WO2008000944A2

WO2008000944A2 - Posterior dynamic stabilisation prosthesis for the vertebral column

Info

Publication number: WO2008000944A2
Application number: PCT/FR2007/001058
Authority: WO
Inventors: Frederic Fortin; Olivier Gilles; Johann Robin; Brice Sennequier
Original assignee: Frederic Fortin; Olivier Gilles; Johann Robin; Brice Sennequier
Priority date: 2006-06-29
Filing date: 2007-06-26
Publication date: 2008-01-03
Also published as: WO2008000944A3

Abstract

The invention relates to a dynamic stabilisation device (2) comprising a one-piece means (21) which forms the viscoelastic core of the device and is made from an elastomer material that is biocompatible with the human body, said one-piece means (21) taking the form of a helical coil (210). Said coil (210) includes two shock-absorbing pads (211 a and b) which are positioned symmetrically on either side and which extend into collar-protected rods, the ends of which are provided with limit stop elements. The two arms of the device (2) form an angle (β) with the neutral axis. The aforementioned shock-absorbing pads (211 a and b) limit large movements by absorbing strong or violent dynamic loads. The device can be adapted to any intervertebral length.

Description

PROSTHESIS OF POSTERIOR DYNAMIC STABILIZATION APPLICABLE TO RACHIS

FIELD OF THE INVENTION The present invention relates to a dynamic stabilization device applicable to the spine which replaces or compensates for the defects of an intervertebral disk.

PRIOR ART: The problem to be solved is to supply the deficient part with a device whose mechanical physical characteristics are as close as possible to a healthy intervertebral disc whose behavior is specific; it is necessary to have the same conditions of stiffness of damping and resistance to static and dynamic stresses of long duration. A first series of inventions resolves it in a very partial way by using devices essentially comprising metal parts.

Thus US006516 proposes a solution that consists in implanting a tube-shaped metal spring between the vertebrae, which can not approach closer to the actual behavior of the intervertebral disc.

Other patents propose combinations of metallic elements by trying to combine the characteristics of these elements to get closer to the result. Thus, US Pat. No. 00858158 presents this kind of combination, with a rigid central part (solid rod) and a peripheral part having recesses. These two sets combined improve the characteristics of the aforementioned first US patent, but gives a behavior still far removed from the desired result Indeed the specific characteristics of the behavior of the disc are difficult to simulate by the combination of metal means. Moreover the fatigue resistance is far from guaranteed, characteristic of the first US patent cited above, but which gives a behavior still far removed from the desired result. Indeed, the specific characteristics of the behavior of the disc are difficult to simulate by the combination of metallic means alone. Other patents are approaching the intended purpose by, combining elastic and viscoelastic means. Thus, patent EP 0669109 describes and claims dorsal vertebral stabilization by implanting a strip of synthetic material inserted between two pedicle screws. This device requires means or insertion tools (patent FR 277449) for putting under tension and in compression said band which can work only in tension compression and possibly bending, but not in the other modes of deformation, which limits its field of application much less wide than that of the present invention. This results in a complexity of implementation with a restricted application.

WO 2044011 discloses and claims a central element formed of a coil spring with several turns: elastic means surrounded or surrounded by a viscoelastic sheath, the combination of these two means, one of which provides elasticity and the other , the viscoelasticity does not lead to the objective, the risks of remanent deformation and cracking then fatigue rupture due to the differences in amplitude of deformation of the two materials coexist and are still present. The complexity of behavior is difficult to pin down, accentuated by the aggressive environment of the in vivo medium.

The patent FR 2812186 also uses the combination of metallic and viscoelastic elements but, as in the previous case, it will necessarily occur a deterioration by fatigue. Patent WO05877121 also uses an elastic central block surrounded by a viscoelastic polymer; the combination of these means tries to reproduce the characteristics of the intervertebral bond, but the combination of two materials with different mechanical properties again causes fatigue fractures, detrimental to the reliability of this type of device.

In addition, this type of invention does not fully restore the functions of the intervertebral joint.

