ITMI952648A1 - REPLACEMENT STABILIZED FROM BEHIND BY KNEE JOINT - Google Patents

Abstract

Sliding knee prosthesis, comprising a femoral implant (1), a tibial implant (2) and a meniscal element (3), in which the meniscal element (3) comprises two spherical cavities (31, 32) for support and the The femoral implant (1) comprises two condyles (10, 11) whose bearing faces (14, 15) are spherical segments of radius (R) equal to that of the spherical cavities (31, 32).

Description

Description of the industrial invention

The present invention relates to a sliding knee prosthesis capable of being used as a stabilized prosthesis from behind, especially in the case in which it is installed as a recovery prosthesis.

Knee prostheses currently known all consist of a femoral implant comprising two condyles and a trochlea and a tibial implant whose plane is covered by a meniscal element, mobile or not, on which the condyles have a sliding support.

In order to be able to adapt a prosthesis to a patient's anatomy, it is necessary to have femoral and tibial implants of different sizes. In addition, in order to respect ligament tensions, it is essential to have meniscal elements of different thicknesses, which greatly multiplies the number of pieces required for an operation.

On the other hand, the knee joint may be subject to slips, or cassettes, due to a certain relaxation of the ligaments or to an accidental absence of these, especially of the posterior cross ligament.

The relaxation of the ligaments is generally observed in the case of a recovery, that is, at the time of implantation of a prosthesis to replace another implanted anteriorly.

To remedy the drawbacks of anterior sliding and lateral relaxations, prostheses stabilized from behind have been proposed, that is, comprising, significantly in the center of the tibial plane, a central protrusion against which, at the moment of flexion, a transverse piece positioned in the recess is supported. intercondylar. Prostheses of this type are described in documents US-A-950298 and GB-A-1067412.

The existing stabilized prostheses from behind, however, do not prevent anything other than the anterior sliding in flexion and are almost exclusively reserved for cases in which the posterior cross ligament is absent.

Prostheses have also been proposed whose tibial plane significantly comprises a block in the center equipped at its end with a sphere cooperating with a hemispherical dome placed in the femoral implant. These prostheses, described especially in documents US-A-3868730 and GB-A-2088724, however, have drawbacks of comfort and durability.

In fact, in the prosthesis that is the subject of document US-A-3868730, the joint is made together with a part between the condyles and the meniscal plane and, on the other hand, the sphere and the dome, which places problems of ligament tension, amplified when there is premature wear of one or the other of the rubbing surfaces.

The prosthesis described in document GB-A-2088724 uses a sphere solely as a joint pad that is made between the condyles and the tibial plane. However, this prosthesis has the drawback of a possible shear phenomenon between the condyles and the plane at the time of axial rotation, leading to the risk of premature wear of the rubbing surfaces. In addition, the flexion is limited by the fact that the dome is extended posteriorly to avoid a possible sliding in extension. Furthermore, due to the non-constant radius of the condyles, it is necessary to provide for a mobility of the spherical head, which is obtained by fixing the same to a piston, with the drawbacks of this type of device.

The present invention has for the purpose of remedying these drawbacks by proposing a sliding knee prosthesis which can be adapted to the recovery and stability from behind, allowing to considerably reduce the number of pieces necessary for a surgical intervention.

A prosthesis according to the present invention, comprising a femoral implant, a tibial implant and a meniscal element, is essentially characterized on the one hand by the fact that the meniscal element comprises two spherical support cavities and, on the other hand, by the fact that femoral regression comprises two condyles whose supporting faces are spherical segments of distinct centers and of equal radius to that of the spherical cavities, said centers being set apart, whatever the size of said femoral implant, by the same distance, allowing a meniscal element is, except for thickness, of constant dimensions, regardless of the size of the femoral implant. According to an additional characteristic of the prosthesis according to the invention, the meniscal element comprises at its upper face, in its central anterior region, a pad having a top inclined plane towards the rear against which it rests, when the knee is in extension, the base of the trochlea into the extremity of the intercondylar recess.

According to another additional feature of the prosthesis according to the invention, the tibial plane comprises on its upper flat face a truncated cone protrusion which is housed in a cavity made in the lower flat face of the meniscal element, allowing, according to the dimensions and shape of the said cavity, a rotation or a free sliding movement of said meniscal element on said tibial plane.

