WO2015018854A1

WO2015018854A1 - Knee prosthesis with ceramic-on-ceramic friction coupling and movable ceramic plate

Info

Publication number: WO2015018854A1
Application number: PCT/EP2014/066877
Authority: WO
Inventors: Laurent Sedel
Original assignee: Assistance Publique - Hopitaux De Paris
Priority date: 2013-08-06
Filing date: 2014-08-06
Publication date: 2015-02-12
Also published as: FR3009492A1; FR3009492B1

Abstract

Knee prosthesis with movable ceramic plate. The invention relates to a knee prosthesis comprising: a. a tibial seat (2, 20, 200) comprising an anchoring stem (22, 202, 212) in the upper part of a prepared tibia of a patient; b. a movable central plate (3, 30, 300) having a lower surface (33, 303) and an upper surface; c. a femoral element (1) designed to be fixed on the lower part of a prepared femur of a patient and having a substantially concave part, intended to come into contact with the lower part of the prepared femur, and a convex part able to cooperate with said movable central plate; the movable plate and the femoral element being made entirely of the same ceramic material and being configured so as to be congruent with each other.

Description

Knee prosthesis with ceramic friction torque on ceramic and mobile ceramic plate.

1. Field of the invention

The field of the invention is that of the articular prosthesis.

More specifically, the invention relates to a total ceramic prosthesis comprising a ceramic mobile plate to replace the knee joint in a patient.

2. Prior Art

The replacement of the knee joint is a frequent intervention. It is estimated that in 2011, approximately 650,000 prostheses were installed in the United States and 110,000 in France. Knee prostheses can be total or partial: unicondylar, total and then hinged or sliding.

Sliding prostheses comprise a condylar femoral component and a tibial base, respectively fixed on the profiled ends of the femur and tibia. The majority of prostheses placed are so-called "sliding" prostheses. These sliding prostheses comprise a femoral piece made of metal or ceramic and a polyethylene tibial component generally embedded in the metal tibial base. Some have a mobile polyethylene tray that can move on the tibial plateau. The theoretical advantage of the moving plate is to reduce the wear of the polyethylene by allowing a more consistent adaptation of the friction surfaces and to improve the flexion of the knee when the displacement of the moving plate is not only rotating but also before back ("drawer" movement), the movable plate moving on the tibial surface in the manner of the meniscus.

These sliding prostheses do not replace the lateral ligaments of the knee and must therefore be placed in perfect harmony with the natural architecture of the knee surfaces and anatomical axes. Some retain the posterior cruciate ligament, others do not, there is then a central hood that prevents the fall of the tibia back. So far, the total prostheses are made of metal and polyethylene. According to this technique, the femoral and tibial bases are made of a metallic material, while a polyethylene pad is mounted fixedly or movably on the tibial base. Other embodiments consist of a ceramic femoral base cooperating with a polyethylene tray, mounted on a tibial base of ceramic or metal. The mobility of the movable plate may be limited by the shape of the metallic receptacle fixed in the tibia which may allow only rotational movements or by a central pin which allows, according to the shape of a lower cavity designed in the movable plate movements rotation and drawer.

However, these materials do not allow to design a joint prosthesis robust enough to allow patients to resume normal physical activity: if it is easy to walk again with a knee prosthesis, patients feel discomfort during a walk extended or ascent and descent stairs. The race or any other important physical activity is otherwise prohibited.

However, the average age of patients decreases considerably. Many interventions are the result of an accident of sport or work, among young people and professionally active. It is therefore difficult and particularly frustrating for these people to have to give up any form of physical activity, or even their professional activity.

In addition, the failure rate of these prostheses is currently 10% after the first ten years. This rate increases in the youngest patients. Failure results in the need to reoperate the patient to replace his prosthesis. However, these re-interventions involve on the one hand a significant suffering for the patient, and on the other hand a significant cost for the health insurance systems. They also represent a legal risk for clinical or hospital institutions.

The failures of prostheses are partly explained by the behavior of patients who persist, despite the prohibitions, to practice a greater physical activity than the prosthesis allows them. But the main cause of these failures lies mainly in the phenomenon of wear of the polyethylene constituting friction torque. The release under mechanical stress of the wear particles generates an inflammatory reaction responsible for joint effusion, but also the creation of a periarticular resorption granuloma. Bone lysis in the femur and / or tibia surrounding the prosthesis was observed, which may result in significant bone loss. This osteolysis can also lead to loosening of the prosthesis. When wear has been very high, the metal parts can be exposed, resulting in massive rejection reactions by production of toxic metal particles (metallose).

