FR2839256A1 - Complete knee prosthesis has femoral element having convex surfaces, each respectively forming an internal and an external condyle, with the radius of curvature of the internal condyle greater than that of the external condyle - Google Patents

Abstract

The knee prosthesis includes a femoral element (1) having a device (8) for anchoring it to the end of a femur and two convex surfaces (5,6) respectively forming internal and external condyles. A tibial element includes a device for anchoring to the end of a tibia and a support plate. An intermediate plate includes two concave surfaces designed to cooperate with the femoral convex surfaces and an inferior face supported against a superior face of the support plate to support the tibial element. The intermediate plate is movable relative to the tibial element. Each of the convex surfaces present, in a anterior-posterior vertical plane passing by their points lower down, a circular bend, with the radius of the curvature of the internal condyle being greater than the radius of curvature of the external condyle.

Description

to mount it fa, con removable on the output shaft of the reducer (12).

  The present invention relates to a total knee prosthesis, of the movable plate type, which comprises in a manner known per se: - a femoral element comprising means for anchoring at the distal end of a femur and two convex surfaces respectively forming an external condyle and an internal condyle, - a tibial element comprising means for anchoring at the proximal end of a tibia and a support plate having an upper face and a lower face, and - an intermediate plate comprising two upper concave surfaces intended to cooperate, with the possibility of sliding, respectively with the convex surfaces of the femoral element and a lower face bearing against the upper face of the support plate of the tibial element, this intermediate plate being

  movable relative to the support plate of the tibial clement.

  This type of prosthesis must in principle allow a faithful reproduction of the natural movement of the knee joint with a limitation of wear and creep linked to the significant and repeated efforts applied to the intermediate plate and this, thanks to the

mobility of the latter.

  However, various studies have enabled the detection of kinetic anomalies on the abovementioned prostheses, anomalies which result in an imperfect, if not impossible, reproduction of certain physiological movements between tibia and femur, in particular of the internal axial rotation (by considering the knee seen face) automatic tibia in flexion which is normally

  about 15 to 20 to 90 of flexion.

  This internal axial rotation, linked to the uneven development of the condylar contours, to the shape of the glenae and to the orientation of the lateral ligaments, participates in the dynamic balance of the knee in flexion and in particular in the action of

  stabilization of muscles and ligaments.

  The present invention therefore relates to a prosthesis such as

  defined in the first paragraph of this description and designed to

  favor the physiological movement of internal axial rotation of the

shin when bending the knee.

  To this end, this prosthesis is characterized in that each of the convex surfaces respectively forming the external condyle and the internal condyle, presents in the vertical anteroposterior plane passing through its teas point, a curvature in an arc of a circle, the radius of the arcuate curvature of the inner condyle being greater than that of the arcuate curvature of the external condyle. Thanks to this arrangement, during the knee flexion, that is to say the rolling and sliding of the condyle on the corresponding concave surfaces of the intermediate plate, the tibia is the seat of a progressive internal axial rotation with respect to

  at femur, with an angle of rotation of up to 4-5.

  It will be specified that the radius of the arcuate curvature of the internal condyle is advantageously in the range from a to 35 mm and that of the arcuate curvature of the condyle

  external in the range from 28 to 38 mm.

  According to another characteristic of the invention, the upper face of the support plate of the tibial element and the lower face of the intermediate plate are congruent and respectively convex and concave, and each of these two faces has the shape of a part of spherical cap, the high point of the spherical cap which defines the upper face of the support plate of the tibial clement being offset laterally towards the internal part of the knee relative to the anchoring means of lt tibial clement, this high point preferably being located on the vertical axis passing through the

  most teas point of the convex surface of the internal condyle.

  According to yet another characteristic of the invention, the upper face of the support plate of the tibial element and the lower face of the intermediate plate are congruent and concave and convex, respectively, and each of these two faces has the shape of a part of a spherical cap. , the point teas of the spherical cap which defines the upper face of the support plate of the tibial element being offset laterally towards the internal part of the knee relative to the anchoring means of the tibial element, this point teas being preferably located on the vertical axis passing through the

  most teas point of the convex surface of the internal condyle.

