DE102008017394B4 - knee replacement - Google Patents

Abstract

Knee endoprosthesis with a tibial component, with a femoral component having two condylar surfaces and with a meniscus part arranged between the femoral component and the tibial component, which has on its upper side two bearing shells for receiving and supporting the condylar surfaces of the femoral component and which has on its underside a meniscal bearing surface displaceable on one Tibial bearing surface rests on the upper side of the tibial component, wherein the meniscal bearing surface and the tibial bearing surface offset from their center in medial or lateral direction each having a projection or a recess and wherein the projection on one of the two bearing surfaces in the recess of the other Bearing surface immersed and thereby forms a storage of the meniscal component on the tibial component, and with adjoining support areas in the lateral or medial part of the two bearing surfaces, characterized in that the projection (15) and the recess (16) are formed crowned and thereby forms a ball-bearing-like mounting of the meniscal component (8) on the tibial component (2) and that the support regions (17, 21) are curved in dorsal-ventral direction and there ...

Description

The The invention relates to a knee endoprosthesis with a tibial component, with one having two Kondylenflächen Femoral and with an arranged between femoral part and tibia part Meniscus part, which on its upper side two cups for Acquisition and storage of the condylar surfaces of the femoral component and which has on its underside a meniscus bearing surface which is displaceable on a tibial bearing surface rests on the top of the tibial component, the meniscal bearing surface and the tibial bearing surface across from their middle in the medial or lateral direction offset respectively a projection or a return and wherein the projection on one of the two bearing surfaces in the return the other storage area dips and thereby storage of the meniscal component on the tibial component forms, and with adjoining support areas in the lateral or medial part of the two storage areas.

In the US 6,013,103 a knee endoprosthesis is described in which the tibial bearing surface is flat and rests on the flat top of the tibial, the displacement of the meniscal component relative to the tibial is done as a pure parallel displacement of the meniscal component parallel to the plane of the tibial bearing surface and the top of the tibial component. Even with unicondylar knee endoprostheses, it is known to support a meniscal component, which in this case has only one bearing shell for the bearing of a femoral condyle, with a flat meniscal bearing surface on a likewise flat tibial bearing surface ( EP 1 584 309 A1 ).

In knee endoprostheses of this type, the meniscal component relative to the tibial component can be moved in different directions and also rotated who, the rotation is usually around the middle of the meniscal component. For this purpose, partly peg-shaped guides are provided ( US 6,013,103 ). However, it is also known to mount the meniscal component on the tibial component in such a way that it is rotated about an axis of rotation which is offset in the medial direction in relation to the middle of the meniscal component ( US 6,013,103 ). To achieve this, special guides must be provided for the meniscal component on the tibial component, for example lateral walls.

A generic knee endoprosthesis is in the WO 03/028586 A2 described. In this, the bearing surfaces are flat.

In In practice it has been found that with knee endoprostheses this Although the anatomical conditions are modeled quite well can be it can But difficulties arise because of this special Construction of the achievable diffraction angle between the femur and Tibia is limited, as the meniscus part, which is opposite to the Tibial component moved only in one plane, limiting the movement of the bones, at strong diffraction angles can bang the bones on the meniscus part, so that thereby the bending angle is limited.

It The object of the invention is to design a generic knee endoprosthesis in such a way that that they are at an optimal replication of anatomical features the healthy knee joint in particular also a high diffraction angle allows.

These Task is a knee endoprosthesis described above Type according to the invention thereby solved, that the projection and the return are crowned are formed and thereby a ball-bearing-like storage of Meniscus part on the tibial part forms and that the support areas are curved in dorsal-ventral direction and there a radius of curvature have at least a factor of 2.5 greater than the radius of curvature of the crowned projections and recesses.