The present invention will solve these problems by implanting between the screw heads a means made in a single piece of viscoelastic material structure that will get very close by the nature of the material chosen for its manufacture characteristics of a healthy joint. Indeed, the shape of device and the viscoelastic nature of the material used for the manufacture of the device object of the invention gives it a hybrid biomechanical behavior between that of a viscoelastic device and a purely elastic device. This device develops more nuanced characteristics and is closer to that of amphiarthrosis, a complex biological entity that can not be easily modeled by a device made from a purely viscous or purely elastic material. This new device will have other advantages:

to be very easily put in place in pedicular screws which are not specific to the device

- to resist in fatigue the aggressive solicitations of the human body in which it is inserted. The drawings for understanding the invention are:

In a first version of the invention

Figure 1 plate 1/16: perspective view of the posterior dynamic stabilization device, object of the invention

Figure 2 plate 1/16: exploded view of the posterior dynamic stabilization device

Figure 2/16 board: exploded perspective view of the posterior dynamic stabilization device with its fastening means on the spine. ,. ,,,

Figure 4 Plate 2/16 a view of the posterior dynamic stabilization device assembled with its fastening means on the spine.

Figure 5 3/16 board: view in cross section of a pedicle screw fastening head corresponding to one end of the posterior dynamic stabilization device. Figure 6 board 3/16 longitudinal sectional view of one end of the device provided with a ring, head of, fastening inserted in pedicle screws

Figure 7 board 4/16 view, of an implantation on the back of two devices implanted on the rachis Figure 8 plate 4/16 perspective view of two devices implanted on the .rachis Figures 9 and 10 plate 5/16 profile views of one of the devices working according to a first mode of work (traction compression)

Figures 11 and 12 plate 6/7 profile views of a device working in a second mode of work, Figure 11: forward flexion, Figure 12: flexion extension

Figure 13 plate 7/16 side view of two devices working according to a third mode of work in lateral bending

Figure 14 Plate 7/16 posterior view of a single device in a fourth mode of work: Twisting. In a second embodiment of the invention:

Figure 15 plate 8/16: front view of the new damping device conforming to the angle of anatomical lordosis β

Figure 16 plate 8/16: perspective view showing the variations of the diameter in different sections that evolve along the turn

Figure 17 board 8/16: exploded view of the various means constituting the device of the invention, central core and rings

Figure 18 plate 8/16: cross-sectional view at the rings of the device. Figure 19 plate 9/16: exploded view of the device and its fastening screws on the spine with clamping plugs

Figure 20 plate 9/16: view of the same assembled device, mounted on the spindle fixation screws mounted with the clamping plugs Figure 21 plate 10/16: side view of the same device mounted on the spine and operating in tension

Figure 22 plate 10/16: side view of the same device mounted on the spine and operating in compression

Figure 23 plate 11/16: profile view of the same device mounted on the spine and operating in flexion (coil placed inside the spine)

Figure 24 plate 11/16: profile view of the same device mounted on the spine and operating in extension (coil placed inside the spine) Figure 25 plate 12/16: rear view of the same device mounted on the spine and operating in left lateral flexion

Figure 26 plate 12/16: posterior view of the same device operating in torsion not fixed on the spine Figure 27 Plate 13/16: posterior view of the device inserted into the screw heads with a first gripper.

Figure 28, 29,30 plate 13/16: views of three devices inserted in the gripper, mounted on the spine by exerting a compressive prestress, without constraint, and with a pre-stretched extension

Figure 31 plate 14/16: view of another gripper taking the device to insert it into the spine

Figure 32 plate 14/16: perspective view of the device version 2

Figure 33 plate 14/16: detailed view of the end of the clamp into which the device for implantation is inserted

Figure 34 plate 15/16: view of another gripper taking the modified version 2 device for a better grip.

Figure 35 plate 15/16: perspective view of the device version 2 whose ends have been modified for gripping

Figure 36 plate 15/16: detailed view of the end of the clamp into which the device whose ends have been modified

Figure 37 Plate 16/16: view of a fixation of another device in three pedicle screws.

Figure 38 16/16 plate seen from a device of asymmetrical shape, corresponding to the previous fixation

In a first embodiment of the invention

The device 1 comprises a means 11 is unique, made in one piece in an elastomeric material with viscoelastic behavior, biostable, and biocompatible with the human body; it is for example a material of the polyurethane type corresponding to that of patent application WO 05030281.

The means 11 comprises a central portion 110. The central portion 110 of the means 11 is formed of at least one coil of helical shape which can work under all the mechanical stresses of traction, compression, flexion extension, and torsion according to a law of behavior close to the biomechanical response of healthy intervertebral connections. The central portion 110 is integral and made of the same elastomeric material, it has no inclusion of synthetic or metallic fiber that could weaken the device by heterogeneous deformations between various elements that can cause cracking altering the fatigue strength.

