Knee joint endoprosthesis

Abstract

Knee joint endoprosthesis (10) with a tibial component (16), a one-piece meniscal component (20) mounted on the tibial component (16), and a femoral component (14) cooperating with the meniscal component (20), the femoral component (14) comprising two femoral articulating surfaces (62, 64) and the meniscal component (20) comprising two meniscal articulating surfaces (58, 60), wherein one femoral articulating surface (62, 64) and one meniscal articulating surface (58, 60) are configured to interact with each other, wherein a posterior stabilizing device (70) with first and second cooperating stabilizing elements (72, 74) is provided, wherein the first stabilizing element (72) is arranged or formed on the meniscal component (20) between the meniscal articulating surfaces (58, 60), and wherein the second stabilizing element (74) is located on the femoral component (14) in the region of a posterior end (82) of the femoral articular surfaces (62,64) is arranged or formed between these, wherein the first stabilizing element (72) has a first concave stabilizing surface (92) pointing in a posterior direction, wherein the second stabilizing element (74) has a second convexly curved stabilizing surface (94) cooperating with the first stabilizing surface (92), characterized in that the meniscus component (20) is rotatably mounted on the tibial component (18) about an axis of rotation (36), that the tibial component (18) has a planar tibial gliding surface (30), that the meniscus component (20) has a planar meniscus gliding surface (34), and that the tibial gliding surface (30) and the meniscus gliding surface (34) are in contact with each other, that the axis of rotation (36) is perpendicular to the tibial gliding surface (30), that the first stabilizing element (72) is in the form of a stabilizing projection (76) is trainedwhich extends from a top surface (56) of the meniscal component (20) transversely to the meniscal gliding surface (34), and that the stabilizing projection (76) is arranged or formed in a posterior direction with respect to the axis of rotation (36), that the knee endoprosthesis (10) comprises a pivot bearing (38) for rotating the meniscal component (20) relative to the tibial component (14) about the axis of rotation (36), that the pivot bearing (38) comprises a guide element for the meniscal component (20), that the guide element projects beyond the tibial gliding surface (30), that the pivot bearing comprises a bearing bolt (40) with a cylindrical head (42) that can be screwed into the tibial component (18), and a head receptacle (54) formed on a bottom surface (32) of the meniscal component rotationally symmetrical to the axis of rotation (36) for positively engaging the head (42), and that the head (42) forms the guiding element.

Description

[0001] The present invention relates to a knee joint endoprosthesis with a tibial component, a meniscal component mounted on the tibial component, and a femoral component interacting with the meniscal component, which femoral component comprises two femoral articulating surfaces and which meniscal component comprises two meniscal articulating surfaces, wherein in each case a femoral articulating surface and a meniscal articulating surface are designed to interact with one another, wherein a posterior stabilizing device with first and second, interacting stabilizing elements is further provided, wherein the first stabilizing element is arranged or formed on the meniscal component between the meniscal articulating surfaces and wherein the second stabilizing element is arranged or formed on the femoral component in the region of a posterior end of the femoral articulating surfaces between these,wherein the second stabilizing element is arranged or formed on the femoral component in the region of a posterior end of the femoral joint surfaces between them, wherein the first stabilizing element has a first, concave stabilizing surface pointing in the posterior direction, wherein the second stabilizing element has a second, convexly curved stabilizing surface cooperating with the first stabilizing surface.

[0002] Knee replacements with a posterior stabilizing device are particularly useful when the posterior cruciate ligament is damaged or removed. The first stabilizing element in such a knee replacement typically forms a simple stop to prevent anterior movement of the femoral component when the knee is sharply flexed, the so-called "drawer effect." However, depending on its size, the first stabilizing element can impede patella movement. If the first stabilizing element is designed to be too delicate, it can break. If it is designed to be sufficiently stable, additional bone from the femur usually has to be removed. This, in turn, weakens the femur.

[0003] Furthermore, conventional knee joint prostheses have the disadvantage of limited flexion. Flexion angles between the femur and tibia greater than 130° are practically impossible. Particularly in cultures where people are accustomed to sitting cross-legged, a restriction of the knee's flexion angle through the implantation of a knee joint prosthesis represents a reduction in the patient's quality of life.

