Knee prosthesis

The present invention relates to the field of medical prostheses knee.

Document WO 96/20656 discloses a knee prosthesis consisting of a femoral implant and a tibial implant. The tibial implant comprises a tibial tray and a tibial insert rotatably mounted on the tibial tray. The femoral implant includes two condyles and a front flange together defining a contact surface with the femur and a convex articulation surface. The contact surface with the femur comprises two rearward planes, two chamfers posterior planes, two distal flat surfaces, an anterior chamfer plane and an anterior flat surface. The articulation surface is formed by the respective articular surfaces of the condyles and the articular surface of the anterior flange.

According to a particular feature of this prosthesis, the sagittal profile of the femoral implant has, regardless of the size of the femoral implant, a geometry and constant dimensions, except in its anterior part. More specifically, the length and orientation, in the sagittal plane, the posterior planar surfaces, chamfers planes posterior and distal flat surfaces of the contact surface with the femur are constant regardless of the size of the femoral implant, as well as the profile of the articular surfaces of the condyles. Vary only in the sagittal plane depending on the size of the femoral implant the length of the anterior chamfer and the profile of the articular surface of the anterior flange.

Retaining geometry and sagittal dimensions constant in the portions of the femoral implant other than the front part can reduce the necessary number of cutting tools for the preparation of the femur during surgery.

However, this advantage is offset by a deterioration of the geometrical conformity of the prosthesis to the natural knee anatomy. A femoral implant size will indeed, in the sagittal plane, the same bearing surface on the tibial insert a femoral implant small, contrary to the anatomy of the knee. In addition, the femoral implants large pose a significant risk of subluxation of the fact that, necessarily, their front edge extends beyond with respect to the bearing surface of the tibial insert, which imbalance the overall geometry of the prosthesis. Because of these drawbacks, it does not seem possible with the prosthesis according to WO 96/20656, to cover all existing femoral sizes.

Document FR 2619306 discloses a femoral implant whose joint surface is different depending on the size. This implant does not reduce the number of cutting tools required for the preparation of the femur as in WO 96/20656.

Are also known knee prostheses, said posterior-stabilized, in which the femoral implant includes a cam. This cam is generally disposed at the top rear portion of the femoral implant, in an intercondylar notch between two condyles of the femoral implant. A projecting central stud on the upper face of the tibial implant is placed in the intercondylar notch to cooperate with the cam from a certain angle of knee flexion in order to prevent the femoral implant to move previously by relative to the tibial implant from this deflection angle,

In these posterior stabilized prostheses, the articular surface or bearing surface of each condyle has a large radius of curvature distally and smaller bending radii posterior part to increase the degree of flexion. Generally, this joint surface is also congruent with the corresponding articular surface of the tibial implant in the distal part to a bending angle of the knee less than the above bending angle at which the cam comes into contact with the stud. In other words, the articular surface of each condyle in the sagittal plane, and to this angle of lower bending a profile in an arc of circle of radius substantially equal to that of the profile, also arcuate, of the corresponding articular surface of the tibial implant. Thus, the knee flexion movement has three phases:<ul><li>a first phase, known as slip, from a bending angle of 0 ° (knee extension position) to the bending angle at which the congruence in the sagittal plane between the articular surface of each condyle and articular surface corresponding to the tibial implant ends, in which the femoral implant pivots relative to the tibial implant around a fixed axis and the articular surfaces of the femoral implant slide over those of the tibial implant;</li><li>a second phase, said intermediate phase, from the bending angle at which the congruence ends at the bending angle at which the cam comes into contact with the pad, in which the femoral implant pivots about an axis and can move in translation in the anteroposterior direction relative to the tibial implant; and</li><li>a third phase, called rolling, from the bending angle when the cam comes into contact with the stud to the end of bending, in which the femoral component rolls posteriorly on the tibial implant.</li></ul>

During the intermediate phase, the friction between the femoral and tibial implants may be very large, causing wear of the articular surfaces, generally made of polyethylene, the tibial implant. Moreover, the lack of congruence between the articulating surfaces of the femoral and tibial implants that the cam comes into contact with the stud abruptly, resulting in a risk of fracture of the stud. Since it is not stabilized in the anterior-posterior direction during this phase, the femoral implant was also a tendency to move previously, which, on the one hand, increases the stress at the interface between the rim prior to the femoral implant and patella and, on the other hand, reduces the lever arm and thus makes the bending of the knee more difficult for the patient.