In a particular embodiment of the prosthesis according to the invention, a block, the end of which is provided with a spherical head, is fixed on the tibial plane in the central posterior region of the same, the center of the said spherical head being aligned with the centers of the spherical segments constituting the bearing surfaces of the condyles; the meniscal plane, subjected to said tibial plane, being hollowed out centrally to allow the passage of said block with play, while an insert comprising a hemispherical cavity in which the spherical head of said block is placed, without play, is introduced and fixed in the 'femoral implant between the two condyles, relative to the intercondiioid cavity.

According to a first variant of this way of manufacturing the prosthesis according to the invention, the insert cavity is retentive when the knee is in extension.

According to a second variant of said way of making the prosthesis according to the invention, the insert cavity is not retentive in extension, so as to allow distal clearance of the femoral implant with respect to the tibial implant.

The serum head block implemented in this embodiment of the prosthesis according to the invention can be fixed to the tibial plane by means of a Morse cone type fixing completed by a screw, in association with an anti-rotation protrusion.

The fixing screw of said block on the tibial plane also allows the fixing of an intermidullary wedge to said plane, the said wedge being of a shape and size suitable for the patient's anatomy and the quality of the bone material.

the fixing of the wedge to the tibial plane is then equally ensured by a fixing of the Morse cone type completed by an anti-rotation protrusion.

The prosthesis according to the invention offers the advantage, compared to the prostheses known to the present, of presenting a perfect congruence between the meniscal element and the condyles for flexion and between the meniscal element and the tibial plane for rotation.

This offers the additional advantage of allowing to considerably reduce the number of pieces necessary for a surgical intervention since it does not require femoral implants of different sizes and meniscal elements that differ only in thickness.

The prosthesis according to the invention also makes it possible to limit the instrumentation, especially since it only requires a single cutting guide, due to the fact that, whatever the size of the femoral implant, the anchoring blocks of the latter are equidistant while the rear section and the bevel are the same, only the height of the front section being variable.

In the simplest configuration of the prosthesis according to the invention, the dimensions and shape of the lower cavity of the meniscal element are different from those of the truncated cone protrusion of the tibial plane, which allows a displacement of said meniscal element on the tibial plane, while retaining a perfect congruence of the meniscal element with the condyles on one side and with the tibial plane on the other side.

The stability from behind of the prosthesis according to the invention is obtained by using a meniscal plane whose lower cavity is of size and shape corresponding to the truncated cone protrusion of the tibial plane, which does not authorize the rotation of the meniscal element around said protrusion.

In the case of a recovery prosthesis, that is, comprising a ball head block and an insert, the joint is made on one side between the condyles and the meniscal element and on the other side between the ball head and the insert.

The choice of the insert cavity, retention or not, depends on the state of the ligaments, a retention cavity allowing the insert and the spherical head to act as a patella, preventing any leakage. The advantages and characteristics of the present invention will derive more clearly from the following description and which refers to the accompanying drawings, which represent several non-limiting embodiments.

In the attached drawings:

- Figure 1 represents a face view of a prosthesis of the invention, in a 90 ° flexion position, on which several femoral implants of different sizes are represented;

Figure 2 represents a profile view of the same prosthesis; Figure 3 shows a front view of a representation of several superimposed femoral implants of the same prosthesis;

Figure 4 shows the same representation in profile view; Figure 5 represents a top view of a meniscal element of a prosthesis according to the invention;

Figure 6 represents a top view of a variant of the same meniscal element;

figure 7 represents an exploded rear view of a prosthesis according to the invention in its invention stabilized from behind;

- figure 8 represents a profile and exploded view, with partial cuts, of the same prosthesis.

figure 9 represents a profile view, with partial cuts, of the same prosthesis in an extended position;

Figure 10 represents a profile view with partial cuts of the same prosthesis in a 90 ° flexion position;

Figure 1 1a represents a plan view of a meniscal element of the prosthesis shown in Figure 7;

- figure 1 1 b represents a view of a tibial plane equipped with this same meniscal plane;

