WO2010018317A1

WO2010018317A1 - Dynamic prosthesis for the extra-discal stabilisation of the intervertebral articulation

Info

Publication number: WO2010018317A1
Application number: PCT/FR2009/000881
Authority: WO
Inventors: Henry Graf
Original assignee: Henry Graf
Priority date: 2008-08-14
Filing date: 2009-07-17
Publication date: 2010-02-18
Also published as: FR2934950A1; FR2934950B1

Abstract

The invention relates to a prosthesis that includes: at least two so-called vertebral rods (110, 120) capable of interacting with at least two different vertebrae; at least two pairs of jaws (153, 163, 173, 183), each pair including first and second jaws and each pair of jaws being arranged in the vicinity of a corresponding rod; at least two slides (130, 140) defining a longitudinal axis of said prosthesis, both the first and second jaws of each pair of jaws being capable of sliding independently from each other along at least two slides along the longitudinal axis thereof; first and second return means (174, 175, 176) capable of respectively returning the first and second jaws of each pair of jaws into contact with a corresponding vertebral rod, each vertebral rod being capable of moving both a first and a second jaw along the slides towards said first and second return means, and each vertebral rod further being articulated relative to each jaw.

Description

DYNAMIC PROSTHESIS FOR EXTRADISCAL STABILIZATION OF INTERVERTEBRAL JOINT

The present invention relates to a dynamic prosthesis for extra-disc stabilization of the intervertebral joint.

The invention lies in the field of the prosthesis, namely that it aims to reproduce, in their nature and their amplitude, the original physiological movements. Typically, a prosthesis for extra-disc stabilization, within the meaning of the invention, allows an amplitude of movement between the vertebrae, which is equal to at least about 50% of the natural physiological amplitude. In other words, if there is a maximum natural amplitude of 10 ° in rotation between two given vertebrae, the prosthesis according to the invention is capable of allowing, at least, a clearance of 5 ° between these two vertebrae.

It will be noted that it is fundamental to make a distinction between, on the one hand, the prosthesis according to the invention which is designed to recreate the intervertebral movement and, on the other hand, a set for osteosynthesis whose sole purpose is to to obtain a bone fusion between two vertebrae. In this respect, it will be recalled that there are substantial structural and functional differences between a prosthesis and an osteosynthesis device, so that a prosthesis can not provide bone fusion and that, similarly, a set for arthrodesis can provide a prosthesis function.

The prosthesis according to the invention is intended to connect at least two adjacent vertebrae, while being generally placed on one side of the spine, namely to the right or left. The implantation of this prosthesis is extra-discal type, namely that it can be located behind, but also in front of the intervertebral space.

A commercial object proposed by the MEDTRONIC Company under the reference AGILE is already known. This device comprises two rigid members adapted to cooperate with two pedicular screws implanted in two adjacent vertebrae. There is further provided a damping pad, which is attached against the end plates of the rigid members, in particular by hot vulcanization, under which conditions this pad can not only be compressed, but also be stretched while remaining attached to these two bodies, thanks to the presence of this link.

This AGILE device further comprises centering means, intended to prevent the two rigid members from offsetting, particularly during bending movements. For this purpose, use is made of a cable secured to one of the two rigid members, which passes through the damping pad and extends into the interior volume of the hollow rigid member opposite.

This known solution, however, has certain disadvantages. In particular, AGILE has a tendency to work too much in bending, which reduces its efficiency and its life span. Note also that this object, which was originally designed as a prosthesis accompanying the vertebral movement, was converted into an osteosynthesis device, because of the administrative constraints on the US territory. Such a transformation has been implemented without structural modification of this object, in order to depress the movement, which highlights its impossibility to reliably ensure one or other of the two functions of prosthesis and arthrodesis , which we have seen are very different.

Stabilization assemblies marketed under the references DYNESIS and NFLEX are also known. These posterior dynamic stabilization systems use the elastic mechanical properties of elastomeric pads to limit the mobility of the pedicle screws during intervertebral movement. Under these conditions, the displacement of each screw is the result of compression deformation of one of these buffers, for bending if the pad is outside the space between the screws, or for extension if the buffer is located between these screws.

