WO2025141277A1 - Novel knee prosthesis - Google Patents

Abstract

The invention relates to a knee prosthesis (1) comprising a bearing element (100) for a femoral implant of a total knee prosthesis, which is intended to be positioned on the tibial side and comprises an upper surface (41) on which a medial cavity (18) for receiving the medial condyle and a lateral cavity (19) for receiving the lateral condyle are arranged, wherein the medial cavity (18), viewed from above, has an ovoid shape with a mediolateral minor axis and an anteroposterior major axis, wherein the cavities (18, 19) have a concave profile and are separated by a raised region (20) located on the upper surface (41) between the two cavities (18, 19), which raised region extends in a horizontal plane along a curved generatrix having a concavity (180) oriented towards the medial cavity (18), wherein the raised region (20) has, along its generatrix, a convex outer profile, and wherein the lateral flank (209) of the raised region (20) has, in the horizontal plane, a radius of curvature greater than the radius of curvature of the medial flank; the invention also relates to any corresponding total knee prosthesis.

Description

New knee prosthesis

Technical Field

The present invention relates to the field of joint prostheses, and more particularly in this particular field a new knee prosthesis.

Prior art

In the field of knee prostheses, many previous proposals have already been made. The most common models of knee prostheses, commonly called sliding prostheses, include a femoral implant which covers the superficial bony surfaces of the lower end of the femur after resection, a tibial implant which covers the superficial bony surfaces of the upper end of the tibia after resection and an insert generally made of high-density polyethylene (UHMWPE). These prostheses preserve the lateral ligaments, the joint capsule, the tendons of the periarticular muscles, as well as the patella whose articular surface is generally replaced; the cruciate ligaments are generally removed at least the anterior one, the posterior one being sometimes preserved. Knee prostheses are therefore intended to replace the natural joint which has become diseased.

Knee prostheses aim to meet a number of requirements, including:

- a tribological requirement: they must undergo a minimum of wear in use, which is determined by the material used and the absence of aggressive shapes, particularly angular ones;

- a kinematic requirement: the functioning of the prosthesis must be as close as possible to the kinematics of the normal knee in order to be comfortable for the patient in all physical activities. This kinematics was updated by IWAKI in 2000 (IWAKI et al. J. Bone Joint Surg. Vol 87-B.NO.8., November 2000) and includes a displacement, of the order of 3mm from front to back, of the medial femoral condyle in the medial cavity of the insert as opposed to a displacement of the lateral condyle in the lateral cavity of the order of 20mm and of 15 to 20° +/- 5° in rotation around a medial axis.

This is the movement that most modern knee prostheses attempt to replicate. Knee prostheses typically have two bumps at the femoral implant called the lateral condyle and the medial condyle, and an anterior articular surface called the trochlea that articulates with the patella. The two condyles are separated by a gap in material, called the intercondylar notch.

Thus, in general, a knee prosthesis consists of three parts: a femoral implant fitted onto the lower end of the femur after resection, a fixed tibial implant supported on the upper surface of the tibia after resection, supporting an articular insert intended to articulate with the femoral implant. The shapes of the articular insert differ from one type of prosthesis to another and characterize the functioning of the prosthesis. The bearing surface for the femoral implant, whether on the tibial implant (two-part prosthesis) or on the articular insert (three-part prosthesis) generally has two hollow cavities, called lateral and medial.

Innovations most often concern the bearing surface for the femoral implant, usually in the form of an insert, and its articulation with the femoral implant. Also, in order to allow physiological movement of the joint, several solutions have been proposed in the state of the art.

In a particular configuration of a knee prosthesis with insert, proposed in patent application FR2796836, the insert has on its upper face between the two medial and lateral cavities which are symmetrical, a central bump (in the shape of a saddle or more precisely a hyperbolic paraboloid) symmetrical, with respect to a sagittal plane. In addition, the medial condyle and the lateral condyle have in the sagittal plane a spiral shape (therefore a continuous variation e of the radius of the turn from front to back) and a rounded curve (of the sinusoid type) in the frontal sections. Finally, in this proposal of the prior art, the shape of the medial cavity is identical in negative to that of the medial condyle when the knee is in full extension at 0°. There is therefore a congruence between the medial condyle and the medial cavity, complete congruence when the knee is in full extension, congruence which decreases during knee flexion.

In patent application FR2932079, there is, in addition to the previous characteristics, a low point (called in English “dwell point”) located behind the central transverse line marking the middle of the insert.

Several prosthetic inventions have sought to reproduce the displacement with asymmetric rotation of the femoral condyles on the insert and in particular during natural flexion of the knee with a rotation according to an arc of 20° +/- 5° of the lateral condyle in the lateral cavity while the medial condyle does not move back and forth and rotates on itself in the medial cavity. Thus, document GB 2253147 includes a partially spherical medial cavity in which a medial condyle itself partially spherical and congruent with the medial condyle rotates. In this configuration, the lateral condyle has two rays in the sagittal plane received in the lateral cavity of the tibia itself comprising 2 rays in the sagittal plane which, by a set of cams with the sagittal rays of the lateral condyle, allows the forward movement of the tibia during the flexion extension movement.

US patent 6,013,103, for its part, proposes a knee prosthesis which comprises a medial cavity of the insert of partially spherical shape in which fits a medial femoral condyle also spherical and congruent with this cavity. Application US 2010/036499 also proposes a medial cavity of the insert in the form of a segment of sphere in which the medial femoral condyle itself is placed in the form of a segment of a sphere. The lateral part of the insert is here flat or convex without a lip in the posterior part. Application US 2017/0189195 uses a femoral element with at the level of the medial condyle, two different convex profiles and a tibial implant with a bearing surface, at the level of the medial cavity, having two concave profiles complementary to the convex profiles of the medial condyle. These configurations generate a passage from one radius of curvature to another with a staircase effect, as well as a possibility of attachment due to the angulations and flats between neighboring radii of curvature between the cavities and a central eminence. A second embodiment proposes a spherical medial condyle shape in a spherical medial cavity of the sphere-in-sphere type.

US patent 20120095563 has a central eminence but flat cavities with a V-shaped angulation separating the flat from the central eminence.

In US application 2016/228255, the lateral cavity has a flat surface and the medial condyle has two mediolateral radii of curvature with posterior femoral lugs in notches of the insert.

The aim of the present invention is to propose a new knee prosthesis comprising an original support element for the corresponding femoral implant, which does not have the drawbacks of the prostheses known from the prior art, in particular those cited above. In particular:

• No sphere-in-sphere interlocking of the medial condyle in the medial cavity which would not allow for forward and backward movement,

• No rotation around an axis in the center of the medial cavity,

• No complex shape with angles or flats that pose tribological problems. The invention particularly aims to improve comfort for the person wearing the prosthesis, by promoting unconstrained kinematics of the prosthesis's operation, which best meets all physiological and tribological requirements, but which also ensures good stability of the prosthetic joint.

Description of the invention

In this context, the present invention relates to total knee prostheses comprising a femoral implant and a support element for the femoral implant, wherein:

- the femoral implant comprises two condyles, called the medial condyle and the lateral condyle, delimiting between them an intercondylar notch, the external profiles of the two condyles which face the support element being convex in shape,

- the support element is intended to be positioned on the tibia side and comprises an upper surface on which are arranged a medial cavity for receiving the medial condyle and a lateral cavity for receiving the lateral condyle, said cavities having a concave profile being separated by a boss extending on the upper surface between the two cavities, said denture being inserted into the intercondylar notch when the femoral implant is resting on the upper surface of the support element, with the medial cavity seen from above which has an ovoid shape with a small medio-lateral axis and a large antero-posterior axis, characterized in that, in a horizontal plane, said denture extends along a curved generatrix having a concavity oriented towards the medial cavity of said support element, said denture having a lateral flank and a medial flank connected by a vertex which define, together, along the entire length of the generatrix of the denture, a section whose external profile is convex and, in particular, in an arc of a circle, with in a horizontal plane, the lateral flank of the denture which has a radius of curvature which is greater than the radius of curvature of the medial flank of the denture, with the presence of no flattening or angulation between the dent and the medial and lateral cavities, the femoral implant being adapted to the bearing element, so that when the femoral implant is in abutment on the upper surface of the bearing element, there is contact between the medial cavity and the medial condyle, contact between the lateral cavity and the lateral condyle and contact, at the same time, between the medial flank of the dent and the part of the medial condyle which delimits the intercondylar notch and between the lateral flank of the dent and the part of the lateral condyle which delimits the intercondylar notch; the contact between the boss and the condyles at the level of the intercondylar notch ensuring, when the femoral implant is in the support position on the upper surface of the support element and moves in flexion from an extension position to a maximum flexion position, the guidance of the movement of the femoral implant during this flexion with a displacement of the contact zone of the lateral condyle in the lateral cavity from the anterior part to the posterior part of the support element, which corresponds to a displacement over a portion of an arc of a circle.

The total knee prostheses according to the invention therefore comprise a support element for a femoral implant of a total knee prosthesis, said femoral implant comprising two condyles, called medial condyle and lateral condyle, delimiting between them an intercondylar notch, the external profiles of the two condyles being convex in shape, said support element being intended to be positioned on the tibia side and comprising an upper surface on which are arranged a medial cavity for receiving the medial condyle and a lateral cavity for receiving the lateral condyle, said medial and lateral cavities having a concave profile and being separated by a boss extending on the upper surface between the two cavities, which is inserted into the intercondylar notch when the femoral implant is resting on the upper surface of the support element. The support element according to the invention is characterized by the fact that, in a horizontal plane, said bump extends along a curved generatrix having an oriented concavity towards the medial cavity of said support element, said dent having a lateral flank and a medial flank connected by a vertex which together define, along the entire length of the generator of the dent, a section whose external profile is convex and, in particular, in the shape of an arc of a circle, with in a horizontal plane, the lateral flank of the dent having a radius of curvature which is greater than the radius of curvature of the medial flank of the dent.

In the context of the invention, by medial flank of the dent, we mean its flank located on the side of the medial cavity, the other flank located on the side of the lateral cavity, being called lateral flank.

