Total bicondylar knee prosthesis made of solid ceramic integrating a pin

Abstract

The present invention relates to a total knee prosthesis made of solid ceramic comprising a femoral element (1), a tibial plateau (3), and a movable plateau (2) forming two joints, as well as a pin (5) for stabilising the movable plateau thereof, for limiting post-surgery movements before natural fibrous tissue has formed, and for ensuring optimum clearance between the different ceramic surfaces. The prosthesis also has: • - mutual friction surfaces that are entirely made of the same ceramic material and two condylar cups (21) on the upper portion of the movable plateau; and • - two condyles (11) on the femoral element that each comprise mutual friction surfaces between which there is a clearance of less than 100 μm when the longitudinal axes of the femoral element and of the tibial plateau form an angle a of between 0° and 75°.

Description

[0001] DESCRIPTION

[0002] TITLE: Total bicondylar knee prosthesis in solid ceramic incorporating a pin.

[0003] Field of invention

[0004] The field of the invention is that of joint prosthesis.

[0005] More specifically, the invention relates to a total solid ceramic prosthesis for replacing the knee joint in a patient comprising a pin for limiting the travel of the movable plate.

[0006] Prior art

[0007] Knee joint replacement, whether partial or total, is a surgical procedure that has been performed for many years. To meet this frequently encountered need for replacement, particularly following rheumatism, accidents, or various illnesses, numerous prostheses have been developed.

[0008] Among them, sliding prostheses represent the majority of the prostheses fitted. These sliding prostheses comprise a femoral condylar part and a tibial base, fixed respectively on the profiled ends of the femur and the tibia. Some have a movable polyethylene plate which can move on the tibial plateau. The theoretical advantage of the movable plate is to reduce the wear of the polyethylene by allowing a more coherent adaptation of the friction surfaces and to improve the flexion of the knee when the movement of the movable plate is done not only in rotation but also from front to back (a "drawer" movement), the movable plate moving on the tibial surface in the manner of the meniscus.

[0009] Until now, total knee prostheses have been made of metal and polyethylene, and have many disadvantages. Indeed, these materials are not sufficiently robust, and do not offer patients the possibility of performing significant physical activities. In addition, metal and polyethylene prostheses have an overall dissatisfaction rate of 50% and a failure rate of 10% after the first ten years. The main cause of these inadequacies is the release of polyethylene wear particles during friction, which cause an inflammatory reaction responsible for joint effusion and periarticular resorption granuloma, but also bone lysis in the femur and / or tibia. The prosthesis can also, in the event of significant wear, see its metal parts exposed and produce toxic metal particles during friction.

[0010] Furthermore, when the friction surfaces of a knee prosthesis comprise at least one polyethylene element, for example of the ultra high molecular weight polyethylene (UHMWPE) type or highly cross-linked polyethylene, the development of fibrous tissue necessary for stabilizing the joint is limited. More recently, prostheses have been developed with improved biocompatibility, or in other words, which are better tolerated by the body than prostheses made of metal and polyethylene. The inventors have notably developed a total knee prosthesis which is the subject of patent FR3032347B1, the mutual friction surfaces of the elements composing it of which are made of the same ceramic material.The main advantage of fitting this ceramic prosthesis to a patient is that it allows the fibrous tissue or "neoligament" to be recreated, which plays the role of a natural ligament after adaptive remodeling. The wear particles, generated in small quantities during the movements of this artificial ceramic joint, do not cause a macrophagic reaction in the body. Consequently, the prosthesis covered by the aforementioned patent FR3032347B1 avoids the problem of osteolysis and the risk of loosening of the prosthesis. In the longer term, the fibrous tissue developed naturally stabilizes the joint created by this knee prosthesis.

[0011] However, the time taken for this resistant fibrous tissue to appear is currently poorly understood and is estimated at a few months. There is therefore a period of time during which this joint is not sufficiently stabilized.

[0012] The configurations of knee prostheses described in the prior art do not allow the knee prostheses to be sufficiently stabilized during the transitional healing phase after knee surgery, during which the fibrous tissue has not yet fully formed.