[0004] An artificial knee joint is known from US 2009 / 0 043395 A1. Modular knee joint endoprostheses are described in EP 1 374 805 A2 and US 5 370 699 A. DE 31 01 789 A1 relates to a knee joint prosthesis.

[0005] It is therefore an object of the present invention to improve a knee joint endoprosthesis of the type described above so that it has sufficient stability even at very large flexion angles.

[0006] This object is achieved according to the invention in a knee joint endoprosthesis of the type described above in that the meniscus component is mounted on the tibial component so as to be rotatable about a rotation axis, that the tibial component has a flat tibial sliding surface, that the meniscus component has a flat meniscus sliding surface and that the tibial sliding surface and the meniscus sliding surface abut one another, that the rotation axis runs perpendicular to the tibial sliding surface, that the first stabilizing element is designed in the form of a stabilizing projection which extends from an upper side of the meniscus component transversely to the meniscus sliding surface and that the stabilizing projection is arranged or designed offset in the posterior direction relative to the rotation axis, that the knee joint endoprosthesis comprises a pivot bearing for rotating the meniscus component relative to the tibial component about the rotation axis,that the pivot bearing comprises a guide element for the meniscus component, that the guide element protrudes beyond the tibial sliding surface, that the pivot bearing comprises a bearing pin with a cylindrical head that can be screwed into the tibial component and a head receptacle formed on an underside of the meniscus component rotationally symmetrically to the axis of rotation for positively receiving the head, and that the head forms the guide element.

[0007] Configuring the stabilization device in a knee joint endoprosthesis of the type described above in this way has the particular advantage that the first stabilizing element acts not only as a stop, but also as a guide for the femoral component, particularly at very large flexion angles. This allows flexion angles of more than 140°, and in particular more than 150°, to be achieved, which are necessary if, for example, one wishes to sit cross-legged. A knee joint endoprosthesis further developed according to the invention therefore enables a patient to practically maintain their quality of life after its implantation, as they do not have to forgo beloved habits. In principle, it would be conceivable to fix the meniscus component immovably to the tibial component.In order to replicate the mobility of a natural knee as closely as possible with the knee joint endoprosthesis, the invention provides for the meniscus component to be mounted on the tibial component so that it can rotate about a rotation axis. It is advantageous for the tibial component to have a flat tibial sliding surface, for the meniscus component to have a flat meniscal sliding surface, and for the tibial sliding surface and the meniscal sliding surface to bear against one another. Sliding surfaces designed in this way allow mobility with minimal surface pressure and therefore minimal wear. Abrasion, particularly of a meniscus component made of plastic, can thus be kept to a minimum. The design of the knee joint endoprosthesis is made particularly simple by the rotation axis running perpendicular to the tibial sliding surface. In this case, it also runs perpendicular to the meniscal sliding surface.To maximize translation of the femoral component in the posterior direction, it is advantageous for the stabilizing projection to be arranged or configured offset in the posterior direction relative to the rotation axis. In other words, it is arranged very far posterior to the meniscal component and thus allows rotation of the femoral component relative to the meniscal component, for example, around a center of rotation or around a rotation axis defined by the first stabilizing surface.

[0008] In order to achieve optimal guidance of the femoral component on the meniscal component, it is advantageous if the first stabilizing surface is inclined relative to the meniscal articular surface at an angle which lies in a range of approximately 70° to approximately 110°. In particular, the angle can be in a range of approximately 85° to approximately 95°. A first stabilizing surface oriented in this way not only forms a stop for the femoral component, in particular the second stabilizing element arranged on it, but also guides this element at the same time. In particular, this not only prevents movement of the femoral component in an anterior direction, but also supports movement in a posterior direction. Such a movement is also known as a "rollback".

[0009] According to a preferred embodiment of the invention, the first stabilizing surface can define a third meniscal articular surface, and the second stabilizing surface can define a third femoral articular surface. In other words, the two stabilizing surfaces form mutually corresponding or interacting articular surfaces, which, however, only perform their function above a certain flexion angle or at very large flexion angles.