Document WO 2011/003621 A1 is known which describes in particular partially ceramic knee prostheses and a device for wearing out these prostheses. However, no prosthesis according to this technique has so far appeared on the market for the following reasons.

Firstly, the prostheses according to this document comprise a metal rod on which is fixed the tibial base, which induces a strong abrasion of the metal. Abrasion of the metal results in the formation of metal debris in the body. The body reacts against these metal particles by producing an inflammatory reaction as described with the polyethylene particles.

In addition, the fixing of ceramic parts on a metal rod is problematic: it is in practice very difficult to fix this type of parts without creating fracture conditions of the ceramic. WO 2011/003621 A1 does not describe any method of fixing these parts. In addition, although the mobile plate is described in ceramic, the large oval opening in the center of the movable plate is in practice impossible to achieve in a solid ceramic material, this form of opening and its dimensions weakening the ceramic. Similarly, the impact of the opening made in the ceramic tray against the stops 18 is likely to induce premature fractures of the ceramic tray, if it was solid ceramic.

One solution to counter these disadvantages is to offer metal parts covered with ceramic. However, the thin layer of ceramic on the surface metal wears out quickly and the metal is quickly exposed, causing the aforementioned inflammatory reactions. This practice has not for the moment shown any superiority.

It is therefore necessary to design total knee prostheses that are more resistant to wear and allow patients to return to normal life. It is further desirable that such prostheses limit inflammatory phenomena.

3. Objectives of the invention

The invention particularly aims to overcome these disadvantages of the prior art.

More specifically, an object of the invention is to provide, in at least one embodiment, a knee prosthesis that is more resistant than current prostheses.

Another object of the invention is to implement, in at least one embodiment, such a prosthesis that allows patients to resume normal physical activity.

The invention also aims to provide, in at least one embodiment, a prosthesis which limits the inflammatory reactions.

The invention also aims, in at least one embodiment, to provide a prosthesis that allows to reform a more resistant fibrous tissue playing the natural role of the ligaments of the knee by remodeling under mechanical stress fibrous structures.

4. Presentation of the invention

These objectives, as well as others that will appear later, are achieved with the aid of a knee prosthesis comprising:

at. a tibial base including an anchor heel for insertion into the upper portion of a prepared tibia of a patient;

b. a centric movable platen having a lower surface and an upper surface; vs. a femoral element adapted to be fixed to the lower part of a prepared femur of a patient, having an essentially concave portion intended to come into contact with the lower portion of the prepared femur and a convex portion adapted to cooperate with said centric movable plate ;

According to the invention, the movable plate and the femoral element are entirely of the same ceramic material and are configured to be congruent with each other.

The term "centric" means an element for centering the knee joint.

Within the meaning of the invention, the movable plate is movable in a forward / backward, lateral and rotary direction. Thus, the movable plate according to the invention is never solely rotary.

It should be noted that the anterior part of said femoral element is also able to cooperate with a ball joint.

Thus, the invention is based on a completely new and original approach to design a total knee prosthesis in which all the surfaces in contact with the elements of the component are made of the same ceramic material. Unlike current prostheses which comprise a femoral element made of metal or ceramic, in contact with a fixed or movable polyethylene tray, the prosthesis according to the invention comprises a mobile plate made of the same ceramic material as the femoral element.

Until now, it has never been proposed, to the knowledge of the Applicant, to put in close contact two ceramic pieces to design a knee prosthesis. It was known to offer ceramic prostheses for the hip, in young people and / or active. However, the mechanical stresses exerted on the knee joint are very different from those exerted on the hip, the joints of the hip and knee having different geometries. The use of ceramics for producing a knee prosthesis in which the friction surfaces of the tibial plateau and the femoral component are entirely ceramic has always been rejected by prosthetists and orthopedic surgeons, and this for different reasons. The first of these Reasons is that the mechanics of the knee is complex. During bending, successive rolling and sliding phases occur. These phases are well tolerated by a couple of hard / soft materials, but can not be envisaged with a hard / hard couple, since the latter only satisfactorily tribologically works if there is a significant congruence between the friction surfaces. The artifact of the movable plate allows a permanent self-centering during the movement with a respect of the congruences and an adaptation to the profile of each patient.

The second is that the ceramic is a material of fragile behavior that can break during the propagation of a crack. This is why the choice of medical grade alumina and the designs favor thicknesses that can avoid this risk.

In addition to the health risk for the patient that these figures reflect, cases of prosthesis rupture represent a cost and a significant legal risk for health professionals. It is to be compared with the risks 10 times higher of reinterventions due to the consequences of the reactions to the debris of wear of the prostheses containing polyethylene.

