Total knee prosthesis with ceramic-on-ceramic friction torque and mobile ceramic plate

Abstract

A total knee prosthesis to be implanted in a human patient includes a femoral element having a longitudinal axis, a tibial plateau having a longitudinal axis and a mobile plate. The mobile plate is interposed between the femoral element and the tibial plateau to form two joints with them wherein: a) the surfaces of mutual friction of the femoral element with the mobile plate and the surfaces of mutual friction of the tibial plateau with the mobile plate are entirely constituted by one and the same massive ceramic material; and b) the mobile plate includes two condylar bowls, and the femoral element includes two condyles, the condyles and the condylar bowls each having surfaces of mutual friction spaced apart from each other by a distance smaller than 100 μm when the longitudinal axes of the femoral element and the tibial plateau form an angle of 0° to 75°.

Claims

1. A total knee prosthesis to be implanted in a human patient, said prosthesis comprising: a femoral element having a longitudinal axis; a tibial plateau having a longitudinal axis; and a mobile plate, said mobile plate being interposed between the femoral element and the tibial plateau to form two joints with them wherein: a. said femoral element, mobile plate and tibial plateau are each formed and entirely constituted out of one and the same ceramic material, and said femoral element, mobile plate and tibial plateau do not include any alloy with plastic material or metal material; b. the surfaces of mutual friction of the femoral element with the mobile plate and the surfaces of mutual friction of the tibial plateau with the mobile plate are entirely constituted by said one and the same ceramic material; and c. the mobile plate comprises two condylar bowls, and the femoral element comprises two condyles, said condyles and said condylar bowls each comprising surfaces of mutual friction spaced apart from each other by a distance smaller than 100 μm when the longitudinal axes of said femoral element and said tibial plateau form an angle of 0° to 75° and wherein said mobile plate comprises an intercondylar stud forming a projection toward said femoral element, said intercondylar stud being monolithically formed with the condylar bowls and having an upper surface and two lateral surfaces, wherein said femoral element comprises an intercondylar gap forming a rail that houses said intercondylar stud, said intercondylar gap having two parallel lateral surfaces, wherein the upper surface of the intercondylar stud corresponds to the shape of the intercondylar gap and the two lateral surfaces of the intercondylar stud correspond to the ones of the parallel lateral surfaces of the intercondylar gap, forming three surfaces of mutual friction.

2. The total knee prosthesis according to claim 1, wherein said condylar bowls and said condyles are spaced apart from one another by a distance of less than 100 μm when the longitudinal axes of said femoral element and of said tibial plateau form an angle of 0° to 60°.

3. The total knee prosthesis according to claim 1, wherein the femoral element and the tibial plateau are mobile in rotation relative to each other on an angular range of flexion of 0° to 135°.

4. The total knee prosthesis according to claim 1, wherein the surfaces of mutual friction of the condyles and of the condylar bowls are cylinder portions generated by revolution having a same radius.

5. The total knee prosthesis according to claim 1, wherein said mobile plate has a perimeter smaller than the perimeter of an upper surface of the tibial plateau.

6. The total knee prosthesis according to claim 1, wherein said tibial plateau comprises at least three stops forming a projection towards said mobile plate, said stops making it possible to limit movements of the mobile plate on the surface of the tibial plateau.

7. The total knee prosthesis according to claim 1, wherein said mobile plate can pivot on said tibial plateau such that a transversal axis of the mobile plate forms an angle up to +15° relative to a transversal axis of the tibial plateau when movement takes place in a clockwise sense and such that the transversal axis of the mobile plate forms an angle of up to −15° relative to the transversal axis of the tibial plateau when movement takes place in an anticlockwise sense.

8. The total knee prosthesis according to claim 1, wherein a space between the surfaces of mutual friction of the mobile plate and of the tibial plateau is smaller than 100 μm.

9. The total knee prosthesis according to claim 1, wherein said ceramic material has a thickness of 4 mm to 14 mm.

10. The total knee prosthesis according to claim 1, wherein said ceramic material is alumina Al.sub.2O.sub.3.

Description

5. LIST OF FIGURES

(1) Other features and characteristic of the invention shall appear more clearly from the following description of a preferred embodiment, given by way of a simple illustratory and non-exhaustive example and from the appended drawings of which:

(2) FIG. 1 is a perspective or three-quarter, exploded view of the prosthesis according to the invention;

(3) FIG. 2 is a sagittal section of the prosthesis according to the invention when the longitudinal axis of the femoral element and the longitudinal axis of the mobile plate form a zero (0°) angle;

(4) FIG. 3 is a sagittal section of the prosthesis according to the invention when the longitudinal axis of the femoral element and the longitudinal axis of the mobile plate form an angle of 45°;

(5) FIG. 4 is a sagittal section of the prosthesis according to the invention when the longitudinal axis of the femoral element and longitudinal axis of the mobile plate form an angle of 135°;

(6) FIG. 5A is a top view of the tibial plateau and of the mobile plate when the transversal axis of the mobile plate and the transversal axis of the tibial plateau form an angle of +15°;

(7) FIG. 5B is a top view of the tibial plateau and of the mobile plate when the transversal axis of the mobile plate and the transversal axis of the tibial plateau form an angle of −15°;

(8) FIG. 5C is a top view of the tibial plateau and of the mobile plate when the transversal axis of the mobile plate and the transversal axis of the tibial plateau form a zero (0°) angle.

6. DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION

(9) The general principle of the invention relies on a total prosthesis for a knee in which the mobile plate, the femoral element and tibial plateau have surfaces of mutual friction made out of one and the same ceramic material. These surfaces of mutual friction are perfectly congruent because of the optimizing of the shape of the surfaces of mutual friction and of the respective distance between the parts. Contrary to the hitherto common and widespread view, ceramic can be used to obtain a particularly resistant knee prosthesis.

(10) This resistance is especially due to the perfect congruency of the parts relative to each other and especially of the mobile plate relative to the femoral element and the mobile plate relative to the tibial plateau. The perfect congruency of the mobile plate with the femoral element provides for optimum friction while generating a minimum of wear debris; its mobility reproduces the overall play of the joint. This play can be sub-divided into two movements: that of the femoral element on the mobile plate associated with the rotational mobility and a drawer-like movement of the mobile plate on the surface of the tibial baseplate. The entire innovation therefore prevents or at least restricts the probabilities of repeat surgery on the knee, especially for young and physical active patients. It furthermore improves the results of the knee prosthesis in terms of the comfort and stability. This perfect congruency is obtained through studies on the part of the inventors, leading to the development of surfaces of mutual friction that prevent the creation of a concentration of mechanical stresses in the prosthesis. The congruency therefore prevents the phenomenon of abnormal wear of the ceramic material.

(11) Referring to FIG. 1, we present a three-quarter and exploded view of the prosthesis according to the present invention.

(12) As can be seen in FIG. 1, the prosthesis according to the invention comprises a femoral element 1, a mobile plate 2 and a tibial plateau 3 fixed to an anchoring heel 4 that is to be mounted on a upper profiled end of a tibia.

(13) The femoral element 1 has the general shape of a hollow partial shell externally defining two condyles 11 appreciably reproducing the shape of natural condyles, the posterior floating part of which, however, with the mobile plateau are cylinder portions and not irregular sphere portions. The condyles 11 could also be sphere portions. The condyles 11 are separated by a slot that on the whole reproduces the natural intercondylar gap 12. The intercondylar gap 12 has two appreciably parallel lateral surfaces 13. The intercondylar gap 12 corresponds to a cylinder portion coaxial with the cylinder portions forming the condyles 11 but with a smaller radius. The intercondylar gap 12 can also take the form of a sphere portion, the center of which is on the axis of revolution of the cylinder portions forming the condyles 11 or on the axis connecting the center of these spheres when the condyles are sphere portions.

(14) Internally, the femoral element defines a femoral housing 16 that is to receive the profiled lower extremity F1 of a femur F. The femoral element 1 can have a protrusion on its anterior face 15 that mimics the trochlea and is intended to cooperate with the patient's patella.

(15) The mobile plate 2 is inserted between the femoral element 1 and the tibial plateau 3. The mobile plate has a lower surface 23 that is essentially or even perfectly plane. On its upper surface, the mobile plate 2 has two condylar bowls 21 separated by an intercondylar stud 24. The intercondylar stud has a surface 25, the shape of which corresponds to the gap 12 as well as two lateral surfaces 23, the shape of which corresponds to the lateral surfaces 13 of the gap. A slight interstice enables the natural liquids to lubricate the joint formed by the prosthesis.

(16) The condylar bowls 21 define areas or surfaces of mutual friction, respectively for the two condyles 11 of the femoral element 1. Advantageously, the bowls 31 and the condyles 11 have surfaces of mutual friction of a perfectly congruent cylindrical shape. This significantly reduces the friction and therefore the wear on these parts. The term “perfectly congruent” will be understood to mean that the parts fit in perfectly with each other and that they are spaced apart at a distance of about 0 μm to 100 μm, preferably from 10 μm to 100 μm and even more preferably from 10 μm and 60 μm, especially when the angle between the longitudinal axis of the femoral element and of the mobile plate forms an angle of 0° to 75°.

(17) As for the intercondylar stud 24, it is engaged in the intercondylar gap 12 of the femoral element 1. The femoral element 1 abuts the surface 14 in the intercondylar gap 12 so that the relative movement of the mobile plate 2 and of the femoral element 1 remains controlled in its amplitude.

(18) During the rotation of the femoral element 1 on the mobile plate 2, the condyles 11 slip or slide in the condylar bowls 21 with the intercondylar stud 32 which moves in the intercondylar gap 12 that forms a sort of rail.