[0010] A design of the femoral component can be simplified, for example, by having a cross-section of the second stabilizing element in a sectional plane defining a sagittal plane with a kidney-shaped or substantially kidney-shaped contour. In particular, the contour of the second stabilizing element and thus of the second stabilizing surface between the femoral joint surfaces can be constant or substantially constant in a medial-lateral direction. The kidney-shaped design also allows for a large contact area in every flexion position in which the two stabilizing surfaces are in contact with each other.

[0011] It is advantageous if the radius or radii of curvature of the second stabilization surface correspond to approximately 0.25 times to approximately 0.55 times the radius or radii of curvature of the femoral joint surfaces. Preferably, the radius or radii of curvature of the second stabilization surface correspond to approximately 0.3 times to approximately 0.5 times the radius or radii of curvature of the femoral joint surfaces. In this way, a non-concentricity of the radius centers of the second stabilization surface and the femoral joint surfaces can be achieved. This easily allows for the desired translation of the femoral component in the posterior direction, which is necessary to prevent the femur from striking the tibia, particularly the tibial component, so that significantly larger flexion angles between the tibia and femur can be achieved compared to conventional prostheses.

[0012] Advantageously, the first stabilizing element is designed in the form of a stabilizing projection that extends from an upper surface of the meniscal component transversely to the meniscal sliding surface. Of course, it can also be slightly inclined relative to the meniscal sliding surface. "Transverse" preferably means an inclination in a range between 75° and 105° between a longitudinal axis defined by the stabilizing projection and a plane defined by the meniscal sliding surface.

[0013] The knee joint endoprosthesis can be designed to be particularly compact if the stabilizing projection encompasses the first stabilizing surface.

[0014] The manufacture of the knee joint endoprosthesis can be simplified in particular by having the stabilizing projection comprise a posterior lateral surface facing in the posterior direction, and by having the posterior lateral surface comprise or define the first stabilizing surface. For example, the stabilizing surface can thus be easily formed directly on the stabilizing projection by machining.

[0015] According to a further preferred embodiment, it can be provided that the femoral component comprises a lateral and a medial condyle, each of which comprises one of the femoral articular surfaces, that anterior ends of the condyles are directly connected to one another, that posterior ends of the condyles are connected to one another via the second stabilizing element, and that the femoral component has a recess delimited by the condyles and the second stabilizing element, into which recess the first stabilizing element projects or engages. This configuration makes it possible, in particular, to design the femoral component as virtually open, i.e., without a structure closing the recess, also known as a so-called "box." As a result, only a minimal amount of bone needs to be removed from the femur to anchor the femoral component.

[0016] The femoral component is particularly easy to manufacture if the recess is designed as a through-hole. This allows machining of the femur to be limited to the absolute minimum.

[0017] It is advantageous if the first stabilizing element on the femoral component and the second stabilizing element on the meniscal component are arranged or configured in such a way that they only come into contact with each other at a predetermined contact angle, which corresponds to a flexion angle between the tibial component and the femoral component. In other words, the stabilizing device only becomes effective at a specific flexion angle, which corresponds to the contact angle. For small flexion angles, i.e., flexion angles smaller than the contact angle, guidance of the femoral component on the meniscal component is achieved exclusively by the interacting femoral and meniscal joint surfaces.At flexion angles greater than the contact angle, the effect of the stabilization device begins and the interacting stabilization elements can in particular support and / or cause a translational movement of the femoral component in the posterior direction.

[0018] The contact angle is advantageously in a range of approximately 60° to approximately 80°. Preferably, it is approximately 70°. In particular, the maximum flexion angle of the knee joint endoprosthesis can be increased by selecting the largest possible contact angle.

[0019] To ensure optimal guidance of the femoral component along the meniscal component with increasing flexion angles, it is advantageous for the first stabilizing element and the second stabilizing element to be in direct contact with each other for each flexion angle that is at least equal to the contact angle. This allows the femoral component to be guided directly along the meniscal component in a defined manner.

[0020] In order to minimize surface pressure and improve the overall stability of the knee joint endoprosthesis, it is advantageous if the first stabilizing surface and the second stabilizing surface lie flat or essentially flat against each other for each flexion angle which corresponds at least to the contact angle.