at Such a configuration form the ball bearing into each other gripping projections and recesses of the Meniscus part and the tibial part a ball-bearing-like storage, by the rotation of the meniscal component on the tibial component a rotation axis is defined, which in the medial or lateral direction opposite to the Offset mid-meniscus part, also allows this ball-bearing-like Storage also in addition to the rotation of the meniscal component relative to the tibial component a pivoting of the meniscal component on the tibial component, the pivot axis runs thereby in the medial-lateral direction and thus substantially perpendicular to the axis of rotation formed by the ball bearing-like bearing, in turn, substantially parallel to the tibial longitudinal axis is arranged. By this pivoting, the meniscus part both in ventral and dorsal direction on its outer edges be lowered, thereby reducing the risk that the meniscus part the flexion of the femur towards the tibia even at large diffraction angles hindered, d. H. there will be larger diffraction angles possible. At the same time it is achieved that the meniscus part in one rotation about an axis that is substantially parallel to the tibial longitudinal axis runs, is rotated about a pivot point, which is opposite the middle of the meniscus part is offset in the medial or lateral direction and thus the anatomical Conditions of the healthy knee joint or the requirements of the individual ligament apparatus largely corresponds.

By the construction features described so there is a multi-dimensional movement possibility for the meniscus part, beyond the pure parallel displacement in a plane goes out and also ensures in a relatively simple manner a defined rotation about a lying outside the center of rotation. The ball-bearing-like storage of meniscal component and tibial component not only allows rotation about this axis of rotation running parallel to the longitudinal axis of the tibia, but also pivoting about the pivot axis extending transversely thereto in the medial-lateral direction, wherein the ball-bearing-like mounting is retained in each case.

The Twisting and pivoting of the meniscus part in relation to the Tibia part is done by the way in that during the pivoting of the femur the condyle surfaces of the Femur rolled in the cups at the top of the meniscus part and be shifted, the condylar surfaces exert lateral forces the meniscus part, which the Meniskusteil opposite the Moving the tibia part and inevitably twisting and turning it. In particular receives in this way also in the flexion of the femur towards the Tibia is a rotation of the tibia about the longitudinal axis, which is characterized shows that the meniscus part is rotated about the ball bearing-like storage. This also corresponds to the anatomical conditions of the natural Knee joint.

By the larger radius of curvature the support areas across from the radius of curvature the crowned protrusions and returns is ensured that meniscal component and the tibial component in the area of projections and returns theirs retained ball-bearing-like storage when the meniscus part opposite Tibia part is moved, making this shift into a twist and pivoting of the meniscal component towards the tibial component, the storage in the area of the projections and recesses is retained.

It can be provided that the support areas curved only in dorsal-ventral direction, but across it Not. this leads to however, that when twisting the meniscus part against the Tibialil a full-surface Installation of the support areas no over the entire range of rotation can be ensured, such all-over Plant can only be reached in certain angular ranges.

A better match the contact surfaces the support areas let yourself reach, if according to a preferred embodiment provided is that the support areas the two storage areas are also curved in lateral-medial direction. Besides, has such a design still has a stabilizing effect, because of the extra curvature the support areas in lateral-medial direction of the lateral displacement of the meniscal component across from the tibial component is counteracted in lateral-medial direction.

at a first preferred embodiment is provided that the support areas in the lateral part the two storage areas Parts of a sphere surface are whose radius is at least by a factor of 2.5 greater as the radius of the crowned projections and recesses, with the centers the crowned protrusions across from the middle of the storage areas in the medial or lateral direction and the center of the spherical surface then offset in the lateral or medial direction. at the training of Stützbe rich as a spherical surface can be a largely flat Installation of the support areas via a larger angular range approach, However, even in this case is not over the entire range of rotation the Meniskusteils such a flat system in large areas to ensure.

It is therefore cheap, if according to one another preferred embodiment the support areas along one or multiple lines that intersect as a line of two cylindrical surfaces result, namely a vertical cylindrical surface, whose central axis passes through the center of the convex projections and recesses and is substantially parallel to the tibial axis, and a horizontal cylindrical surface, the central axis through which in the dorsal-ventral direction running curvature defined center passes and essentially in medial-lateral Direction runs. If the support areas are formed in this way, also results in rotation of the Implant part opposite the tibial component about an axis of rotation, with the central axis of the vertical Cylinder surface coincides over a larger angular range a full-surface Installation of support areas, so that also the surface pressure and thus the abrasion can be reduced.

at a particularly preferred embodiment is provided that the projections and recesses and the support areas essentially to a common horizontal plane of the meniscal component rich, ie end at about the same height of the meniscus part.

