FR2844704A1 - Mobile plate knee prosthesis comprises tibial base fixed on tibia upper end, intermediate friction plate received on tibia base having projection engaged in plate opening and femoral element anchored at femur lower end - Google Patents

Abstract

The knee prosthesis comprises a tibial base (2) which is fixed on the upper end of the tibia. There is an intermediate friction plate (3) which is received on the tibial base (10) and able to be displaced quasi-freely on it. A femoral element (1) is anchored at the femur lower end and is provided with two symmetrical condyles (5) supported congruently on the intermediate friction plate. The tibial base (2) is provided with a projection (12) directed in a direction perpendicular to the plane which contains it and oriented in the direction of the femoral element. The intermediate friction plate has an opening (14) which engages the projection so as to limit its displacement on the tibial base. The femoral element has an inter-condylian groove (7) of corresponding dimensions to the projection so as to engage with it during operation of the articulation when the prosthesis is placed.

Description

KNEE PROSTHESIS WITH MOBILE TRAY

  The present invention relates to a knee prosthesis of the movable plate type.

  Traditionally, a knee prosthesis comprises a tibial element, also called tibial base, intended to be fixed at the upper end of the tibia, a femoral element, intended to be anchored at the lower end of the femur, and traditionally reproducing the forms femoral condyles, and in addition, an intermediate sliding plate, interposed between these two elements. 10

  The intermediate plate conventionally comprises, at its face directed towards the femoral element of the concave surfaces, capable of cooperating with the convex parts of the condyles of the femoral element, and at its face directed towards the tibial element, a substantially flat and horizontal surface coming to bear on the corresponding surface of the tibial element.

  During the operation of the joint, the femoral element and the tibial base exert significant compressive and torsional stresses at the level of the intermediate plate, causing wear of the plastic material constituting said plate, traditionally made of polyethylene.

  In fact, the greatest possible congruence is sought between the femoral element and the intermediate friction plate, in order to reduce as much as possible the risks of creep and wear of the intermediate polyethylene plate. This is the reason why prostheses of the type in question have already been described using such a friction plate, movable either in translation or in rotation, such as for example in

  the document FR-A-2 735 017, or even by combining the two movements.

  If undoubtedly, the implementation of such an intermediate friction friction plate 30 makes it possible to limit the creep and the wear thereof, the fact remains that the relative movements of this intermediate friction plate do not allow not to result in the greatest possible congruence of the femoral element at the level of said plateau, so that the risks of loosening either of said femoral element or

of the tibial base remain.

  The object of the present invention is therefore to make it possible to reproduce in a dissociated manner, as in the natural knee, the sliding and rolling movements of the condyles, during flexion, and this, by promoting the displacement of said movable friction plate. according to the different orientations of the tibia relative to the femur, that is to say according to the different anatomical movements of flexion / extension. To this end, the invention provides a knee prosthesis with an intermediate movable friction plate, comprising - a tibial base, intended to be fixed on the upper end of the tibia; 10 - an intermediate friction plate, intended to be received on the tibial base, and capable of moving almost freely on the latter; - A femoral element, intended to be anchored at the lower end of the femur, and provided with two symmetrical condyles or not coming to bear congruently on said intermediate friction plate. This prosthesis is characterized - in that the tibial base is provided with a projection directed in a direction substantially perpendicular to the plane which contains it, and oriented in the direction of the femoral element; - in that the intermediate friction plate is provided with a through lumen, intended to cooperate with said projection, so as to control its movement on the tibial base; - And in that the femoral element is provided with an inter-condylar groove, of corresponding dimensions or slightly larger than those of said projection, so as to cooperate with it during the operation of the joint

  at which said prosthesis is placed.

  In other words, the invention consists in putting in place at the level of the tibial base a projection, intended to cooperate on the one hand, with the intermediate friction plate, in order to limit its displacement, and d on the other hand, with the femoral element, so as to impose a displacement constraint on said intermediate plate during the rotation of the femoral element in flexion or extension phases, and not by the cooperation of said intermediate plate with the tibial base, as described in the prior art, in particular in the aforementioned document FR-A-2 735 017. According to a characteristic of the invention, the projection with which the tibial base is provided, is

  located in the vicinity of the plumb of the anchoring stud of said base within the tibia.

  In addition, the inter-condylar groove with which the femoral element is provided, is configured so that when the joint is in extension, the projection of the tibial base abuts against the end of the groove, thus limit the angular movement of

  the joint, and thus limit any risk of hyper-extension.

  According to another characteristic of the invention, the intercondylar groove with which the femoral element is provided, is configured such that when it is capable of abutting against said projection during bending, to induce translation towards the rear of the intermediate friction plate, and as a corollary, maintain the congruence of the condyles with said plate until a flexion of at least 900 of the joint. According to another characteristic of the invention, the two condyles constituting a fundamental part of the femoral element, each have two successive radii of curvature 15 in the sagittal plane, the variation of said radii of curvature occurring substantially in line with the vertical passing by the anchoring studs of said element

  femoral at the lower end of the femur.

