FR2935896A1 - Anteroposterior insertion type disc prosthesis for replacing intervertebral disk between upper and lower vertebrae of patient, has plates and intermediate core made of colorless organic polymer thermoplastic reinforced by carbon fibers - Google Patents

Abstract

The prosthesis has two plates (1, 2) comprising fixation surfaces (1b, 2b) fixed to upper and lower vertebrae, respectively. An intermediate core (3) has a sliding surface (3b) placed in contact with a contact surface (2a) of one of the plates. The anatomical shapes of the fixation surfaces of the plates are respectively adapted to the shapes of vertebral plates of the vertebrae. The plates and the core are made of polyether ether ketone (PEEK)(RTM: colorless organic polymer thermoplastic) reinforced by carbon fibers.

Description

The present invention relates to the field of medical prostheses, and more particularly to disc prostheses intended for the replacement of an intervertebral disc in a patient.

A disc prosthesis is known, such as that described in document FR 2 805 733, and consists of two parts articulated in rotation with respect to each other and intended to be each fixed respectively to one of two adjacent vertebrae. . Such a disc prosthesis has the disadvantage of inducing a significant lateral shift of at least one of the adjacent vertebrae.

away from the middle axis of the patient's column when tilting on the sides or front to back. This shift induces stress in the muscles and ligaments of the patient's spine, and adversely affects the stability of the prosthesis.

In order to more faithfully reproduce the movements provided by a

natural intervertebral disc, it has been proposed by WO 02/089701 a disc prosthesis for replacing an intervertebral disc between a first vertebra and an upper vertebra two adjacent lower vertebrae of a patient, comprising three movable parts including:

a first plate, having a first contact surface, and having a first

opposed fixation face shaped to be fixed to the first vertebra, the first plate extending in first and second distinct directions substantially perpendicular,

a second plate, having a second contact surface, and having a second opposite fixing face shaped to be fixed to the second vertebra, the

second plate extending in third and fourth distinct directions substantially perpendicular,

an intermediate core, having first and second opposite sliding faces intended to respectively come into complementary contact with the contact surfaces of the first and second plates, movable in

translation with respect to at least one of the first or second plates in at least two directions.

When implanting the prosthesis, the first and third directions are intended to be substantially contained in the mediosagittal plane of the patient, while the second and fourth directions are intended to be

substantially contained in a frontal plane of the patient.

The mobility in translation of the intermediate core with respect to at least one of the first or second trays makes it possible to limit the phenomenon of 91F17Ei'.dnc 2 shifting of the vertebrae away from the mean axis of the patient's column during tilting movements. Such a prosthesis is generally made with metal trays and an intermediate polyethylene core, to promote the relative sliding of the core between the trays. A disadvantage of such a prosthesis is that the friction between the polyethylene and the metal generate a significant amount of debris, especially polyethylene. In addition, there is a phenomenon of progressive creep of the polyethylene under the effect of the mechanical stresses of compression during use, creep that results in a variation of the disc height over time, which is detrimental to the patient and limits the stability and longevity of the prosthesis. And for good durability and stability of the intermediate polyethylene core, it must have a fairly high height. Finally, the use of an intermediate ceramic core or traditional PEEK (polyetheretherketone) is only possible for large core heights to avoid any risk of breakage of these materials that are too fragile thin. As a result, the prostheses comprising at least three moving parts together with an intermediate polyethylene core have a very large overall height, incompatible with the natural intervertebral disc space. The constitution in three relatively high parts of such a prosthesis forces the practitioner to dig, plan and prepare the first and second vertebrae to insert the prosthesis. This results in significant operating time and degradation of the "bone capital" of the patient that weakens the vertebrae and may compromise a possible replacement of the prosthesis during a recovery. It is also important to ensure reliable anchoring of disc prostheses in the vertebrae to avoid any risk of ejection that can cause serious injury to the patient, including the spinal cord. A first problem proposed by the invention is to design a disc prosthesis capable of providing the patient with a mobility as close as possible to that of an intervertebral disc, which generates little debris during its use, and which has an increased longevity. Simultaneously, the present invention aims at designing a disc prosthesis that can be inserted and fixed between two adjacent vertebrae without having to prepare the vertebrae by excessive planing, thus optimally preserving the bone capital, while ensuring reliable fixation of the prosthesis for avoid any risk of ejection. To achieve these and other objects, the invention provides a disc prosthesis for replacing an intervertebral disc between a first and an adjacent lower first and a second lower vertebra of a patient, comprising at least three movable parts therebetween including: a first tray, having a first contact surface, and having a first opposing attachment face shaped to be attached to the first vertebra, the first tray extending in first and second distinct directions substantially perpendicular, - a second plate, having a second contact surface, and having a second opposing fixing face shaped to be fixed to the second vertebra, the second plate extending in third and fourth substantially perpendicular directions; an intermediate core, having a first and a second opposite sliding face for to come respectively in complementary contact 1s with the contact surfaces of the first and second plates, displaceable in translation relative to at least one of the first or second plates in at least two directions, in which - the first fixing face of the The first tray has an anatomical shape adapted to the shape of the vertebral plateau of the first vertebra and / or the second attachment face of the second tray has an anatomical shape adapted to the shape of the vertebral plateau of the second vertebra, - the first and second trays and the intermediate core are made of polyetheretherketone (PEEK) reinforced with carbon fibers. The use of carbon fiber-reinforced polyetheretherketone (PEEK) makes it possible to effectively limit the friction between the moving parts of the disc prosthesis, and to limit the generation of debris, thus making it possible to significantly increase the service life. of the prosthesis. Such a material also makes it possible to produce trays and an intermediate core of small thickness and nevertheless having satisfactory mechanical characteristics, in particular avoiding any risk of deformation or rupture, and reducing the overall height of the prosthesis in order to make it compatible with the natural intervertebral space of the patient. Carbon fiber reinforced PEEK differs from traditional PEEK 35 in that it includes sections of carbon fibers. Carbon fiber-reinforced PEEK is thus much stronger and more resistant than traditional PEEK and also has coefficients of carbon fiber / PEEK reinforced PEEK wear and friction factor 911 = DEP.doc carbon fibers lower than those of a traditional PEEK / traditional PEEK contact.