[0013] Objectives of the invention The invention aims in particular to overcome the aforementioned drawbacks of the prior art

[0014] In particular, the present invention aims to provide a total knee prosthesis whose stability is improved, in comparison with knee prostheses known from the prior art.

[0015] The invention also aims to provide a prosthesis making it possible to obtain, at each stage of walking, better contact between the mutual friction surfaces of the elements constituting the prosthesis, in comparison with known knee prostheses.

[0016] Another objective of the invention is to provide a knee prosthesis of simpler construction, the mutual friction surfaces of which have a congruence just as effective as known knee prostheses.

[0017] Another objective of the invention is to provide a prosthesis which allows patients to resume normal physical activity when the fibrous tissue has reconstituted itself into a sort of ligament.

[0018] Presentation of the invention

[0019] These objectives, as well as others which will appear subsequently, are achieved using a total knee prosthesis intended to be implanted in a human patient, the prosthesis comprising solid ceramic parts: a femoral element having a longitudinal axis, a tibial plateau having a longitudinal axis, and a mobile plateau, the mobile plateau being interposed between the femoral element and the tibial plateau to form with them two articulations, in which: the mutual friction surfaces of the femoral element with the mobile plateau, and the mutual friction surfaces of the tibial plateau with the mobile plateau are entirely made of the same ceramic material;and the movable plate comprises in its upper part two condylar cups and the femoral element comprises two condyles, the condyles and the condylar cups each comprising mutual friction surfaces between which there is a clearance of less than 100 μm when the longitudinal axes of the femoral element and the tibial plate form an angle a of between 0° and 75°.;

[0020] According to the invention, the prosthesis further comprises a pin for holding the movable plate on the tibial plate, a first end of which is intended to be housed in a cavity of the tibial plate and the second end of which, opposite the first end, is intended to be housed in a hole of the movable plate, the pin is essentially cylindrical in shape and fitted with hard friction in said cavity of said tibial plate. By "solid ceramic part", is meant, within the meaning of the present invention, a part entirely made of one or more ceramic materials.

[0021] Similarly, in the present invention, mechanical "play" means the space left between two imperfectly assembled parts.

[0022] The inventors have developed an improvement to the ceramic knee prosthesis covered by French patent FR3032347B1, which consists of the introduction of a pin for holding the mobile plate on the tibial plate capable of stabilizing the prosthesis.

[0023] The main advantage of the prosthesis according to the invention is that it has a configuration that allows it to be stabilized, as soon as the prosthesis is fitted to the patient. More precisely, it allows the travel of the mobile plate on the surface of the tibial plateau of the knee prosthesis to be limited and stabilized, and more particularly limits lateral movements. To do this, the tibial plateau is advantageously provided with a cavity in which the pin is inserted so as to allow the rotation of the mobile plate relative to the tibial plateau. Thus, the prosthesis according to the invention is better stabilized than the solutions of the prior art, in particular during the first months after the knee prosthesis is fitted to the patient. In other words, the prosthesis according to the invention is less dependent on the presence of fibrous tissue to be stabilized compared to existing knee prostheses, while allowing the development of this fibrous tissue.

[0024] Indeed, the use of ceramic has the advantage of allowing the development of a dense and resistant fibrous tissue, which develops in a few months and acts as a ligament in the long term. The joint created is thus more stable and resistant to stress, and allows patients to keep their prosthesis longer and return to normal physical activity. It also offers very good biological resistance which is explained by the fact that ceramic / ceramic friction produces very little debris compared to metal and polyethylene prostheses. The clearance of less than 100 pm between the mutual friction surfaces allows perfect congruity between the mutual friction surfaces, particularly in the load zone (for example in a static standing position or in movement).The movements allowed by the rotating and drawer pin allow a natural adaptation of the surfaces in contact during the application of the load, the fibrous tissue subsequently perpetuating this optimum contact.

[0025] In addition, the hard friction fit of the pin allows, on the one hand, to avoid breakage of the parts when inserting the pin into the tibial plateau and, on the other hand, to ensure good retention of the pin by the tibial plateau. This configuration offers the possibility for the pin to optimize functions of limiting and stabilizing the travel of the mobile plateau on the surface of the tibial plateau.