In the context of the invention, and regardless of the embodiment variant of the support element of the knee prosthesis according to the invention, the medial cavity seen from above has an ovoid shape with a small medio-lateral axis and a large antero-posterior axis. The medial cavity and the lateral cavity define cavities with a concave external profile in all directions. Such choices of cavity make it possible to better adapt to the shape of the most common condyles.

Regardless of the embodiment variant of the support element present in the knee prostheses according to the invention, there is no flat/flat surface, nor any angulation between the boss and the medial and lateral cavities. This makes it possible to meet the tribological criterion and thus minimize wear of the prosthesis. Furthermore, the support element and the condyles do not have any lugs or pins. The cavities and the condyles have curved profiles which present a continuous variation, in all directions. This also makes it possible to minimize wear of the prosthesis and the feeling of the patient who does not perceive any catching or sudden stopping of the movement of his knee. In the context of the invention, the guidance of the movement of the femoral implant during flexion and extension movements is therefore essentially ensured by the shape of the proposed boss.

Furthermore, advantageously, in the knee prostheses according to the invention, there is no discontinuity in the sagittal and frontal curvatures of the medial and lateral condyles, nor discontinuity in the curvatures of the medial cavity and the lateral cavity but a continuous variation of the radius defining their external surface.

Generally, the upper surface of the support element has a maximum width located on a medio-lateral axis A2 and an antero-posterior axis A1 which extends perpendicular to the medio-lateral axis A2 by intersecting the medio-lateral axis A2 in its middle A, with the medio-lateral axis A2 which intersects the peripheral edges of the medial and lateral cavities opposite the dent, respectively at points M and L, with AM=AL=Lmax. Cm is the center of the radius Rm of the medial flank of the dent and Cl is the center of the radius RI of the lateral flank of the dent; The centers Cm and Cl of the radii of curvature of the medial flank and the lateral flank of the dent are located in an area which is a square with side length equal to 2Lmax, extending outward from the medial cavity from a point located at the interior of the medial cavity on the medio-lateral axis A2 at a distance of 14 from Lmax +/- 2mm from M, said square being cut in its middle by the medio-lateral axis A2.

According to a first variant embodiment of a support element present in a knee prosthesis according to the invention, the medial and lateral flanks of the boss have parallel curvatures, which correspond to concentric arcs of circles.

According to a particular form of the invention, the center Cm of the radius of curvature Rm of the medial flank and the center Cl of the radius of curvature RI of the lateral flank are the same and located on the axis A2 in M +/-2mm.

According to a second embodiment variant of a support element present in knee prostheses according to the invention, the maximum width Ib of the section of the bossing decreases along its generator from the anterior part to the posterior part of the support element. This contributes, in particular, to limiting the forward movement of the femoral implant during knee flexion. Thus, the anteroposterior stability of the knee prosthesis is further promoted, as well as the backward rolling during knee flexion known as "roll-back".

In this second variant, the dent therefore has medial and lateral flanks which are divergent. Thus, the centers Cm and Cl of the medial and lateral flanks of the dent are not confused.

According to this second embodiment variant, advantageously, the centers of the radii of curvature Rm of the medial flank and RI of the lateral flank of the dent are separated and located inside a square of 14 of Lmax on the side of which M is the center. In a first illustration, Cm the center of the radius of curvature Rm of the medial flank is on the axis A2 in M +/- 2mm and Cl the center of the radius of curvature RI of the lateral flank is in this square of ¹ 4 of Lmax on the side in front of M, so for example at a distance of 1/8th of Lmax or in another configuration Cl the center of the radius of curvature RI of the lateral flank of the dent is located in M +/- 2mm and Cm, the center of the radius of curvature of the medial flank of the dent is located in this square of ¹ 4 of Lmax on the side towards the rear of M at a distance of 1/8th of Lmax.

In another advantageous configuration, Cm the center of the radius of curvature Rm of the medial flank of the dent and Cl the center of the radius of curvature RI of the lateral flank of the dent are located in a square of side 1/4 Lmax of which M is the center, Cm being located on A2 towards the medial side at a distance of 1/8 of Lmax +/- 2mm and Cl being located in this square in front of Cm on a parallel to A1, at a distance of 1/8Lmax +/- 2mm.

In another advantageous configuration, Cm the center of the radius of curvature Rm of the medial flank of the dent and Cl the center of the radius of curvature RI of the lateral flank of the dent are located in a square of side 1 Lmax of which M is the center, Cm being located on A2 towards the medial side at a distance of ^1/4 Lmax +/- 2mm and Cl being located in this square in front of Cm on a parallel to A1, at a distance of % Lmax +/- 2mm.

According to another variant embodiment, the centers Cm and Cl of the radii of curvature Rm and RI of the medial and lateral flanks of the dent can be located in an area limited by, on one side, a parallel to A1 passing through M, on the opposite side by a parallel to A1 crossing A2 at a distance Lmax (=MA=ML), in front by a parallel to A2 tangent to the anterior edge of the insert and below by A2.

Regardless of the embodiment or variant of the support element present in the knee prosthesis of the invention and regardless of the position of these centers, Cm center of the radius of the medial flank of the dent and Cl center of the radius of the lateral flank of the dent, the minimum radius of curvature Rrn _min of the medial flank intersects the axis A2 at a point which is located at the transition point between the medial flank and the medial cavity and the maximum radius of curvature Rl _max of the lateral flank intersects the axis A2 at a point which is located at the transition point between the lateral flank and the lateral cavity, Rrn _min and Rl _max being defined as follows:

- Ririmm of the medial flank which is between the alpha point on A2 at 3Lmax/4 +/- 2mm and the gamma point on A2 at 7Lmax/8 +/- 2mm and is, preferably, equal to 7Lmax/8 +/- 2mm,

- Rl _max of the lateral flank which is between the delta point on A2 at 9Lmax/8 +/- 2mm and the beta point on A2 at 5Lmax/4 +/- 2mm and is, preferably, equal to 9Lmax/8 +/- 2mm.

According to particular embodiments of the support element according to the invention, the bump is raised towards the anterior part and/or towards the posterior part of the support element. In particular, the upper surface of the support element according to the invention may have the shape of a saddle curved towards the medial part or of a hyperbolic paraboloid curved towards the medial part in the horizontal plane.

Advantageously, the lowest points of the medial and lateral cavities are located behind the A2 axis.

In the context of the invention, when the femoral implant is in the support position on the upper surface of the support element and moves in flexion from an extension position to a maximum flexion position, the contact between the boss and the condyles at the level of the intercondylar notch ensures the guidance of the movement of the femoral implant during this flexion with a displacement of the contact zone of the lateral condyle in the lateral cavity from the anterior part to the posterior part of the support element, which corresponds to a displacement over a portion of an arc of a circle.

Any total knee prosthesis that fits this definition that has a guiding and stabilizing boss is part of the invention. The displacement of the contact area of the lateral condyle into the lateral socket advantageously corresponds to a movement, in particular, over a portion of a circular arc corresponding to an arc of approximately 20°+/-5°.

In particular, the portion of the arc of a circle on which the contact zone of the lateral condyle in the lateral cavity moves along a vertical axis has its center in the zone between a parallel to A1 passing through a point located at a distance of 1/4Lmax from M+/-2mm in the medial cavity and a parallel to A1 passing through a point located on A2 outside the medial cavity at a distance of Lmax +/-2mm from M, and limited in front by a parallel to A2 at a distance of 1/2Lmax and also behind by a parallel to A2 at a distance of 1/2Lmax.

Thus, during flexion movement, the femoral implant moves in rotation around a transverse axis and the lateral condyle experiences a movement with on the one hand a rotation along a horizontal axis, called transverse, and a rotation along a vertical axis of rotation whose center is located on the medial side in the area between a parallel to A1 passing through a point located at a distance of 1/4Lmax from M+/-2mm in the medial cavity and a parallel to A1 passing through a point located on A2 outside the medial cavity at a distance of Lmax +/-2mm from M, and limited in front by a parallel to A2 at a distance of 1/2Lmax and also behind by a parallel to A2 at a distance of 1/2Lmax.

Thus, the flexion displacement of the femoral implant is close to that of the physiological knee.

By “approximately” 20°+/-5°, we mean an arc of 15°+/-2° to 25°+/-2°. The value of this arc will, in particular, depend on the size of the implant which corresponds to the size of the knee of the patient on whom the knee prosthesis will be implanted.

According to an alternative embodiment of the knee prostheses according to the invention, in a frontal plane, the external profile of the intercondylar notch is congruent with the external profile of the boss, and this in any support position of the femoral implant on the upper surface of the support element, when the latter moves in flexion from an extension position to a maximum flexion position.

According to the second variant embodiment of the support element according to the invention, the knee prosthesis according to the invention comprises a support element whose maximum width Ib of the section of the bulge decreases along its generator from the anterior part towards the posterior part of the support element and, due to the congruent shapes of the external profiles of the bulge and the intercondylar notch, the maximum width of the intercondylar notch decreases from the anterior part towards the posterior part of the femoral implant.

According to preferred embodiments of the knee prostheses according to the invention, the condyles have an external profile in the sagittal plane, the generator of which is a spiral, in particular the medial condyle has an external profile in the sagittal plane, the generator of which is a logarithmic spiral which is inscribed in the external profile in the sagittal plane of the lateral condyle whose generating spiral has a radius with a lower decrease than that of the generator of the external profile of the medial condyle. This allows, in particular, to:

- make knee flexion easier and more comfortable by reducing tension on the lateral ligaments,

- facilitate rotation of the external condyle in extreme flexion corresponding to an angle of 120° or more, which is a great advantage for kneeling.

According to other preferred embodiments of the knee prostheses according to the invention, which can be combined with the previous ones, the medial cavity seen from above has an ovoid shape with a small medio-lateral axis and a large antero-posterior axis and has in the sagittal plane passing through its large antero-posterior axis a curvature corresponding in the same plane to that of the medial condyle segment in contact with said medial cavity when the femoral implant is in the extension position. This has the advantage of containing the movement of the medial condyle in the medial cavity and limiting its displacement when the femoral implant is in the support position on the upper surface of the support element and moves in rotation (also called flexion displacement) from an extension position to a maximum flexion position, a position in which, due to the decrease in the radius of the condyle, a clearance of approximately 3 mm will appear between the medial condyle and the medial cavity, which corresponds to the physiological clearance of the knee. In other words, from the extension position to the maximum flexion position, there is a displacement of the medial condyle in the medial cavity from the anterior part to the posterior part of the support element, in particular over a distance of approximately 3 mm.