[0021] Furthermore, surface pressure between the stabilizing elements can be kept as low as possible if a first radius of curvature of the first stabilizing surface and a second radius of curvature of the second stabilizing surface correspond or substantially correspond to one another. In particular, a planar or substantially planar contact of the two stabilizing surfaces can be achieved.

[0022] It is advantageous if the first stabilizing surface is designed in the form of a hollow spherical or substantially hollow spherical surface. Such a first stabilizing surface can, in particular, lead to a rotation in the lateral and / or medial direction of the femoral component on the meniscal component.

[0023] In order to enable at least partially guided rotation of the femoral component and the meniscal component laterally or medially, it is advantageous if the first stabilization surface defines a center of rotation.

[0024] Advantageously, the center of rotation is offset posteriorly relative to the first stabilizing element. This allows for defined rotation, which can also simultaneously cause translation of the femoral component in the posterior direction.

[0025] To best absorb forces acting parallel to the meniscal gliding surface on the first stabilizing element, it is advantageous if the distance between the center of rotation and the meniscal gliding surface is smaller than the distance between a free end of the first stabilizing element and the meniscal gliding surface. This further supports translational movement of the femoral component in the posterior direction with increasing flexion angles, especially at very large flexion angles.

[0026] Furthermore, it may be advantageous if the first stabilizing surface is designed in the form of a hollow cylindrical or substantially hollow cylindrical surface. A first stabilizing surface shaped in this way makes it possible to specify a rotation about a rotation axis running in a lateral-medial direction and, particularly when a radius of curvature of the first guide surface is smaller than a radius of curvature of the femoral joint surfaces, supports an eccentric movement of the femoral component relative to the meniscal component in order to move it in a posterior direction, particularly at very large and increasing flexion angles.

[0027] The first stabilizing surface can be designed particularly easily if it defines a rotation axis. For example, it can form a section of a hollow cylindrical surface.

[0028] To ensure that the femoral component is guided along the meniscal component, especially at very large flexion angles, it is advantageous if the rotation axis is offset posteriorly relative to the first stabilizing element. For example, the rotation axis can even be positioned posterior to the meniscal component.

[0029] It is also advantageous if the distance between the rotation axis and the meniscal sliding surface is smaller than the distance between a free end of the first stabilizing element and the meniscal sliding surface. Such a configuration allows, in particular, optimal guidance of the femoral component on the meniscal component, whereby, in particular, a lifting of the femoral component from the meniscal component at very large flexion angles can be prevented or substantially prevented.

[0030] The meniscal component is particularly easy to form when the rotation axis runs parallel to the meniscal sliding surface. It can then be machined, for example, with a milling cutter.

[0031] In order to simulate the most natural knee movement possible with the knee joint endoprosthesis, it is advantageous if the axis of rotation runs in a medial-lateral direction.