The main disadvantage of these known devices lies in the lack of articulation between the screw and the buffer. Therefore, when the screw is rotated in the context of the flexion-extension movement, it imposes the bending work stamp. Under these conditions, this buffer thus solicited in turn imposes a rotation to the screw, which is not within the scope of the natural physiological intervertebral movement. That being said, the invention aims to remedy these various disadvantages. For this purpose, it relates to an extradiscal stabilization prosthesis of the intervertebral joint, comprising at least two rods, called vertebral rods, adapted to cooperate with at least two different vertebrae; at least two pairs of jaws, each of which comprises a first and a second jaw, each pair of jaws being placed in the vicinity of a corresponding rod; at least two slides defining a longitudinal axis of said assembly, both the first and second jaws of each pair of jaws being slidable independently of each other along at least two slides, according to their longitudinal axis, first and second return means, adapted respectively to recall the first and second jaws among each pair of jaws in contact with a corresponding vertebral rod, each vertebral rod being adapted to move both a first and a second jaws, along the slides, against the first and second return means, each vertebral rod being further articulated relative to each jaw.According to other features: said articulation between the rod and each jaw is exerted according to a single point of contact between this rod and the facing walls of each jaw, at least one jaw comprises a connecting arm rec curved with a radius of curvature greater than the radius of curvature of the stem. the curved branch is secured to two studs, mounted on two slides, slidably. at least one return means comprises two springs, each of which is mounted on a corresponding slideway, these two springs being adapted to recall a branch bent against the vertebral stem. at least one jaw comprises a hinge nipple against a corresponding vertebral stem. at least one return means comprises a solid flexible body and the stud belongs to a rigid flank, integral with this flexible body. the first and second return means are combined into a single return means comprising a central return member, bordered by two flanks each of which defines a respective first jaw, in that two pairs of slides are provided, each pair defining a respective second jaw, and in that each pair of slides is slidable with respect to the flank adjacent to the jaw defined by these slides, this pair of slides being however integral in translation with the opposite flank, at least in the direction of a rapprochement of the two flanks towards each other. the central return member is a helical spring. each stem belongs to a corresponding vertebral screw, in particular to a pedicle screw. - Each rod is secured to a connecting element, adapted to connect two vertebral screws to be implanted in the same vertebral stage. the prosthesis comprises means for limiting the stroke between two adjacent rods. the means for limiting the stroke are means for limiting the compression of a deformable body belonging to a return means. the means of limiting the compression comprise a rigid chamber, extending at a distance from the walls of the deformable body, in the rest position of the latter. the prosthesis comprises means for preventing sliding of the slides and jaws along the rods, along the main axis of the latter, in at least one direction. two slides are adapted to guide the rods, in particular by cooperation of an area of these rods whose cross section substantially corresponds to the distance separating these slides. The invention will be described hereinafter with reference to the accompanying drawings, given solely by way of non-limiting example, in which: FIGS. 1 and 4 are perspective views, illustrating two arrangements which are not part of the invention, but which serve to better understand the latter; FIGS. 2 and 3, as well as 5 and 6, are side views, illustrate the implementation of the arrangements of FIGS. 1 and 4; Figure 7 is a perspective view, similar to Figure 1, illustrating a prosthesis according to the invention; Figures 8 and 9 are side views similar to Figures 2 and 3, illustrating the implementation of the prosthesis of Figure 7; Fig. 10 is a graph, illustrating the variation of the intervertebral inclination as a function of the force applied by the patient, in different embodiments of the invention; FIG. 11 is a curve, similar to FIG. 10, illustrating this variation according to another implementation of the invention; Figures 12 and 13 are views, respectively in perspective and side, illustrating a further embodiment of the prosthesis according to the invention; Figure 14 is a perspective view illustrating a prosthesis according to a further alternative embodiment of the invention; Figure 15 is a side view, illustrating an alternative embodiment of the prosthesis of Figure 14; Figures 16, 17 and 18 are perspective views illustrating a prosthesis according to a further variant of the invention; Figure 19 is a perspective view, illustrating the implementation of the prosthesis of Figures 16 to 18; Figure 20 is an exploded perspective view illustrating various components of a further embodiment of the invention; Figures 21 and 22 are longitudinal sectional views, illustrating the prosthesis of Figure 20, in two positions of use; and FIG. 23 is a graph, similar to FIG. 10, illustrating the variation of the intervertebral inclination as a function of the applied force, for the embodiment of FIGS. 20 to 22. The arrangements illustrated in FIGS. are not part of the invention, insofar as they do not make it possible to reproduce the natural physiological movements. Nevertheless their description is interesting because it allows to better understand the invention itself.

The arrangement of Figure 1 comprises first two vertebral screws, which are partially illustrated. These two screws, respectively assigned references 10 and 20, comprise a cylindrical shaft 12, 22, more particularly visible in Figure 1. These two screws are for example pedicle screws comprising, in a conventional manner, a threaded zone intended to penetrate into the vertebral body. However, it can be provided to use, not a pedicle type screw, but any other type of vertebral screw. Thus, this screw can be implanted in the vertebral body, either laterally or anteriorly, or in the vertebral body through the pedicle. In general, any insertion which ensures the screw a stable solidarization with the vertebra can be provided. It is then implanted in the vertebra by a thread and makes exceed, outside the vertebra, a nipple that cooperates with a jaw, as will be described below. This nipple can also be supported by a mechanical member other than a thread, such as for example a clip or hooks placed on the vertebral body and / or the intervertebral bone blades.