Another prejudice against the use of ceramics in the context of a total knee prosthesis is the possibility that the friction of two ceramic pieces against each other will produce a screeching with each movement; noise being heard by the patient and sometimes even by the patient's entourage. This phenomenon has already been observed in some hip prostheses and is particularly troublesome for the patient on a daily basis. The design of the pieces as well as the interposition of metallic particles is the element in cause most often reported. The invention avoids this disadvantage by providing a sufficiently thick ceramic thickness. The use of cement during the placement of the prosthesis also limits this phenomenon.

Preferably, said ceramic material has a thickness of between 4 mm and 14 mm. The Applicant has indeed found that ceramic prostheses whose thickness is outside this range are brittle, which is not desirable. The Applicant has, moreover, surprisingly found that the behavior of two ceramic pieces against each other made it possible to obtain a prosthesis that is very strong and stronger than existing ones. The perfect congruence between the femoral element and the movable plate makes it possible to reduce the friction between the parts and consequently the risk of wear of the prosthesis. A clearance between parts of a few tens of microns is ideal to allow liquids to penetrate into the interface ensuring the lubrication of the contact and the absence of noise often related to dry friction. Preferably, the clearance between the parts must be between 10 μιη and 100 μιτι. Below 10 μιτι, the liquid will not circulate sufficiently. Beyond 100 μιτι, the risk of stress concentration on part of the prosthesis becomes too high.

In the sense of the invention and in the description which follows, the perfect congruence of the parts relative to each other is obtained when the parts fit perfectly and when there is no area at the friction surfaces of the parts against each other in which the mechanical stresses are concentrated. This perfect congruence can also be described as ideal in the description.

This perfect or ideal congruence of the rubbing elements is obtained thanks to the choice of simple shapes of the friction surfaces: the condylespace / movable plate are portions of cylinders with the same radius of curvature and the contact surface movable plateau / tibial base is flat. These forms are obtained by specific manufacturing and lapping techniques, mastered by the industry specialized in medical prostheses. Briefly, the profiles of the different parts produced are evaluated by measuring the radii of curvature of the various parts after subjecting the parts to different wear tests. The purpose of these measurements is to obtain a spacing between the parts, and more precisely between the movable plate and the femoral element, between 10 μιη and 100 μιτι.

In addition, ceramics are more tolerated by the body than metal or polyethylene. The advantage of ceramic-ceramic friction is to allow the recreation of a fibrous tissue or "neoligament" playing the role of natural ligaments after adaptive remodeling. In fact, the formation of a fibrous tissue more resistant and of better quality with the prostheses according to the invention than with conventional prostheses in which the friction surfaces are metal against polyethylene or ceramic against polyethylene. The wear particles, generated in small amounts during the movements of the joint, do not cause macrophage reaction in the body. Consequently, the prostheses according to the invention make it possible to avoid the problem of osteolysis and the risk of loosening of the prosthesis observed with the current prostheses.

On the contrary, the Applicant notes that small amounts of alumina particles can generate a particularly dense fibrous tissue, denser than that formed around current prostheses. This fibrous tissue helps strengthen and stabilize the joint capsule and ligaments. Therefore, the prostheses according to the invention allow patients to find a knee joint more stable and more resistant to effort. This feature allows patients to keep their prosthesis longer and regain normal physical activity.

For all these reasons, the prostheses according to the invention are more resistant and limit or even avoid the disadvantages observed with current prostheses in which the movable plate is made of polyethylene. The present invention thus enables patients to return to a normal life with a higher level of physical activity than is currently allowed. It is no longer necessary to reoperate them to replace the used prosthesis or, at the very least, the expiry date of a new operation is considerably delayed compared to current prostheses.

Preferably, the ceramic material is an alumina ceramic (Al ₂ O ₃ ), which makes it possible to obtain the synthesis of a fibrous fabric of better quality than other ceramics. Such materials are of surgical quality, that is to say that they must comply with the standards in force relating to materials for the manufacture of surgical prostheses. For example, the alumina ceramic may be a polycrystalline dense ceramic obtained from an aluminum oxide powder compressed at temperatures of about 1600 ° C by the HIP (High Isostatic Pressure) process.

Preferably, the ceramic has a particle size less than 2 μιτι. More preferably, the ceramic used for the manufacture of the prosthesis according to the invention has a particle size between 0.5 μιη and 2 μιτι. Even more preferably, the ceramic has a particle size of 1 μιη and 2 μιτι. The particle size of the ceramic material is determined by any method well known to those skilled in the art.