The present invention aims, firstly, to provide a prosthetic knee system that allows for, as the prosthesis according to WO 96/20656, reduce the number of cutting tools for the preparation of the femur, but who respects more natural knee anatomy.

To this end, there is provided, according to a first aspect of the invention, a prosthetic knee system comprising a set of femoral implants of increasing respective sizes, each of said femoral implants including at least one condyle and an anterior flange, the or each condyle including posterior and distal flat surfaces for contact with the femur and an articular surface, the anterior flange including an anterior chamfer plane contact with the femur, the orientation in the sagittal plane of the or each posterior flat surface, the orientation and length in the sagittal plane of the or each flat distal surface and orientation in the sagittal plane of the previous plan bevel being identical for all the femoral implants said overall length in the sagittal plane of the anterior chamfer increasing with size for all the femoral implants of the said set, characterized in that the radius of curvature in the sagittal plane of a distal portion of the articular surface of the or each condyle increases with size for at least two femoral implants of the said set.

Thus, in this first aspect of the invention, the dissociating changes depending on the size of the contact surface with the femur and the condyle articular surface of the distal part of the femoral implant. As the radius of the distal part of the articular surface of each condyle increases with size for at least two femoral implants of the set, the knee anatomy is better respected. One can therefore cover a wider range of femoral sizes.

Advantageously, the distance between a reference coronal plane tangent to the articular surface of the or each condyle when the knee is extended and the most distal point of the sagittal profile of the articular surface of the or each condyle also increases with size for said at least two femoral implants.

Preferably, the radius of curvature in the coronal plane of the distal portion of the articular surface of the or each condyle increases with size also for said at least two femoral implants.

Preferably, also, the length in the sagittal plane of the posterior flat surface for contact with the femur of the or each condyle increases with size for all the femoral implants of the said set.

The or each condyle of each femoral implant may further comprise, between its rear flat surface and the distal flat surface, a posterior plane chamfer contact with the femur, orientation and length in the sagittal plane of the posterior plane bevel being identical for all the femoral implants of the said set.

The anterior flange of each femoral implant may further include an articulating surface and, between the front plane and an upper end of the front edge chamfer, an anterior planar surface contact with the femur. In this case, the articular surface of the anterior flange may have a groove intended to cooperate with the patella or a patellar implant, and a thickening having a triangular sagittal profile may be provided on the contact surface with the femur of the anterior flange at the angle formed by the previous plan bevel and the flat front surface and in an area opposite the throat, this excess thickness defining a chamfer whose sagittal profile has a point of origin on the anterior chamfer plane and orientation that are identical to all the femoral implants of the said set and a length which increases with size for all the femoral implants of the said set.

Advantageously, the thickness of a distal portion of the or each condyle and the thickness of a rear portion of the or each condyle are identical for all the femoral implants of the said set, and for each femoral implant, the thickness of the distal portion of the or each condyle is substantially equal to the thickness of the posterior portion of the or each condyle.

In a typical embodiment of the invention, each femoral implant includes two condyles, the distal part of the articular surface of each condyle is substantially a portion of a sphere, and the spacing between the respective centers of curvature of the distal portions of the surfaces articular condyles increases with size for the said at least two femoral implants. The radius of curvature of the distal part of the articular surface of each condyle and the distance between the respective centers of curvature of the distal parts of the articular surfaces of the condyles may nevertheless be identical for at least two femoral implants of the said set. The radius of curvature and the aforementioned distance can, for example, increase both sizes of femoral implant.