The arrangement of Figure 1 further comprises two slides 30 and 40, extending substantially along the axis A, connecting the two screws 10 and 20, once the latter implanted in the vertebrae. Each slide consists of a corresponding rod 30, 40 which can be rigid, or have a slight possibility of deformation, in the direction of bending. In any case, in the latter case, this possibility of deformation is controlled. When seen from the side, whether rigid or not, each rod may be straight, or have a slight curvature, in order to adapt to the intervertebral curvature where appropriate. Each screw 10 or 20 is associated with two jaws, one of which is fixed and the other is slidably mounted relative to the two rods 30 and 40. There are 50 and 60 the two fixed jaws, as well as 70 and 80 both. movable jaws.

The four jaws have the same structure, namely that each of them comprises two studs 51, 61, 71, 81 of attachment to a corresponding rod. The pads 51 and 61 of the fixed jaws are provided with a screw 52, 62, allowing the attachment of this stud on the two rods 30 and 40.

In addition, each pair of studs facing each other is connected, via a respective connecting leg 53, 63, 73 and 83. Each connecting leg is bent, in plan view, namely along the axis of FIG. each screw, so as to form an articulated contact with the barrel of a corresponding screw. In top view, each screw has a radius of curvature corresponding to its diameter while each curved branch has a radius of curvature, greater than the diameter of this screw, which allows this joint. In addition, as shown in Figure 2, each branch is circular in cross section, which also ensures the articulation of the jaw relative to the cylindrical barrel of the screw.

Each branch can be rigid, or be able to deform, at least in places, under the effect of constraints whose intensity is much higher than gravity. On the other hand, all the branches have a proper form, namely that their shape is invariant under the effect of gravity, as well as other constraints of similar intensity.

Note also that the two movable jaws 70 and 80 are adjacent, namely that they are arranged on the opposite sides of the two barrels. On the other hand, the two fixed jaws are distant from one another, namely that they are present on the opposite faces of the two barrels 12 and 22. Two springs 74 and 84 are interposed between the two mobile jaws facing each other. and 80. These springs tend to push each movable jaw 70 or 80, towards the fixed jaw 50 or 60 associated therewith. Each barrel 12 or 22 is circular, in cross section. In addition, each branch is also circular, also in a cross section. Finally, as seen above, the branches have a curved profile, namely that the two opposite branches define approximately an oval, whose radius of curvature is greater than the radius of the circular drum.

Under these conditions, each barrel 12 or 22 defines, with each leg 53, 73, 63 or 83, a substantially punctual articulation, illustrated by its points P in FIG. 2. In other words, there are three degrees of freedom, in rotation, between each branch and the shaft with which it cooperates. In this figure 2, the springs 74 and 84 are schematically illustrated. As a variant not shown, this articulation can be achieved by means of a non-point contact, flat type on flat. These two flats, one of which belongs to the shaft and the other of which belongs to the branch, define a relatively weak zone of contact, which allows a possibility of sub-luxation, likened to the articulation within the meaning of the present invention.

The operation of the arrangement described above will now be explained. It is assumed that the two screws 10 and 20 are pedicle screws and that the upper part of these screws, in FIG. 1, is directed towards the back of the patient when the latter is standing. placing the jaws around the screws 10 and 20. It is assumed in the present example that this arrangement is intended to form a stay. Under these conditions, in the absence of stress, the free ends of the two screws are separated by a distance, which is greater than that separating these screws once associated with the jaws. In other words, for mounting, it is first of all to bring these two screws together, for example by means of a tool not shown. The two jaws, as well as the two rods, are then axially brought together relative to the screws so as to introduce the two barrels 12 and 22 through the two eyelets, defined by the different jaws. Then releases the external action exerted by the tool, so that the barrels 12 and 22 are pressed against the fixed jaws 50 and 60.

If the patient wished to exert an intervertebral flexion, namely to lean forward, the two screws 10 and 20 would tend to deviate one from the other. the other, along the axis A. This is however impossible because the two barrels 12 and 22 abut against the fixed jaws 50 and 60. The arrangement of FIG. 1 thus substantially prevents any intervertebral flexion movement. so that it can not satisfactorily fulfill a prosthesis function, whereas, during an intervertebral extension, the screws 10 and 20 tend to approach each other, along the axis A. Unlike the bending, this relative movement of the screws is possible, insofar as the latter then push the movable jaws 70 and 80 towards each other, against the springs 74 and 84. These movable jaws therefore tend to slide along rods 30 and 40.