Advantageously, the tibial base comprises an anchor heel in the form of an irregular Morse taper. The irregular Morse taper shape is designed to fit the shape of the patient's tibia. It ensures a very good centering of the tibial base in the profiled end of the patient's tibia.

The dimensions of the parts constituting the prosthesis are a function of the size and dimensions of the joint to be replaced. For example, the movable platen may have a maximum thickness of between 4 to 14 mm. This ceramic thickness is sufficient to avoid the squealing phenomenon mentioned above.

Advantageously, the upper surface of the movable plate has two condylar cuvettes and the lower part of the femoral element has two condyles, said condyles and said condylar cuvettes each having perfectly congruent mutual friction surfaces.

In a first embodiment of the invention, said tibial base further comprises a housing for receiving a centric piece, said centric piece coming into contact with the lower surface of the movable plate.

In such an embodiment, the tibial base is then made of a metallic material, preferably titanium.

This centric piece totally ceramic is built on a model similar to the liner used in hip prostheses. The addition of the centric piece in a metal piece fixed in the patient's bone ensures a stable fixation of the components. Such a centric piece makes it possible to offer a ceramic-ceramic friction surface with the lower surface of the movable plate. As mentioned previously, it is disadvantageous to offer a ceramic friction surface against metal or plastic. It is also difficult to produce a tibial base whose upper surface would be ceramic while the anchor heel would be metal, because of the difficulty of fixing ceramic on metal and major risks of fracture that this causes. The centric piece makes it possible to overcome this problem by making the connection between a metal tibial base and a ceramic mobile plate. Inserted into the adjusted housing of the tibial base, the movements of said centric piece are limited.

Thus, according to this first embodiment, the invention relates to a knee prosthesis comprising:

at. a tibial base including an anchor heel for insertion into the upper portion of a prepared tibia of a patient and a housing for receiving a ceramic center piece;

b. said centric ceramic piece;

vs. a centric movable platen having a lower surface for engaging said centric piece and an upper surface;

d. a femoral element adapted to be fixed to the lower part of a prepared femur of a patient, having an essentially concave portion intended to come into contact with the lower portion of the prepared femur and a convex portion adapted to cooperate with said centric movable plate ;

the convex portion of the femoral element and the upper surface of the movable platen being entirely made of the same ceramic material and being configured to be congruent with each other.

In this case, the femoral element, the centric piece and the movable plate are entirely made of the same ceramic material.

Advantageously, the housing of the metal tibial base has an inner peripheral edge of frustoconical fitting and the centric fixed part has a frustoconical peripheral edge of corresponding shape to the frustoconical inner edge, so that the centric fixed part is enclosed. tightly in the housing.

Advantageously, the centric fixed part projects out of the housing.

Advantageously, the movable plate and the centric fixed part have plane mutual friction surfaces. This characteristic makes it possible in particular for the mobile plate to slide perfectly on the centric fixed part, which makes it possible to obtain a movement of the joint that is more fluid and more natural, with conservation of the different physiological phases of sliding, rolling characteristics of the knee joint.

Preferably, the centric fixed piece has a taper angle of Morse taper type: 5 ° 40 "In a variant of the invention, the centric piece is fixed on the tibial base, for example, the centric fixed piece can be welded, glued, screwed etc. to the tibial base Preferably the centric fixed part is ceramic and more preferably made of the same ceramic material as the movable plate.

Also in an interesting variant of this embodiment, the femoral element comprises on its anterior surface a protuberance mimicking a trochlea to articulate with the patella of the patient. This trochlea should be more prominent to partially replace the articular part of the patella that would be removed surgically and not replaced by a prosthesis, usually polyethylene, thus avoiding the consequences of a polyethylene button in a totally ceramic prosthesis. Patellar prostheses are not always the rule and many studies have shown that replacement of the patella joint has no significant advantages over a patella simply relieved of its diseased cartilage (spongialization). The dimensional adjustment of the femoro-patellar joint would thus be achieved by the addition of a noticeable thickness on the femoral condylar component.

In a variant of this first embodiment, the upper part of centric fixed part has a constant thickness. In other words, the centric fixed part is flat.

In another variant of this first embodiment, the central fixed part comprises on its upper face a central pin cooperating with a housing in the tibial base and a housing in the movable plate. Advantageously, the central stud is of the same ceramic material as the central fixed part, preferably alumina.