The prosthetic system according to the invention may further comprise at least one tibial implant, preferably a set of tibial implants of different sizes, the or each tibial implant comprising at least one articular surface able (s) to cooperate with the or the articular surfaces of the condyles or of at least one corresponding femoral implant to allow knee flexion. Preferably, the or each articular surface of the or each tibial implant is substantially a same radius of sphere portion the radius of the distal part of the articular surface of the or each condyle of the or each corresponding femoral implant.

The present invention seeks, second, to overcome the disadvantages mentioned above related to posterior stabilized knee prostheses.

To this end, it is provided according to a second aspect of the invention, a posterior stabilized knee prosthesis comprising a femoral implant and a tibial implant, the femoral implant comprising at least one condylar articulating surface and a cam, the tibial implant comprising at least one articular surface for (s) cooperate with the condylar or articular surfaces of the femoral implant to permit bending of the prosthesis and a stud intended to cooperate with the cam at a certain angle flexion of the prosthesis subsequently to stabilize the femoral component relative to the tibial implant, the sagittal profile of the or each condylar articular surface being congruent with the sagittal profile of the corresponding articular surface of the tibial implant for a bending of the prosthesis at least up to a determined angle, characterized in that the cam and the pad are arranged so that the cam comes into contact with the pad to a bending angle of the prosthesis substantially equal to the determined angle.

Thus, in this second aspect of the invention, the contact between the cam and the pad comes as the condylar articulating surfaces are congruent with the corresponding articular surfaces of the tibial implant. The femoral implant and goes directly from a sliding phase at a rolling phase. All the drawbacks of the current prostheses linked to the existence of an intermediate phase between the sliding phase and the rolling stage are therefore deleted.

Typically, the articular surface of the stud is a rear planar surface that is aligned with the most distal point of the sagittal profile of the articular surface or each condyle when the knee is in extension.

The sagittal profile of the or each condylar articulating surface includes a portion substantially in an arc extending at least substantially from the most distal point of the sagittal profile and at least substantially up to a point of the sagittal profile located posteriorly relative to most distal point and at a position such that the line passing through this point and the posterior portion of the center of curvature of circular arc makes the determined angle with the line passing through the most distal point and the center of curvature. Substantially from the posterior point and to an upper rear end of the sagittal profile, said sagittal profile is preferably substantially an arc of smaller radius circle to the radius of the arcuate portion.

Other features and advantages of the present invention will become apparent upon reading the following detailed description of several embodiments with reference to the accompanying drawings in which:<ul><li>Figure 1 is a sagittal view (side view) of a knee prosthesis according to the invention;</li><li>Figure 2 is a coronal view (front view) of the knee prosthesis according to the invention;</li><li>Figure 3 is a perspective view of a femoral implant forming part of the knee prosthesis according to the invention;</li><li>Figure 4 is a sagittal view of a tibial tray of a tibial implant part of the knee prosthesis according to the invention;</li><li>Figure 5 is a perspective view of a tibial insert of a tibial implant part of the knee prosthesis according to the invention;</li><li>Figure 6 is a sagittal view of the tibial insert shown in Figure 5;</li><li>7A and 7B show in sagittal view of the femoral implant of the knee prosthesis according to the invention;</li><li>8A to 8D are views showing four different sagittal positions of flexion of the knee prosthesis according to the invention;</li><li>Figures 9 and 10 are schematic views, respectively sagittal and coronal of the knee prosthesis according to the invention showing four different sizes of femoral implant and two different sizes of tibial component with the tibial implant cut at its upper part to highlight the lower part of the femoral implant; and</li><li>Figures 11 and 12 are respectively schematic views in section and from above of a cutting guide that can be used to prepare the femur before the establishment of the knee prosthesis according to the invention.</li></ul>

Referring to Figures 1 to 3, a knee prosthesis bi-condylar posterior stabilized according to the invention comprises a femoral component 1 and a tibial implant 2 intended to be fixed respectively to the femur and tibia. The patellar implant of the prosthesis is not shown as similar to the existing ones.

The femoral implant 1 comprises, on either side of an intercondylar notch 3, two condyles 4a, 4b joined by a front edge 5, also called trochlea. Each condyle 4a, 4b comprises a rear portion 6a, 6b and a distal portion 7a, 7b.