This is more particularly illustrated in FIG. 3, where we find the four branches, the two barrels, as well as the springs 74 and 84. It is noted that, during this intervertebral extension, the barrels 12 and 22 move, not only in rotation, but also in translation according to the arrows F, which pushes the branches 73 and 83 against the springs 74 and 84. However, since the jaws 53 and 63 are fixed, they do not move, which creates two free spaces E between the walls opposite these jaws and barrels facing. Then, when the patient stops this extension movement, or if the force thus exerted is less than the stiffness of the springs 74 and 84, the latter push the barrels 12 and 22 back to their original position, illustrated in FIG. .

Figure 4 illustrates another arrangement that does not form part of the invention. In this FIG. 4, the mechanical elements which differ from those of FIGS. 1 to 3 are represented by the same numbers, assigned the reference "prime".

In this variant, the jaw 60 'is no longer fixed, like that 60 of the first mode, but on the contrary is free to slide along the rods 30 and 40. This sliding takes place against two additional springs 75 and 85 , interposed between the pads 61 'of the jaw 60' and stops 31, 41, fixedly mounted on the slides 30 and 40.

The mounting of the jaws and screws, belonging to this second arrangement, operates in a similar manner to that described with reference to the first arrangement. Once the barrels 12 and 22 introduced into the eyelets defined by the different jaws, these barrels bear against the respective jaws 50 and 60 '. Since the jaw 60 'is now movable, a balance is established between the forces exerted respectively by the screws 20, the "inner" springs 74 and 84, as well as the "outer" springs 75 and 85. more precisely, the screw 20 exerts a force tending to push it away from the first screw 10, namely a feedback against the action of the surgeon tending to bring them closer, and the springs 74 and 84 also tend to push the screw 20, opposite the screw 10. In contrast, the springs 75 and 85 tend to bring the screw 20 towards the first screw 10.

In this second arrangement, intervertebral flexion is now possible, in a "partial" way. Thus, when the patient leans forward, the branch 53 of the fixed jaw still holds (a screw 10, while the screw 20 pushes the leg 63 'of the movable jaw 60' against the two springs 75 and 85 At the same time, the springs 74 and 84 tend to push the leg 83 of the jaw 80 towards the shaft 22 of the screw 20, as shown in FIG.

On the other hand, the fixed jaw 50 prevents any displacement of the screw 10, as in the first arrangement. Again, a physiological movement can not be reproduced, so that the intermediate arrangement of Figure 4 can not be likened to a prosthesis according to the invention. In order to further explain the manner in which this intervertebral flexion is effected, FIG. 10 shows a curve illustrating the variations of the angle α as a function of the force F. More precisely, F corresponds to the force bending exerted by the patient, from the neutral position, while α corresponds to the value of the intervertebral flexion or, in other words, to the distance between the two screws 10 and 20.

The outer springs 75 and 85 are prestressed, namely that there is first a zone I in which the patient exercises a prior force, in order to overcome this prestressing. In other words, as long as the patient does not exert a threshold force, denoted Fo, he does not succeed in "overcoming" this prestressing and thus induces no intervertebral flexion, namely that the value of the angle α remains zero.

Then, when the patient exerts a force greater than this threshold force F ₀ , the value of the bending angle increases linearly with the force exerted by the patient, according to the stiffness characteristic of the spring (zone II). This angle α then increases to a value noted α _ma χ, which corresponds to a value Fmax, corresponding to the maximum physiological force that the patient can apply. In the context of the prosthesis in which the present invention is located, this value of α is relatively large as seen above.

This type of curve makes it possible to explain the distinction existing between the notions of stiffness and prestressing. Thus, if there was no prestress, the force-displacement curve would correspond to a stretch of straight line, extending from the origin. In other words, the least force exerted by the patient would tend to push the screw, against the springs 75 and 85. This would be of little benefit, insofar as this situation would lead to an overall instability of the system.

On the other hand, the higher the prestressing, the greater the value of the threshold force Fo, before the actual movement of the patient occurs. On the curve, there is in dashed lines an embodiment in which the springs 75 and 85 have the same stiffness, but have a greater prestress. We find a higher threshold force Fo, as well as a maximum angle α _ma χ 'lower.

In addition, if these springs 75 and 85 have different stiffnesses, this influences the slope of the line extending from the point Fo. Thus, for the same prestressing, we find in mixed lines an arrangement in which the springs 75 and 85 are steeper. In other words, the maximum angle α _ma χ "that the patient can reach, exerting the maximum physiological force, is less important.that the one α _ma χ- Note that it is possible to adjust the value of the prestressing, slightly modifying the embodiment of (a FIG. 4. Thus, if the stops 31 and 41 are replaced by nuts, mounted on a threaded end of the rods 30 and 40, it is then possible to modify the axial position of these nuts, by screwing or unscrewing them.This action is then accompanied by a corresponding variation of the prestressing, imparted to the springs 75 and 85.