[0026] Preferably, the hole is oblong in shape so as to allow rotation and translation of the mobile plate relative to the tibial plate along an anteroposterior axis.

[0027] The mobile plate of the prosthesis is mobile in rotation, but is also mobile along an axis in an anteroposterior direction, or in other words, it is mobile in the width direction of the tibial plateau. More precisely, the direction of the anteroposterior axis is substantially perpendicular to the direction of the longitudinal axis of the tibial plateau.

[0028] In the present description, "substantially perpendicular" means directions or planes which are perpendicular to each other at plus or minus 5°, preferably which are perpendicular.

[0029] Conversely, the configuration of this pin prosthesis does not allow movements of the mobile plate in a transverse direction, that is to say in a direction substantially perpendicular to the direction of the previously defined anteroposterior axis. In other words, the mobile plate cannot move in the direction of the length of the tibial plateau. In this way, the travel of the mobile plate of the prosthesis is limited, which has the effect of increasing the stability of the joint, even in the absence of fibrous tissue. The authorized movements allow, at each time of walking, to obtain optimum contact between the surfaces.

[0030] Furthermore, preserving a certain latitude in the movements allows the prosthesis to obtain a movement of the knee close to the natural movement. Advantageously, the mobile plate is able to translate on the tibial plateau along the anteroposterior axis and over a distance of between 3 and 6 millimeters (mm) on either side of the longitudinal axis, i.e. a total distance of between 6 and 12 millimeters. Preferably, the mobile plate is able to translate on the tibial plateau along the anteroposterior axis and over a distance of 4.5 millimeters (mm) on either side of the longitudinal axis, i.e. a total distance of 9 millimeters.

[0031] Advantageously, there is a clearance between the mutual friction surfaces of the mobile plateau and the tibial plateau of less than 100 micrometers (pm).

[0032] Advantageously, the space between the mutual friction surfaces of the mobile plate and the tibial plate is also between 0 μm and 100 μm, preferably between 10 and 100 μm, and more preferably between 10 μm and 60 μm. The selection of the distance between the mutual friction surfaces is of prime importance. Indeed, the inventors have previously demonstrated that this distance, in order to ensure optimal congruence without altering the comfort and functioning of the prosthetic joint, should preferably not be below 10 μm and above 100 μm, preferably not beyond 60 μm. Indeed, below 10 μm, the liquid risks not circulating sufficiently. Beyond 100 μm, the risk of stress concentration on a part of the prosthesis becomes too high.

[0033] Preferably, the mutual friction surfaces of the tibial plateau with the mobile plateau are essentially flat.

[0034] Advantageously, there is a clearance between the mutual friction surfaces of the pin and the hole.

[0035] Preferably, the pin is made entirely of the same ceramic material as the femoral element, the tibial plateau and the mobile plateau.

[0036] Advantageously, the ceramic material has a thickness of at least 5 mm, preferably between 5 mm and 14 mm.

[0037] The inventors found that ceramic prostheses with a thickness outside this range are brittle and therefore cannot be used in the form of ceramic / ceramic friction.

[0038] Advantageously, said ceramic material is chosen by AI2O3 alumina or delta alumina. Such aluminas make it possible to obtain the synthesis of a fibrous tissue of better quality compared to other ceramics. Such materials must comply with the standards in force relating to materials for the manufacture of surgical prostheses.

[0039] For example, the alumina ceramic may be a dense polycrystalline ceramic obtained from an aluminum oxide powder. Such a ceramic may in particular be produced by hot pressing the aluminum oxide powder at a temperature of approximately 1600°C by a hot isostatic pressure process (usually designated by the acronym HIP (acronym in English for “High Isostatic Pressure”)). A ceramic suitable for implementing the invention is a ceramic conforming to the ISO-6474-1 standard. The prosthesis may also be formed from a composite comprising a matrix in which ceramic fibers are incorporated. Alternatively, the prosthesis may also be formed by 3D printing.