The anatomical forms of the first fixation faces of the first and

second trays allow a quick and easy placement of the prosthesis between the two adjacent vertebrae without having to perform leveling planing or other preparation of the vertebrae, especially since the overall height of the prosthesis may be low, substantially equal to the natural intervertebral space.

The significant reduction in friction resulting from the use of carbon fiber-reinforced polyetheretherketone (PEEK), combined with the particular architecture of the intermediate-core prosthesis displaceable in translation relative to at least one of the adjacent trays, makes it possible to reduce important way the stresses induced on the contact surfaces between the trays

and the vertebrae. The anatomical shapes of the attachment faces of the plates themselves participate in the anchoring and the retention of the prosthesis, avoiding the use of anchoring pins intended to sink into the vertebrae, pins that would not not easily feasible polyetheretherketone (PEEK) reinforced with carbon fibers and present high risk of breakage.

Advantageously, it can be provided that:

the first plate is intended to be fixed to the lower vertebral plateau of the first vertebra,

the first fixing face of the first plate is convex in the first and second directions.

Preferably, it can be provided that:

the second plate is intended to be fixed to the upper vertebral plateau of the second vertebra,

the second fixing face of the second plate is substantially plane in the third and fourth directions.

Such shapes of the first and second trays are well adapted to the natural anatomy of the vertebrae.

According to an alternative, it can be provided that:

the second plate is intended to be fixed to the upper vertebral plateau of the second vertebra,

the second fixing face of the second plate is substantially plane in the third direction and convex in the fourth direction. 91 FDE1.doc Such a convexity in the fourth direction of the second attachment face of the second plate makes it possible to marry at best the natural anatomical shape of the second vertebra when the second plate extends in the fourth direction along a length likely to induce conflict with

5 vertebral vertebrae.

Advantageously, the attachment faces of the first and second plates may comprise a plurality of notches respectively perpendicular to the first direction and the third direction, the attachment faces and their notches being preferably coated with porous titanium. The notches allow to limit

risks of slipping of the trays with respect to the vertebrae, in particular just after the fitting of the prosthesis. Once the prosthesis is installed, bone material will gradually fill the notches, and all the more easily if the fixing faces and their notches are coated with porous titanium, promoting good osseointegration.

Preferably, at least one of the trays comprises a border at the periphery, said border preferably being discontinuous, which limits the translational movements of the intermediate core with respect to said plate. This effectively limits the risk of ejection of the intermediate nucleus which could cause serious lesions in the patient.

Advantageously, it can be provided that:

one of the sliding faces of the intermediate core and the contact surface of one of the plates come into contact with one another according to a contact surface substantially in the form of a spherical cap,

the other sliding surface of the intermediate core is flat and comes into contact

with the contact surface of the other tray according to a planar contact surface.

Preferably, the intermediate core may comprise at least one groove on its planar sliding face, preferably passing through the center of the plane sliding face of the intermediate core. Such groove allows the supply of body fluids to better lubricate the contact between the face of

plane sliding of the intermediate core and the contact surface of the plate.