During the intervertebral extension, the cooperation of the branches 53 and 73, as well as the screw 10, operates in a manner analogous to that illustrated in FIG. 3. On the other hand, the screw 20 pushes the movable arm 83, against the springs 74 and 84, while the additional springs 75 and 85 tend to keep the other movable leg 63 'in contact with the barrel 22. In other words, there is no longer any free space between the leg 63' and the barrel 22, in Figure 6, contrary to what is shown in Figure 3. Figure 7 illustrates an embodiment corresponding to a prosthesis according to the invention. In this figure, the mechanical elements that differ from those of Figure 4 there bear the same numbers, assigned the reference "prime".

This embodiment according to the invention differs from the arrangements described above, in that the jaw 50 'is now mobile, and no longer fixed like that 50 of Figures 1 and 4. Thus, this jaw 50' is slidably mounted on the slides 30 and 40, against springs 76 and 86, interposed between the pads 51 'of this jaw and the end stops 32 and 42. There is therefore a possibility of movements approximating those of physiological nature.

The mounting of the screws 10 and 20 of this prosthesis, in the eyelets defined by the different jaws, operates in a manner similar to that described above with reference to the second arrangement. Once this introduction is completed, two force balances are established, namely firstly between the screw 10, the springs 74 and 84, as well as those 76 and 86 and, secondly, between the screw 20, the springs 74 and 84, as well as those 75 and 85. These force balances are similar to that described with reference to the second arrangement, between the screw 20, the inner springs and the outer springs.

In the case of intervertebral flexion, the operation is symmetrical, namely that the cooperation of the two screws with the four jaws takes place in a manner similar to that described with reference to the right of FIG. 5 for the screw 20 and the two movable jaws. 60 'and 80. This is illustrated in Figure 8, which includes the branch 53' of the movable jaw 50.

Moreover, during the extension, the operation is also symmetrical, namely that the cooperation of the two screws and the four jaws takes place in a manner similar to that described on the right of FIG. 6, with reference to the screw 20 and the two movable jaws 60 'and 80. Such an intervertebral extension is illustrated in FIG. 9. As is apparent from FIGS. 7 to 9, the jaws 50 'and 70 form a first pair of jaws, associated with two return means, namely on the one hand the pair of springs 76 and 86 and, on the other hand, the couple of springs 74 and 84. In addition, the jaws 60 'and 80 form a second pair of jaws, associated with a first and a second return means respectively formed by the springs 74 and 84 on the one hand, and by the springs 75 and 85 on the other hand.

The equilibriums of force occurring during the implementation of the prosthesis of FIG. 7 are to be compared with those explained with reference to the curve of FIG. 10. It will be noted that the more the springs described below are stiff and or prestressed, the more they tend to oppose the movement of the movable jaws. In the context of the present invention, namely the prosthesis, the springs used are therefore stiff and possibly low preload (s), to allow movements of large amplitude, aimed at reproducing the natural physiology . Figure 12 illustrates a further alternative embodiment of the invention. In this figure 12 the mechanical elements similar to those of Figure 7 are assigned the same reference numbers, increased by 100.

This embodiment of FIG. 10 differs from that of FIG. 7 in that the two movable jaws 70 and 80, as well as the two springs 74 and 84, are replaced by a single mechanical member, namely a flange 165. The latter comprises a flexible body 174, made for example of an elastomeric material, and two rigid flanks 170 and 180. Each flank is further provided with a stud 173, 183, of generally spherical shape, adapted to cooperate with the walls next to a corresponding shaft 112 or 122. There is also another flange 166, whose structure is generally similar to that of the flange 165. It thus comprises a flexible body 175, bordered by two rigid flanks 160 and 161. However, , only the flank 160 is provided with a stud 163, adapted to cooperate with the walls facing the barrel 122. Finally, there is an additional flange 167, identical to that 166, which comprises a flexible body 176, and two flanks rigid 150 and 151, including only that 150 is provided with a pin 153, intended to cooperate with the shaft 112.

In this embodiment of FIG. 12, the slides 130 and 140 are bent in such a way as to form two ends 135 which interconnect each other. these slides. Thus, advantageously, these two slides can be formed by a single filiform element folded on itself in the manner of a loop.

In addition, advantageously, the distance separating the slides 130 and 140 along an axis perpendicular to their main axis, is close to the cross section of the screws. This allows the slides to provide a guiding function of these screws, to maintain them in a good position for permanent cooperation with the different nipples. Thus, in this figure 12, the screws 110 and 120 have a throat 110 'and 120' of smaller transverse dimension, cooperating with the two slides for the purpose of the guidance explained above.