[0040] List of figures

[0041] Other characteristics and advantages of the invention will appear more clearly on reading the following description of an example of implementation, given as a simple illustrative and non-limiting example, and the appended figures among which:

[0042] [Fig. 1]: Figure 1 illustrates a schematic perspective and exploded view of the prosthesis according to the invention;

[0043] [Fig. 2]: Figure 2 illustrates a schematic and exploded bottom view of the prosthesis of Figure 1;

[0044] [Fig. 3]: Figure 3 illustrates a schematic perspective view of the prosthesis of Figure 1;

[0045] [Fig. 4]: Figure 4 illustrates a profile view of the prosthesis according to the invention when the longitudinal axis of the femoral element and the longitudinal axis of the mobile plate are directed in substantially parallel directions;

[0046] [Fig. 5]: Figure 5 illustrates a profile view of the prosthesis according to the invention when the longitudinal axis of the femoral element and the longitudinal axis of the mobile plate form an angle of 30°.

[0047] [Fig. 6]: Figure 6 illustrates a sagittal section taken at the median plane of the prosthesis of Figure 4. [Fig. 7]: Figure 7 illustrates a frontal section of the prosthesis according to the invention.

[0048] Detailed description of the invention

[0049] The general principle of the invention is based on a total knee prosthesis having improved stability, compared to knee prostheses of the prior art, thanks to the presence of a pin and a particular configuration. The knee prosthesis comprises in particular a mobile plateau, a femoral element, a tibial plateau and a pin. The femoral element is intended to fit onto the prepared distal end of a patient's femur, and reproduces the shape of the trochlea, while the tibial plateau is intended to be anchored in the upper end of the tibia. The mobile plateau is located between the femoral element and the tibial plateau to form two articulations.

[0050] The elements of the prosthesis are entirely made of ceramic, or at least have the same ceramic material on their mutual friction surfaces. These mutual friction surfaces are perfectly congruent thanks to the optimization of the shape of the mutual friction surfaces and the respective distance between the parts. In particular, the perfect congruence of the parts with respect to each other ensures optimal friction while ensuring sufficient stability, and generates a minimum of wear debris. It also ensures the reproduction of the overall joint play of the knee thanks to the adaptation obtained by the mobility of the mobile plate.

[0051] Figures 1 to 3 are perspective and exploded views of the prosthesis according to the present invention, while Figures 4 and 5 are side views of the prosthesis. A sagittal section of the prosthesis, taken at its median plane, is also shown in Figure 6.

[0052] As can be seen in Figure 1, the prosthesis according to the invention comprises a femoral element 1, a mobile plate 2, a tibial plate 3 fixed on an anchoring heel 4 intended to be mounted on a profiled upper end of a tibia, and a pin 5 interposed between the mobile plate 2 and the tibial plate 3.

[0053] The femoral element 1 has the general form of a hollow partial shell externally defining two condyles 11 substantially reproducing the shape of the natural condyles, but the lower floating part of which with the movable plate are portions of cylinders and not portions of irregular spheres. The condyles 11 could also be portions of a sphere. The condyles 11 are separated by a slot which generally reproduces the natural intercondylar void. The intercondylar void 12 has two lateral surfaces 13 oriented in substantially parallel directions. In the present description, "substantially parallel" means directions, axes or planes which are parallel to each other at plus or minus 5°, preferably which are parallel.

[0054] The intercondylar void 12 corresponds to a portion of cylinder coaxial with the portions of cylinder forming the condyles 11, but of smaller radius. The intercondylar void 12 can also take the form of a portion of sphere whose center is located on the axis of revolution of the portions of cylinder forming the condyles 11 or on the axis connecting the center of the spheres when the condyles are portions of sphere.

[0055] Internally, the femoral element defines a femoral housing 16 intended to receive the profiled lower end F1 of a femur F. The femoral element 1 may have on its anterior face 15 a surface mimicking in a hollow the shape of the patella and intended to cooperate with the patient's patella.

[0056] The movable plate 2 is inserted between the femoral element 1 and the tibial plate 3. The movable plate has a lower surface 22 which is essentially flat, with the exception of a hole 20 positioned on its central part.