In addition, the fact that the groove passes through the center of the planar sliding face of the intermediate core makes it possible to eliminate a manufacturing irregularity when this planar sliding face is produced by turning. In fact, when training the flat sliding face, the cutting speed of the tool

in the center of the plane sliding face is almost zero. This causes an alteration of the surface condition and the possible appearance of imperfections such as a small tip of residual material. The presence of the groove in the center of the sliding face makes it possible to easily eliminate the area likely to present a surface irregularity. Advantageously, the intermediate core may comprise on its planar sliding face two grooves perpendicular to one another and intersecting in the center of the planar sliding face of the intermediate core. The two grooves make it possible to better lubricate the contact surface between the intermediate core and the plate. Other objects, features and advantages of the present invention will become apparent from the following description of particular embodiments, with reference to the accompanying figures, in which: FIG. 1 is a perspective view of a disc prosthesis; according to the invention; Figure 2 is a side view of the disc prosthesis of Figure 1; FIG. 3 is a rear view of the prosthesis of FIG. 1; Figure 4 is a perspective view of the second tray of the prosthesis of Figure 1; Figures 5 and 6 are sectional views of the prosthesis of Figure 1 in different configurations; and FIG. 7 is a perspective view of the intermediate core of the prosthesis of FIG. 1. An embodiment of the disc prosthesis according to the invention is shown in FIG. 1. It is a disc prosthesis with anteroposterior insertion. This comprises a first plate 1, having a first contact surface 1a (not visible in FIG. 1), and having a first opposite fixing face 1b shaped to come into contact with the first vertebra. The first plate 1 extends in a first direction 1-1 and in a second direction I1-11 distinct substantially perpendicular. The prosthesis comprises a second plate 2, having a second contact surface 2a, and having a second opposite fixing face 2b shaped to come into contact with the second vertebra. The second plate 2 extends in a third direction 11I-III and in a fourth direction IV-IV distinct substantially perpendicular. After implantation of the prosthesis, the first and third directions 1-1 and III-III are intended to be substantially contained in the mediosagittal plane of the patient, while the second and fourth directions 11-11 and IV-IV are intended to be substantially contained in a frontal plane of the patient. The prosthesis further comprises an intermediate core 3 having a first sliding face 3a (not visible in FIG. 1) and a second opposite face 3b of sliding 3b intended to respectively come into complementary contact with the bearing surfaces. contact la and 2a of the first and second plates 1 and 2. The intermediate core 3 is movable in translation relative to at least one of the first or second plates 1 and 2 according to at least two

directions.

In the embodiment described in FIGS. 1 to 7, the intermediate core 3 is displaceable in translation with respect to the second plate 2 along the two directions III-III and IV-IV as well as in any direction contained in the plane defined by those -this.

The first attachment face 1b of the first plate 1 has an anatomical shape, that is to say a shape adapted to the natural shape of the vertebral plateau of the first vertebra. Similarly, the second fixation face 2b of the second plate 2 has an anatomical shape, that is to say a shape adapted to the natural shape of the vertebral plateau of the second vertebra.

The first and second trays 1 and 2 as well as the intermediate core 3 are made of polyetheretherketone (PEEK) reinforced with carbon fibers.

In the embodiment shown in Figures 1 to 7, the first plate 1 is intended to come into contact with the lower vertebral plate of the first vertebra, while the second plate 2 is intended to come into contact

20 with the upper vertebral plateau of the second vertebra. It is more particularly seen in Figures 2 and 3 that the first attachment face lb of the first plate 1 is convex in the first and second directions 1-1 and II-11. The convexities C1 and C2 (materialized in dotted lines) of the first fixing face 1b can be provided by the use of a single radius of curvature or by

Several successive radii of curvature.

The curvatures of the convexities C1 and C2 of the first attachment face 1b of the first plate 1 are adapted to the curvatures of the natural concavities of the lower vertebral plateau of the first vertebra, so as to marry the best shape.

FIGS. 2 and 3 show more particularly that the second fixing face 2b of the second plate 2 is substantially plane along the third and fourth directions III-III and IV-IV. This planar configuration allows the second plate 2 to come at best in contact with the upper vertebral plateau of the second vertebra, vertebral plateau which is generally substantially flat.