  The particular geometries above favor, during an axial change such as a bending of the knee, a pinching of the support plate at the level of the high point (respectively point teas) of its upper face, point through which will then pass the vertical pivot axis "iprivilegie" of the intermediate plate by

  relation to the support plate of the tibial clement.

  Such displacement of the pivot axis relative to the axis passing through the anchoring means of the tibial element, results in bending of the knee, by a movement of internal axial rotation of the tibia relative to the femur , movement which can reach fifteen degrees and thus contribute to the rotation effect

internal axial previously mentioned.

  Furthermore, the prosthesis according to the invention advantageously comprises means for limiting the extent of the pivoting of the intermediate plate relative to the support plate of the tibial clement. These means preferably include a stud protruding above the upper face of the support plate of the tibial element and an oblong hole in the form of an arc of a circle centered on the vertical axis passing through the top point of the cap spherical when the latter is convex, or the teas point of the spherical cap when the latter is concave, cap defining the upper face to said support plate, this oblong hole being provided in the lower face of the intermediate plate and capable of receiving said block with possibility of pivoting and translation to said plate

  intermediate with respect to said support plate.

  In addition, the tibial element anchoring means are advantageously constituted by a rod intended to be implanted.

in the medullary canal of the tibia.

  The invention is described below in more detail with reference to the accompanying drawings showing by way of nonlimiting examples, two preferred embodiments of this invention, drawings in which: - Figure 1 is a schematic front view of a embodiment of the prosthesis according to the invention, - Figure 2 is a schematic representation of the principle of the prosthesis of Figure 1, in which the condyles are symbolized by a cone, the knee being extended, - Figure 3 is a schematic view of the principle of the prosthesis of FIG. 2, but observed from another angle, the knee being in flexion, - FIG. 4 is a front view of the femoral clement of the prosthesis of FIG. 1, - Figure 5 is the superposition of a sectional view along the line VV of Figure 4 and diune sectional view along the line V'-V 'of this Figure 4, - Figure 6 is a front view of the plate intermediate of the prosthesis of figure 1, - figure 7 is t a top view of the intermediate plate of Figure 6, - Figure 8 is a front view of the tibial element of the prosthesis of Figure 1, - Figure 9 is a top view of the tibial element of Figure 8, - Figure 10 is a left view of the tibial element of Figure 8, and Figure 11 is a front view of the tibial element of a

  another embodiment of the prosthesis according to the invention.

  As shown in FIG. 1, the prosthesis represented comprises a femoral element 1 secured to the femur F. a tibial element 2 secured to the tibia T and an intermediate plate 3 disposed between

  femoral clement 1 and tibial clement 2.

  The femoral element 1, made of an appropriate material having good mechanical resistance, such as for example a metal or a ceramic, comprises in a manner known per se a front trochlear surface 4 of generally convex shape comprising externally a groove reproducing the trochlea. The trochlear surface 4 is extended at its lower part towards the rear by two convex articular surfaces 5, 6 connected by an intermediate surface 7, the surfaces 5, 6 reproducing respectively the internal femoral condyle and the external femoral condyle. The femoral element 1 further comprises anchoring means a

  the distal end of femur F having undergone an appropriate resection.

  These anchoring means can be constituted by two vertical studs 8, 8 'intended to be inserted respectively in the internal condyle and the external condyle of femur F with possible use.

a sealing material.

  According to a characteristic of the present invention, each of the surfaces 5, 6 has in the vertical anteroposterior plane passing through its teasest point, a curvature in an arc of a circle, the radius of the curvature in an arc of a circle of the internal condyle being greater than that of the arcuate curvature of the external condyle. The ratio of the radius of said arcuate curvature of the inner condyle to that of said arcuate curvature of the outer condyle can for example be in the range of 1.1 to

  1.3 and take for example the value 1.11.