The front edge 5 and the condyles 4a, 4b together define a contact surface with the femur and an articulation surface. The contact surface with the femur comprises two rearward planes 8a, 8b, two chamfers plans after 9a, 9b, two distal flat surfaces 10a, 10b, an anterior chamfer plane 11 and a front flat surface 12. The articulation surface is convex. It comprises the respective joint surfaces 13a, 13b, of the condyles and the articular surface 14 of the anterior rim.

On the two distal flat surfaces 10a, 10b of the contact surface with the femur are provided two pads 15a, 15b intended to be introduced in corresponding holes in the distal femur, subsequent to the intramedullary axis, to stabilize rotating the femoral implant, that is to say against rotation relative to the femur. A thickening 16 along the distal portion of the intercondylar notch 3, on the contact surface with the femur, and intended to be received in a corresponding recess in the distal end of the femur, allows to provide additional rotational stability to the femoral implant.

The articulation surface 14 of this front edge, as shown in Figures 2 and 3, a groove 17 extending centrally from the upper end of the articulating surface 14 to the intercondylar notch 3. This groove 17 has the function of guiding the patellar implant during movements of the knee, in a manner known per se. To compensate for the lack of material due to the groove 17, an excess thickness 18 is provided on the contact surface with the femur in a central area opposite to the groove 17. This thickened portion 18 has a triangular sagittal profile and defines a chamfer 18 ' at the angle formed by anterior chamfer 11 and the front surface 12,

The tibial implant 2 comprises a tibial base 19 and a tibial insert 20 rotatably mounted on the tibial tray. The base 19 includes a tibial tray 21 and a rod 22 anchor in the tibia, integral with the plate 21. The tibial insert 20, also called meniscal insert has on its underside a slightly frustoconical orifice (not shown) formerly in the sagittal plane and centrally in the coronal plane. This frustoconical orifice receiving a slightly frustoconical corresponding pad 23 projecting on the upper face of the tibial tray 21 (figure 4), slightly tapered pin 23 allowing rotational movement of the tibial insert relative to the tibial tray.

The upper face of the tibial insert 20 has two depressions 24a, 24b (Figures 5, 6) whose respective surfaces constitute the joint surfaces of the tibial insert adapted to cooperate with the articular surfaces 13a, 13b of the condyles and a lower portion of the articular surface 14 of the anterior rim. More specifically, a main portion 240a, 240b of the surface of each depression 24a, 24b constitutes an articulation surface for bending the prosthesis, and an anterior peripheral portion 241 a, 241 b having in the sagittal plane, a more large radius of curvature than the main portion 240a, 240b is a zone of clearance against which can come to rest the bottom portion of the articular surface 14 of the front edge when the knee is hyperextended.

A pin 25, also called spine is further projecting on the upper face of the tibial insert. The pin 25 comes to rest in the intercondylar notch 3 of the femoral implant and adapted to cooperate with an intercondylar cam 26 provided between the condyles 4a, 4b, in the posterior part of the femoral implant, for posterolateral stabilize the prosthesis , that is to say, prevent the femoral implant to move earlier with respect to the tibial component during flexion of the knee, as will be explained later.

The femoral implant 1 is typically made of metal, for example cobalt-chromium or ceramic. The tibial base plate 19 is typically made of metal, such as cobalt-chromium. The tibial insert 20 is itself made of polyethylene and more particularly ultra high molecular weight polyethylene.

According to the invention, the joint surfaces 13a, 13b of the condyles and the articular surfaces 240a, 240b of the tibial insert 20 are shaped such that each articular condylar surface 13a, 13b is congruent in the sagittal plane with the articular surface 240a, 240b corresponding to a knee flexion (prosthesis) of from 0 ° to 90 °.