In particular, in the knee prostheses according to the invention, the section of the denture has a convex external profile with a radius of curvature R20 and the section of the notch has a concave external profile with a radius of curvature R10, with the radii of curvature R20 and R10 being substantially identical, with sufficient clearance to avoid tightening between the femoral implant and the support element at the level of the denture. By "substantially identical" is meant that it is an adjustment with clearance because there must be no tightening. The space between the denture and the intercondylar notch is, in particular, between 1 and 2 mm, knowing that the weight of the patient and therefore the pressure can reduce the clearance.

Advantageously in the context of the invention, in the knee prostheses according to the invention, the contact between the support element and the femoral implant is made along a continuous zone which extends at the level of the upper surface of the support element, from one of the cavities to the other, passing through the boss.

In particular, at each degree of flexion between the extension position and the maximum flexion position of the femoral implant, the contact areas of the two condyles in the two cavities are connected by an isthmus corresponding to the contact surface between the boss and the intercondylar notch of the femoral implant. In practice, when the knee prosthesis is implanted in the body of a subject, the contact areas of the two condyles in the two cavities are generally ovoid, from the extension position to a flexion position corresponding to an angle of 100°, or even 120° or more, depending on the pressure exerted on the femoral implant. The pressure exerted on the femoral implant is, in particular, a function of the weight of the subject.

According to variants of implementation of the support elements and knee prostheses according to the invention, the denture is raised towards the anterior part and/or towards the posterior part of the support element. By way of illustration, it is possible for the intercondylar notch and the denture of the support element to have external profiles which have congruent shapes, which are inscribed in two hyperbolic paraboloids. In particular, the denture of the support element can be inscribed in a hyperbolic paraboloid curved in the horizontal plane in the shape of a crescent with medial concavity, the external profiles of the denture and the intercondylar notch having congruent shapes of curved hyperbolic paraboloids with medial concavity.

Whatever the embodiment variant of the support element of the prostheses according to the invention, the upper surface of the support element may have a circumference which has a symmetrical shape with respect to the anteroposterior axis A1 or the upper surface of the support element may have a circumference which has a non-symmetrical shape with respect to the anteroposterior axis A1, with, in particular, a lateral circumference smaller than the medial circumference.

Conventionally in total knee prostheses proposed in the prior art, the support element according to the invention may constitute an articular insert intended to be interposed between the femoral implant and a tibial implant intended to be placed on the end of the tibia, if necessary after resection. In particular, said articular insert may comprise a lower face intended to be placed on the tibial implant, in particular by reversible fitting, in a housing located on the upper surface of the tibial implant.

The knee prostheses according to the invention can take different forms. In particular, the support element is an articular insert intended to be interposed between the femoral implant and a tibial implant. Thus, in general, the knee prostheses according to the invention also comprise a tibial implant intended to be placed on the end of the tibia, if necessary after resection and the support element is an articular insert intended to be interposed between the femoral implant and the tibial implant. The articular insert may be mobile in rotation about an axis perpendicular to the support plate of the tibial implant. But, advantageously, said articular insert will be fixed to the tibial implant, the fixing being able to be done by any suitable attachment means, in particular by removable fitting such as a direct assembly of the elastic fitting type or an indirect assembly using in particular screwing. According to a particular embodiment, the tibial implant comprises on its upper surface, a housing and the articular insert comprises a lower face intended to be placed by reversible fitting in said housing.

According to other embodiments, the support element may directly constitute the tibial implant. In this case, most often, the support element will comprise in the lower part, a support surface intended to rest on the end of the tibia, if necessary after resection.

Brief description of the drawings

Figure 1 is a schematic perspective view of a support element of a right knee prosthesis according to the invention, highlighting the curved nature of the boss extending between the two medial and lateral cavities.

Figure 2A represents a schematic perspective view from below of an example of a femoral implant of a knee prosthesis according to the invention, which comprises two medial and lateral condyles delimiting between them an intercondylar notch which constitutes an opening between the two condyles. In this case, the intercondylar notch has parallel edges and is adapted to a support element as shown in Figure 4D and the condyles are connected to each other only by a connection located in the anterior part of the femoral implant, at the level of the lower part of the trochlea, and more precisely at the level of the condylotrochlear groove.

Figure 2B is a view similar to Figure 2A, but illustrates another femoral implant variant in which the intercondylar notch forms a seamless connecting bridge with the two condyles, which extends from the anterior portion of the femoral implant to its posterior portion. In this case, in each bearing position, the intercondylar notch has an external profile which faces the bearing element whose shape is congruent with the external profile of the boss of the bearing element of Figure 1. This view is enlarged compared to that shown in Figure 3. The intercondylar notch has diverging edges towards the anterior portion of the implant and is adapted to a bearing element as shown in Figure 1.

Figure 3 is a schematic perspective view, from the anterior part of the prosthesis, representing the femoral implant in the support position on the support element, when the prosthesis is in the extension position.

Figure 4A is a schematic perspective view similar to Figure 1 of the bearing element of Figure 3, highlighting the contact area (shown in gray) between the femoral implant and the bearing element, according to the bearing position shown in Figure 3, but according to a view from the posterior part of the bearing element. The gray area schematically represents the location of the contact area between the two parts, when the intercondylar notch forms a seamless connecting bridge. with the two condyles, which extends from the anterior part of the femoral implant to its posterior part.

Figure 4B is a schematic sectional view along the horizontal plane shown in Figure 3, of the prosthesis in the position shown in Figure 3, from a top view, with the knee in extension. The hatched area represents the contact area between the two condyles and the support element, whether the intercondylar notch is empty as in Figure 2A or continuous forming a seamless connecting bridge with the two condyles as in Figure 2B. The gray area schematically represents the location of the contact area between the notch and the intercondylar notch, when the latter forms a seamless connecting bridge with the two condyles, which extends from the anterior part of the femoral implant to its posterior part, knowing that in reality this contact area follows the external profile of the notch.

Figure 4C is a schematic top view of an example of the upper surface of a support element according to the invention, showing its circumference and the axes A1 and A2 and the distance Lmax, in particular. In this exemplary embodiment, the circumference of the support element is symmetrical with respect to the axis A1. The centers of the medial and lateral cavities are C1 and C2. The different reference points on the medio-lateral axis A2 are Lmax = AM = AL; alpha on the axis A2 is located 3/4 of Lmax from M; gamma on the axis A2 is located 7/8 of Lmax from M; delta on the axis A2 is located 9/8 of LMax from M; beta on the axis A2 is located 5/4 of LMax from M; A zone, called the center zone, represents an area where the centers of the radii Rm and RI of the medial (Rm) and lateral (RI) flanks of the denture can be placed according to different variants of the invention. This zone is limited by the axis A2, a parallel to A2 tangent to the anterior edge of the insert, a parallel to A1 passing through M and a parallel to A1 crossing the axis A2 at M' at a distance Lmax from M (MM' = AM=Lmax).

Figure 4D is a schematic top view of an example of the upper surface of a support element according to the invention, showing a dent which has an identical section along its generator. The references 208 and 209 here represent the flanks of the dent, at the level of the widest part of the dent, that is to say at the base of its section, which corresponds to the change in curvature corresponding to the start of the cavities. The centers Cm of the medial flank 208 and Cl of the lateral flank 209 of the dent are both located on A2 at M +/- 2 mm.

Figure 4E corresponds to a schematic view of another example of embodiment of a support element according to the invention, in which the maximum width Ib of the section of the dent decreases along its generator from the anterior part towards the posterior part of the support element. Here the two centers Cm and Cl are inside a rectangle with center M and side 1/4 of Lmax. In this example, the center Cm of the medial radius of the dent is located on A2 at a distance 1/8 Lmax +/-2mm from M, and the center Cl of the lateral radius of the dent is located in front of A2 on a parallel A'2 to A2 at a distance dl of 1/8 Lmax +/-2mm from M.

Figure 4F corresponds to a schematic view of a preferred embodiment of a support element according to the invention, in which the maximum width Ib of the section of the dent decreases along its generator from the front part towards the rear part of the support element. Here the center Cm is on A2 at a distance of 1/4 of Lmax +/- 2mm from M and the center Cl is on A’2 parallel to A2 in front, at a distance dl of 1/4 Lmax +/-2mm.

Figure 5 is a schematic perspective view, from the anterior part of the prosthesis, representing the femoral implant in the support position on the support element, when the prosthesis is in the flexion position corresponding to an angle of approximately 120° between the femur and the tibia.

Figure 6A is a schematic perspective view similar to Figure 4A of the support element of Figure 5, highlighting the contact zone (shown in gray) between the femoral implant and the support element, according to the support position shown in Figure 5 (flexion corresponding to an angle of approximately 120° between the femur and the tibia), when the intercondylar notch forms a seamless connecting bridge with the two condyles, which extends from the anterior part of the femoral implant to its posterior part.

Figure 6B is a schematic sectional view along the horizontal plane shown in Figure 3, of the prosthesis shown in Figure 5 (therefore in the maximum flexion position), from a top view. The hatched area schematically represents the location of the contact zone between the bump and the intercondylar notch, as well as between the medial 8 and lateral 9 condyles and the medial 18 and lateral 19 cavities when the intercondylar notch forms a seamless connecting bridge with the two condyles, and extends from the anterior part of the femoral implant to its posterior part, knowing that in reality this contact zone follows the external profile of the bump. What is in dotted lines corresponds to the position in Figure 4B.

Figure 7 is a schematic sectional view of the knee prosthesis of the preceding figures when the latter is in the extended position, according to a sagittal plane made at the level of the medial condyle and the medial cavity; the femoral implant and the support element are shown at a distance from each other for greater clarity. Here the low point 200 of the medial cavity 18 is located behind the median axis IXB.