The central portion 110 also does not comprise assembly of parts by screwing, gluing or welding which could have the same undesirable effects by incomptability of different means or material. The posterior dynamic stabilization device 1 further comprises, at its two ends, rings 12a and 12b of biocompatible rigid material (such as titanium alloy) whose function is to allow the connection of the central means 11 with pedicle screws 2a and 2b ; the heads of said pedicle screws 2a and 2b have cavities in which the rings 12a and 12b are interlocked and are themselves locked by clamping screws 21a and 21b.

To ensure this connection and transmit the mechanical stresses to the central portion 110 forming part of the means 11, the rings 12a and 12b surround the parts 112a and 112b of the means 11; they are overmolded during the manufacturing phase of the means 11. The rings 12a and b abut each side on shoulders 111a and 111b for a total of four shoulders for the means 11 are two at the end of the central portion 110, two at the end of the means 11 which thus prevent slipping of the rings 12a and b with said means 11. The rings 12a and 12b are sufficiently thick to withstand the contact pressure on the screws 2a and 2b when tightening the screws. plug 21a and 21b on the rings 12a and 12b (Figure 5) and to limit the deformations that may damage the viscoelastic portions 112a and 112b; they may also comprise means for not injuring the shoulders defined above.

The screws 21a and 21b are tightened to a determined torque high enough to lock the means 11 between the two pedicle screws 2a and 2b but avoiding any crushing of the rings 12a and 12b. The tightening of the rings 12a and 12b combined with the blocking without play of said rings with the means 11, makes it possible to transmit the intervertebral forces and the resulting displacements to the part Central 110 of the means 11 which acts as a damper and dynamic stabilization.

The combination of the means 11 of viscoelastic behavior with the fastening means which are the rings 12a and 12b and the pedicle screws 21a and 21b, gives the device 1 a good dynamic stabilization without any complex combination of inserts.

The Device 1, whether mounted alone or in number, can withstand all types of mechanical stresses that it transforms into static or dynamic responses, in single or combined working mode, which allows displacements according to a near viscoelastic constitutive law. An intervertebral connection To stabilize the intervertebral space, two devices 1 are mounted on the spine, each able to support alone or associated with another device the usual working modes defined:

Compression Traction, Flexion Extension, Lateral Flexion, and Torsion.

In all these modes of work the device or devices taken separately or combined exert a restoring force to all the dynamic stresses to which it is subjected according to a law of viscoelastic behavior.

In the case of two devices 1 (Figure 7 and 8) mounted on the spine, these restoring forces have the following effects:

In traction, the two devices 1 elongate (FIG. 9) In compression, the two devices 1 are shortened

(Figure 10)

In bending, the two devices 1 flex and lengthen (FIG. 11)

In Extension, the two devices 1 flex and shorten (FIG. 12)

In Lateral Bending one of the two devices elongates while the other compresses (Figure 13)

In torsion, the device 1 is twisted by an angle between the fastening means, during the rotation of the vertebrae (FIG. 14) Moreover, the implantation of one or more of these devices poses no problem, and the device 1 does not not afraid of the phenomena of fibrosis of the medium, unlike the springs or other complex devices of the prior art.

This device consists of a single means essential to its operation, which demonstrates its simplicity vis-à-vis those of the prior art, and suddenly its effectiveness.

In a second embodiment of the invention:

The dynamic stabilization device 2 perfecting the prior device 1 comprises: A one-piece viscoelastic soul means 21 made of the same elastomer material with biostable viscoelastic behavior and biocompatible with the human body, or in a material with equivalent characteristics that would fulfill the same functions.

The one-piece means 21 is formed of a coil 210 of helical shape which is symmetrically continuous on each side by two damping blocks 21a and b, themselves extended by rods 212a and b, of non-circular section (to avoid the rotation in the rings, and whose ends are abutments 111a); said monobloc means 21, molded in manufacture in the same viscoelastic material is capable of working in all forms of dynamic stresses: traction, compression, flexion extension, torsion, lateral flexion according to laws of dynamic behavior which approach the best of a healthy intervertebral connection.

The essential differences between the means and the functions of the device 2 with respect to the device 1 are as follows:

The spiral-shaped turn 210 is attached laterally to the viscoelastic damping blocks 211a and 211b, which did not exist in the device 1. These blocks 211a and b serve to limit the large displacements, by absorbing the dynamic or severe dynamic stresses, which the first device 1 could not contain.