Thus, as shown in Figures 1 and 7A, the sagittal profile of the articular surface 13a, 13b of each condylar portion has an arc of circle 27a, 27b extending at least from the most distal point, P1, P1 b, sagittal profile, preferably for a P0a point prior P0B to the most distal point P1 a, P1 b as shown in Figure 7A, and P2a to a point P2b of the sagittal profile located posteriorly relative to the point most distal P1, P1 b and a position such that the right, D2a, D2b, through this later point P2a, P2b and the center of curvature, Ca, Cb of the portion in a circular arc 27a, 27b or orthogonal to the line, P1a, P1b, passing through the most distal point P1 a, P1 b and the center of curvature Ca, Cb, and the sagittal profile, 28a, 28b, each joint surface 240a, 240b of the insert tibial is a circular arc substantially the same radius as the radius, R0, of the arcuate portion 27a of circle 27b of the sagittal profile of each condylar articular surface 13a, 13b.

The sagittal profile 28a, 28b of each articular surface of the tibial insert 20 may have exactly the same radius R0 that the arcuate portion 27a circle, 27b of each condylar articular surface. However, preferably, the radius of sagittal profile 28a, 28b is slightly larger than, a maximum value of 0.3 mm to a radius R0 of 22 mm to 30 mm, that of the portion 27a in a circular arc, 27b to reduce the stresses on the articular surfaces 240a, 240b due to the difference of elasticity between the material from which is made the femoral implant 1 and one in which is made the tibial insert 20.

This shape of the articular surfaces of the condyles 4a, 4b and the tibial insert 20 allows the femoral implant to slide on the articular surfaces of the tibial insert 20, by pivoting about the axis passing through the centers of curvature Ca , Cb, during a knee flexion from 0 ° to 90 °. During the sliding phase, the prosthesis is stable because the rotation of the femoral implant takes place around a fixed axis, namely the aforementioned axis through the centers of curvature Ca, Cb. In addition, the fact that the condylar articular surfaces 13a, 13b and the joint surfaces 240a, 240b of the tibial insert 20 are congruent to a large bending angle serves to distribute the contact stress between the femoral implant and the tibial implant over a large area of ​​contact.

From the later point P2a, P2b, and to its upper rear end, 29a, 29b, the sagittal profile of each condylar articular surface 13a, 13b has a radius of curvature R1 smaller than the radius R0 of the portion circular arc 27a, 27b, in order to increase the degree of flexion of the prosthesis. This radius of curvature R1 is preferably constant over the entire portion of the sagittal profile ranging from later point P2a, P2b with the upper rear end 29a, 29b, that is to say, in other words, the portion sagittal profile between the point P2a, P2b and 29a, 29b is preferably a circular arc. In exemplary typical embodiment, R1 radius of curvature is selected so that the degree of bending associated with this portion of the sagittal profile is within a range of 65 ° to 75 °, to obtain a total degree of bending for prosthesis of 155 ° to 165 °.

Preferably, the portion 13a articular surface 13b of each condyle having the sagittal arc profile 27a circle, 27b is a portion of a sphere, and therefore has the same radius R0 in the sagittal plane and the coronal plane, as illustrated to figures 1 and 2, and the articular surfaces 240a, 240b of the tibial insert are portions of a sphere, substantially the same radius as the radius R0. The articular surfaces of the condyles and the tibial insert are thus also congruent in the coronal plane. As for the upper posterior portion of the joint surface 13a, 13b of each condyle, that is to say, the portion having the profile in the sagittal radius R1 of arc, it preferably has a profile of circular arc radius R0 in the coronal plane.

The intercondylar cam 26 is a half cylinder-shaped bar joining the two condyles 4a, 4b. The articular surface of the cam 26 consists of the sagittal profile surface semicircular half-cylinder. The cam 26 is tangent to the plane containing the straight D2a, D2b associated to the sagittal profile of each condyle and is located relative to the plane of the side of the posterior upper end 29a, 29b of the condyles (7A, 8A).

Pin 25 of the tibial insert has a posterior planar surface 30 which is aligned with the most distal points P1a, P1b of the condylar articular surfaces 13a, 13b, that is to say, located in the same coronal plane that points P1a, P1b, when the knee is in extension. The posterior planar surface 30 is the articular surface of the stud 25, intended to cooperate with the articular surface of the cam 26.