Figure 11c represents a plan view of the same tibial plane equipped by the same meniscal plane in a different position;

- Figures 12a and 12 b respectively represent a profile view and a plan view of a first way of making the wedge of the tibial implant of the prosthesis according to the invention;

- Figures 13a and 13 b respectively represent a profile view and a plan view of a second way of making the wedge of the tibial implant of the prosthesis according to the invention;

Figures 14a and 14b respectively represent a rear view and a plan view of a third way of manufacturing the wedge of the tibial implant of the prosthesis according to the invention;

- Figure 15 represents a profile view of a cutting guide allowing the installation of a prosthesis according to the invention;

- figure 16 represents a face view of the same cutting guide.

If reference is made to figures 1 and 2, it can be seen that a prosthesis according to the invention comprises a bicondylar femoral implant 1, a wedge-shaped tibial base 2 20 and a meniscal element 3.

The femoral implant 1 includes two condyles 10 and 1 1 separated by an intercondylar recess 12 and prolonged by a trochlea 13.

The supporting faces 14 and 15 of the condyles, 10 and 11 respectively, have a certain curvature in the longitudinal direction and another in the transverse direction, these curvatures being of constant and identical radius R, so that the supporting faces 14 and 15 are spherical segments of centers a and b respectively.

Figures 3 and 4, where superimpositions of 3 femoral implants 1 of different sizes are shown, allow us to better understand that the supporting surfaces 14 and 15 of the condyles, 10 and 11 respectively, are, whatever the size of the femoral implant. 1 of the spherical sectors of two spheres A and B of centers a and b respectively.

The meniscal element 3, placed on the plane 21 of the tibial base 2, comprises in its upper face 30 two spherical cavities 31 and 32 of the same radius R, intended to receive the condyles, respectively 10 and 1 1, in sliding support. perfect congruence of the condyles 10 and 1 1 with the meniscal element 3, whatever the angle of flexion.

Figures 1 and 2 show 4 femoral implants I of increasing sizes. This difference in size results in an enlargement of the trochlea 13 and of the condyles 10 and 11 by means of external lateral extensions, respectively 17 and 18, while the distance that separates the centers a and b of the spherical segments that form the supporting faces 14 and 15, remains the same regardless of the size of the femoral implant 1, which allows the same meniscal implant 3 to be used.

It will also be noted that the anchoring blocks 10 'and 11 of the femoral implant 1 are, whatever the size of the latter, of identical spacing and positions, and that the posterior section and the necessary chamfer are the same, and that only the height of the front section varies, which will be described more precisely in Figures 15 and 16.

By way of example, the installation of a current prosthesis requires for a patient of a given size, four femoral implants of different sizes, a tibial implant and meniscal implants of the corresponding dimensions and in five different thicknesses, i.e. a total of 25 pieces, while a prosthesis according to the invention requires only 10 pieces, ie four femoral implants, a tibial implant and 5 meniscal elements which differ only in thickness. On the other hand, it can be seen in figures I and 2 that the tibial plane 21 comprises above in its central anterior region a truncated cone protrusion 22 which allows both to fix the meniscal element 3 and to limit its displacement, according to the dimensions. transversal and the shape of the cavity 36 made in the meniscal element 3 and in which the truncated cone protrusion 22 is housed, as shown in Figures 5 and 6.

Figure 5 represents a meniscal element 3 whose cavity 36 is of a shape and size corresponding to the truncated cone protrusion 22, so that the movement of the meniscal element 3 on the tibial plane 21, not shown, is limited to rotation, for example for a prosthesis stabilized from behind.

Figure 6 represents a meniscal element 3 whose cavity 36 is larger than that in the truncated cone protrusion, which allows the translation of the meniscal element 3 on the tibial plane 21, not shown.

It can also be seen in Figures 1 and 2 that the meniscal element 3 comprises, above the front part of the recess 33, a bearing 34 representing an inclined plane 35 above, against which the base 19 of the trochlea 13 rests. at the bottom of the intercondylar recess 14 when the knee is in extension, in order to prevent any anterior sliding.

If reference is still made to figures 7 and 8, it can be seen that, in the case of a shoot, a block 4 is fixed on the plane 21 of the tibial base 2, the end of which is provided with a spherical head 40.