In this first embodiment, the limitation of the movements of the mobile plate can be devolved solely to the generation of fibrous tissues. The upper surface of the centric fixed part itself fixed in the tibial base has a cavity receiving a ceramic pad; it enters a lower cavity mobile platform. This cavity of eccentric shape allows rotation and "drawer" movements while limiting them. Depending on the characteristics of the patient and the surrounding tissues, the surgeon has the choice to use or not this variant.

In a second embodiment of the invention, the tibial base does not include a housing for a centric piece. In this case, the upper surface of the tibial base is flat and smooth, which facilitates the sliding of the movable plate. According to the second embodiment, the tibial base is then entirely made of the same ceramic material as the movable plate and the femoral element, preferably alumina.

In other words, the knee prosthesis according to the second embodiment of the invention comprises:

b. a centric movable platen having a lower surface and an upper surface;

vs. a femoral element adapted to be fixed to the lower part of a prepared femur of a patient, having an essentially concave portion intended to come into contact with the lower portion of the prepared femur and a convex portion adapted to cooperate with said centric movable plate ;

wherein, the tibial base, the movable platen and the femoral component are entirely of the same ceramic material and are configured to be congruent with each other.

Advantageously, the movable plate has a perimeter smaller than the perimeter of the upper surface of the tibial base. Movements of the mobile plate are then limited by the generation of fibrous tissue and surrounding muscles and ligaments.

In an advantageous variant of this second embodiment, the tibial base also has at its upper surface at least one abutment, preferably three abutments, more preferably at least four abutments, said at least one abutment making it possible to limit the abutments. movement of the movable plate to the surface of the tibial base, while continuing to allow rotation and drawer movements to improve the mobility of the knee while maintaining a perfect congruence surfaces.

5. List of figures

Other characteristics and advantages of the invention will appear more clearly on reading the following description of a preferred embodiment, given as a simple illustrative and nonlimiting example, and the appended drawings, among which:

Figure 1 shows a perspective and exploded view of a knee prosthesis according to a first embodiment of the invention;

Figure 2 illustrates another view of the prosthesis shown in Figure 1;

Figure 3 shows a side view of the assembled prosthesis according to Figures 1 and 2;

Figure 4 is a perspective view of a first variant of the tibial base according to a second embodiment of the invention;

Figure 5 is a perspective and exploded view showing the movable plate and the tibial base shown in Figure 4;

Figure 6 is a perspective view of a second variant of the tibial base according to a second embodiment of the invention;

Figure 7 is a perspective and exploded view showing the movable plate and the tibial base shown in Figure 6;

Figure 8 is a top view of the movable platen moving on the surface of the tibial base, as shown in Figure 7.

6. Description of embodiments of the invention

The general principle of the invention is based on a total knee prosthesis in which the movable plate and the femoral element, as well as the movable plate and the optional centric fixed part, have their respective friction surfaces made of the same ceramic material, these surfaces being perfectly congruent. Contrary to the idea commonly used so far, ceramics make it possible to obtain a particularly resistant knee prosthesis. This resistance is also due to the perfect congruence of the parts relative to each other, including the movable plate relative to the femoral element. The perfect congruence of the movable plate with the femoral element ensures an optimal friction while generating a minimum of wear debris, its mobility ensures the reproduction of the global articular game decomposed in two movements: that of the femoral element on the moving plate associated with the rotational mobility and drawer of the movable plate on the surface of the tibial base. The whole of the innovation thus makes it possible to avoid or at least to limit the probabilities of re-operation of the knee. In the sense of the invention, this perfect congruence is obtained by leaving a game, or a space, between the pieces between 10 μιη and 100 μιτι.

In addition, ceramics is a material that is particularly well tolerated by the body, in particular alumina ceramics. In fact, the ceramic wear particles, in small quantities, do not cause a reaction with foreign bodies responsible for the destruction of the prosthesis and the peripheral bone tissue (osteolysis). It has furthermore been observed that the presence of ceramics favors the synthesis of a stronger and thicker fibrous tissue than that obtained with polyethylene and / or metal prostheses. This quality of the fibrous tissue is important because it helps to stabilize and strengthen the knee joint thus replaced.

Thus, the prostheses according to the invention are stronger than current prostheses. They allow the operated patient to recover a better quality of life by allowing him a higher level of physical activity like the practice of a sport or the exercise of a professional activity.

6.1. Description of a first embodiment of the invention

In relation to FIGS. 1 to 4, a first embodiment of a knee prosthesis according to the invention is presented. This type of prosthesis belongs to the category of total dentures called "sliding" and movable plate.