The ball-bearing support of the meniscal component on the tibial component, which is achieved by recesses and projections engaging therein, may comprise both a projection on the meniscal component and a corresponding recess on the tibial component and a projection on the tibial component and a corresponding return on the meniscal component, so here there is a reversal possible. The same applies to the curvature of the support areas in the lateral-medial direction, this curvature can be formed so that the support area on the tibial component is curved upwards or downwards, while then of course the Vaulting in the lateral-medial direction in the meniscal component is opposite.

The curvature the support areas in ventral-dorsal direction, however, must always be chosen so that the Meniskusteil when pivoting in the ventral direction the Lowering the ventral outer edge and when pivoting in a dorsal direction, the dorsal outer edge, d. H. this curvature needs always run so that the center of curvature below the storage area is arranged between the meniscal component and the tibial component.

The following description of preferred embodiments of the invention used in conjunction with the drawings for further explanation. Show it:

1 a perspective schematic view of a tibial component and a spaced meniscus part in a viewing direction on the top of the tibial component;

2 : a view similar 1 looking at the underside of the meniscal component;

3 a perspective view of the underside of the meniscal component;

4 a side view of the meniscus part with a cylindrical surface for illustrating the curvature of the support region of the meniscal component in the dorsal-ventral direction;

5 FIG. 2: a perspective top view of the meniscus part with the cylindrical surface of the 4 and additionally, a cylindrical surface of a vertical cylinder coaxial with the rotational axis of the meniscal component opposite the tibial component;

6 : a perspective view of the meniscus part of the 5 from the underside thereof with representation of the two cylindrical surfaces of 5 ;

7 a sectional view of the meniscus part of 3 along line 7-7 in 3 and

8th a sectional view taken along line 8-8 in FIG 3 ,

In the 1 illustrated knee endoprosthesis 1 includes a tibial component 2 with a stalk 3 for fixing the tibial component 2 on a tibia and with a storage area 4 Serving top, continues to be a femur 5 attached to the distal end of a femur with two adjacent convex condylar surfaces 6 . 7 and one between the tibia part 2 and the femdom 5 arranged meniscus part 8th , which on its upper side two juxtaposed bearing shells 9 . 10 in which the Kondylenflächen 6 . 7 dip, and with a meniscus storage area 11 at the bottom of the meniscus part 8th ,

The condylar surfaces 6 . 7 can in the bearing shells 9 . 10 be moved so that on the one hand a pivoting of the femur against the tibia is possible and on the other hand to a certain extent a lateral displacement of Kondylenflächen 6 . 7 in the longitudinal direction of the bearing shells 9 . 10 , this allows a combined rolling-sliding movement between meniscus part 8th on the one hand and femdom 5 on the other hand. As the training of the bearing shells 9 . 10 and the condylar surfaces 6 . 7 is not of primary importance for the present invention, the bearing shells 9 . 10 and the feminine judgment 5 with the condylar surfaces 6 . 7 only in 1 shown, in the following figures, the representation is limited to the meniscus part 8th and the tibia part 2 (without handle), here are the bearing shells 9 . 10 on the top of the meniscus part 8th not shown, but the top of the meniscal component 8th is just shown, but in fact is of an embodiment according to the representation of 1 with cups 9 . 10 to go out at the top.

Both the tibia part 2 as well as the meniscus part 8th are substantially U-shaped with two adjacent side panels 12 . 13 and a connecting this web-shaped intermediate part 14 , The tibial bearing surface 4 points in the medial side part 12 on its upper side a spherical projection 15 on, the center of the spherical projection 15 is opposite the middle of the tibia part 2 between the two sides 12 . 13 lies in the medial direction and is located approximately in the middle of the medial side part 12 , the radius of the spherical projection 15 is in the range between 20 mm and 30 mm, preferably in the range between 22 mm and 26 mm.