  FIG. 5 shows at the level of the vertical anteroposterior plane passing through the teasest point of the convex surface 5, in bold line, the external contour of the convex surface 5 and, at the level of the vertical anteroposterior plane passing through the point the plus teas of the convex surface 6, in thin line, the external contour of this convex surface 6. These contours therefore correspond respectively to the shape of the curvatures in an arc of a circle which surfaces 5 and 6 present respectively in the antero-posterior planes

  vertical passing through the teasest points of these two surfaces.

  It will be noted that the length of the arcuate curvature of each convex surface depends in particular on the size of the femur and can therefore vary from one prosthesis to another. Thus, by way of nonlimiting example, each curvature can extend substantially over any

  the posterior part of the condyle correspond.

  Figures 2 and 3 schematize the characteristic according to the invention of the above-mentioned radius difference. Figure 2 corresponds to the case where the femur F-prosthesis-tibia T system is in the extended position and Figure 3 to the case where the femur F-prosthesis-tibia T system is in the flexion position at more than 90, the angle a of internal axial rotation taking in the latter case a value

slightly greater than 5.

  In these two figures, the femoral clement is represented by a cone trunk whose end ending in the large face symbolizes the internal condyle (then the curvature in an arc of a circle presents the largest radius) and the end ending over there

  small face symbolizes the external condyle.

  The tibial element 2, also in an appropriate material having good mechanical resistance such as for example a metal or a ceramic, comprises in a manner known per se, means for anchoring to the proximal part of the tibia T. for example a rod 9 slightly inclined with respect to the vertical in order to be able to be inserted easily in the medullary canal of the tibia T, the proximal part of which has undergone a plane bone cut which resects a thickness of bone corresponding substantially to the thickness of the element

tibial 2.

  The latter further comprises an upper support plate 10

  having an upper face 11 and a lower face 12.

  The 10-rod support plate assembly 9 is stiffened by

  fins 13 integral with both this plate and this rod.

  As for the intermediate plate 3, made of a material allowing easy sliding of the contacting surfaces, for example of high density polyethylene, it comprises, in a manner known per se, two upper concave surfaces 14, 15 intended to receive, with the possibility of sliding, respectively the convex surfaces 5, 6 of the femoral part, these backs being perfectly congruent

  respectively with the concave surfaces 14, 15.

  The intermediate plate 3 further comprises a lower face 16 bearing against the upper face 11 of the tibial element, this intermediate plate -3 being movable in pivoting and in antero-posterior and lateral translation by

tibial audit report 2.

  In accordance with the present invention, the upper face 11 of the support plate 10 of the tibial element 2 and the lower face 16 of the intermediate plate 3 are congruent and respectively convex and concave. Furthermore, each of these faces 11, 16 has the shape of a spherical cap, the high point of the spherical cap defining the upper face 11 of the tibial element 2 being offset laterally towards the internal part of the knee relative to the rod.

anchor 9.

  Alternatively, and as shown in Figure 11, the support plate of the tibial element may have an upper face lla concave. In this case the lower face of the intermediate plate is convex; in addition the upper face lla and the convex lower face of the intermediate plate congruent wind and each in the form of a spherical cap, the point teas of the cap correspond to the face lla being offset laterally towards the part

  internal knee relative to the anchor rod 9.

  Furthermore, the high point of the convex spherical cap defining the face 11, or the teas point of the concave spherical cap defining this face, is located substantially on the axis.

  vertical passing through the teasest point of the internal condyle.

  Thanks to the difference in radius of the curvatures in the arc of a circle of the surfaces 5, 6 of the femoral element, during the knee flexion, the tibia T is the seat of a progressive internal axial rotation, relative to the femur F. Furthermore, due to the particular position of the top point of the convex spherical cap defining the upper face 11 of the tibial clement 2 (or point teas when this spherical cap is concave), position which is offset towards the internal part of the knee relative to the anchor rod 9, the pivoting movement of the intermediate plate 3 will take place in a preferred manner around the vertical axis passing through this high point (respectively point teas), with consequently a strong contribution to the effect of rotation

  internal axial tibia during knee flexion.