By analogy with the embodiment of FIG. 7, the flanks 150, 160, 170 and 180 ensure the function of the movable jaws 50 ', 60', 70 and 80. In addition, the flexible body 174 ensures the function of the springs 74. and 84, the flexible body 175 provides the function of the springs 75 and 85, while the flexible body 176 provides the function of the springs 76 and 86. Finally, the respective studs 53, 163, 173 and 183 provide the function of the branches 53 ' , 63 ', 73 and 83. In this regard, it should be noted that the connection between each pin and the corresponding shank is of point type, which allows a possibility of articulation, as described above with reference to the first embodiment. . Each flexible body 174, 175 and 176 is associated with a value of stiffness, as well as prestressing, like the springs of the first embodiment. In addition, this flexible body can be surrounded by means of a rigid chamber, which thus constitutes a limit of deformation. Under these conditions, the force-displacement curve comprises, no longer two zones as before, but three different zones, as illustrated in FIG.

Areas I and II, similar to those of FIG. 10, are thus found, which respectively correspond to the prior force exerted by the patient to overcome the prestressing, then to a linear variation of the angular displacement as a function of the force. . Finally, there is a zone III in the form of asymptote, which corresponds to the abutment of the flexible body against the walls of the rigid chamber.

In the preceding examples, prostheses have been illustrated which connect only two vertebral stages. However, we can plan to connect, according to the invention, at least three vertebral stages. For this purpose, two main variants described below can be envisaged.

Thus, one can first associate several prostheses, similar to one or the other of those described above, as shown in Figure 13. On it, there are three pedicle screws 10i, IO ₂ and IO ₃ , and a first prosthesis I connecting a first pair of vertebrae 10i and IO ₂ , and a second prosthesis Ii connecting the other pair of adjacent vertebrae IO2 and IO3. In this Figure 13, as in Figure 15 described below, each prosthesis is shown in side view, very schematically. In addition, advantageously, it is planned to articulate the two prostheses

I and II relative to each other. For this purpose, we can associate them with a spherical separation member P, of the "pearl" type, which is in particular in accordance with one of those described and claimed in the French patent application 07 59227, filed in the name of the same Applicant. November 22, 2007, the contents of which are incorporated by reference. Note further that in Figure 13, the slides of the prostheses I and II are straight in opposition to the curved shape that will be described in the following embodiment.

As an alternative, it may be envisaged to connect at least three intervertebral stages to the month with a prosthesis according to the invention, illustrated in FIG. 14. On the latter, the mechanical elements analogous to those of FIG. same reference numbers, increased by 100.

The embodiment of FIG. 14, for three vertebral stages, differs from that of FIG. 12, for two vertebral stages, in that the slides 230 and 240 have larger axial dimensions, so as to extend in the vicinity of these three vertebrae. In addition, there are two flanges 265-ι and 2652, each of which connects the intermediate pedicle screw 215 with one or the other end pedicle screw 210, 220. As in the embodiment of FIG. 12, each boudin is provided with two pins respectively 273i, 273 ₂ , 283i and 283 ₂ , each of which allows the articulation relative to a corresponding pedicle screw. Finally, two other flanges 266 and 267 are placed in the vicinity of the curved ends 235 of the slides. Other embodiments not shown can be provided from the arrangement of FIG. 14. Thus, at least one of the strands can be replaced by springs, similar for example to those of FIGS. 1, 4 and 7.

In the embodiment of Figure 14, the two long slides are straight seen from the side, as the shorter slides of the first embodiments. However, as illustrated in Figure 15, it can be provided to produce slides 230 'and 240' having a curved shape, in side view. In this case, they advantageously have their concavity directed towards the spine. Moreover, in the case of a curved profile like that of FIG. 15, it is advantageous to provide a functional clearance between the walls opposite the slide and the flanges, in order to facilitate the movement of the latter along these lines. slides.

We will now describe a method of fitting the prosthesis of Figure 14, for which it is assumed that the pedicle screws 210, 215 and 220 have no throttling. It is first of all to implant these screws by placing on each of them a tapered end, for example of conical shape. In addition, the various tubes are assembled on the slides. Due to their elastic nature, and in the absence of screws, it will be noted that the different studs facing each other are in mutual contact. Then, the assembly formed by the slides and the flanges on the screws, provided with their pointed end. The latter then inserts between the elastic beads and then pushes them back so as to create a prestress. Finally, when the assembly is in the position of FIG. 14, the various tapered ends are removed, which is advantageously replaced by an element similar to that P of FIG. 13.

In this embodiment, this pearl P prevents the jaws from sliding along the barrel screws, opposite the vertebral bodies. Advantageously, it is possible to provide an additional bead in the vicinity of the vertebral bodies, in order to prevent sliding in the direction of the latter. In this case, these beads are introduced along the barrel of the screws, before placing the slides and the flanges. Figures 16 to 19 illustrate a further embodiment of the invention. In these figures, the mechanical elements similar to those of Figure 12 are assigned the same reference numbers, increased by 200.