[0032] The above description therefore includes in particular the embodiments of knee joint endoprostheses defined in the following numbered sentences: 1. Knee joint endoprosthesis (10) with a tibial component (16), a meniscal component (20) mounted on the tibial component (16) and a femoral component (14) cooperating with the meniscal component (20), which femoral component (14) comprises two femoral articulation surfaces (62, 64) and which meniscal component (20) comprises two meniscal articulation surfaces (58, 60), wherein in each case a femoral articulation surface (62, 64) and a meniscal articulation surface (58, 60) are designed to cooperate with one another, wherein furthermore a posterior stabilization device (70) with first and second cooperating stabilization elements (72, 74) is provided, wherein the first stabilization element (72) is arranged or formed on the meniscal component (20) between the meniscal articulation surfaces (58, 60) and wherein the second stabilization element (74) on the femoral component (14) is arranged or formed in the region of a posterior end (82) of the femoral articular surfaces (62, 64) between them,characterized in that the first stabilizing element (72) has a first, concave stabilizing surface (92) pointing in the posterior direction and that the second stabilizing element (74) has a second, convexly curved stabilizing surface (94) cooperating with the first stabilizing surface (92). 2. Knee joint endoprosthesis according to sentence 1, characterized in that the meniscus component (20) is mounted on the tibial component (18) so as to be rotatable about an axis of rotation (36). 3. Knee joint endoprosthesis according to sentence 1 or 2, in that the tibial component (18) has a flat tibial sliding surface (30), in that the meniscal component (20) has a flat meniscal sliding surface (34) and in that the tibial sliding surface (30) and the meniscal sliding surface (34) abut one another. 4. Knee joint endoprosthesis according to sentence 3, characterized in that the axis of rotation (36) runs perpendicular to the tibial sliding surface (30). 5. Knee joint endoprosthesis according to one of the preceding sentences, characterized in that the first stabilizing surface (92) is inclined by an angle (120) relative to the meniscal articular surfaces (58, 60), which angle (120) lies in a range of approximately 70° to approximately 110°. 6. Knee joint endoprosthesis according to one of the preceding sentences, characterized in that the first stabilizing surface (92) defines a third meniscal articular surface (122) and that the second stabilizing surface (94) defines a third femoral articular surface (124). 7. Knee joint endoprosthesis according to one of the preceding sentences, characterized in that a cross section of the second stabilizing element (74) in a sectional plane defining a sagittal plane has a kidney-shaped or substantially kidney-shaped contour (84). 8. Knee joint endoprosthesis according to one of the preceding sentences, characterized in that a radius of curvature or radii of curvature (112, 114) of the second stabilizing surface (94) corresponds approximately to 0.25 times to approximately 0.55 times a radius of curvature (116) or radii of curvature of the femoral joint surfaces (62, 64), preferably approximately 0.3 times to approximately 0.5 times. 9. Knee joint endoprosthesis according to one of the preceding sentences, characterized in that the first stabilizing element (72) is designed in the form of a stabilizing projection (76) which extends from an upper side (56) of the meniscal component (20) transversely to the meniscal sliding surface (34). 10. Knee joint endoprosthesis according to sentence 9, characterized in that the stabilizing projection (76) comprises the first stabilizing surface (92). 11. Knee joint endoprosthesis according to sentence 9 or 10, characterized in that the stabilizing projection (76) comprises a posterior side surface (77) pointing in the posterior direction and that the posterior side surface (77) comprises or defines the first stabilizing surface (92). 12. Knee joint endoprosthesis according to one of the sentences 9 to 11, characterized in that the stabilizing projection (76) is arranged or formed offset in the posterior direction relative to the axis of rotation (36). 13. Knee joint endoprosthesis according to one of the preceding sentences, characterized in that the femoral component (14) comprises a lateral and a medial condyle (66, 68), which each comprise one of the femoral articular surfaces (62, 64), that anterior ends (86) of the condyles (66, 68) are directly connected to one another, that posterior ends (82) of the condyles (66, 68) are connected to one another via the second stabilizing element (74), and that the femoral component (14) has a recess (88) delimited by the condyles (66, 68) and the second stabilizing element (74), into which recess the first stabilizing element (74) projects or engages. 14. Knee joint endoprosthesis according to sentence 13, characterized in that the recess (88) is designed in the form of an opening (90). 15. Knee joint endoprosthesis according to one of the preceding sentences, characterized in that the first stabilizing element (72) on the femoral component (14) and that the second stabilizing element (74) on the meniscal component (20) are arranged or designed in such a way that they only come into contact with one another from a predetermined contact angle (126), which corresponds to a flexion angle between the tibial component (18) and the femoral component (14). 16. Knee joint endoprosthesis according to sentence 15, characterized in that the contact angle (126) is in a range of approximately 60° to approximately 80°. 17. Knee joint endoprosthesis according to one of the preceding sentences, characterized in that the first stabilizing element (72) and the second stabilizing element (74) are in direct contact with each other for each flexion angle which corresponds at least to the contact angle (126). 18. Knee joint endoprosthesis according to one of the sentences 15 to 17, characterized in that the first stabilizing surface (92) and the second stabilizing surface (94) lie flatly or substantially flatly against one another for each flexion angle which corresponds at least to the contact angle (126). 19. Knee joint endoprosthesis according to one of the preceding sentences, characterized in that a first radius of curvature (100) of the first stabilizing surface (92) and a second radius of curvature (112, 114) of the second stabilizing surface (94) correspond to one another or substantially correspond to one another. 20. Knee joint endoprosthesis according to one of the preceding sentences, characterized in that the first stabilizing surface (92) is designed in the form of a hollow spherical or substantially hollow spherical surface (96). 21. Knee joint endoprosthesis according to one of the preceding sentences, characterized in that the first stabilizing surface (92) defines a center of rotation. 22. Knee joint endoprosthesis according to sentence 21, characterized in that the center of rotation is offset in the posterior direction relative to the first stabilizing element (72). 23. Knee joint endoprosthesis according to sentence 21 or 22, characterized in that a distance of the center of rotation from the meniscal sliding surface is smaller than a distance of a free end of the first stabilizing element (72) from the meniscal sliding surface (34). 24. Knee joint endoprosthesis according to one of the sentences 1 to 19, characterized in that the first stabilizing surface (92) is designed in the form of a hollow cylindrical or substantially hollow cylindrical surface (96). 25. Knee joint endoprosthesis according to one of the sentences 1 to 19, characterized in that the first stabilizing surface (92) defines an axis of rotation (98). 26. Knee joint endoprosthesis according to sentence 25, characterized in that the axis of rotation (98) is offset in the posterior direction with respect to the first stabilizing element (72). 27. Knee joint endoprosthesis according to sentence 25 or 26, characterized in that a distance (102) of the rotation axis (98) from the meniscal sliding surface (34) is smaller than a distance (104) of a free end (106) of the first stabilizing element (92) from the meniscal sliding surface (34). 28. Knee joint endoprosthesis according to one of the sentences 25 to 27, characterized in that the axis of rotation (98) runs parallel to the meniscal sliding surface (58). 29. Knee joint endoprosthesis according to one of the sentences 25 to 28, characterized in that the axis of rotation (98) runs in a medial-lateral direction.