In view of FIGS. 1 to 3, the represented prosthesis comprises

a femoral element 1;

a tibial base 2; and a movable plate 3, the plate 3 being placed between the femoral element 1 and the tibial base 2.

The femoral element 1 is in the general form of a hollow partial shell defining externally two condyles 11 substantially reproducing the shape of the natural condyles, but whose posterior part floating with the movable plate are portions of cylinders. They are separated by an intercondylar vacuum 12, which globally reproduces the natural intercondylian void. Internally, the femoral component defines a femoral housing 13 for receiving the profiled lower end Fl of a femur F. In more detail, the femoral housing 13 defines two condylar housings 14 separated by an intercondylar pad 15. The femoral component 1 thus has a substantially conventional configuration with particular features thickening of the trochléenne part, a cylindrical shape of the posterior portion of the condyles.

According to the invention, the femoral element 1 is entirely made of a material containing or consisting of a ceramic, such as Al ₂ O ₃ alumina.

The tibial base 2 here comprises two separate components reported on one another. The tibial base 2 thus comprises an anchoring heel 21 intended to be mounted on a profiled upper end of a tibia and a centric fixed part 25 which is fixedly received on or in the anchoring heel 21.

The anchoring heel 21 comprises an anchoring keel 22 which is intended to be inserted and held in a corresponding bore formed in the upper end T1 of a tibia T. Above the anchor keel 22, the anchoring heel 21 forms a tray housing 23 which advantageously defines a frustoconical fitting peripheral edge 24. It can thus be said that the tray housing 23 forms a bottom surrounded by a rim internally forming the frustoconical fitting edge 24.

According to the invention, the anchoring heel 21 is made of titanium. The outer surface of the titanium being configured to be fixed without cement.

The centric fixed part 25 is fixedly received inside the housing 23. For this purpose, the centric fixed part 25 has a frustoconical fitting peripheral edge 28 intended to fit snugly into the housing 23. with an intimate contact with the frustoconical fitting edge 24. The central fixed part 25 defines an upper friction surface 26 which projects out of the tray housing 23. This upper friction surface 26 is preferably perfectly flat: it does not comprise no outgrowth or recessed relief. In a non-drawn variant, it may comprise a cylindrical orifice accepting a ceramic stud unifying this plate with the movable plate.

Similarly, the lower surface 27 may also be flat and parallel to the upper surface 26, so that the centric fixed part 25 has a constant thickness. It can thus be said that the centric fixed part 25 is in the form of a wafer of constant thickness whose circumference is profiled to fit into the tray housing 23 of the anchoring heel 21. According to a drawing not shown , the thickness of the part 23 can marry more closely the internal shape of the tibial base.

According to the invention, the centric fixed part 25 is entirely alumina Al ₂ 0 ₃ . The centric fixed part 25 can be entirely made of alumina. The movable plate 3, which is disposed between the centric fixed part 25 and the femoral element 1, is a single piece having a contoured upper surface and a lower face defining a friction surface 33, preferably perfectly flat, intended to come into contact with each other. of friction with the upper surface 26 of the central fixed part 25. In a non-drawn variant, the lower face comprises an eccentric-shaped orifice for inserting a cylindrical central stud; the shape of the orifice allows rotational and drawer movements according to the needs of the patient by avoiding movements of too great amplitude. The profiled upper surface comprises two condylar cuvettes 31 separated by a protruding intercondylar pad 32. The condylar cuvettes 31 define zones or friction surfaces, respectively for the two condyles 11 of the femoral component 1. Advantageously, the cuvettes 31 and the condyles 11 have mutual friction surfaces cylindrical perfectly congruent, so that there is substantially no play or gap between them. This significantly reduces the friction, and therefore the wear of these parts. As for the intercondylar block 32, it is engaged in the intercondylar void 12 of the femoral component 1. During the rotation of the femoral element 1 on the movable plate 3, the condyles 11 slide or slide in the condylar cuvettes 31 with the intercondylar block 32 which moves in the intercondylar vacuum 12 which forms a kind of rail. Advantageously, the intercondylar block 32 does not significantly limit the displacement of the femoral element 1 on the mobile plate 3. In addition, it should be noted that the movable plate 3 can move freely without any stress on the centric fixed part 25, being given that their mutual surfaces or zones of friction 26, 33 are perfectly flat.

According to the invention, the mobile plate 3 is entirely made of Al ₂ O ₃ alumina. In a second variant of this first embodiment, the central fixed part comprises a central cylindrical stud on either side of its lower and upper surfaces. The movable plate then comprises on its lower surface a housing for housing the central block, and the tibial base also comprises a housing for housing the central block of the fixed part. Such an embodiment makes it possible to confer on the knee joint thus replaced rotation and "drawer" movements better controlled. This central block deliberately limits the movement. The surgeon has the advantage of choosing the option with or without intentional limitation of the mobility of the moving plate.