[0057] On its upper surface, the movable plate 2 has two condylar cups 21 separated by an intercondylar stud 24. The intercondylar stud has a surface 25 whose shape corresponds to the void 12 as well as two lateral surfaces 23 whose shape corresponds to the lateral surfaces 13 of the void. A slight gap allows natural liquids to lubricate the joint formed by the prosthesis.

[0058] The condylar cups 21 define mutual friction zones or surfaces, respectively for the two condyles 11 of the femoral element 1. Advantageously, the cups 21 and the condyles 11 have mutual friction surfaces of perfectly congruent cylindrical shape. This significantly reduces friction, and therefore the wear of these parts. In the present description, the term "perfectly congruent" is defined as parts that fit perfectly together, and are spaced apart by a distance of between approximately 0 μm and 100 μm, preferably between 10 μm and 100 μm, more preferably between 10 μm and 60 μm, in particular when the angle between the longitudinal axes of the femoral element and the movable plate forms an angle of between 0° and 75°.

[0059] As for the intercondylar stud 24, it is engaged in the intercondylar void 12 of the femoral element 1. The element 24 abuts against the surface 14 in the intercondylar void 12 so that the relative movement of the mobile plate 2 and the femoral element 1 remains controlled in its amplitude.

[0060] When the femoral element 1 rotates on the movable plate 2, the condyles 11 slide or slide in the condylar cups 21 with the intercondylar stud 24 which moves in the intercondylar void 12 which forms a sort of rail.

[0061] As can be seen in Figure 4, the longitudinal axis L of the tibial plateau and the longitudinal axis L' of the femoral element form a zero angle (0°). In Figure 5, the axes L and L' form an angle a of approximately 30°, which corresponds approximately to an angle formed by the knee when walking.

[0062] The condyles 11 are formed by portions of a cylinder of radius R and whose axis of revolution intersects the axes L and L' at the center O. It should be noted that the condyles could be portions of a sphere of center O and radius R'. Preferably, the radii R and R' have a length between 22 mm and 38 mm, preferably between 25 mm and 35 mm. The radius R" of the intercondylar void cannot be represented on these sections, the surface of the void being hidden here.

[0063] In the same way, the radius R" of the portion of sphere or cylinder forming the intercondylar void can be between 14 mm and 30 mm, preferably between 17 mm and 25 mm. The radii R, R' and R" are measured between the axis of the cylinder of revolution or the center of the sphere, and the friction surface of one part against the other.

[0064] These particular dimensions make it possible to design knee prostheses for individuals of different builds while avoiding the concentration of stresses on a specific area of ​​the ceramic material. In other words, these dimensions make it possible to obtain the perfect congruence necessary to produce a prosthesis, in which the femoral element, the mobile plateau, the tibial plateau and the pin are made of solid ceramic. It should be noted that natural condyles generally have a spherical shape made of several successive spheres whose radii decrease from front to back, the center of the spheres having an elliptical shape. The shape proposed in the present description is different from the natural shape in order to ensure ideal congruence of the elements of the prosthesis with respect to each other during movement of the knee, and therefore their production in ceramic.In fact, the centers of the cylinder or sphere portions of the friction surfaces between the movable plate and the femoral element are not on an ellipse but on an axis.

[0065] On its opposite surface and facing the tibial plateau, the movable plateau 2 has a hole 20 intended to receive a pin 5. The hole 20 of the tibial plateau may have a rounded shape, and more preferably an oblong shape. The hole 20 is positioned at the center of the tibial plateau, or in other words, is centered at the longitudinal axis L of the tibial plateau 3. In this way, as shown in Figure 2, the hole 20 and the intercondylar stud 24 of the tibial plateau 2 are both aligned and included in the same intersecting plane with the longitudinal axis L of the tibial plateau 3. Thus, the tibial plateau 2 is configured so that its intercondylar stud 24 can fit into the intercondylar void 12, and that its hole 20 can receive a pin 5, while allowing good congruence.Preferably, the void and condylar stud are spaced from each other by a distance of between 0 pm and 100 pm when the longitudinal axis of the femoral element and the longitudinal axis of the movable plate form an angle of between 0° and 60°.