[0033] The following description of preferred embodiments of the invention serves to explain it in more detail in conjunction with the drawings. They show: Fig. 1: a schematic representation of a knee joint endoprosthesis in a slightly hyperextended position of the knee; Fig. 2: a perspective, partially open-cut view of the knee joint endoprosthesis from Fig. 1 from diagonally behind; Fig. 3: an exploded view of the Fig. 2 depicted knee joint endoprosthesis essentially from behind; Fig. 4: a view of the arrangement from Fig. 3 essentially from the front; Fig. 5: a sectional view of the knee joint endoprosthesis in Fig. 1 along line 5-5; Fig. 6: a sectional view analogous Fig. 5 at a flexion angle of 70° between femur and tibia; Fig. 7: a sectional view analogous Fig. 5 at a flexion angle of 90° between femur and tibia; Fig. 8: a sectional view analogous Fig. 5 at a flexion angle of 110° between femur and tibia; Fig. 9: a sectional view analogous Fig. 5 at a flexion angle of 135° between femur and tibia; and Fig. 10: a sectional view analogous Fig. 5 at a flexion angle of 155° between femur and tibia.

[0034] In the Fig. 1 to 10, an embodiment of a knee joint endoprosthesis, designated by reference numeral 10, is schematically illustrated. It comprises a femoral component 14 anchorable to a femur 12, a tibial component 18 anchorable to a tibia 16, and a meniscal component 20 mounted on the tibial component 18.

[0035] The tibial component 18 comprises a plate 22, which is essentially kidney-shaped in plan view, from whose underside 24 a stem connection piece 26 protrudes. Modular stems can be connected to the stem connection piece 26 with a correspondingly provided coupling device in order to securely anchor the tibial component 18 to the tibia 16. An upper side 28 of the plate 22 is flat and defines a tibial sliding surface 30. The meniscal component 20 rests flatly against this with its underside 32. The underside 32 forms a flat meniscal sliding surface 34.

[0036] The meniscus component 20 is rotatably mounted on the tibial component 18 about a rotation axis 36, which perpendicularly intersects both the tibial sliding surface 30 and the meniscal sliding surface 34. For this purpose, a pivot bearing 38 is provided, which comprises a rotationally symmetrical bearing pin 40 with a cylindrical head 42. A pin section 46 provided with an external thread 44 protrudes from the head 42 in the direction of the tibial component 18. A blind hole 50 provided with an internal thread 48 and open towards the meniscus component 20 is formed on the tibial component 18. The internal thread 48 corresponds to the external thread 44, so that the bearing pin 40 can be screwed into the tibial component 18. As a guide element for the meniscus component 20, only the head 42 then protrudes beyond the tibial sliding surface 30.A short cylindrical section 42 is formed on the head 42, coaxial with the rotation axis 36 and projecting opposite the bolt section 46. A tool holder (not shown in detail) is provided on or in this section, which enables the bearing bolt 40 to be screwed into the tibial component 18 using a suitable screwing tool.