Figure 8 is a schematic sectional view along a sagittal plane highlighting the spiral character of the external profiles of a medial condyle and a lateral condyle according to one of the preferred embodiments of the invention, in which the medial condyle is inscribed inside the lateral condyle. Figure 9A is a schematic sectional view of the knee prosthesis shown in exploded view in Figure 7, along the frontal plane IXA shown in Figure 4B, when the knee prosthesis is in the extended position, with the femoral implant and the bearing element in contact with each other. To facilitate understanding, the femoral implant and the bearing element are shown slightly apart. The shaded area schematically represents the location of the contact zone between the femoral implant and the bearing element, when they are in contact with each other.

Figure 9B is a schematic sectional view of the knee prosthesis shown in exploded view in Figure 7, according to the frontal plane IXB shown in Figure 4B, when the knee prosthesis is in the extended position, with the femoral implant and the bearing element in contact with each other. The gray area schematically represents the location of the contact zone between the femoral implant and the bearing element, when the latter are in contact with each other, in the case where the intercondylar notch forms a bridge which extends from one to the other of the condyles and extends from the anterior part to the posterior part of the femoral implant. To facilitate understanding, the femoral implant and the bearing element are shown at a distance and the contact zone shown in gray.

Figure 9C is a schematic sectional view of Figure 7, along the frontal plane IXC shown in Figure 6B, when the knee prosthesis is in a flexion position corresponding to an angle of 120°, with the femoral implant and the support element in contact with each other. To facilitate understanding, the femoral implant and the support element are shown at a distance and the contact area shown in gray, in the case where the intercondylar notch forms a bridge which extends from one to the other of the condyles and extends from the anterior part 52 to the posterior part 53 of the femoral implant 2. In the case where the intercondylar notch is an empty space as exemplified in FIG. 2A, the part 210 does not exist and the contact between the insert 100 and the femoral component 2 is made only at the level of the flanks 208 and 209 of the eminence.

Figure 10A is a schematic view along a sagittal plane, of the medial condyle according to Figure 8 in contact with the medial cavity, when the knee prosthesis is in the extended position.

Figure 10B is a schematic view along a sagittal plane, of the medial condyle according to Figure 8 in contact with the medial cavity, similar to Figure 10A, but when the knee prosthesis is in the maximum flexion position, corresponding to an angle of approximately 120°.

Figure 11 A is a schematic view along a sagittal plane, of the lateral condyle according to Figure 8 in contact with the lateral cavity, when the knee prosthesis is in the extended position. Figure 11B is a schematic view along a sagittal plane, of the lateral condyle according to Figure 8 in contact with the lateral cavity, similar to Figure 10A, but when the knee prosthesis is in the maximum flexion position, corresponding to an angle of approximately 120°.

Figure 12 is a schematic perspective view of a prosthesis according to the invention in which the support element is an articular insert interposed between the femoral implant and a tibial implant.

Description of the embodiments

A knee prosthesis is intended to be implanted in an individual to replace their knee damaged by disease. Also, the various elements of the latter are defined by reference to its use, that is to say during the operation of the prosthetic knee once the femoral implant is positioned on the end of the femur and the bearing element on the end of the tibia of a subject respectively. The femoral implant is intended to be adapted after resection on the lower femoral epiphysis. The bearing element is intended to be adapted, directly or indirectly, after resection on the upper tibial epiphysis. When the bearing element is adapted, indirectly, after resection on the upper tibial epiphysis, in this case, it will correspond to an articular insert positioned between the femoral implant and a tibial implant and it is the tibial implant which will be adapted on the upper tibial epiphysis. Conventionally, in the field of knee prostheses, the following terms are used:

- the extension position, corresponds to the case where the knee prosthesis is in a position which corresponds to the knee stretched, that is to say that the femur and the tibia which come, respectively, in extension of the femoral implant and the support element form an angle of 0°;

- the flexion positions correspond to the case where the knee is bent, that is to say that the femur and the tibia which come, respectively, in extension of the femoral implant and the support element form a non-zero angle. The maximum flexion position generally corresponds to an angle equal to or greater than 120°;

- the anterior part of the prosthesis (and therefore the anterior parts of the femoral implant and the support element) corresponds to the part which is positioned, when the prosthesis is implanted in an individual, towards the front face of the individual; the posterior part of the prosthesis (and therefore the posterior parts of the femoral implant and the support element) corresponds to the part which is positioned, when the prosthesis is implanted in an individual, towards the rear face of the individual;

- The parts (cavity, condyle, etc.), called medial, of the prosthesis correspond to the parts which will be positioned on the crotch side of the individual and the parts (cavity, condyle, etc.), called lateral, of the prosthesis correspond to the parts which will be positioned on the outside of the individual's leg; - The sagittal and frontal planes are understood in the anatomical sense. Also, a sagittal plane extends perpendicular to a frontal plane. A sagittal plane extends between the anterior and posterior parts of the prosthesis, while a frontal plane extends between the lateral end and the medial end of the prosthesis. A horizontal or transverse plane extends perpendicular to the sagittal and frontal planes.

In the context of the invention, a convex profile or shape means a profile or shape that is curved towards the outside of the part considered (femoral implant, support element), a concave profile or shape means a profile or shape that is curved towards the inside of the part considered (femoral implant, support element). Furthermore, when it is a question of a concave or convex profile or shape, this excludes points of change of curvature. Furthermore, the notion of concavity or convexity can correspond to a variable radius of curvature, but advantageously, the radius of curvature will be constant and said curved profile or said concave or convex shape will correspond to an arc of a circle.

As is apparent from the figures and, in particular, from figure 3, the subject of the invention relates to a total knee prosthesis 1 conventionally comprising a femoral implant 2 and a support element 100 which will be positioned on the tibia side. The support element 100 is also the subject of the invention. In the description which follows, the emphasis will be placed on the specific features of the invention, and only the upper part of the support element will be shown, knowing that the lower part may correspond to that conventionally present in a tibial implant (forming the support element on its own) or to that conventionally present in an articular insert cooperating with a tibial implant, which will be positioned, on the tibia, most often after resection. In knee prostheses according to the invention, conventionally, the femoral implant and the tibial implant are both preferably made of a biocompatible stainless metal alloy, and the joint insert will generally be made of a plastic material, such as polyethylene. However, one or more elements of the prosthesis may also be made of alumina ceramic or alumina and zirconia, or biocompatible resins for example. Preferably, the support element will constitute an articular insert which will be placed on a tibial implant, which allows better attachment to the tibia bone. If the articular insert is made of a plastic material, generally high-density polyethylene enriched with Vitamin E, the tibial implant and the femoral implant will generally be metallic. If the articular insert is made of ceramic, the femoral implant will then advantageously be made of ceramic.

Conventionally, the femoral implant 2 has, in side view as partially shown in figures 3, 5 and 12, in particular, a substantially non-symmetrical U-shape between the branches of which is delimited a housing 500 for fixing on the lower epiphysis of the femur, in particular by fitting together two projecting lugs 600, visible on Figures 7, 9B and 12. Such lugs are optional, the placement and fixing of the femoral implant 2 on the epiphysis of the femur can be done by elastic force fitting or by cementing.

As can be seen from Figure 2A, the femoral implant 2 comprises on a lower face 700 which faces the support element 100, two condyles, respectively a medial condyle 8 and a lateral condyle 9, delimiting between them an intercondylar notch 10 which delimits a space existing between the two condyles. As can be seen in Figure 2A, but is more apparent in Figure 12, which illustrates another embodiment, in a conventional manner, at the level of the anterior part 52 of the femoral implant 2, a femoral trochlea 110 extends in the anterior extension of the two condyles 8, 9 respectively medial and lateral and comprises two cheeks medial 120 and lateral 130 extending the external profile of the condyles 8 and 9 respectively medial and lateral. The two trochlear cheeks 120, 130 are joined by a trochlear groove 150 extending in the anterior extension of the intercondylar notch 10.

In the example shown in Figure 2A, the medial condyle 8 and the lateral condyle 9 are separated by a void of material which corresponds to the intercondylar notch 10. The medial condyle 8 and the lateral condyle 9 delimit the intercondylar notch 10, at their parts 108 and 109, respectively. The medial condyle 8 and the lateral condyle

9 are only connected at the level of the anterior part 52 of the femoral implant 2. The connection between the medial condyle 8 and the lateral condyle 9, located in the anterior part 52 of the femoral implant 2, is made at the level of the lower part of the trochlear groove 150, and more precisely at the level of the condylotrochlear groove 160.

It is also possible that the intercondylar notch 10 connects seamlessly with the two medial and lateral condyles 8 and 9 and forms a connecting bridge 170 which extends from one to the other of the condyles and extends from the anterior part 52 (more precisely from the condylotrochlear groove 160) to the posterior part 53 of the femoral implant 2. Such an embodiment is shown in Figure 2B. Although it is not very visible in this figure, the external profile 101 of the intercondylar notch

10 which faces the support element 100 is concave in shape. This is evident, however, in Figure 9B, which shows a sectional view in a frontal plane of the femoral implant 2, opposite the support element 100. The two medial and lateral condyles 8, 9 of the femoral implant 2 form bumps. They are shaped in such a way that their section, along a sagittal plane, has the shape of a spiral, the radius of curvature of which decreases from the anterior part 52 of the femoral implant 2 forming the femoral trochlea 1 10 towards the posterior part 53 of the femoral implant 2.

As can be seen from Figure 1, the support element 100 has an upper surface 41, in which two cavities are provided: a medial cavity 18 for receiving the medial condyle 8 and a lateral cavity 19 for receiving the lateral condyle 9. Each of the cavities has a concave profile, regardless of the vertical plane considered. The two medial 18 and lateral 19 cavities are separated by a bump 20 which extends from the anterior part 42 to the posterior part 43 of the support element 100, taking a curved shape. Thus, the bump 20 is located in the central part of the support element 100. The bump 20 connects seamlessly with the two medial 18 and lateral 19 cavities. The bump 20 has, in top view, a curvature 180 oriented towards the medial cavity 18. In other words, in a horizontal plane or in top view, the medial flank 208 (located on the medial cavity 18 side) of the bump 20 has a concave profile, and the lateral flank 209 (located on the lateral cavity 19 side) has a convex profile. In a horizontal plane or in top view, the boss 20 therefore extends along a curved generatrix whose concavity is oriented towards the medial cavity 18. In particular, the medial flank 208 and the lateral flank 209 are connected by a vertex 210 and the medial flank 208, the lateral flank 209 and the vertex 210 together form, in a sagittal plane, an external profile of convex shape. The medial flank 208 and the lateral flank 209 have, in a horizontal plane, an external profile in the form of an arc of a circle, with the lateral flank 209 having a radius of curvature greater than the radius of curvature of the medial flank 208. The radius of curvature will depend on the width of the implant. The length of each flank 208 and 209 is different and depends on the radius of the profile of said flank.