[0066] The dimensions of this hole 20 are established so as to be able to insert the pin 5, while leaving a mechanical clearance 500 between the friction surfaces of the pin 5 with the hole 20 of the tibial plateau. For example, the length of this hole 20 is determined so that the pin 5 can move 4.5 mm on either side of the longitudinal axis L of the tibial plateau.

[0067] Since the lower surface 22 of the movable plate and the upper surface 31 of the tibial plate are both essentially flat, the movable plate 2 can move on the tibial plate within the limits of the movements permitted by the pin 5 and the hole 20.

[0068] The tibial plateau 3 has on its lower surface a solid alumina ceramic rod intended to be cemented in the upper end of the prepared tibia of a patient. The tibial plateau 3 also comprises an upper surface 31, opposite the aforementioned lower surface, which is intended to cooperate with the lower surface 22 of the movable plateau 2. The movable plateau and the tibial plateau are positioned so that there is a clearance 300 between their mutual friction surfaces which is preferably less than 100 μm.

[0069] The upper surface of the tibial plateau 3 comprises a cavity 30 intended to accommodate the pin 5, the function of which is to limit the translational movement of the movable plateau 2. The cavity 30 is cylindrical in shape and has dimensions adapted to the insertion of the pin 5. As for the pin, it has a cylindrical shape having a preferred diameter of the order of 9 millimeters (mm), and preferably has a height of the order of 20 mm.

[0070] The pin 5 is positioned in the cavity 30 by the surgeon at the time of the patient's knee operation, and is therefore considered to be removable. More precisely, the pin is fitted with hard friction in the cavity 30 of the tibial plateau so that it is sufficiently held by the tibial plateau. The friction fitting limits the risk of breakage of the parts when the ceramic pin is placed. When the pin 5 is correctly positioned in the cavity 30, it protrudes from the tibial plateau by a preferred height of approximately 9 mm. This part of the pin 5, which protrudes from the tibial plateau 3, can thus be housed in the hole 20 of the movable plateau.

[0071] In this way, when the parts constituting the prosthesis are assembled, the pin is both inserted into the cavity 30 of the tibial plateau, and housed in the hole 20 of the movable plateau. However, while the pin 5 is fitted with hard friction in the tibial plateau, there is play between the upper part of the pin and the hole in the movable plateau. The pin 5 is thus positioned so as to maintain good congruity of these different parts, and to allow good maintenance of the pin which contributes to the stability of the movable plateau 2 in the knee prosthesis.

[0072] The movable plate 2 plays, within the articulation formed by this prosthesis, the role of meniscus. Its perimeter is smaller than that of the tibial plate 3 so that it can move within the limits of the movements authorized by the pin 5 in cooperation with the hole 20. The movable plate can thus rotate, relative to the tibial plate, around its longitudinal axis which is directed in a direction substantially parallel to the axis of the tibial plate. When the hole 20 is of preferred oblong shape, the movable plate 20 can also slide in an anteroposterior direction, represented in the figures by the anteroposterior axis A, on the upper surface of the tibial plate. On the other hand, in all the cases envisaged, the movable plate cannot move in a transverse direction such as represented by the axis T in Figure 3.In fact, its movements are limited by the cooperation of the pin, the hole present on its lower surface, and the cavity of the tibial plateau. In this way, such a configuration has the effect of allowing the degrees of freedom in the movement necessary to obtain natural movements obtained by a knee, while limiting the movements likely to cause imbalances.

[0073] Furthermore, the fact that the mobile plate 2 has a smaller perimeter than that of the tibial plate 3 allows the prosthesis to have a slightly pivoting movement around the longitudinal axis of the mobile plate and the tibial plate, this longitudinal axis essentially coinciding with the longitudinal axis of the tibia. It should be noted that the longitudinal axis of the mobile plate is essentially parallel, preferably perfectly parallel, to the longitudinal axis of the tibial plate.