In another embodiment of the invention (not shown in the figures), the second fixing face 2b of the second plate 2 is substantially plane in the third direction III-III and convex in the fourth direction IV-IV. The convexity of the second fixation face 2b of the second plate 2 then makes it possible to come into contact with the upper vertebral plateau of the second vertebra, even in the areas where the vertebral occlusions are located. Such convexity along the fourth direction IV-IV is useful when the second plate 2 extends along a longer length in the fourth direction IV-IV to cover at least part of the uncus area. As best seen in Figures 1 and 2, the attachment faces 1b and 2b of the first and second plates 1 and 2 comprise a plurality of notches 4 respectively perpendicular to the first direction 1-1 and the third direction III- III. Such notches 4 make it possible to limit the risks of ejection of the prosthesis according to the first and third directions 1-1 and III-III. FIGS. 5 and 6 show more particularly that: the first sliding face 3a of the intermediate core 3 and the first contact surface 1a of the first plate 1 come into contact with one another in a surface of contact S1 substantially shaped spherical cap; - The second sliding surface 3b of the intermediate core 3 is flat and comes into contact with the contact surface 2a of the second plate 2 according to a flat contact surface S2. The intermediate core 3 is displaceable in translation relative to the second plate 2. By way of example, there is shown in FIG. 6 a lateral inclination of the patient. We see that the intermediate core 3 has moved relative to its initial rest position (Figure 5) by a translation along the fourth direction IV-1V. The translational movement of the intermediate core 3 effectively limits any lateral shifting of the first and second vertebrae relative to each other during lateral inclination of the patient. Such a translational movement is also possible along the third direction III-III, as well as along other directions contained in the plane defined by the third and fourth directions III-III and IV-IV when the patient combines a motion of lateral inclination with a tilting movement forwards or backwards. In order to avoid a movement beyond what is physiologically possible or desirable, and to avoid the ejection of the intermediate core 3, the second plate 2 may include an edge 5 at the periphery.

The border 5 limits the translation movements of the intermediate core 3 relative to the second plate 2. It is seen more particularly in Figure 4 that the border 5 is discontinuous along the periphery of the second plate 2. This discontinuity allows 53 the supply and circulation of body fluids to lubricate the contact between the second sliding surface 3b of the intermediate core 3 and the second contact surface 2a of the second plate 2. It is thus possible to improve the sliding between the intermediate core 3 and the second plateau 2 between which 5 occur the movements generally of greater amplitude. Still to lubricate this contact between the intermediate core 3 and the second plate 2, we see more particularly in Figure 7 that the intermediate core 3 has two grooves 6a and 6b on the second sliding surface 3b plane. In this way, the supply of body fluids is promoted in order to best lubricate the entire contact between the intermediate core 3 and the second plate 2. The two grooves 6a and 6b are mutually perpendicular and intersecting in the center of the second sliding face 3b planar intermediate core 3. The embodiment of at least one groove 6a or 6b passing through the center of the second sliding face 3b plane of the intermediate core 3 eliminates a manufacturing imperfection when the second sliding face 3b is achieved by turning with a progressive radial advance tool from the periphery of the second sliding face 3b towards its center. Indeed, the tool then has a substantially zero cutting speed in the center of the second sliding face 3b, which generally induces a locally unsatisfactory surface condition that the grooves 6a or 6b can remove. The use of polyetheretherketone (PEEK) reinforced with carbon fibers significantly reduces friction and thus the generation of debris. In addition, the mechanical characteristics of this particular material make it possible to produce disk prostheses of overall height H (FIG. 2) which is small, compatible with the natural intervertebral space, by using very small thicknesses of materials for trays 1 and 2 and for the intermediate core 3, thicknesses to which other materials (metal, polyethylene, ceramic, ...) are unsatisfactory because too soft, too fragile or too brittle. The overall height H is measured at the base of the notches 4. The height of the notches 4 is indeed not taken into account, they being intended to sink into the vertebral trays. In practice, good results have been obtained by using carbon fiber-reinforced polyetheretherketone (PEEK) having substantially one or more of the following mechanical properties: Mechanical properties Values Measuring methods Tensile strength 220 to 230 Mpa ISO 527-2 Flexural modulus 18 to 20 GPa ISO 178 Bending strength 335 Mpa ISO 178 Resiliency lzod 9 to 11 KJIm2 ISO 180 Young's elastic modulus 18 GPa Wear coefficient (reinforced PEEK torque 0.34.10. ASTM F-732 with Carbon Fibers / PEEK Reinforced with Carbon Fibers) With such a carbon fiber reinforced polyetheretherketone (PEEK), an intermediate core prosthesis 3 of height h of about 4.5 mm (Figure 5) and overall height H of about 5.5 mm (Figure 2). Good results have also been obtained using polyetheretherketone (PEEK) reinforced with carbon fibers marketed by INVIBIO under the reference LT1CA30. The present invention is not limited to the embodiments which have been explicitly described, but it includes the various variants and generalizations thereof within the scope of the claims below.