The block 4 is fastened to the plane 21 on the one hand by inserting a front extension 41 of the block 4 on the truncated conical projection 22 of the plane 21 which internally comprises for this effect a truncated cone cavity 42 and on the other hand by means of a screw 43 tightened in a threaded hole 23 which also allows the fixing of the wedge 20 which is compared.

In order to avoid the rotation of the wedge 4, a protrusion 44, coming out under the block 4, is introduced into a hole 25 made in the upper face 24 in the plane 21 in its rear central region.

It should be noted that the plane 21 may not include the hole 25, in which case the projection 44 is positioned at the rear end of the block 4 and is inscribed in the recess of the plane 21 in order to prevent the rotation of the block 4.

The meniscal element 3, as can be seen more precisely in figures 1 1a, 1 1 b and 1 1c, includes a rear central recess 33 allowing the passage of the block 4 and separating the two spherical cavities 31 and 32.

The recess 33 is such that there is a certain play between the block 4 and the meniscal element 3, so that the latter can slide on the plane 21 and rotate around the extension 41 with a degree / of freedom of the order of 10 ° , as this is represented in the figure

1 1 c.

In Figures 7, 8, 9 and 10, it can be seen that between the condyles 10 and 11 of a femoral implant Γ, with respect to the intercondylar recess 12, an insert 5 comprising a hemispherical cavity is introduced and fixed by suitable means not shown 50 intended to house the spherical head 40 of the block 4, the center c of this hemispherical cavity 50 being aligned with the centers of the spherical segments which form the bearing surfaces 14 and 15 of the condyles 10 and 11.

As can be seen from Figure 5, the cavity 50 is not retentive, that is, the introduction of the spherical head 40 is made in the axis of the femoral implant Γ, so that there can be a play of the stal in extension.

However, in a variant, not shown, the cavity 50 is retentive in extension, i.e. the spherical head 40 is introduced posteriorly into the cavity 50 when the knee is in flexion, so that the head 40 and the insert 5 act as a patella , maintaining the femoral implant Γ and the tibial implant 2, which is possible due to the alignment of centers a, b and c.

The configuration of the prosthesis must be improved by choosing a wedge that is better suited to the patient's anatomy and the state of the bone material.

The choice of the wedge can be made from those shown in figures 12a, 12b, 13a, 13b, 14a and 14b.

In these figures it can be seen that the fixing of the wedges 200, 201 and 202 to the tibial plane 21. visible only in figure 12a, it is realized by embedding of the Morse cone type completed by a tightening screw and by an antirotating projection 203.

Figures 12a and 12b show a wedge 200 with a generally square cross section, comprising laterally longitudinal ribs 204.

In figures 13a and 13 b you can see a wedge 201 with a round cross-section of decreasing diameter from top to bottom and whose surface is streaked with grooves 205, not shown in figure 13a, whose depth is constant.

Figures 14a and 14 b show a wedge 202 comprising a sensibly cylindrical body 206 comprising three radial fins, two side wings 207 and a rear wing 208, the side wings 207 each making an angle of 70 with the rear wing 208 °, the wings 207 and 208 being of decreasing width from top to bottom, the rear wing 208 being less wide than the side wings 207.

Finally, if you refer to figures 15 and 16, you can see a cutting guide 6 that allows you to make the anterior and posterior sections and the chamfer for installing the femoral implant 1 whatever the size of the latter, different sizes being represented in Figure 15.

The cutting guide 6 comprises on one side two positioning stems 60 and 61, where holes allow the insertion of nails, intended to be inserted into the bores provided to house the anchoring blocks 10 'and 11 of the femoral implant 1, and on the other hand, to guide the saw, slots 62, 63 and 64 for the posterior cut and bevels, and three slots 65, 66 and 67 for the anterior cut for three femoral implant sizes 1, the upper edge 68 serving driving for a fourth size.