  According to another characteristic of the invention, the thickness of the posterior condyles is increased compared to the rest of the femoral implant, and this, with the aim of achieving greater flexion, and consequently, greater travel of

the joint thus prosthetic.

  The manner in which the invention can be implemented and the advantages which ensue therefrom will emerge more clearly from the example of embodiment which follows, given by way of indication and not

  limiting, in support of the appended figures.

  Figure 1 is a schematic exploded perspective view of the prosthesis

according to the invention.

  FIGS. 2, 3 and 4 are schematic perspective representations of the prosthesis according to different degrees of flexion, respectively 00, 90 and 130 of flexion.

  FIGS. 5 to 10 are diagrammatic representations in section of the prosthesis according to the invention, according to different degrees of flexion, respectively 00, 20, 400,

600, 900, 130

  Figure 11 is a schematic sectional view of the femoral implant 35 according to the invention.

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  Figures 12, 13, 14 and 15 are schematic cross-sectional representations of said femoral implant, respectively along a line 12-12, 13-13, 1414, 15-15 of Figure 11.

  The knee prosthesis according to the invention therefore basically comprises three distinct elements, respectively a femoral element (1), intended to be anchored at the lower end of the femur, prepared for this purpose, a tibial base (2 ), intended to be anchored at the upper end of the tibia also prepared for this purpose (resection), and an intermediate friction plate (3). The femoral element (1) and the tibial base (2) are made of metal, and in particular of cobalt / chromium alloy, well known for this application, or any other material, such as

than ceramic for example.

  The femoral element is inserted at the lower end of the femur, in particular by means of anchoring studs (6), more precisely two anchoring studs, extending under the two condyles (5), which is provided with said femoral element. These condyles are symmetrical at all of their areas of cooperation with the intermediate plate (3). On the other hand, the trochlea (4) is asymmetrical, the throat

  Trochlean being oriented in 1840 from the inside to the outside.

  The tibial base (2), also metallic, basically has a base 25 proper (10), planar, the underside of which is extended by an anchoring rod (11), intended to be inserted at the level of the tibia after resection of its end

  superior by means of an appropriate ancillary.

  The intermediate friction plate (3) is made of plastic, typically of high density polyethylene.

  This plate is capable of moving freely on the base (10), both in translation back and forth and in rotation, in a known manner. It has on its upper face two concavities (9), each intended to cooperate in a congruent manner each with a condyle (5) of the femoral element (1).

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  On the other hand, according to a fundamental characteristic of the invention, this intermediate friction plate is limited in its movement by cooperation with a projection (12), extending from the tibial base, and oriented substantially perpendicularly to the base (10). This projection is also made of polyethylene, but is reinforced with a metal rod or any other material, in order to give it a certain rigidity, taking into account its cooperation with the femoral element, as described below. In order to cooperate, among other things, with the intermediate friction plate (3), the latter has a through light of oblong or ellipsoidal shape, the major axis of which is oriented along the axis of symmetry of said plate.

  As a corollary, the femoral element (1) has an intercondylar groove (7), the depth and width of which are complementary to those of the projection (12) apart from play, to allow cooperation with the latter. In the example described, this projection 15 has a substantially hemispherical upper part. In fact, the intercondylar groove (7) has a complementary shape, substantially semi-cylindrical.

  This inter-condylar groove extends substantially from the lower end of the trochlea to the vicinity of the departure of the posterior condyles, as can be seen in FIG. 4.

  In doing so, the femoral element cooperates with the intermediate friction plate whatever the degree of flexion of the joint considered, as can be observed.

in particular in FIGS. 5 to 10.

  More precisely, in maximum extension, that is to say for an angular movement of 00, the projection (12) comes to bear against the end (8) of the intercondylar groove (7), preventing an additional movement of the articulation and therefore

limiting any hyper-extension.

  When fleeing and as the flexion occurs, the cooperation of the projection (12) of the tibial base with the inter-condylar groove (7) firstly induces a sliding movement of the condyles on said plateau, then when the projection abuts against the other end (13) of the intercondylar groove, a displacement of said intermediate plate 35 in the posterior region of the joint, as can be observed on the

Figures 6 to 10.

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  The stroke of the plate on the base is in fact limited by the cooperation of the through lumen (14) with which it is provided, with the projection (12) of the tibial base. Typically, this stroke is between eight and twelve millimeters. It is chosen so that there is always congruence between the condyles (5) of the femoral element and the 5 concave cavities of the intermediate friction plate until a flexion of the order of 900.