The boss 20 will ensure the reception of the intercondylar notch 10. That is to say that it is configured so that when the femoral implant 2 is supported on the support element 100, with a contact between the medial cavity 18 and the medial condyle 8, on the one hand and a contact between the lateral cavity 19 and the lateral condyle 9, on the other hand, there is also a contact, at the same time, between the medial flank 208 of the boss 20 and the part 108 of the medial condyle 8 which delimits the intercondylar notch 10 and between the lateral flank 209 of the boss 20 and the part 109 of the lateral condyle 9 which delimits the intercondylar notch 10, as can be seen in FIG. 4A. Figure 4A represents the contact zone between the femoral implant 2 of Figure 2B and the support element 100 shown in Figure 1, when the femoral implant 2 is supported on the support element 100 in the extended position as shown in Figure 3. Figure 4B, which is a schematic sectional view at the base of the section of the boss 20 (section IVB of Figure 3), highlights the contact zones 183 and 193, between the medial and lateral flanks 208 and 209 of the boss 20 and the parts 108 and 109 of the medial and lateral condyles 8 and 9 which delimit the intercondylar notch 10. During the relative movement in flexion of the femoral implant 2 with respect to the support element 100, these contact zones 183 and 193 move, but there is contact, in any flexion position, between the medial flank 208 of the bump 20 and the part 108 of the medial condyle 8 which delimits the intercondylar notch 10 and between the lateral flank 209 of the bump 20 and the part 109 of the lateral condyle 19 which delimits the intercondylar notch 10, which allows the guidance and control of the movement of the lateral condyle 9, in the lateral cavity 19.

The dent 20 has a section (cross-section, i.e. a section taken in a vertical plane which is perpendicular to its generator) whose external profile facing the femoral implant 2 is convex.

As is more apparent in Figure 9B, which is a sectional view along a frontal plane, the respective external profiles 181 and 191 of the two medial 18 and lateral 19 cavities are concave in shape and the external profile 201 of the bump 20 is convex in shape and forms an arc of a circle. Thus, the boundary between the bump 20 and each cavity can be defined as the point of change of convex/concave curvature. In the context of the invention, there is no flatness or angulation between the bump 20 and the medial 18 and lateral 19 cavities.

In particular, this external profile 201 of the bump 20 has the shape of an arc of a circle. In other words, the bump 20 is a half-torus or a portion of a half-torus which is curved and whose section can be constant or variable. If the section is constant, the medial flank

208 and the lateral flank 209 form concentric circular arcs in a horizontal plane. Such an embodiment is illustrated in Figure 4D in which the two centers are in M+/-2mm.

Figure 4D shows a schematic view of an embodiment of the dent 20 in which the medial 208 and lateral 209 flanks have parallel curvatures in a horizontal plane, which therefore correspond to concentric arcs of a circle. It can thus be considered that the section of the dent 20 is identical along its generator. In Figure 4D, the medial 208 and lateral 209 flanks which are visible are represented at the base of the section of the dent 20, that is to say at the level of the change in curvature corresponding to the start of each medial 18 and lateral 19 cavity. Thus, at this level, the medial flank 208 has its minimum radius of curvature Rrn _min and the lateral flank

209 has its maximum radius of curvature Rl _max . In the example illustrated, the center Cm of the radius of curvature Rm of the medial flank 208, as well as its minimum radius of curvature Rm _min and the center Cl of the radius of curvature RI of the lateral flank 209, as well as its maximum radius of curvature Rl _max are coincident with M (+/- 2mm). The radius of curvature Rm of the medial flank 208, as well as its minimum radius of curvature Rrn _min is between the distance separating the points M and a (+/- 2mm) and the distance separating the points M and y (+/- 2mm) and the radius of RI of the lateral flank 209, as well as its maximum radius of curvature Rl _max of the lateral flank 209 is between the distance separating the points M and 5 (+/- 2mm) and the distance separating the points M and p (+/- 2mm).

To understand Figure 4D, reference should first be made to Figure 4C, which shows a schematic top view of the circumference of the upper surface 41 of the support element 100. The upper surface 41 has a maximum width located on a medio-lateral axis A2 and an antero-posterior axis A1 extends perpendicular to the medio-lateral axis A2 by intersecting the medio-lateral axis A2 in its middle A. The medio-lateral axis A2 intersecting the peripheral edges 308 and 309 of the medial 18 and lateral 19 cavities opposite the bump 20, respectively at points M and L, with AM=AL=Lmax. In the illustrated example A1 and A2 are perpendicular and the circumference of the upper surface 41 is symmetrical with respect to the axis A1. Point a is located on axis A2, in medial cavity 18, at a distance 3Lmax/4 from M, point y is located on axis A2, in medial cavity 18, at a distance 7Lmax/8 from M, point 8 is located on axis A2, in lateral cavity 19, at a distance 9Lmax/8 from M and point |3 is located on axis A2, in lateral cavity 19, at a distance 5Lmax/4 from M. The geometric center of medial cavity 18 is denoted C1 and the geometric center of lateral cavity 19 is denoted C2.

The width of the intercondylar notch 10 and its shape are adapted to those of the boss 20 to allow contact, both, between the medial flank 208 of the boss 20 and the part 108 of the medial condyle 8 which delimits the intercondylar notch 10 and between the lateral flank 209 of the boss 20 and the part 109 of the lateral condyle 9 which delimits the intercondylar notch 10 when the femoral implant is in the support position on the upper surface 41 of the support element 100 and moves in flexion from an extension position to a maximum flexion position, and thus ensures the guidance of the movement of the femoral implant 2, during this femoral movement. Thus, in the case of a bearing element 100 having a bossing with parallel medial 208 and lateral 209 flanks (as in FIG. 4D), a suitable femoral implant 2 will have an intercondylar notch 10 delimited by portions 108 and 109 of the condyles which, in a horizontal plane, extend according to concentric arcs of a circle. Such an example of a femoral implant 2 is shown in FIG. 2A.

Figure 4E shows a schematic view of another embodiment of the dent 20 in which the medial 208 and lateral 209 flanks have non-parallel curvatures in a horizontal plane, and which correspond to a reduction in the width Ib of the dent 20 from the anterior part 42, towards the posterior part of the support element 100. The width Ib of the dent is taken according to the section of the dent, therefore perpendicular to its generator and corresponds to the width at the base of the section (which is therefore the maximum width of said section). In the example illustrated in this figure, the maximum radius of curvature Rrn _max of the medial flank 208 has its center Cm on the medio-lateral axis A2 at a distance Lmax/8 +/- 2mm from M, and the minimum radius of curvature Rl _min of the lateral flank 209 has its center Cl on an axis A'2 parallel to the axis A2, but offset from the latter. The axis A'2 is located between the medio-lateral axis A2 and the anterior part of the support element, with the distance di between the medio-lateral axis A2 and the axis A'2 which is equal to Lmax/8, in this example.

Figure 4F shows a schematic view of another embodiment of the boss 20 in which the medial 208 and lateral 209 flanks have non-parallel curvatures in a horizontal plane, and which correspond to a reduction in the width Ib of the boss 20 of the anterior part 42, towards the posterior part of the support element 100. In the example illustrated in this figure, the minimum radius of curvature Rrn _min of the medial flank 208 has its center Cm on the medio-lateral axis A2 at a distance Lmax/4 +/-2mm from M, and the maximum radius of curvature Rl _max of the lateral flank 209 has its center Cl vertically above Cm on an axis A'2 parallel to the axis A2, but offset from the latter. The axis A'2 is located between the medio-lateral axis A2 and the anterior part 42 of the support element, with the distance d, between the medio-lateral axis A2 and the axis A'2 which is equal to Lmax/4 +/- 2mm, in this example.

In these two embodiments of Figures 4E and 4F, the dent is on the medial sides

208 and lateral 209 diverging towards the anterior part 42 of the support element 100. The width of the intercondylar notch 10 and its shape being adapted to those of the bump 20 to allow contact, at the same time, between the medial flank 208 of the bump 20 and the part 108 of the medial condyle 8 which delimits the intercondylar notch 10 and between the lateral flank

209 of the boss 20 and the part 109 of the lateral condyle 9 which delimits the intercondylar notch 10 when the femoral implant is in the bearing position on the upper surface 41 of the bearing element 100 and moves in flexion from an extension position to a maximum flexion position, and thus ensure the guidance of the movement of the femoral implant 2, during this femoral movement, in the case of a bearing element whose boss has medial 208 and lateral 209 flanks diverging towards the anterior part 42 of the bearing element 100, a suitable femoral implant 2 will also have an intercondylar notch 10 delimited by parts 108 and 109 of condyles which diverge towards the anterior part 52 of the femoral implant 2. Such an example femoral implant 2 is shown in Figure 2B.

The geometry choices for the support element 100 illustrated by figures 4A to 4F are given for purely illustrative purposes and many other construction choices can be adopted by those skilled in the art, depending on the size of the prosthesis adapted to the size and weight of the patient on which it is to be implanted. The centers Cm and Cl can in particular be placed in the so-called center zone as illustrated in Figure 4C, zone limited by A2 at the bottom, a parallel to A2 tangent to the anterior edge of the support element in front, a parallel to A1 passing through M and a parallel to A1 crossing A2 at a distance Lmax from M. The presence of a central bump 20 which extends in a horizontal plane along a curved generatrix with a concavity 180 oriented towards the medial cavity 18 of the support element 100, with the lateral flank 209 of the bump 20 which has a radius of curvature which is greater than the radius of curvature of the medial flank 208 of the boss 20, cooperates with the intercondylar notch 10, to guide the movement of the lateral condyle 9 in the lateral cavity 19. The dimensions of the central boss 20 and of the intercondylar notch 10 are chosen to ensure contact between the boss 20 and the medial 8 and lateral 9 condyles at the level of this intercondylar notch 10, throughout the flexion movement when the femoral implant 2 is in the support position on the upper surface 41 of the support element 100 and moves in flexion from an extension position to a maximum flexion position. Thus, guiding the movement of the femoral implant 2 during this flexion is possible with a displacement of the contact zone of the lateral condyle 9 in the lateral cavity 19 from the anterior part 42 to the posterior part 43 of the support element 100, which corresponds to a displacement over a portion of a circular arc of 15° +/- 5°.