In addition, the coil 210 may preferably have a variable diameter section as one moves toward the middle of the helical portion (FIG. 16) in order to optimize the compromise between stiffness and damping and to better distribute the constraints in the turn.

The one-piece means 21 comprises rods 212a and b, which have transverse sections of polygonal shapes or with the presence of flats or non-circular section to prevent the rings 22a and 22b overmolded on the means 21 to rotate during the torsional urges of the vertebrae; which also makes it possible to exert a restoring force during the torsional stresses of the device 2.

The dynamic behavior of the new device 2 is thus significantly improved, while retaining the other dynamic characteristics of the device 1.

The two damping blocks 211a and b and the rods 212a and b provided with their stops 111a, thus form two symmetrical branches connected by the turn 210, each branch forms an angle β corresponding to the anatomical lordosis of the spine, thereby allowing the device 2 to exert a permanent restoring force towards the anatomical lordosis in order to return the deficient intervertebral connection to its normal anatomical position.

Unlike the first device 1, the turn 210 of the device 2 is not coaxial with the axis of the branches because the turn 210 is attached laterally to the damping blocks 21a and b.

The device 2 thus has a more compact shape than the device 1 and therefore a smaller footprint. Thus the device 2 can be inserted more easily between two pedicle screws separated by any distance, as short as it is, to which it fits in all cases.

All modes of work retraction, compression, flexion extension, lateral bending, torsion (figures 21 to 26) are possible without inconvenience and can occur independently or simultaneously

The rings 22a and 22b made of rigid material as in the first version surround without play the rods 212a and b; they comprise at their ends grooves 220a and 220b gripping means of the device 2 by a specific clamp Ps used for its mounting in the pedicle screws 2a and 2b before proceeding to tightening by the threaded plugs 21a and 21b.

A forceps Ps has been designed to facilitate the gripping of the device 2, but it has other characteristics:

It allows prestressed distraction or compression at the time of installation of the device, which allows the device 2 to adapt to each pathology encountered.

This gripper Ps can mount two devices 2 on the spine in several configurations: -Figure 28 with a distraction preload exerting a compressive biasing force on the vertebrae -Figure 29 without preload of assembly -Figure 30 with a compression preload exerting a distraction force in distraction on the vertebrae.

In addition, the device 2 can work in two steps to absorb the efforts it undergoes; it actually has a double compression damping, thanks to the combination of operation of the turn 210 and damping blocks 211 a and b. In a first step, the central turn 210 is deformed under the dynamic stresses of compression until contact of the damping blocks 211a with 211b, which makes it possible to damp the said dynamic stresses thus absorbed by deformation of said turn 210. In a second time: the damping blocks 211a and b come into contact, and the dynamic stresses are absorbed by compression of the viscoelastic material of the two blocks, in contact, without further deforming the turn 210, which allows to absorb and then block the dynamic stresses in compression even violent.

In two other variants of the device 2 design arrangements provide other advantages:

-cas No. 1 all means remain identical, but the rings 222a and b no longer include grooves 220 a and b, there is a reduction in size along the length of the device 2, which reduces the length of the device ( figure 32)

-cas No. 2 all means remain identical but the stops (111a and b) has pins (1110) which allow easier insertion with the clamp Ps, which allows to exert compressive prestressing on the device 2 and arranged (Figure 35)

Finally, in a last variant of the device 2, the new device 3 (FIG. 38) is asymmetrical, its two branches equipped with their rings 222 and 322 on each side of the turn 210 have different lengths (shorter or longer), the viscoelastic element 31 is always monobloc, but a ring 222 is placed identical to that of the first version on the first branch and another longer ring 322 on the other branch. This configuration allows the insertion of the device 3 into three pedicle screws 2a, 2b, 2c (see FIG. 27), which has the following advantages:

to maintain a dynamic damping state between the pedicle screws

- To stiffen the connection between the screws 2b 2c by obtaining a single device 3 formed of a flexible intervertebral connection juxtaposed with an adjacent rigid connection that is the ring 322, arrangement that is encountered in arthrodesis. The dynamic stabilization devices (2) or (3) have branches whose axes form an angle (β) with respect to the neutral axis, and are not coaxial with the winding axis of the coil (210) which makes the devices (2) or (3) more compact by allowing it to adapt to any intervertebral distance.

Finally the device 2 can be attached to the vertebrae with mono axial or poly axial screws.