8A to 8D show the femoral implant in different positions of flexion. Note that, because of their relative positions, the cam 26 and the stud 25 come into contact with each other at a bending angle α of 90 ° (Figure 8C), or just at the transition between the radius R0 of curvature and the radius of curvature R1 of the sagittal profile of the articular surface of each condyle. The femoral implant and goes directly from a sliding phase on the tibial insert to a rolling phase. The fact of the invention to remove the intermediate phase that exists in current prosthetic posterior stabilized knee sliding between the stage and the rolling stage, including the following benefits:<ul><li>wear of the articular surfaces of the tibial insert 20 is reduced,</li><li>the contact between the cam 26 and pin 25 is less abrupt manner, </li><li>the stresses exerted between the front edge 5 of the femoral implant and patellar implant (or the ball when the latter is not replaced) are lower, and</li><li>the lever arm and more importantly, facilitating the bending of the knee to the patient.</li></ul>

Moreover, not making contact the cam 26 and pin 25 at a bending angle of 90 °, it further reduces the stresses exerted on the stud 25. This is in fact between 0 ° and 90 ° bending loads that in a knee is the highest (such fillers may range up to eight times the body weight depending on the activity), the peak strength being at 20 ° for walking, 50 ° for uphill slope, 60 ° stair climbing and 90 ° for the stair descent.

The knee prosthesis according to the invention is provided in various sizes, typically four to six sizes incremented anteroposterior width and mediolateral width of a value of about 4 mm. Figures 9 and 10 show, by way of example, four femoral implants 1₁, 1₂, 1₃, 1₄ of different sizes. It will be noted, with reference also to FIG 7B, the sagittal direction, β1, of each rear surface 8a, 8b, that is to say the angle which, in the sagittal plane, each posterior surface 8a, 8b with a reference direction, eg the vertical direction, the sagittal length L2 and β2 sagittal orientation of each posterior chamfer 9a, 9b, the sagittal L3 length and orientation of each sagittal β3 distal surface 10a, 10b, the sagittal β4 orientation of posterior chamfer 11, the sagittal direction β5 and origin sagittal PS on the anterior chamfer 11 of chamfer 18 ', the position of the sagittal anchoring pins 15a, 15b, and the sagittal geometry and dimensions of the thickening 16 are constants depending on the size and thus are identical for all the femoral implants 1₁ 1₄. The β6 sagittal direction and the sagittal length L6 of the anterior surface 12 may be constant or vary depending on the size.

In this way, the number of cutting instruments required for preparation of the femur during surgery is reduced. Thus, for example, a single instrument may be provided for use in the distal femur, the posterior cut, the posterior chamfer, the distal cut, anterior chamfer and the anterior section corresponding respectively to the posterior surfaces 8a, 8b, the chamfers post 9a, 9b, the distal surfaces 10a, 10b, anterior chamfer 11 and the anterior surface 12 of the femoral implant, as well as sections respectively corresponding to the thickened portions 16 and 18. figures 11 and 12 show, by way for example, such an instrument, having slots 31-34, respectively, the posterior cut, the posterior chamfer, the anterior chamfer and the section corresponding to the thickened portion 18, the slots 35-38 for the anterior cut according to the size of the femur, and slots 39-40 for the distal cut and the section corresponding to the thickened portion 16.

However, to better respect the natural knee anatomy, reduce the risk of subluxation and better fit the shape of the distal femur, certain characteristics of the femoral implant increase with the size, namely:<ul><li>the radius R0 of the spherical portion constituting the distal and posterior lower portion of the joint surface 13a, 13b of each condyle,</li><li>the radius R1 of the sagittal profile of the upper posterior portion of the joint surface 13a, 13b of each condyle,</li><li>the distance DT between CS reference coronal plane tangent to the articular surface of each condyle when the prosthesis is extended and the most distal point P1a, P1b of each condyle,</li><li>the length L1 of each sagittal posterior surface 8a, 8b,</li><li>sagittal length L5 of the chamfer 18 '</li><li>the distance (coronal) EC between the respective curvature centers Ca, Cb of the spherical portions of the articular surfaces of the condyles (the width of the intercondylar notch 3 and the geometry and dimensions in the coronal plane of the excess thickness 16 remain, however, preferably constant), and</li><li>the distance (coronal) between the anchor pads 15a, 15b.</li></ul>