Advantageously, the medial cavity 18 has, in top view, an ovoid shape, as illustrated in FIGS. 4A, 4B, 6A and 6B, the major axis of the ovoid extending along the anteroposterior axis of the medial cavity 18. The lateral cavity 19 has, for its part, generally, in top view, a crescent-type shape, as highlighted in FIGS. 4A, 4B, 4D to 4F, 6A and 6B.

As can be seen from these figures, in top view, the upper surface 41 of the support element 100 has the shape of a bean, the concave zone 44 of which is located at the level of the posterior part 43. The concave zone 44 particularly promotes the preservation of the posterior cruciate ligament where appropriate. The posterior end of the bump 20 is therefore located at the level of this concave zone 44.

There is cooperation between the upper surface 41 of the support element 100 and the lower face 700 of the femoral implant 2. When the femoral implant 2 is supported on the upper surface 41 of the support element 100, there is contact between the medial cavity 18 and the medial condyle 8, contact between the lateral cavity 19 and the lateral condyle 9 and contact between the bossing 20 and the intercondylar notch 10. Figures 3 and 5 show the femoral implant of Figure 2B supported on the surface 41 of the support element 100 of Figure 1, in two different positions, respectively in the extension position (0° angle) and in the maximum flexion position (120° angle) of the knee prosthesis.

In the example illustrated in these figures, the boss 20 and the intercondylar notch 10 have congruent shapes which fit together with play, as is apparent from figures 9A to 9C. However, the principle of the invention is the same without this congruence, given that the guidance is ensured by the contact maintained throughout the flexion movement between the medial flank 208 of the boss 20 and the part 108 of the medial condyle 8 which delimits the intercondylar notch 10, on the one hand, and between the lateral flank 209 of the boss 20 and part 109 of the lateral condyle 9 which delimits the intercondylar notch 10, on the other hand.

As can be seen from Figure 2A and Figure 2B, the intercondylar notch 10, when viewed from below, has a curvature oriented towards the medial condyle 8. In other words, the medial leg 108 (located on the medial condyle 8 side) of the intercondylar notch 10 has a concave profile, in a horizontal plane and the lateral leg 109 (located on the lateral condyle 9 side) has a convex profile. In particular, as is apparent from Figures 9A to 9C, the external profile of the bump 20 corresponds exactly but in a hollow and mirrored manner to the external profile of the intercondylar notch 10 which separates the medial 8 and lateral 9 condyles. In particular, as is apparent from Figure 9B, in a plane extending perpendicular to the generatrix of the bump, the convex external profile 201 of the bump 20 and the concave external profile 101 of the intercondylar notch 10 form arcs of circles with radii of curvature R20 and R10 respectively which are substantially identical.

Furthermore, the movement of the lateral condyle 9 in the lateral cavity 19 is accompanied by a rotation of the latter around its transverse axis, during flexion of the prosthesis. Thus, during the flexion movement of the femoral implant 2, the path of a point which follows the intercondylar notch 10 is shorter than the path followed by a point located on the lateral condyle 9 resting in the lateral cavity 19. In Figures 9A and 9C, the convex external profiles 201a and 201b of the boss 20 and the concave external profiles 101a and 101b of the intercondylar notch 10 are not arcs of a circle, but have an ovoid shape, because the section is not taken perpendicular to the generatrix of the boss 20.

According to the invention, it is the curvature of the boss 20 and the contact zones between the latter and the intercondylar notch 10 which ensure, on the one hand, the stability of the prosthesis and on the other hand kinematics conforming to the natural movement of the knee, when the constituent elements (femoral implant 2 and support element 100, in particular) of the knee prosthesis 1 according to the invention pass from an extension position to a flexion position, and this up to a maximum flexion position. According to the invention, in any position of the knee prosthesis 1, the femoral implant 2 bears on the upper bearing surface 41 of the bearing element 100, with a bearing of the surface of the intercondylar notch 10, on the surface of the bulge 20, or more precisely with a bearing at least between the medial flank 208 of the bulge 20 and the part 108 of the medial condyle 8 which delimits the intercondylar notch 10, on the one hand, and between the lateral flank 209 of the bulge 20 and the part 109 of the lateral condyle 9 which delimits the intercondylar notch 10, on the other hand. This ensures both guidance and stability of the femoral element during its relative rotational movement, with guidance and stability not being dissociated. Figure 9B highlights the congruent nature of the two external profiles of the notch intercondylar notch 10 and the bump 20 with contact or the presence of play. In the example illustrated in Figure 2B and Figures 9A to 9C, in particular, the support and therefore the contact between the two external profiles of the intercondylar notch 10 and the bump 20 is made both at the level of the parts 108 and 109 of the condyles delimiting the intercondylar notch 10, and at the level of the apex 210 of the external profile of the intercondylar notch 10. When the notch is open as in Figure 2, the contact between the condyles 8 and 9 and the bump is made at the level of the faces of the latter at 108 and 109.

The curved boss 20 allows for asymmetric rotation of the two medial 8 and lateral 9 condyles: the curved boss 20 allows for guiding the rotational movement of the femoral implant 2, the medial condyle 8 and the lateral condyle 9 following the guidance of the intercondylar notch 10 on the curved boss 20, like a monorail train which follows the curvature of its central rail.

Thus, when the femoral implant 2 is in the support position on the upper surface 41 of the support element 100 and moves in rotation (flexion movement) from an extension position illustrated in FIG. 3 to a maximum flexion position illustrated in FIG. 5, the intercondylar notch 10 and the boss 20, by their shape, or even their congruence, ensure the guidance of the movement of the femoral implant 2 during this rotation with a displacement of the contact zone of the lateral condyle 9 in the lateral cavity 19 from the anterior part 42 to the posterior part 43 of the support element 100. Thus, during the movement of the knee prosthesis 1 according to the invention, the lateral condyle 9 of the femoral implant 2 describes, in addition to its rotation around its transverse axis, a rotation around a vertical axis which is located on the side medial which crosses an area between a parallel to A2 passing through a point located at a distance of 1/4Lmax from M+/-2mm in the medial cavity and a parallel to A2 passing through a point located on A2 outside the medial cavity at a distance of Lmax +/-2mm from M, and limited in front by a parallel to A2 at a distance of 1/2Mmax and behind also by a parallel to A2 at a distance of 1/2Lmax.

In particular, the contact area of the lateral condyle 9 in the lateral cavity 19 moves along a curved path, as can be seen from the comparison:

- figures 4A and 4B, on the one hand, which respectively present a top view of the surface 41 and a top sectional view which therefore highlights the contact zones 183 and 193 of the boss 20 and the intercondylar notch 10 between the medial flank 208 of the boss 20 and the medial leg 108 of the intercondylar notch 10 and between the lateral flank 209 of the boss 20 and the lateral leg 109 of the intercondylar notch 10, when the knee prosthesis is in extension; the contact surface 300 with the femoral implant 2 is shown in gray, when the notch intercondylar notch 10 is full and forms a connecting bridge 170 between the two condyles as in figure 2B and hatched the contact zone between the two medial and lateral condyles when the intercondylar notch is continuous between the two condyles as in figure 2B as well as when the intercondylar notch is an empty space between the two condyles as in figure 2A.

- figures 6A and 6B, on the other hand, which respectively present a top view of the surface 41 and a top sectional view which therefore highlights the contact zones 183 and 193 of the boss 20 and the intercondylar notch 10 between the medial flank 208 of the boss 20 and the medial leg 108 of the intercondylar notch 10 and between the lateral flank 209 of the boss 20 and the lateral leg 109 of the intercondylar notch 10, when the knee prosthesis is in maximum flexion. The contact surface 300 with the femoral implant 2 is shown in hatching, when the intercondylar notch 10 is full and forms a connecting bridge 170 between the two condyles.

In particular, it is clear from these figures that the displacement of the contact zone 192 of the lateral condyle 9 in the lateral cavity 19 can take the form of a portion of a circular arc of approximately 20°+/-5. This rotation takes place around a vertical axis which crosses a zone between a parallel to A1 passing through a point located at a distance of 1/4Lmax from M+/-2mm in the medial cavity and a parallel to A1 passing through a point located on A2 outside the medial cavity at a distance of Lmax +/-2mm from M, and limited in front by a parallel to A2 at a distance of 1/2Mmax and also in the rear by a parallel to A2 at a distance of 1/2Mmax. It should be noted that since the lateral condyle 9 moves in the lateral cavity 19, the transverse axis around which the femoral implant 2 moves in rotation is not fixed and experiences a backward movement in projection in a horizontal plane.

The boss 20, by its curvature oriented towards the medial cavity 18 (concave medial profile and convex lateral profile, in top view), ensures the guidance of the femoral implant 2, when the latter is rotating around its transverse axis and allows an asymmetrical displacement of the condyles 8 and 9. Indeed, between the extension position and the maximum flexion position of the prosthesis, the contact zone 182 of the medial condyle 8 moves only a few millimeters from front to back or from back to front in the medial cavity 18, while the contact zone 192 of the lateral condyle 9 moves along a curved trajectory, in the lateral cavity 19, and this from the anterior part 42, towards the posterior part 43 of the support element 100, as is evident, in particular, from figures 3 to 6.

