. Concentrations of stresses will form on the implant, calling into question its duration and the vitality of the annulus.

 The present invention will make it possible to solve these problems.

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DESCRIPTION We will describe the invention starting with the product, that is to say the prosthesis itself, then the implementation process which results from it, the drawings making it possible to understand the invention are the following:
Figure 1 of board 1/4 shows a preferred form of the intervertebral disc prosthesis (perspective view)
Figure 2 of the board 1/4 is a vertical sectional view of the envelope
Figure 3 of the board 1/4 is a horizontal sectional view of a possible variant of said envelope.

Figure 4 of plate 1/4 shows a variant of the envelope (viewed in horizontal section in the plane of the core)
Figure 5 of the board 1/4 is a view of the same envelope when it is compressed.

 Figure 6 of sheet 2/4 shows the same envelope compressed and placed in its insertion tube.

Figure 7 of plate 2/4 shows the envelope about to be introduced into the cavity
Figure 8 of plate 2/4 shows a vertical profile view of an introduction of the envelope through an orifice made in the annulus
Figure 9 of the 3/4 board shows the position of the envelope during deployment
Figure 10 of the 3/4 board shows the envelope deployed in the cavity
Figure 11 of plate 3/4 shows the injection phase of the filling product in the deployed envelope
Figure 12 of the 3/4 board shows the placement of the prosthesis after injection and cutting of the connection pipes

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Figure 13 of the 3/4 board is a vertical sectional view of the prosthesis after injection of the filling product.

 Figure 14 of plate 4/4 shows the various phases of the process P resulting from the product.

 The prosthesis 1 of the vertebral disc comprises: - a closed casing 2 - a means acting as a core 3 which may be cylindrical, it is integrated into the casing 2 by one of its faces - an inlet pipe 4.

 a filling material 5 adapted to the material of the envelope 2.

- an orifice or vent pipe 6
The material 5 can be a polymer or a composite material (for example of the polyurethane type) biologically compatible with the human body. The closed envelope 2 can have all the possible shapes desired by the operator, thanks to the type of material previously chosen. Its material is sufficiently flexible and elastic to maintain a good shape memory when the stresses applied are relaxed, these shapes being adaptable to each specific case of cavity to be filled. The filling material 5 and that of the envelope 2 are of the same family (of the organic chemical compound type) this in order to obtain, after polymerization of the material 5, a single block with the envelope, having mechanical characteristics at least equal to those of the nucleus of the intervertebral disc.

 The casing 2 is formed by lower and upper walls 21 and 22 connected to each other by a peripheral wall 23. To obtain good compression capacity, these walls have a thickness c which is variable at each point and which can be determined in production as a function of the response. mechanical and elasticity that we want to obtain. Thanks to these previous features

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 the envelope 2 can be introduced by compressing it in the cavity C to be filled, when its compression is relaxed, this envelope 2 comes to perfectly fit the walls of said cavity to which it must adapt without subjecting it to excessive stresses. This compression method followed by an expansion with relaxation of the stresses can be carried out:: - either by engaging the casing 2 in a pipe 12, the latter being compressed and then pushed into the pipe 12 with a pusher 13, said pipe 12 being in front of the opening of the cavity.

 either by self-compression of the casing 2 obtained by vacuum suction, through pipes 4 and 6 integrated into the casing 2, the vacuum compression of the prosthesis 1 making it possible to maintain the vacuum by tightening said pipes, using suitable means such as soft jaw pliers or clips with a high clamping rate.

 In both cases the compressed volume of the envelope 2 is reduced to the strict minimum; it is always less than the volume of the cavity C. On the other hand, the volume of the relaxed envelope is always greater than the volume of the cavity C before expansion.

 The means 3 playing the role of core is preferably cylindrical, it is made of the same material and integrated into the underside of the casing 2 at the time of manufacture, its function is to give the prosthesis 1 mechanical characteristics as close as possible to those of the nucleus. To allow in certain cases to have a minimum space requirement of compressed volume, it is necessary to remove the core so that it can enter an orifice 15 of the cavity which is even smaller.

 The inlet pipe 4 is an integral part of the envelope, it is made of the same material as the latter and integrated during manufacture, in order to avoid disparities in mechanical characteristics.

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 detrimental to the implementation of the prosthesis, it allows to obtain a perfect sealing continuity in the prosthesis avoiding any connection sources of drawbacks.