In the medial side part 12 of the meniscal component 8th is one to the projection 15 complementary return 16 into the lead 15 dips when the meniscus part 8th directly on the tibia part 2 rests. As a result, a ball-bearing-like storage between the tibia part 2 on the one hand and the meniscus part on the other 8th on the other hand trained. By this storage can once the meniscus part 8th be rotated about an axis of rotation which is substantially parallel to the tibial longitudinal axis and thus substantially perpendicular to the top of the meniscal component 8th is arranged. However, it is also possible by this ball-bearing-like storage to pivot the meniscal component relative to the tibial component, for example, about a pivot axis extending in the medial-lateral direction.

In the area of the lateral side part 13 is the top of the tibia part 2 as a support area 17 educated. In this support area has the tibial bearing surface 4 a curved contour, and that is this support area 17 curved both in the anterior-posterior direction and in the medial-lateral direction. In both cases, the curvature is selected in the embodiment shown in the drawing so that the centers of curvature below the support area 17 lie, the radius of curvature is relatively large in both curvatures, in the illustrated embodiment, the radius of curvature in ventral-dorsal direction is about 2.5 times larger than the radius of curvature of the spherical projections 15 and returns 16 , In lateral-dorsal direction is the radius of curvature of the support area 7 for example by a factor of 2.5 to 3 greater than the radius of curvature of the projection 15 and the return 16 ,

The exact contour of the support area 17 may be chosen differently, for example, the curvatures in ventral-dorsal direction may be the same as the curvatures in the medial-lateral direction, so that one essentially a spherical support area 17 receives. But it is also possible that the support area 17 has the shape of a torus, but a torus whose longitudinal axis is additionally curved in the circumferential direction out of the plane, as corresponds to the curvature in anterior-dorsal direction.

In the embodiment shown in the drawing is a special form of the support area 17 selected. This support area 17 is namely spanned by a variety of cutting lines 18 resulting from the penetration of two cylinders, namely a vertical cylinder 19 and a horizontal cylinder 20 ,

The vertical cylinder 19 has a longitudinal centerline passing through the highest point of the projection 15 passes and extends substantially parallel to the longitudinal axis of the tibia, this axis forms the axis of rotation of the meniscal component 8th opposite the tibia part 2 when these parts are twisted against each other.

The horizontal cylinder 20 describes the curvature in dorsal-ventral direction, the longitudinal center line of the horizontal cylinder 20 runs in lateral-medial direction and the radius of the horizontal cylinder 20 corresponds to the radius of curvature of the curvature of the support area 17 in dorsal-ventral direction. Between the horizontal cylinder 20 and the vertical cylinder 19 with different radius results in a variety of cutting lines 18 , which then together the support area 17 build up.

The meniscus storage area 11 is complementary to the tibial bearing surface 4 formed, so that when planting the meniscus part 8th on the tibia part 2 a substantially full surface area once in the area of the projection 15 and the return 16 and secondly in the area of the support area 17 results in this support area 17 lies the meniscus part 8th with one to the support area 17 complementary support area 21 at this.

The storage described results in the exertion of horizontal forces on the meniscal component 8th the possibility for the meniscus part 8th , facing the tibia part 2 once, in the form of a rotation about the axis of rotation substantially coinciding with the central axis of the vertical cylinder 19 coincides, and on the other hand by pivoting the meniscus part 8th about a horizontal pivot axis, which is substantially perpendicular to the wall of the vertical cylinder 19 stands. In a middle position, this pivot axis thus extends substantially in the lateral-medial direction, with a rotation of the meniscal component 8th opposite the tibia part 2 This pivot axis is also rotated in accordance with the angle of rotation, and this leads to a substantially full-surface contact of the meniscal component on the tibial component even during a rotation. At the same time during this rotation, the meniscus part is pivoted about this pivot axis, so that the respective outer edge is lowered, and thereby the joint is given a margin for a larger diffraction angle.