There is a flange 365 comprising a cylindrical flexible body 374 bordered by two flanks 370, 380 rigid end. It is further provided four slides, the first two 330i, 33Û ₂ belong to a curved wire 330, so as to form a passage loop 350 of a first pedicle screw 310. Moreover, the other two slides 340i, 340a belong to another wire 340 also curved, forming a passage loop 360 of the other pedicle screw 320. Each passage loop defines a jaw within the meaning of the invention.

Each screw has a median area of smaller diameter, like an hourglass. This median zone cooperates, in an articulated manner, both with a corresponding jaw 350 or 360, as well as with a stud facing 373 or 383, as in the previous embodiments.

The first wire 330 is slidably mounted in orifices 370 ', formed in the first sidewall 370, adjacent to the loop 350, and also slidably extends into openings 374' made in the flexible body. The ends of this wire are finally fixed on the opposite side 380, by any appropriate means. Alternatively, it can be provided that these ends pass through the opposite flank slidably, and are further provided with a stop means for retaining the flank. In other words, the latter is integral in translation of the screw 310 in the direction of a compression of the flexible body, namely a rapprochement between the two sides. Similarly, the second wire 340 slidably extends successively through orifices 380 'formed in the sidewall 380 which is adjacent to the loop 360, and then additional openings 374 "made in the flexible body. above with reference to the first wire, the second wire may be either fixed on the flank 370 opposite the loop 360, or slidably mounted relative to the latter, being associated with stop means.

In the case of intervertebral flexion, as illustrated in Figure 19, this induces the mutual distance of the two pedicle screws. Under these conditions, the right screw 320 takes the left flank 370 to the right, while the left screw 310 takes the right flank 380 to the left, which induces a rapprochement of the two flanks. Under these conditions, the flexible body 374 is compressed, so that it plays a damping function and tends to bring the two screws towards each other, in their original position. In addition, during an intervertebral extension, not shown in the figures, each loop tends to move away from the pedicle screw, with which it was originally in contact. This displacement is accompanied by a corresponding compression of the flexible body, which thus again provides a damping function and tends to bring the assembly back to its initial rest position.

As is apparent from the foregoing, not only the extension but also the intervertebral flexion leads to a compression of the flexible body, which therefore acts as a shock absorber in one or the other of the cases. There are thus differences between this embodiment of FIG. 16 and, for example, that of FIG. 7. Thus, in this FIG. 7, each pair of jaws is associated with two distinct return means, each of which works in a respective meaning. On the other hand, in the embodiment of FIG. 16, these two return means are combined into a single return means 374, managing the two opposite directions of displacement. It can be seen that the more flexible the body 374, the more it allows a large movement between the two vertebrae. Thus, in the case of the prosthesis according to the invention, it is advantageous to choose a flexible body that is not very rigid, in order to allow a large intervertebral deflection. However, it can be expected to associate with this flexible body a deformation limit. Thus, it is possible for example to surround this flexible body 374 by means of a cylindrical rigid chamber 390, welded to one or the other of the flanks, as illustrated in FIG.

Referring to Figure 21 wherein the flexible body is in the rest position, the walls of the latter extend at a distance from those of the chamber. Under these conditions, at a certain stage of the deformation, the walls of the flexible body come into contact with those of the chamber, which prevents any further movement (FIG. 22).

In the previous embodiment, the chamber 390 makes it possible to limit the deformation of the flexible body 374, which consequently leads to limiting the relative movement between the two pedicle screws. However, it is possible to use other means to limit this race. By way of non-limiting example and in a manner that is not shown, mention may be made, for example, of any appropriate stop means, making it possible to stop the running of the slideways with respect to the rigid flanks.

The implementation of the device of Figures 16 and following, provided with a chamber as shown in Figures 20 to 22, is more particularly illustrated in Figure 23, which is similar to Figure 10. There is thus a curve illustrating the variations in the clearance between the two vertebrae as a function of the force F exerted on the flexible body 374.

The origin of this curve corresponds to a rest position, namely free of stress on the flexible body, when the screws are not inserted between the pins and a corresponding jaw. Then, when setting up this screw, this leads to a certain compressive force on the flexible body, coming into equilibrium with a certain clearance between the screws. This corresponds to the point (Fo; αo) on the curve.

Then, when the patient leans forward or backward, as we have seen above, this leads in both cases to the compression of the flexible body, which opposes this movement. In addition, the presence of the chamber forms a limit of movement, which is translated by the asymptote A corresponding to an intervertebral inclination α _max . The curve of the force as a function of the displacement is thus limited between, on the one hand, the "relative" origin formed by the points Fo and αo and, on the other hand, this asymptote A.

In the embodiment of Figures 16 and following, the return member is a solid flexible body. However, as an alternative, it can be provided to use a coil spring, extending along the axis connecting the two screws. The two free ends of this spring are then fixed, by any appropriate means, against the respective rigid flanks. This embodiment is advantageous, insofar as it makes it possible to reduce the friction in use, in particular by comparison with the friction related to the movement of the rods in the orifices of the flexible body.