The vent pipe 6 which can be an extension of the inlet pipe 4 allows the residual air to be evacuated, the core 3 itself channeling the injection flow and the air outlet by playing the role of a chamber separating the intake of the filling product 5 from the air exhaust (FIG. 4)
From the above description of the product (prosthesis 1) we will now describe the resulting process P:
According to FIG. 14 of plate 4/4, Method P comprises 5 essential phases: -A phase 1 which consists in compressing the envelope 2 in a volume smaller than that of the cavity thus allowing the introduction of said envelope into the cavity C.

dans le même matériau que celui de l'enveloppe 2 ; une fois polymérisé il possède les mêmes caractéristiques que celle du nucléus du disque -A phase 2 which is the introduction of the envelope itself operating as follows: either by pushing it towards an orifice 15 formed in the cavity C. or by introducing it through a conduit 12 placed in contact with the orifice 15, the thrust being effected by means of a small specific tool (for example of the push-button type with rounded tip) - A phase 3 which corresponds to the deployment of the envelope which takes place automatically as soon as the envelope leaves the pipe 12, and that the vacuum ceases to be applied before the injection of the product by loosening the pipes 4 and 6, the envelope coming to perfectly fit the shape of the cavity C without lack or discontinuity, the injection of the product s '' using hose 4, for example using a small syringe (suitable for the case to be treated). This product is preferably chosen

in the same material as that of envelope 2; once polymerized it has the same characteristics as that of the disc nucleus

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-A phase 4 which consists in stopping the injection when it is observed that the filling product comes flush with the end of the vent pipe 6 and which also makes it possible to put the casing 2 in slight prestress to cause small residual folds integrating by filling the hollows of the lower base of the vertebra, ensuring better intervertebral attachment after injection of the filling product -A phase 5 which consists in cutting, at the level of the annulus, the pipes 4 and 6 after polymerization of the filling material 5
The prosthesis 1 put in place following the process P described is self-stable over time, this stability is ensured by a natural barrier preserved as soon as it is put in place, on which an orifice 15 is made in the disc (annulus) which is very weak dimension.

grâce au pouvoir isolant du matériau choisi, joue le rôle d'une barrière race au pouv rol iere 9 thermique, évitant de faire subir à l'environnement corporel des températures élevées qui seraient incompatibles avec la mise en place de cette prothèse.In terms of the mechanical and thermal stresses undergone by the body environment, tests carried out on intervertebral discs have shown that the pressures linked to the injection generate extremely low stresses on the peripheral annulus and the adjacent vertebral bodies, therefore bearable by the human body, these constraints linked to the injection forces allow the material to be housed in the folds of the envelope without danger. In addition, during the rise in temperature which occurs during the polymerization of the filling product 5, the casing 2

thanks to the insulating power of the chosen material, plays the role of a race barrier to thermal power, avoiding subjecting the body environment to high temperatures which would be incompatible with the fitting of this prosthesis.

Claims (8)

CLAIMS CLAIMS 1-Prosthesis (1) of intervertebral disc characterized in that it comprises: - a closed envelope (2) -an inlet pipe (4) -a filling material (5) adapted to the material of the envelope (2 ) - an orifice or vent pipe (6) 2-Prosthesis (1) of intervertebral disc according to claim 1 characterized in that the material (5) which constitutes it, is preferably a polymer or a composite material biologically compatible with the human body of the same family as the material of the 'envelope, for example of the organic chemical type in order to allow a block polymerization of the prosthesis (1) having mechanical characteristics at least equal to those of the core of a healthy vertebral disc.  3-Prosthesis (1) of intervertebral disc according to claims 1 and 2 characterized in that its envelope (2) is made of a flexible, elastic material, having a good shape memory and capable of adapting to all cavities .  4-Prosthesis (1) of the intervertebral disc according to any one of the preceding claims, characterized in that its envelope (2) is formed by three lower and upper walls (21 and 22) connected together by a peripheral wall <Desc / Clms Page number 9>  (23), these walls having a thickness e variable at each point and determinable in manufacture as a function of the mechanical response and the desired elasticity, thus allowing the envelope (2) to be introduced by compression into the cavity C to fill and come to marry perfectly this one, when you release its compression.  5-Prosthesis for replacing an intervertebral disc according to any one of the preceding claims, characterized in that it comprises a core (3) preferably cylindrical, integrated into at least one of the faces of the envelope (2) at the time of its manufacture, made of the same material in order to give said envelope (2) characteristics which are closest to that corresponding to the replaced part of the intervertebral disc.  6-Replacement prosthesis of an intervertebral disc according to any one of the preceding claims, characterized in that: - the pipe (4) is an integral part of the envelope (2), composed of the same material as the latter and integrated in manufacturing to avoid

 disparities in mechanical characteristics detrimental to the implementation of the prosthesis (1) and also making it possible to obtain perfect sealing of said prosthesis (1) -the vent pipe (6) extends through the casing the pipe inlet (4) for evacuating residual air, the core (3) channeling the product injection flow and the air outlet by playing the role of a chamber separating the inlet of the product from filling (5) of the air exhaust. <Desc / Clms Page number 10>  7-Prosthesis (1) for replacing an intervertebral disc according to one of the preceding claims characterized in that its casing (2) is made of a material inducing very low mechanical stresses and behaving like an insulating thermal barrier screw with respect to the body environment during the polymerization of the filling product (5) 8-Device for fitting an intervertebral disc prosthesis, according to one of the preceding claims characterized in that it comprises: a pipe (12) having the function of maintaining the envelope (2) in a reduced volume . a push rod (13) having the function of introducing the envelope (2) into the cavity (C)