6.2. Description of a second embodiment of the invention

Figures 5 to 9 relate to a second embodiment of the invention.

In this embodiment, the upper surface of the tibial base is flat and smooth. The tibial base includes no housing for receiving a centric piece, the prosthesis then being devoid of centric piece. For the sake of clarity, the femoral component is not represented again. In other words, the femoral element in this second embodiment is identical to that described in FIGS. 1 to 3.

FIG. 4 shows a perspective view of a tibial base 20 according to a first variant of the second embodiment of the invention. As stated above, a tibial base according to the second embodiment does not include a housing for receiving a centric piece. The base 20 comprises a tibial plateau 201 having an upper surface 203 perfectly flat and smooth. The tibial plateau has a front face 205 and a rear face 204, both of convex shape. According to the invention, the tibial base 20 is entirely made of the same ceramic material, preferably Al ₂ O ₃ alumina.

FIG. 5 presents a perspective and exploded view of the tibial base 20 with a mobile plate 30. This mobile plate 30 is similar to the mobile plate 3 of the first embodiment: it comprises in particular a lower surface 303 intended to enter contact with the upper surface 203 of the tibial base 20. The surface 303 is also flat and smooth. The plate 30 has on its upper surface two condylar cups 301 and an intercondylar pad 302. The upper surface of the plate 30 is intended to cooperate with a femoral element not shown in this diagram, because identical to that shown in Figures 1 to 3.

As can be seen in FIG. 5, the tray 30 has a perimeter slightly smaller than the perimeter of the tibial tray 201. The movable tray 30 can move to the surface 203 of the tibial tray 201 in a forward / backward, lateral direction and rotation.

In doing so, the friction of the plate 30 against the surface 203 is limited and generate little Al ₂ O ₃ alumina ceramic particles. On the other hand, the particles generated contribute to the formation of a fibrous capsule making it possible to strengthen the lateral ligaments and the capsule of the replaced joint.

It is understood that according to the invention, the movable trays 3 and 30 can be interchanged between the first and second embodiments of the invention. In this variant, no element retains the movement of the plate 30 at the plateau surface 203 211. The movable plate 30 is held in place by the patella, the ligaments and the muscles in place as well as by the tension obtained during the treatment. intervention when choosing the thickness of prosthetic parts.

A second variant of the second embodiment in which the movable plate 30 is identical to that described in FIG. 5 is presented in relation to FIGS.

From Figure 6, the tibial base 200 includes an anchor keel 212 for insertion into the prepared tibia of a patient. The tibial base 200 also comprises a tibial plateau 211 having a front face 215 and a face rear 214, both of convex shape. The upper surface 213 of the plate 211 is flat and perfectly smooth. However, it has on its surface three stops 216 to retain the movement of the movable plate. The tibial base 200 is entirely made of ceramic, preferably Al ₂ O ₃ alumina ceramic.

FIG. 7 is a perspective and exploded view of the tibial base 200 and the movable plate 30. The perimeter of the plate 30 is smaller than that of the plate 211 so that the plate 30 can be inserted and moved between the plates. abutments 216 of the tibial base 200. As previously, the femoral element is not shown because identical to that described in Figures 1 to 4. It should also be noted that the plate 3 can cooperate with the base 200 , provided that its perimeter is smaller than that of the plate 211 so that it can be placed and move between the stops 216.

FIG. 8 is a view from above of the movable plate 30 cooperating with the plate 211 of the base plate 200. As shown in this figure, the plate 30 is rotated on the surface 211 of the tibial base plate. 200. Its movement is limited by stops 216.

The plate 30 and the base 200 are both entirely made of the same ceramic material, preferably Al ₂ O ₃ alumina.

6.3. Placement of a prosthesis according to the invention

When the prostheses according to the invention are placed in the knee of the patient, the lower end of the femur is profiled by the surgeon to fit into the femoral housing 13 of the femoral component 1. Correspondingly, the end The upper tibia is profiled to receive the anchoring heel 21. In case of wear of the mutual friction surfaces of the knee prosthesis, any debris or ceramic dust generates the synthesis of a strong fibrous tissue, forming a shell tissue that envelops the components of the knee prosthesis extending from the femur to the tibia. A tissue shell is formed around the synthetic joint. This tissue shell is enhanced by the production, as the patient moves, small ceramic particles produced during the friction of ceramic parts against each other. 7. Conclusion

Thus the present invention is based on the synergy of various factors:

- A cylindrical profiling of the movable plate relative to the femoral element to design perfectly congruent parts, that is to say that the space between them is between 10 μιη and 100 μιη; and

the friction surfaces of the parts constituting the prosthesis according to the invention are made of the same ceramic material, preferably alumina.