In the various embodiments described above, the prosthesis according to the invention comprises at least two vertebral screws. In these conditions, the various screws are generally located on the same side of the spine, at a distance from the median vertical axis of the latter, with reference to the standing patient. It is also possible to implement two sets of vertebral screws, on either side of this median axis, each set of screws then belonging to a corresponding prosthesis.

However, as an alternative, it may be provided to use, not vertebral screws, maize rods each belonging to a connecting element, for example connecting two pedicle screws belonging to the same vertebral stage. Under these conditions, the prosthesis according to the invention comprises at least two of these rods, placed one below the other substantially along the median vertebral axis, as well as jaws, slides and return means, such as in the previous embodiments.

Claims

REVENPtCATtONS

1. Extra-discal stabilization prosthesis of the intervertebral joint, comprising at least two rods (12, 22; 112, 122; 212, 217, 222; 312, 322), called vertebral rods, adapted to cooperate with at least two different vertebrae; at least two pairs of jaws each having first and second jaws (50, 60, 70, 80; 150, 160, 170, 180; 250, 260, 2701, 2702, 2801, 2802; 350, 360, 370 380), each pair of jaws being placed in the vicinity of a corresponding rod; at least two slides (30, 40; 130, 140; 230, 240; 3301, 3302, 3401, 3402) defining a longitudinal axis of said prosthesis, both the first and second jaws of each pair of jaws being adapted to sliding, independently of one another, along at least two slides, along their longitudinal axis; first and second biasing means (74, 84; 75, 85; 76, 86; 174; 2741; 2742; 374) adapted to respectively bias the first and second jaws among each pair of jaws towards a corresponding vertebral rod, each vertebral rod being able to move, in use, both the first and second jaws along the slideways, against the first and second return means, each vertebral rod being further articulated with respect to each jaw.

2. Prosthesis according to claim 1, characterized in that said hinge between the rod and each jaw is exerted as a single point of contact between the rod and the walls facing each jaw.

3. Prosthesis according to claim 2, characterized in that at least one jaw (50, 60, 70, 80) comprises a bent connecting leg (53, 63, 73, 83) with a radius of curvature greater than the radius of curvature of the stem.

4. Prosthesis according to claim 3, characterized in that the curved branch is integral with two pads (51, 61, 71, 81), mounted on two rails (30, 40), slidably.

5. Prosthesis according to claim 3 or 4, characterized in that at least one biasing means comprises two springs (74, 84, 75, 85, 76, 86), each of which is mounted on a corresponding slide, these two springs. being able to recall a branch bent against the vertebral stem.

6. Prosthesis according to claim 2, characterized in that at least one jaw (170, 180) comprises a pin (173, 183) of articulation against a corresponding vertebral rod (112, 122).

7. Prosthesis according to claim 6, characterized in that at least one biasing means comprises a solid flexible body (174) and the pin (173, 183) belongs to a rigid flank (170, 180), integral with this body flexible.

8. Prosthesis according to any one of the preceding claims, characterized in that the first and the second biasing means are combined into a single return means comprising a central return member (374), bordered by two flanks (370, 380 each of which defines a respective first jaw, two pairs of slides (330, 340) are provided, each pair defining a respective second jaw (350, 360), and each pair of slides is slidable relative to the adjacent flank. the jaw defined by these slides, this pair of slides being however integral in translation of the opposite flank, at least in the sense of a rapprochement of the two flanks towards each other.

9. Prosthesis according to the preceding claim, characterized in that the central return member is a helical spring.

10. Prosthesis according to any one of the preceding claims, characterized in that each rod (12, 22) belongs to a corresponding vertebral screw, in particular to a pedicle screw (10, 20).

11. Prosthesis according to one of claims 1 to 9, characterized in that each rod is secured to a connecting element adapted to connect two vertebral screws intended to be implanted in the same vertebral stage.

12. Prosthesis according to any one of the preceding claims, characterized in that it comprises means (390; 392) for limiting the stroke between two adjacent rods.

13. Prosthesis according to the preceding claim, characterized in that the stroke limiting means are means for limiting the compression of a deformable body (374) belonging to a biasing means.

14. Prosthesis according to the preceding claim, characterized in that the compression limiting means comprise a rigid chamber (390), extending at a distance from the walls of the deformable body (374), in the rest position of the latter.

15. Prosthesis according to any one of the preceding claims, characterized in that it comprises means for preventing slippage of the slides and jaws along the rods, along the main axis of the latter, in a less a sense.

16. Prosthesis according to any one of the preceding claims, characterized in that two slides are adapted to guide the rods, in particular by cooperation of a zone (110 ', 120') of these rods (110, 120). whose cross section substantially corresponds to the distance separating these slides (130, 140).