The Rotation about the axis of rotation thus always takes place about an axis of rotation, the off-center is arranged and offset in the medial direction, the pivoting additionally forced out about a pivot axis that extends substantially horizontally and their angle opposite the medial-lateral Direction changes with the rotation angle of the meniscus part.

The forces that lead to a displacement of the meniscal component relative to the tibial component are essentially transmitted to the meniscal component by the remote judgment when the joint is flexed, that is, in particular, the condylar surfaces are transmitted 6 . 7 over the bearing shells 9 . 10 Such forces, which lead to a rotation and pivoting of the meniscal component relative to the tibial component.

The tibia part 2 and the feminine judgment 5 consist in a conventional manner normally of a biocompatible metal, such as titanium or a titanium alloy, while the meniscus part preferably consists of a sterilizable and biocompatible plastic, such as high density polyethylene. Due to the described shape of the bearing surfaces is a full-scale investment in the area between the tibia part and the Meniskusteil achieved, and this leads to the avoidance of force peaks and to reduce the wear of the adjacent bearing surfaces.

In the embodiment shown in the drawing, the projection 15 and the return 16 offset towards the center of the bearing surface in the medial direction, the support area, however, in the lateral direction. It is also possible in principle that a reverse arrangement is selected, then the projection 15 and the return 16 offset in the lateral direction and the support area 17 against it in the media direction. As a result, of course, the axis of rotation of the meniscus part 8th shifted accordingly. The more common case is the arrangement of the axis of rotation in the medial part of the bearing surface, but it may be necessary, in particular due to a change in the band structure, to displace the axis of rotation not in the medial direction but in the lateral direction relative to the center of the bearing surface.

Claims (5)

Knee endoprosthesis with a tibial component, with a femoral component having two condylar surfaces and with a meniscus part arranged between the femoral component and the tibial component, which has on its upper side two bearing shells for receiving and supporting the condylar surfaces of the femoral component and which has on its underside a meniscal bearing surface which is displaceable on one Tibial bearing surface rests on the upper side of the tibial component, wherein the meniscal bearing surface and the tibial bearing surface offset from their center in medial or lateral direction each having a projection or a recess and wherein the projection on one of the two bearing surfaces in the recess of the other Immersed bearing surface and thereby forms a storage of the meniscal component on the tibial component, and with adjoining support areas in the lateral or medial part of the two bearing surfaces, characterized in that the projection ( 15 ) and the return ( 16 ) are formed spherical and thereby a ball-bearing-like storage of the meniscal component ( 8th ) on the tibial component ( 2 ) and that the support areas ( 17 . 21 ) are curved in dorsal-ventral direction and there have a radius of curvature which is greater by at least a factor of 2.5 than the radius of curvature of the convex projections and recesses ( 15 . 16 ). Knee endoprosthesis according to claim 1, characterized in that the support areas ( 17 . 21 ) of the two storage areas ( 4 . 11 ) are also curved in the lateral-medial direction. Knee endoprosthesis according to claim 2, characterized in that the support areas ( 17 . 21 ) of the two storage areas ( 4 . 11 ) Are parts of a spherical surface whose radius is at least by a factor of 2.5 to 3 greater than the radius of the convex projections and recesses ( 15 . 16 ), the centers of the crowned protrusions ( 15 . 16 ) opposite the middle of the storage areas ( 4 . 11 ) are offset in the medial direction and the center of the spherical surface in the lateral direction. Knee endoprosthesis according to claim 2, characterized in that the support areas ( 17 . 21 ) along one or more lines extending as a line of intersection of two cylindrical surfaces ( 19 . 20 ), namely a vertical cylindrical surface ( 19 ) whose central axis through the center of the convex projections and recesses ( 15 . 16 ) and extends substantially parallel to the tibial longitudinal axis, and a horizontal cylindrical surface ( 20 ) whose center axis passes through the center defined by the curvature extending in the dorsal-ventral direction and extends substantially in the medial-lateral direction. Knee endoprosthesis according to one of the preceding claims, characterized in that the projections and recesses ( 15 . 16 ) and the support areas ( 17 . 21 ) substantially to a common horizontal plane of the meniscal component ( 8th ) pass.