Thus, contrary to the solutions proposed in particular in document US 2017/0189195, as well as in application US 2010/036499, it is not cooperation spherical-shaped cavities and condyles with sphere-in-sphere interlocking which ensures the guidance of rotation, but the central boss 20 which cooperates with the intercondylar notch 10 of the femoral implant 2. According to certain embodiments, the central boss 20 and the intercondylar notch 10 may be congruent both at the lateral 208 and medial 209 flanks and possibly but not necessarily at the apex 210 of the boss 20. This further facilitates the control of the movement of the femoral implant 2. The congruence is assessed in each position of the femoral implant 2 bearing on the surface 41 of the bearing element 100. That is to say that at each position of movement in flexion from the extension position to the maximum flexion position, there is contact between the intercondylar notch 10 and the bump 20, at the level of the lateral 208 and medial 209 flanks and possibly the apex 210 when the intercondylar notch 10 is full. However, there is play between the two parts, and in particular at the level of the bump 20, to avoid tightening between the two parts. It should also be noted that in the knee prostheses 1 of the invention, and as illustrated in the figures, there are no stops, pins, lugs or gears in the medial 18 and lateral 19 cavities. There are also no flats or angulations in the medial 18 and lateral 19 cavities. The lateral 8 and medial 9 condyles each have a profile which is convex at all points, that is to say they do not include a sudden change in curvature defining two different convex profiles, as is the case, in particular, in application US 2017/0189195. Likewise, the two medial 18 and lateral 19 cavities each have a profile which is concave at all points, that is to say that they do not include a sudden change in curvature defining two different concave profiles, as, in particular, is the case in application US 2017/0189195.

The curved bump 20 and the fact that the external profile of the intercondylar notch 10 matches the external profile of the curved bump 20, at least at the level of the medial 208 and lateral 209 flanks of the bump 20 during the flexion movement of the femoral implant 2, allows both transverse stabilization, anteroposterior stabilization and rotational stabilization, the medial condyle 8 (or more precisely its part 108 which constitutes a leg of the intercondylar notch 10) of the femoral implant 2 being blocked in rotation by its contact with the anterior and posterior parts of the medial flank 208 of the curved bump 20 on which it abuts.

Along its generator, the maximum width Ib of the section of the dent 20 can be constant along the entire length of the dent. It is also possible, as in the example illustrated in Figures 1 to 10B, that the width Ib decreases from the anterior part 42 to the posterior part 43 of the support element 100. In this case, in the case of congruent shapes of the external profiles of the dent 20 and the intercondylar notch 10, the width of the intercondylar notch 10 is also decreasing from the part anterior 52 to the posterior part 53 of the femoral implant 2. To allow movement in flexion, when it is full and forms a connecting bridge 170 between the two condyles, the height of the intercondylar notch 10 will also increase from the anterior part 52 to the posterior part 53 of the femoral implant 2.

Advantageously in certain embodiments of the invention where the intercondylar notch 10 is solid, and as is evident in particular from FIGS. 4A and 6A, the contact between the support element 100 and the femoral implant 2 is made along a continuous zone 300 which extends at the level of the upper surface 41 from one to the other of the medial 18 and lateral 19 cavities, passing through the boss 20. In particular, at each degree of flexion between the extension position and the maximum flexion position of the femoral implant 2, the contact zones 182 and 192 respectively of the two medial 8 and lateral 9 condyles in the two medial 18 and lateral 19 cavities are connected by an isthmus 202 corresponding to the contact surface between the boss 20 and the intercondylar notch 10 of the femoral implant. More precisely, the isthmus 202 is an isthmic surface which follows the external profile of the bossing and therefore extends, not only on the summit 210 of the latter, but also on its medial 208 and lateral 209 flanks.

Furthermore, the contact area between the dent 20 and the intercondylar notch 10 moves back and forth over the dent when the knee prosthesis 1 bends from its fully extended position (0° angle) to its maximum flexion position (120° angle or more). The contact is made on the flanks of the dent (medial contact area 183 at the medial flank 208 and lateral contact area 193 at the lateral flank 209), with a back and forth movement of the contact area 193 on the lateral flank 209 of the dent 20. The contact may extend to the apex 210 of the dent 20, when the intercondylar notch 10 forms a connecting bridge 170.

The surface area of this contact zone 300, in particular continuous, decreases from the extension position to the maximum flexion position. In particular, in the maximum flexion position, the contact surface area of the lateral condyle 9 in the lateral cavity 19 is less than the contact surface area of a position with less flexion, and may even take the form of an almost linear surface in certain configurations. When the knee is flexed beyond 120° the contact area of the lateral condyle 9 in the lateral cavity 19 is lower than when the condyle is in an extension position, as can be seen in FIG. 11 B, in particular.

As illustrated in Figure 8, according to a preferred embodiment, the lateral 8 and medial 9 condyles have, in the sagittal plane, an external profile which is a turn whose radius decreases continuously (according to the mathematical definition: for each mm towards the rear, the radius decreases by E). The 2 profiles of the medial 8 and lateral 9 condyles have the shape of a turn; The turn of the medial condyle 8 is inscribed inside the turn of the lateral condyle 9. In in the examples illustrated, the medial cavity 18 has an ovoid shape, with a small mediolateral axis and a large antero-posterior axis. Preferably, this medial cavity 18 has, in the sagittal plane, an antero-posterior curvature corresponding to the shape of the medial condyle 8 when the knee prosthesis is in extension. Advantageously and as illustrated in FIG. 10A, the external profile 181 of the medial cavity 18 matches the shape of the external profile 82 of the medial condyle 8 with which it is in contact, when the knee prosthesis is in extension (straight extended knee corresponding to an angle between the femur and the tibia of 0°). In this figure, just as in FIG. 7, the low point 200 of the medial cavity 8 is located behind the axis A2.

There is thus no anteroposterior mobility in the medial cavity 18 when the knee is stretched in full extension. In this position, according to a sagittal section shown in Figure 10A extending along the major axis of the medial cavity 18, contact with the medial condyle 8 is made over the entire surface of the cavity. Figure 10B, which represents a section similar to that of Figure 10A, but when the knee prosthesis is in a flexion position corresponding to an angle of 120°, shows that the medial condyle 8 moves little in the medial cavity 18. This movement, which takes place from the posterior part 43 to the anterior part 42, or from the anterior part 42 to the posterior part 43, is advantageously 3 to 5 mm at most. This mobility corresponds to the difference between the anteroposterior diameter of the external profile 181 of the medial cavity 18 and the radius of curvature of the spiral corresponding to the external profile 82 of the medial condyle 8, in this position. This small displacement is allowed by the fact that the medial cavity has the negative shape of the medial condyle 8 when the knee is stretched to 0°, but as the radius of the spiral of the medial condyle 8 decreases slightly during flexion, it will find itself in a cavity with an anteroposterior diameter greater than it from a degree of flexion of 45°. The presence of this play provides greater comfort to the patient.

Furthermore, for a given flexion angle, in the sagittal plane, the curvatures of the external profiles 82 and 92 of the medial 8 and lateral 9 condyles are inscribed in the curvatures of the external profiles 181 and 191 of the corresponding cavities 18 and 19, which means that the contact zones 182 and 192 between condyles and cavities are surfaces which progressively decrease during flexion from 0 to 120° as the radius of the turns of the medial 8 and lateral 9 condyles decreases in the sagittal plane.

Conversely, the contact area 192 of the lateral condyle 9 in the lateral cavity 19 moves greatly back and forth, as is evident from the comparison:

- of figure 11 A which shows a view along a sagittal plane of the lateral condyle 9 in the lateral cavity 19, when the knee prosthesis 1 is in extension; and

- of figure 11 B which shows a view along a sagittal plane of the lateral condyle 9 in the lateral cavity 19, when the knee prosthesis 1 is in maximum flexion. Regarding the lateral condyle 9 and the lateral cavity 19 the concavity of the lateral cavity 19 may have its lowest point behind the mediolateral axis A2, the locus of the lowest contact points from the front (full extension position) to the rear (maximum flexion position) following the rotational curvature of the condyle parallel to the flank 209 of the bossing 10.

It should be noted that the support elements 100 and femoral implants 2 illustrated in the figures correspond to prostheses for a right knee. The support elements 100 and femoral implants 2 for a left knee correspond to their mirror image.

In Figure 12 the other parts of a knee prosthesis 1 according to the invention are shown, in the case of a knee prosthesis in which the support element is an articular insert 4. In such a case, the support element 100 which is an articular insert 4 is interposed between the femoral implant 2 and a tibial implant 3. The tibial implant 3 comprises at least one support plate 21 intended to rest by its lower surface 212 on the end of the tibia, if necessary after resection.

The insert 4 which corresponds to a support element 100 according to the invention, for its part, is supported by a lower face 45 on the upper surface of the plate 21 of the tibial implant 3. The assembly between the two can be done by reversible interlocking, in particular according to an elastic snap-fastening, in a housing 211, located on the upper surface of the plate 21 as shown in figure 12.

The tibial implant 3, for its part, also comprises a medullary anchoring rod 240 extending from the lower face 212 of the plate 21 and intended to rest against a resected epiphyseal surface of the tibia (not shown).