  We therefore observe in the operation of the joint provided with such a prosthesis, a dissociation of the movement between rolling of the condyles on the plate, then sliding of the plate for the most significant flexions. In doing so, one results in a better reproduction of the natural kinematics of the joint considered, with a retreat of the center of rotation during flexion, thus allowing to significantly increase the amplitude of the flexion. In addition, this mechanical device makes it possible to replace the anatomical and functional play of the cruciate ligaments. In maximum flexion, typically at 130, there is partial coaptation of the condyles (5) with the intermediate friction plate, which does not present a drawback within the meaning of the invention insofar as, in this position, the stresses exerted on the intermediate plate are relatively low. 20 On the other hand, we observe that during the first stages of bending, and during

  the extension, the congruence between the condyles and the plateau is maximum.

  In addition, and in order to promote this congruence, the condyles have two successive radii of curvature of different value, depending on the size of the femoral implant.

  The variation in the radius of curvature occurs substantially at the base of the anchoring stud (6). As regards the posterior region of the condyles, the radius of curvature typically varies according to the sizes between 25 and 33 millimeters. While 30 with respect to the anterior condyle area, this variation is typically understood

between 25 and 38 millimeters.

  The particular shape thus conferred, both on the femoral element, on the tibial base, and on the intermediate friction plate, enables the rolling and sliding movements of the condyles to be reproduced dissociated during flexion.

  At the same time, in order to give the prosthesis a greater degree of flexion, the posterior condyles have an extra thickness, compared to the rest of the implant, as can be better seen on the different section views of the invention. .

  This extra thickness makes it possible to increase the radius of curvature of the condyle at this level, promoting flexion.

  Furthermore, because of the possible movement of the intermediate friction plate, both in translation and in rotation, the practitioner has greater room for maneuver when positioning the tibial base, since the plate becomes in a way 10 self-adaptive in relation to its cooperation with the femoral element.

  In addition, by this self-adaptation, the condyles - tray interface undergoes fewer stresses, because said tray is automatically oriented according to the configuration

  desired, under the action of said condyles.

  In addition, by optimizing the congruence of the femoral element at the level of the intermediate friction plate, the wear of said intermediate plate is limited, and

  pal-so we extend the life of the prosthesis.

  This congruence is retained taking into account the fact that the intermediate fiiction plate moves in translation and in particular recedes simultaneously with the bending, and that in addition, taking into account its relative freedom of mobility on the base (10), it is at

  even to operate a rotational movement.

Claims (7)

  1. Knee prosthesis with movable friction intermediate plate, comprising: - a tibial base (2), intended to be fixed on the upper end of the tibia; - An intermediate friction plate (3), intended to be received on the tibial base (10), and capable of moving almost freely on the latter; - a femoral element (1), intended to be anchored at the level of the lower end of the femur, and provided with two symmetrical or non-symmetrical condyles (5) 10 coming to bear congruently on said intermediate friction plate (3) , characterized: - in that the tibial base (2) is provided with a projection (12) directed in a direction substantially perpendicular to the plane which contains it, and oriented in the direction of the femoral element (1); - in that the intermediate friction plate (3) is provided with a through lumen (14), intended to cooperate with said projection (12), so as to limit its movement on the tibial base; - And in that the femoral element (1) is provided with an inter-condylar groove (7), of dimensions corresponding to those of said projection (12) or slightly greater, so as to cooperate with it during operation of   the joint at which said prosthesis is placed.   2. Knee prosthesis with movable intermediate friction plate according to claim 1, characterized in that the projection (12) with which the intermediate friction plate is provided, is located in the vicinity of the plumb of the anchor rod. (11) of the tibial base (10).   3. Knee prosthesis with movable intermediate friction plate according to one of claims 1 and 2, characterized in that the intercondylar groove (7), of which   is provided with the femoral element (1), is configured such that when the articulation at the level of which said prosthesis is placed is in extension, the projection (12) of the intermediate friction plate (3) abuts against the end (8) of the groove, thereby limiting the angular movement of the joint. 35 4. Knee prosthesis with an intermediate movable fiiction plate according to one of   Claims 1 to 3, characterized in that the inter-condylar groove (7), condylar with which the femoral element is provided, is configured such that when it comes into abutment (13) against said projection during bending, it induces the rearward translation of the intermediate friction plate and consequently   the decline in the center of rotation of the joint.   5. Knee prosthesis with movable friction intermediate plate according to one of the   Claims 1 to 4, characterized in that the upper end of the projection 10 (12) is substantially hemispherical, and in that the inter-condylar groove (7)   is of substantially semi-cylindrical shape.   6. Knee prosthesis with movable friction intermediate plate according to one of the   Claims 1 to 5, characterized in that the two condyles (5) constituting the fundamental part of the femoral element (1) each have two radii of   successive curvature in the sagittal plane, the variation of said radii of curvature occurring substantially perpendicular to the vertical passing through the anchoring studs (6) of said femoral element at the lower end of the femur. 7. Knee prosthesis with movable friction intermediate plate according to one of the   Claims 1 to 6, characterized in that the thickness of the posterior condyles is increased compared to the rest of the femoral implant, with the aim of achieving greater flexion, and consequently, a greater travel of the prosthesis joint.