[0074] The femoral element 1, the mobile plate 2, the tibial plate 3, and the pin 5 are all four made of AI2O3 ceramic conforming to the ISO-6474-1 standard. The ceramic is chosen here for its advantageous effects, and in particular, with regard to its resistance.

[0075] For example, the ceramic may have a particle size of less than 2 μm. Preferably, the ceramic used for the manufacture of the prosthesis has a particle size of between 0.5 μm and 2 μm. Even more preferably, the ceramic has a particle size of between 1 μm and 2 μm. The particle size of the ceramic material is determined according to any method well known to those skilled in the art.

[0076] Variants

[0077] Different variants of the invention may be envisaged. For example, the condyles and condylar cups may both have the shape of a portion of a cylinder while the intercondylar void and stud take the shape of a portion of a sphere. Conversely, the condyles and condylar cups may both have the shape of a portion of a sphere while the intercondylar void and stud take the shape of a portion of a cylinder.

[0078] In other words, the surfaces intended to be in contact, such as the condyles and condylar cups or the intercondylar void and stud, must have the same profile, which can be, for example, in the form of a sphere, cylinder or torus.

[0079] In variants, R and R' may be equal. The dimensions of the prostheses and the parts constituting them are easily determined by those skilled in the art. It is indeed common to offer different sizes of prostheses to adapt to the differences in size of the operated patient. These various embodiments make it possible to design a prosthesis in which the mechanical stresses are not concentrated on a specific area, thus avoiding the appearance of cracks in the ceramic.

Claims

CLAIMS 1. Total knee prosthesis intended to be implanted in a human patient, said prosthesis comprising solid ceramic parts: a femoral element (1) having a longitudinal axis (L'), a tibial plateau (3) having a longitudinal axis (L), and a mobile plateau (2), said mobile plateau (2) being interposed between the femoral element (1) and the tibial plateau (3) to form two articulations with them, in which: the mutual friction surfaces of the femoral element (1) with the mobile plateau (2), and the mutual friction surfaces of the tibial plateau (3) with the mobile plateau (2) are entirely made of the same ceramic material;and the movable plate (2) comprises in its upper part two condylar cups (21) and the femoral element (1) comprises two condyles (11), said condyles (11) and said condylar cups (21) each comprising mutual friction surfaces between which there is a clearance of less than 100 pm when the longitudinal axes (L, L') of said femoral element and said tibial plate form an angle a of between 0° and 75°, characterized in that it further comprises a pin (5) for holding the movable plate (2) on the tibial plate, a first end of which is intended to be housed in a cavity (30) of the tibial plate (3) and the second end of which, opposite the first end, is intended to be housed in a hole (20) of said movable plate (2), said pin is essentially cylindrical in shape and fitted with hard friction in said cavity of said tibial plate (3).; 2. Knee prosthesis according to claim 1, characterized in that said hole is oblong in shape so as to allow rotation and translation of the movable plate (2) relative to the tibial plate along an anteroposterior axis (A).

3. Knee prosthesis according to one of claims 1 or 2, characterized in that said movable plate (2) is capable of translating on said tibial plate (3) along said anteroposterior axis (A) and over a distance of between 3 and 6 millimeters on either side of said longitudinal axis (L).

4. Knee prosthesis according to any one of the preceding claims, characterized in that there is a clearance (300) between the mutual friction surfaces of said movable plate (2) and said tibial plate (3) of less than 100 μm.

5. Knee prosthesis according to any one of the preceding claims, characterized in that the mutual friction surfaces of the tibial plateau (3) with the movable plateau (2) are essentially flat.

6. Knee prosthesis according to any one of the preceding claims, characterized in that there is a clearance (500) between the mutual friction surfaces of said pin (5) and said hole (20).

7. Knee prosthesis according to any one of the preceding claims, characterized in that said pin (5) is entirely made of the same ceramic material as said femoral element (1), said tibial plateau (3) and said mobile plateau (2).

8. Knee prosthesis according to any one of the preceding claims, characterized in that said ceramic material has a thickness of at least 5 mm, preferably between 5 mm and 14 mm.

Images