Claims

R E V E N D I C A T IO N S

1-posterior dynamic stabilization device (1) characterized in that it comprises a means (11) central single-piece made of a single block of elastomeric material viscoelastic behavior biostable and biocompatible with the human body, said means (11) having a central turn (110 of helical shape made in the same elastomeric material as the means (11) and able to respond to all the usual mechanical stresses in the intervertebral space

2- posterior dynamic stabilizing device (1) according to claim 1 characterized in that it comprises at its two ends rings (12a and 12b) biocompatible rigid material for connection to the central means (11) with pedicle screws ( 2a and 2b), the heads of said pedicle screws (2a and 2b) having cavities in which are inserted the rings (12a and 12b) itself blocked by clamping plugs (21a and 21b).

3- posterior dynamic stabilization device (1) according to claims 1 and 2 characterized in that the rings (12a and 12b) abut each side on shoulders (111a and 111b) preventing slipping of the rings (12a and 12b). ) with said means (11) and are sufficiently rigid to withstand the contact pressure on the pedicle screws (2a and 2b) when tightening the plugs (21a and 21b) by limiting the deformations without damaging the viscoelastic portions (112a and 112b) , the tightening of the rings (12a and 12b) combined with the locking without play of said rings with the means (11), for transmitting integrally the intervertebral forces and the resulting displacements to the central portion (110) of said means (11) which thus plays its role of damper and dynamic stabilization by allowing the device (1) to work separately or simultaneously according to all the working modes encountered in the stresses imposed by the e human body -.

4-dynamic stabilizing device (2) improving the device (1) comprising a means (21) monobloc, viscoelastic core made of an elastomeric material with behavior viscoelastic, and having rings (220 a and b) at its ends said means (21) monobloc being formed of a coil (210) of helical shape characterized in that said coil (210) comprises symmetrically on each side: two branches formed of two damping blocks (211a and b), themselves extended by rods (212a and b), of non-circular section to prevent rotations inside the rings (220a and b) and whose ends are stops (11 la), the two branches of the device (2) making an angle (β) with the neutral axis, thereby allowing the device 2 to exert a permanent restoring force towards the anatomical lordosis in order to reduce the deficient intervertebral connection to its normal anatomical position.

5 - dynamic stabilization device (2) according to claim 4 characterized in that the coil (210) has a variable diameter section (d), as one moves towards the middle of the helical portion to optimize the compromise stiffness damping and better distribute the stresses in the turn.

6-dynamic stabilization device (2) according to one of the preceding claims characterized in that the device (2) can work in two steps to absorb the compression forces it undergoes through the combination of operation of the coil

(210) and viscoelastic blocks (211 a and b)

firstly, the central turn (210) deforms under the dynamic stresses of compression until it reaches the damping blocks (21a and b), damping the dynamic stresses absorbed by deformation of said turn (210)

second stage: the damping blocks (21 a and b), being in contact, the dynamic stresses are absorbed, then blocked by compression of the viscoelastic material of the two blocks in contact, this without deformation of the turn (210), which allows to cope with violent dynamic compression urges.

7-dynamic stabilization device (2) according to one of the preceding claims characterized in that the device (2) comprises a first arrangement on the rings (222a and b) which no longer include grooves (220 a and b), which allows a reduction of space over the length of the device (2) 8-dynamic stabilization device (2) according to one of the preceding claims characterized in that the device (2) comprises a second arrangement concerning the stops (11 la and b) which have at each end pins (1110), s inserting in a gripper (Ps) exerting a prestress in compression on the device (2) thus modified.

9-Dynamic stabilization device (3) according to one of the preceding claims characterized in that the new device (3) is asymmetrical, the two branches of the viscoelastic monobloc element (31) on each side of the coil having different lengths, thus allowing insertion of the device (3) into three pedicle screws (2a, 2b, 2c) allowing

to maintain a dynamic damping state between the pedicle screws (2a and 2b)

- To stiffen the connection between the screws (2b and 2c) by the mere presence device (3) formed of a flexible intervertebral connection juxtaposed with an adjacent rigid connection, the ring (322) ensuring the rigidity of the connection thus obtained, that the we meet in arthrodesis.

10 -Dispositif dynamic stabilization (2) or (3) according to claims 4 and 9 characterized in that the axes of each branch which form an angle (β) relative to the neutral axis are not coaxial with the axis winding the coil (210), which makes the device (2) or (3) more compact by allowing it to adapt to any intervertebral distance.