Claims (2)

CLAIMS1 - Disc prosthesis for replacing an intervertebral disk between a first and a second lower vertebra adjacent to a patient, comprising at least three moving parts including: - a first plate (1) having a first surface contact member (1a), and having an opposite first attachment face (1b) shaped to be fixed to the first vertebra, the first plate (1) extending in first (I-1) and second (II-II) distinct directions substantially perpendicular, - a second plate (2), having a second contact surface (2a), and having a second opposite fixing face (2b) shaped to be fixed to the second vertebra, the second plate (2) s extending according to third (III-111) and fourth (IV-IV) distinct substantially perpendicular directions, - an intermediate core (3) having a first (3a) and a second (3b) opposing sliding faces for to come respectively in complementary contact with the contact surfaces (1a, 2a) of the first (1) and second (2) trays, movable in translation relative to at least one of the first (1) or second (2) ) trays in at least two directions, characterized in that: - the first fixation face (lb) of the first plate (1) has an anatomical shape adapted to the shape of the vertebral plate of the first vertebra and / or the second face of fixation (2b) of the second plate (2) has an anatomical shape adapted to the shape of the vertebral plate of the second vertebra, - the first (1) and second (2) plates and the intermediate core (3) are made of polyetheretherketone (PEEK) reinforced with carbon fibers. 2 - disc prosthesis claim 1, characterized in that: - the first plate (1) is intended to be fixed to the lower vertebral plateau of the first vertebra, - the first attachment face (1 b) of the first plate (1) is convex along the first (1-I) and second (11-II) directions. 3 - Prosthesis according to one of claims 1 or 2, characterized in that: - the second plate (2) is intended to be fixed to the upper vertebral plateau of the second vertebra, 35 - the second attachment face (2b) the second plate (2) is substantially plane according to the third (III-III) and fourth (IV-IV) directions. FDEP.dac 12 4 - Prosthesis according to one of claims 1 or 2, characterized in that: the second plate (2) is intended to be fixed to the upper vertebral plateau of the second vertebra, - the second fixation face (2b) of the second plate (2) is substantially plane according to the third (III-III) direction and convex according to the fourth (IV-IV) direction. 5 - prosthesis according to any one of claims 1 to 4, characterized in that the attachment faces (1b, 2b) of the first (1) and second (2) trays comprise a plurality of notches (4) respectively perpendicular to the first direction (1-I) and the third direction (II-III), the fixing faces (1b, 2b) and their notches (4) preferably being coated with porous titanium. 6 - prosthesis according to any one of claims 1 to 5, characterized in that at least one of the trays (1, 2) comprises an edge (5) peripherally, preferably discontinuous, which limits the translational movement of the intermediate core (3) relative to said plate (1, 2). 7 - prosthesis according to any one of claims 1 to 6, characterized in that: - one of the sliding surfaces (3a, 3b) of the intermediate core (3) and the contact surface (1a, 2a) of one of the plates (1, 2) come into contact with one another according to a contact surface (Si) substantially in the shape of a spherical cap, - the other sliding surface (3a, 3b) of the intermediate core (3) is flat and comes into contact with the contact surface (1a, 2a) of the other plate (1, 2) according to a planar contact surface (S2). 8 - prosthesis according to one of claims 1 to 7, characterized in that the intermediate core (3) comprises at least one groove (6a, 6b) on its sliding surface (3a, 3b) plane, preferably passing through the center of the plane sliding face (3a, 3b) of the intermediate core (3). 9 - prosthesis according to claim 8, characterized in that the intermediate core (3) comprises on its sliding face (3a, 3b) plane two grooves (6a, 6b) perpendicular to each other and intersecting in the center of the sliding face ( 3a, 3b) of the intermediate core (3). 10-disc prosthesis according to any one of claims 1 to 9, characterized in that the polyetheretherketone (PEEK) reinforced with carbon fibers has substantially one or more of the following mechanical characteristics: 9117) EP.do. 13 Mechanical properties Values Measuring methods Tensile strength 220 to 230 MPa ISO 527-2 Flexural modulus 18 to 20 GPa ISO 178 Flexural strength 335 MPa ISO 178 Izod resilience 9 to 11 KJ / m2 ISO 180 Elastic modulus Young 18 GPa Wear coefficient (reinforced PEEK torque 0.34.10`6 mm3N-'mm- 'ASTM F-732 by carbon fibers / PEEK reinforced with carbon fibers)