Claims (14)

CLAIMS 1. Sliding knee prosthesis comprising a femoral implant, a tibial implant and a meniscal element, characterized on the one hand by the fact that the meniscal element (3) comprises two spherical supporting cavities (31, 32), and on the other hand partly due to the fact that the femoral implant (1) includes two condyles (10, 1 1) whose supporting faces (14, 15) are spherical segments of distinct centers (a, b) and of equal radius (R) to that of the spherical cavities (31, 32), the said centers (a, b) being spaced, whatever the size of the said femoral implant (I), by the same distance, allowing the meniscal element (3) to be, with the exception of the thickness, of constant dimensions regardless of the size of the femoral implant (I). 2. Prosthesis according to claim 1, characterized by the fact that the anchoring blocks (10 ', 11') of the femoral implant (I) have identical spacing and positions whatever the size of the said femoral implant (1). 3. Prosthesis according to claim 1 or claim 2, characterized in that the anterior section and the chamfers necessary for the implementation of the femoral implant (1) are identical whatever the size of the said femoral implant (1), only the height of the anterior section being variable. 4. Prosthesis according to any one of the preceding claims, characterized in that the meniscal element (3) comprises on its upper face, in its central anterior region, a cushion (34) having an upper inclined plane (35) against which it is to take hold, when the knee is in base extension (15) of the trochlea (13) at the end of the intercondylar recess (12). 5. Prosthesis according to any one of the preceding claims characterized in that the tibial plane (21) comprises on its upper flat face (24) a truncated cone protrusion (22) intended to be housed in a cavity (36) made in the lower flat face (30 ) of the meniscal element (3). 6. Prosthesis according to claim 5, characterized in that the dimensions of the cavity (36) of the meniscal element (3) are greater than the dimensions of the truncated cone protrusion (22) of the tibial plane (21), so as to allow free movement sliding of said meniscal element (3) on said tibial plane (21). 7. Prosthesis according to claim 5, characterized in that the shape and dimensions of the cavity (36) of the meniscal element (3) correspond to the shape and dimensions of the frusto-conical projection (22) of the tibial plane (21), so not to allow the rotation of said meniscal element (3) on said tibial plane (21). Prosthesis according to any one of claims 1 to 4, characterized in that on the one hand a block (4), the end of which is provided with a spherical head (40), is fixed on the tibial plane (21) in the central region posterior of this, the center (c) of said spherical head (40) being aligned with the centers (a, b) of the spherical segments constituting the supporting surfaces (14, 15) of the condyles (10, 11); on the other hand, the "leniscal plane (21), subject to the said tibial plane (21), is hollowed out centrally to allow the passage with play of the said block (4); and on the other hand an insert (5), comprising a hemispherical cavity (50) in which the spherical head (40) of said block (4) takes place, without play, is introduced and fixed in the femoral implant (Γ ) between the two condyles (10, 1 1) compared to the high intercondylar indentation (12). 9. Prosthesis according to claim 8, characterized by the fact that the cavity (50) of the insert (5) is retentive when the knee is in extension, the spherical head (40) being introduced posteriorly into the insert (5). 10. Prosthesis according to claim 8, characterized in that the cavity (50) of the insert (5) is not retentive when the knee is in extension so as to allow distal play, the spherical head (40) being introduced into said insert (5) along the axis of the femoral implant (Γ). 1 1. Prosthesis according to any one of claims 8, 9 and 10, characterized in that the block (4) is fixed to the tibial plane (21) by means of an assembly of the Morse cone type completed by a screw (43), associated with a projection (44) anti-rotation. Prosthesis according to any one of claims 8 to 11, characterized in that the recess (33) of the meniscal element (3) is of such dimensions that there is a certain play between the block (4) and the meniscal element (3), so that said meniscal element (3) can slide on the tibial plane (21) and rotate around the block (4) with a degree of freedom of the order of 10 °. 13. Prosthesis according to any one of the preceding claims, characterized in that the wedge (200, 201, 202) of the tibial implant (2) is fixed to the tibial plane (21) by means of a Morse cone type assembly completed by a screw clamp and an anti-rotation projection (203). 14. Cutting guide allowing the installation of the femoral implant (I) of the prosthesis according to any one of claims I to 7, characterized in that it comprises two positioning shanks (60, 61) and slots (62, 63, 64) for guiding a saw for making the posterior cut and bevels, and slots (65, 66, 67) for guiding the saw for making the anterior cut according to the size of said femoral implant (1).