  It will be specified that the abovementioned pivoting movement will advantageously be limited by limiting means which can, for example, be constituted on the one hand, by a stud 17 forming above the upper face 11 (respectively upper face lla) and on the other hand , by an oblong hole 18 in the form of an arc of a circle center on the vertical axis passing through the high point (respectively point teas) of the spherical cap defining the upper face 11 (respectively upper face lla); the oblong hole 18 is made in the lower face 16 of the intermediate plate 3 and is dimensioned to be able to receive the stud 17. The stud 17 and the hole 18 are more precisely dimensioned so that said plate

  intermediate 3 can pivot and move in antero- translation

  posterior and lateral, relative to the support plate 10.

  We therefore have, thanks to the present invention, a knee prosthesis to restore as faithfully as possible the physiological movement of internal axial rotation of the tibia during

knee flexion.

Claims (8)

RESELL I CAT I ONS   1. Total knee prosthesis, of the movable plate type, which comprises in known manner on the ground: - a femoral element (1) comprising anchoring means (8) at the distal end of a femur (F) and two convex surfaces (5, 6) respectively forming an internal condyle and an external condyle, - a tibial element (2) comprising anchoring means (9) at the proximal end of a tibia (T) and a plate d support (10) having an upper face (11; lla) and a lower face (12), and - an intermediate plate (3) comprising two concave surfaces (14, 15) intended to cooperate, with the possibility of sliding, respectively with the convex surfaces (5, 6) of the femoral element and a lower face (16) bearing against the upper face (11) of the support plate of the tibial element, this intermediate plate being movable relative to the plate 'support of the tibial clement, characterized in that each of the convex surfaces (5, 6) respectively forming the internal condyle and the external condyle, present in the vertical anteroposterior plane passing through its teasest point, a curvature in an arc of a circle, the radius of the curvature in an arc of a circle of the internal condyle being greater than that   of the arcuate curvature of the external condyle.   2. Prosthesis according to claim 1, characterized in that the upper face (11) of the support plate (10) of the tibial element (2) and the lower face (16) of the intermediate plate (3) are congruent and respectively convex. and concave, and each of these two faces has the shape of a part of a spherical cap, the high point of the spherical cap which defines the upper face (11) of the support plate of the tibial element being offset laterally towards the internal part of the knee relative to the anchoring means (9) of the tibial clement.   3. Prosthesis according to claim 2, characterized in that said top point of the spherical cap is located on the vertical axis passing through the most teas point of the convex surface (5) of the internal condyle.   4. Prosthesis according to claim 1, characterized in that the upper face (lla) of the support plate of the tibial element and the lower face of the intermediate plate are congruent and respectively concave and convex, and each of these two faces has the shape of a part of spherical cap, the point teas of the spherical cap which defines the upper face (lla) of the support plate of the tibial element being offset laterally towards the internal part of the   knee relative to the anchoring means (9) of the tibial element.   5. Prosthesis according to claim 4, characterized in that said point teas of the spherical cap is located on the vertical axis passing through the most teas point of the convex surface of the internal condyle.   6. Prosthesis according to any one of the claims   previous, characterized in that it further comprises means (17, 18) for limiting the pivoting of the intermediate plate by   relative to the support plate of lt tibial clement.   7. Prosthesis according to claim 6, characterized in that said means for limiting the pivoting of the intermediate plate comprise a stud (17) projecting above the upper face (11; lla) of the support plate (10) of tibial element (2) and an oblong hole (18) in the form of an arc of a circle center on the vertical axis passing through the top point of the spherical cap when it is convex, or the teas point of the spherical cap when the latter is concave, cap defining the upper face (11; lla) to said support plate, this oblong hole being provided in the lower face (16) of the intermediate plate (3) and able to receive said stud (17) with possibility of pivoting and translation   to said intermediate plate with respect to said support plate.   8. Prosthesis according to any one of claims   precedents, characterized in that the means for anchoring the tibial element (2) are advantageously constituted by a rod