Claims

Claims 1 Total knee prosthesis (1) comprising a femoral implant (2) and a support element (100) for the femoral implant (2), in which: - the femoral implant (2) comprises two condyles (8, 9), called medial condyle (8) and lateral condyle (9) delimiting between them an intercondylar notch (10), the external profiles of the two condyles (8, 9) which face the support element (100) being convex in shape, - the support element (100) is intended to be positioned on the tibia side and comprises an upper surface (41) on which are arranged a medial cavity (18) for receiving the medial condyle (8) and a lateral cavity (19) for receiving the lateral condyle (9), said cavities (18, 19) having a concave profile and being separated by a boss (20) extending on the upper surface (41) between the two cavities (18, 19), said boss (20) being inserted into the intercondylar notch (10) when the femoral implant (2) is resting on the upper surface (41) of the support element (100), with the medial cavity (18) seen from above which has an ovoid shape with a small medio-lateral axis and a large antero-posterior axis, characterized in that, in a horizontal plane, said denture (20) extends along a curved generatrix having a concavity (180) oriented towards the medial cavity (18) of said support element (100), said denture (20) having a lateral flank (209) and a medial flank (208) connected by a vertex (210) which define, together, along the entire generatrix of the denture (20), a section whose external profile is convex and, in particular, in an arc of a circle, with in a horizontal plane, the lateral flank (209) of the denture (20) which has a radius of curvature which is greater than the radius of curvature of the medial flank (208) of the denture (20), with the presence of no flattening or angulation between the denture (20) and the medial (18) and lateral (19) cavities, the femoral implant (2) being adapted to the element bearing, so that when the femoral implant (2) is bearing on the upper surface (41) of the bearing element (100), there is contact between the medial cavity (18) and the medial condyle (8), contact between the lateral cavity (19) and the lateral condyle (9) and contact, both, between the medial flank (208) of the boss (20) and the part (108) of the medial condyle (8) which delimits the intercondylar notch (10) and between the lateral flank (209) of the boss (20) and the part (109) of the lateral condyle (9) which delimits the intercondylar notch (10); the contact between the boss and the condyles (8, 9) at the level of the intercondylar notch (10) ensuring, when the femoral implant is in the support position on the upper surface (41) of the support element (100) and moves in flexion from an extension position to a maximum flexion position, the guidance of the movement of the femoral implant (2) during this flexion with a displacement of the contact zone (192) of the lateral condyle (9) in the lateral cavity (19) from the anterior part (42) to the posterior part (43) of the support element (100), which corresponds to a displacement over a portion of an arc of a circle. 2 Prosthesis (1) according to claim 1, characterized in that the upper surface (41) of the support element (100) has a maximum width located on a medio-lateral axis A2 which intersects the peripheral edges (308 and 309) of the medial (18) and lateral (19) cavities opposite the denture (20), respectively at points M and L, the distance between M and L being equal to 2Lmax, the centers Cl and Cm of the radii of curvature of the lateral flank (209) and of the medial flank (208) of the denture (20) are located in an area which is a square with a side equal to 2Lmax, extending towards the outside of the medial cavity from a point located inside the medial cavity on the medio-lateral axis A2 at a distance of 14 from Lmax +/- 2mm from M, said square being cut in its middle by the axis mediolateral A2. 3 Prosthesis (1) according to claim 1, characterized in that the medial (208) and lateral (209) flanks of the denture (20) have parallel curvatures, which correspond to concentric arcs of a circle, the upper surface (41) of the support element (100) having a maximum width located on a medio-lateral axis A2 and an anteroposterior axis A1 extending perpendicular to the medio-lateral axis A2 by intersecting the medio-lateral axis A2 in its middle A and the medio-lateral axis A2 intersecting the peripheral edges (308 and 309) of the medial (18) and lateral (19) cavities opposite the denture (20), respectively at points M and L, with AM=AL=Lmax, the centers of the radii of curvature Cm and Cl of the medial flank (208) and of the lateral flank (209) being merged and located on the axis A2 and on a segment [M - 2 mm; M + 2 mm], the minimum radius of curvature Rrn _min of the medial flank (208) at the level of the transition point between the medial flank and the medial cavity and the maximum radius of curvature Rl _max of the lateral flank (209) at the level of the transition point between the lateral flank and the lateral cavity being defined as follows: - Rrn _min of the medial flank (208) which is between 3Lmax/4 +/- 2mm and 7Lmax/8 +/- 2mm and is preferably equal to 7Lmax/8 +/- 2mm, Rl _max of the lateral flank (209) which is between 9Lmax/8 +/- 2mm and 5Lmax/4 +/- 2mm and is preferably equal to 9Lmax/8 +/- 2mm. Prosthesis (1) according to claim 1 or 2, characterized in that the maximum width Ib of the section of the denture (20) decreases along its generatrix from the anterior part (42) towards the posterior part (43) of the support element (100). Prosthesis (1) according to claim 1 or 2, characterized in that the medial (208) and lateral (209) flanks of the denture (20) have parallel curvatures, which correspond to concentric arcs of a circle. Prosthesis (1) according to claim 4 or 5, characterized in that, in top view, the upper surface (41) of the support element (100) having a maximum width located on a medio-lateral axis A2 and an antero-posterior axis A1 extending perpendicular to the medio-lateral axis A2 by intersecting the medio-lateral axis A2 in its middle A and the medio-lateral axis A2 intersecting the peripheral edges (308 and 309) of the medial (18) and lateral (19) cavities opposite the bossing (20), respectively at points M and L, the center of the radii of curvature of the medial flank (208) and of the lateral flank (209) being located in a square of 1/2 Lmax on the side with M which is the center of the square. Prosthesis (1) according to claim 4 or 5, characterized in that, in top view, the upper surface (41) of the support element (100) having a maximum width located on a medio-lateral axis A2 and an antero-posterior axis A1 extending perpendicular to the medio-lateral axis A2 by intersecting the medio-lateral axis A2 in its middle A and the medio-lateral axis A2 intersecting the peripheral edges (308 and 309) of the medial (18) and lateral (19) cavities opposite the bossing (20), respectively at points M and L, the center of the radii of curvature of the medial flank (208) and of the lateral flank (209) being located in a square of % Lmax +/- 2mm on the side with M which is the center of the square. Prosthesis (1) according to claim 4 or 5, characterized in that the minimum radius of curvature Rmmin of the medial flank (208) at the transition point between the medial flank and the medial cavity has its center Cm on the medio-lateral axis A2 in M, and the maximum radius of curvature Rlmax of the lateral flank (209) at the transition point between the lateral flank and the lateral cavity has its center Cl on the axis A'2, with the axis A'2 which is located between the medio-lateral axis A2 and the anterior part (42) of the support element (100), with the distance dl between the medio-lateral axis A2 and the axis A'2 which is equal to Lmax/8 +/- 2mm, or the maximum radius of curvature Rlmax of the lateral flank (209) has its center Cl on the medio-lateral axis A2 in M, and the minimum radius of curvature Rmmin of the medial flank (208) has its center Cm on the axis A'2, with the axis A'2 which is located between the medio-lateral axis A2, and the posterior part (43) of the support element (100), with the distance dl between the medio-lateral axis A2 and the axis A'2 which is equal to Lmax/8 +/- 2mm. 9 Prosthesis (1) according to any one of claims 1 to 8, characterized in that at the transition point between the medial flank and the medial cavity, the radius of curvature Rm _min intersects the axis A2 on a segment which is between 3Lmax/4 starting from M +/- 2mm and 7Lmax/8 starting from M +/- 2mm and preferably intersects it at 7Lmax/8 starting from M +/- 2mm and, at the transition point between the lateral flank and the lateral cavity, the radius of curvature Rl _max intersects the axis A2 on a segment which is between 9Lmax/8 starting from M +/- 2mm and 5Lmax/4 starting from M +/- 2mm and preferably intersects it at 9Lmax/8 starting from M +/- 2mm. 10 Prosthesis (1) according to any one of claims 1 to 9, characterized in that the upper surface (41) of the support element (100) has a circumference which has a symmetrical shape relative to the antero-posterior axis A1. 11 Prosthesis (1) according to any one of claims 1 to 10, characterized in that the upper surface (41) of the support element (100) has a circumference which has a non-symmetrical shape with respect to the antero-posterior axis A1, with a lateral circumference smaller than the medial circumference. 12 Prosthesis (1) according to any one of claims 1 to 11, characterized in that the boss (20) is raised towards the front part (42) and/or towards the rear part (43) of the support element (100). 13 Prosthesis (1) according to any one of claims 1 to 12, characterized in that the support element (100) constitutes an articular insert (4) intended to be interposed between the femoral implant (2) and a tibial implant (3) intended to be placed on the end of the tibia, if necessary after resection, said articular insert (4) comprising a lower face (45) intended to be placed on the tibial implant (3), in particular, by reversible fitting into a housing (211) located on the upper surface of the tibial implant (3). 14 Prosthesis according to any one of claims 1 to 13, characterized in that in a frontal plane, the external profile (101) of the intercondylar notch (10) is concave in shape, and the intercondylar notch (10) forms a connecting bridge (170) without discontinuity with the two condyles (8, 9), which extends from the anterior part (52) of the femoral implant (2) to its posterior part (53). 15 Prosthesis according to claim 14, characterized in that in a frontal plane, when the femoral implant (2) is in the support position on the upper surface (41) of the support element (100) and moves in flexion from an extension position to a maximum flexion position, the external profile (101) of the intercondylar notch (10) is congruent with the external profile of the bump (20). 16 Prosthesis according to claim 15, characterized in that the support element (100) is in accordance with claim 4, that is to say that the maximum width Ib of the section of the boss (20) decreases along its generator from the anterior part (42) towards the posterior part (43) of the support element (100) and, due to the congruent shapes of the external profiles of the boss (20) and the intercondylar notch (10), the maximum width of the intercondylar notch (10) decreases from the anterior part (52) towards the posterior part (53) of the femoral implant (2). 17 Prosthesis according to one of claims 1 to 16, characterized in that the section of the bump (20) has a convex external profile (201) with a radius of curvature R20 and the section of the intercondylar notch (10) has a concave external profile (101) with a radius of curvature R10, with the radii of curvature R20 and R10 which are substantially identical, with sufficient clearance to avoid tightening between the femoral implant (2) and the support element (100) at the level of the bump (20). 18 Prosthesis according to one of claims 1 to 17, characterized in that the contact between the support element (100) and the femoral implant (2) is made along a continuous zone (300) which extends at the level of the upper surface (41) of the support element (100), from one to the other of the cavities (18, 19), passing through the boss (20). 19 Prosthesis according to any one of claims 1 to 18, characterized in that the condyles (8, 9) have an external profile (82, 92) in the sagittal plane, the generator of which is a spiral. 20 Prosthesis according to any one of claims 1 to 19, characterized in that the medial cavity (18) has in the sagittal plane passing through its major anteroposterior axis a curvature corresponding in the same plane to that of the medial condyle segment in contact (8) with said medial cavity (18) when the femoral implant (2) is in the extended position. 21 Prosthesis according to one of claims 1 to 20, characterized in that in top view, the upper surface (41) of the support element (100) has a maximum width located on a medio-lateral axis A2 and the medial (18) and lateral (19) cavities have their lowest point which is located between the medio-lateral axis A2 and the posterior part (43) of the support element (100).