The geometry and dimensions of the tibial insert 20 are of course adapted to those of the femoral implant. However, it was observed by the present inventor that can reduce the number of tibial inserts to cover the different prosthesis sizes required while maintaining a good conformity to the anatomy of the knee, by varying the radius R0, the distance DT, EC spacing and the spacing between the anchoring pins 15a, 15b only every two sizes, as shown in figures 9 and 10. In the example of figures 9 and 10, one can see that the two smaller femoral implants 1₁, 1₂ have the same radius of curvature R0₁₂ and Ca same centers of curvature₁₂Cb₁₂And the two largest femoral implants 1₃, 1₄ have the same radius of curvature R0₃₄, Greater than the radius R0₁₂, And Ca same centers of curvature₃₄Cb₃₄. Thus, the same tibial insert 20₁₂ can be used for the two femoral implants smaller 1₁, 1₂And one tibial insert 20₃₄ can be used for the two femoral implants larger 1₃, 1₄. The rays R0₁₂ and R0₃₄ are equal for example to 24 mm and 26 mm, respectively. Preferably, the size of the tray of the tibial base also varies every two sizes, as illustrated in Figures 9 and 10 where two board sizes 21₁₂ and 21₃₄ are shown.

Furthermore, in order to obtain a same spacing in extension and flexion between the respective sections of the femur and the tibia during the surgical procedure, the thickness E1 of the distal portion 7a, 7b of each condyle is equal to thickness, E2, from the rear portion 6a, 6b of each condyle (Figure 7B), these two thicknesses E1, E2 held constant regardless of the size of the femoral implant and typically having a value of 9.15 mm.

It will be observed in the light of Figures 9 and 10, that increasing the radius R0 of the spherical portion of the articular surface of the condyles according to the size while holding constant the distal and posterior thickness E1, E2 of the condyles of femoral implant, the thickness of each condyle in the region of the posterior chamfer 9a, 9b is reduced, which can weaken the femoral implant at the corners formed between the posterior chamfer 9a, 9b, the posterior surface 8a, 8b and the distal surface 10a, 10b. In the present invention, in the design of the femoral implant, it is ensured that the thickness of each condyle at the abovementioned angles are at least equal to a predetermined minimum value. To do this, it does not draw the posterior chamfer 9a, 9b of each condyle after having drawn the joint surface 13a, 13b and the posterior and distal surfaces of contact with the femur 8a, 8b, 10a, 10b of each condyle .

The present invention is described below by way of example only. It will be clear to the skilled person that modifications can be made without departing from the scope of the claimed invention. In particular :<ul><li>chamfers post 9a, 9b may be removed; in such a case, the contact surface with the femur of the femoral implant only includes two posterior surfaces, two distal surfaces, an anterior chamfer and an anterior surface and posterior surface each form a corner (right) with the distal surface correspondingly;</li><li>the anterior surface 12 could also be removed; in this case the front flange 5 would stop at the upper end of the anterior chamfer 11, and the prosthesis of the invention would be a femoral knee prosthesis, the patellofemoral joint is not prosthesized;</li><li>could provide only a single condyle instead of two;</li><li>the cam could be in a form other than intercondylar bar, ie for example in the form of a surface of a third condyle between a medial condyle and a lateral condyle of the femoral implant;</li><li>the tibial insert may be fixed relative to the tibial tray, even if the solution in which the tibial insert is rotatable relative to the tibial tray appears preferable where the prosthesis is posterior stabilized; alternatively, also, the tibial insert may be movable both in rotation and in translation relative to the tibial tray in a manner known per se;</li><li>Coronal profile of the distal and posterior part of the articular surface of each condyle may be flat or arcuate different circle of radius that of the portion in a circular arc of the sagittal profile.</li></ul>