(19) The mobile plate 2 can move freely in translation without any stress on the tibial plateau 3, the lower surface 22 of the mobile plate and upper surface 31 of the tibial plateau being both essentially or even perfectly plane.

(20) The tibial plateau has an upper surface 31 that is to cooperate with the lower surface 22 of the mobile plate 2. The mobile plate 3 has three stops 32 on its upper surface. These three stops 32 restrict the translational motion of the mobile plate 2. On its lower face, it has a massive rod made of alumina ceramic that is to be cemented in the upper extremity of a patient's prepared tibia.

(21) Indeed, the mobile plate 2 herein fulfils the role of the meniscus. Its perimeter is smaller than that of the tibial plateau 3 so that it can enter into movement within the limits of the space defined by the stops 32. It can therefore slide in translation from front to rear and/or laterally on the upper surface of the tibial plateau: this has the effect of allowing further degrees of freedom in movement for the patient and a movement very close to the natural movement of the knee. It can also pivot about its longitudinal axis, parallel to the axis of the tibial plateau.

(22) The femoral element 1, the mobile plate 2 and the tibial plateau 3 are all three made out of ceramic Al.sub.2O.sub.3 according to the ISO-6474-1 standard.

(23) FIGS. 2, 3 and 4 are sagittal sections of the prosthesis assembled according to the invention. The references are identical with those of FIG. 1. These sections are made in a sagittal plane spaced apart by a distance of about 20-27 mm from the median plane of the prosthesis.

(24) As can be seen in FIG. 2, the longitudinal axis L of the tibial plateau and the longitudinal axis L′ of the femoral plate herein form a zero (0°) angle. In FIG. 3, the axis L and L′ form an angle α of about 45°. This corresponds approximately to the angle formed by the knee when walking. In FIG. 4, the angle α formed by the angles L and L′ is about 135°. This enables the patient to walk up staircases or perform moderate exercise.

(25) As can also be seen in FIG. 2, the condyles 11 are formed by cylinder portions with a radius R, the axis of revolution of which intersects the axis L and L′ at the center O. It must be noted that the condyles could be sphere portions with a center O and a radius R′. Preferably, the radii R and R′ have a length of 22 mm to 38 mm, preferably 25 mm to 35 mm. The radius R″ of the intercondylar gap cannot be shown in these sections. The surface of the gap is herein concealed.

(26) In the same way, FIGS. 5A to 5C present a top view of the relative movement of the mobile plate 2 on the tibial plateau 3. As can be noted, the perimeter of the plate 2 is smaller than that of the plateau 3 so that the mobile plate 2 can shift on the surface of the plateau 3. The three stops 32 define a perimeter or field of movement of the mobile plate 2. These top views are intended to illustrate the amplitude of the permitted movement of the mobile plate relative to the tibial plateau.

(27) As can be seen in FIGS. 5A and 5B, the plate 2 can pivot about its longitudinal axis, parallel to that of the tibial plateau (not shown in the figures). More specifically, the transversal axis of the tibial plateau 2 can form an angle β of about 15° relative to the transversal axis T′ of the mobile plate 2.

(28) By convention, an angle is denoted as being an angle of +15° when the rotation is made in the clockwise sense (FIG. 5B) and −15° when the rotation is made in the anticlockwise sense (FIG. 5C).

7. VARIANTS

(29) Different variants of the invention can be envisaged. For example the condyles and condylar bowls can both have the shape of cylinder portions while the intercondylar gap and the intercondylar stud take the form of a sphere portion. Conversely, the condyles and condylar bowls can both take the shape of a sphere portion while the intercondylar gap and intercondylar stud take the shape of a cylinder portion. It is also possible for one condyle and its corresponding condylar bowl to take the shape of a sphere portion while the other will take the shape of a cylinder portion.

(30) In another variant, compatible with the variants listed here above, the tibial plateau is devoid of stops. In this case, the leg of the patient being operated on is held still by a splint while fibrous tissue is formed about the prosthesis to stabilize the replaced joint.

(31) An exemplary embodiment of the present disclosure overcomes the drawbacks of the prior art.

(32) An exemplary embodiment provides a knee prosthesis that is more resistant than presently used prostheses.

(33) An exemplary embodiment implements a prosthesis of this kind that allows patients to resume normal physical activity.

(34) An exemplary embodiment proposes a prosthesis that limits inflammatory reactions.

(35) An exemplary embodiment proposes a prosthesis that enables the re-forming of a fibrous tissue that is more resistant, and plays the natural role of the knee ligaments by remodeling fibrous structures under mechanical stress.

(36) An exemplary embodiment proposes a prosthesis, the joint or articular surfaces (the surfaces of mutual friction) of which have improved congruency in a load-bearing area.

(37) An exemplary embodiment proposes a prosthesis that enables greater amplitude of motion as compared with known knee prostheses.

(38) Although the present disclosure has been described with reference to one or more examples, workers skilled in the art will recognize that changes may be made in form and detail without departing from the scope of the disclosure and/or the appended claims.