Thus, the total knee prostheses according to the invention have all of their surfaces or zones of mutual friction made of the same ceramic material. As a result, the wear is greatly reduced and the production of debris or ceramic dust is very low. In addition, the small amount of these causes a fibrous reaction in the form of a tissue cladding. In addition, the minimum thickness of 4 mm ceramic pieces gives them sufficient strength to avoid breaking. Thus, the prostheses according to the invention are more resistant, more stable and allow patients to regain a level of physical activity greater than that allowed with current prostheses.

Claims

1. Knee prosthesis comprising:

at. a tibial base (2, 20, 200) including an anchor (22, 202, 212) for insertion into the upper portion of a prepared tibia of a patient; b. a centric movable platen (3, 30, 300) having a lower surface (33, 303) and an upper surface;

vs. a femoral component (1) adapted to be attached to the lower portion of a prepared femur of a patient having an essentially concave portion (13) for contacting the lower portion of the prepared femur and a convex portion adapted to cooperate with said centric movable platen (3, 30);

characterized in that the movable plate and the femoral element are entirely of the same ceramic material and are configured to be congruent with each other.

2. The prosthesis of claim 1 wherein the ceramic material is Al ₂ O ₃ alumina.

3. Prosthesis according to claim 1 or 2 wherein the ceramic has a particle size between 0.5-2 μιτι, preferably between 1-2 μιτι.

4. Prosthesis according to one of the preceding claims wherein the upper surface of the movable plate (3, 30) has two condylar cuvettes (31, 301) and the lower part of the femoral element (1) has two condyles (11). said condyles (11) and said condylar cuvettes (31, 301) each having perfectly congruent mutual friction surfaces.

5. Prosthesis according to any one of the preceding claims wherein said ceramic material has a thickness of between 4 and 14 mm.

6. Prosthesis according to one of the preceding claims wherein said tibial base (2) further comprises a housing (23) for receiving a centric piece (25), said centric piece (25) coming into contact with the lower surface of the movable plate (3).

7. Prosthesis according to claim 6 wherein the housing (23) of the tibial base (2) has an inner peripheral edge (24) frustoconical fitting and the centric fixed part (25) has a frustoconical peripheral edge (28). of corresponding shape to the frustoconical inner edge (24), so that the centric fixed part (25) tightly fits in the housing (23).

8. Prosthesis according to claim 6 or 7 wherein the centric piece (25) has a constant thickness.

9. Prosthesis according to any one of claims 6 to 8 wherein the movable plate (3) and the centric piece (25) have flat mutual friction surfaces (33, 26).

10. Prosthesis according to any one of claims 6 to 9 wherein the centric piece (25) projects out of the housing (23).

11. Prosthesis according to one of claims 6 to 10 wherein the centric piece (25) is fixed on the tibial base (21).

12. Prosthesis according to one of the preceding claims wherein the femoral element (1) comprises on its anterior surface a protrusion mimicking a trochlea to articulate with the patella of the patient.

13. Prosthesis according to one of claims 6 to 12 wherein the tibial base (21) is a metal material, preferably titanium.

14. Prosthesis according to one of claims 6 to 13 wherein the centric piece (25) is made of ceramic material, preferably alumina.

15. Prosthesis according to one of claims 6 to 14 wherein the central fixed part (25) comprises a central stud cooperating with a housing in the tibial base (2) and a housing in the movable plate.

16. The prosthesis of claim 15 wherein the central pad is of the same ceramic material, preferably alumina.

17. Prosthesis according to any one of claims 1 to 5 and 12 wherein said tibial base (20, 200) does not include a housing for a centric piece.

The prosthesis of claim 17 wherein said movable platen (30) has a perimeter less than the perimeter of the upper surface of the tibial base (20, 200).

19. Prosthesis according to claim 18 wherein said tibial base (20, 200) further has at its upper surface (213) at least one stop (216), preferably three stops, more preferably at least four stops, said at least one stop for limiting the movements of the movable plate (30) to the surface of the tibial base.

20. Prosthesis according to one of claims 16 to 19 wherein said tibial base (20, 200) is entirely of a ceramic material, preferably a same ceramic material as said movable plate (30) and said femoral element (1). .