[0037] The meniscus component 20 has a head receptacle 54 on its underside 32, which is rotationally symmetrical to the rotation axis 36 and enables a positive fit of the head 42 with the section 52. The pivot bearing 38 thus allows the meniscus component 20 to be rotated about the rotation axis 36 relative to the femoral component 14. Regardless of the rotational position, the tibial sliding surface 30 and the meniscal sliding surface 34 lie flat against one another.

[0038] On an upper side 56 of the meniscus component 20, two symmetrical or substantially symmetrical meniscus articulation surfaces are formed, namely a medial meniscus articulation surface 58 and a lateral meniscus articulation surface 60. These are configured to correspond or substantially correspond to interact with medial and lateral femoral articulation surfaces 62 and 64, which form outer surfaces of two femoral condyles, namely a medial condyle 66 and a lateral condyle 68, of the femoral component 14. Ideally, the femoral articulation surfaces 62 and 64 each form a section of a spherical surface. The femoral articulation surfaces 62 and 64, together with the meniscus articulation surfaces 58 and 60, are configured such that the adjacent articulation surfaces slide and / or roll against each other.

[0039] The knee joint endoprosthesis 10 is a posteriorly stabilized knee joint endoprosthesis 10. For this purpose, it comprises a posterior stabilization device 70. This comprises a first stabilization element 72 on the meniscal component 20 and a second stabilization element 74 on the femoral component 14. The first stabilization element 72 is in the form of a stabilization projection 76, which defines a longitudinal axis 78 that runs essentially perpendicular to the meniscal sliding surface 34 and has a posterior lateral surface 77 pointing in the posterior direction. The stabilization projection 76 thus protrudes essentially perpendicularly from the upper side 56 of the meniscal component 20. It is arranged between the meniscal articular surfaces 58 and 60 near a posterior end 80 of the meniscal component 20. It is essentially offset posteriorly to the axis of rotation 36.

[0040] At this point, it should be noted that both the tibial component 16, which can optionally also be of modular design, the meniscal component 20 and the femoral component 14 are each preferably formed in one piece.

[0041] The second stabilizing element 74 is arranged between posterior ends 82 of the condyles 66 and 68 and connects them in a lateral-medial direction. A cross-section of the second stabilizing element 74 has a kidney-shaped or essentially kidney-shaped contour 84 in a sectional plane defining a sagittal plane. Anterior ends 86 of the condyles 66 and 68 are directly connected to one another. Overall, a recess 88 in the form of an opening 90 is thus defined, which is bounded laterally by the condyles 66 and 68 and posteriorly by the second stabilizing element 74. If the femoral articular surfaces 62 and 64 rest on the corresponding meniscal articular surfaces 58 and 60, the first stabilizing element 72 engages or protrudes into the opening 90.

[0042] The first stabilization element 72 has a concavely curved first stabilization surface 92 pointing in the posterior direction. The posterior side surface 77 encompasses or defines the first stabilization surface 92. A second stabilization surface 94 of the second stabilization element 74, which is convexly curved, is formed in cooperation with the first stabilization surface. The first stabilization surface 92 is in the form of a hollow cylindrical surface 96. This defines an axis of rotation 98, which runs parallel to the meniscal gliding surface 34 in the medial-lateral direction. A radius of curvature 100 of the surface 96 is essentially constant. The axis of rotation 98 is offset in the posterior direction relative to the first stabilization element 72. Furthermore, a distance 102 of the rotation axis 98 from the meniscus sliding surface 36 is smaller than a distance 104 of a free end 106 of the first stabilizing element 92 from the meniscus sliding surface 34.The posterior side surface 77 thus encompasses or defines the first stabilization surface 92.

[0043] The second stabilization surface 94 has two merging cutouts 108 and 110 of cylindrical surfaces whose radii of curvature 112 and 114 differ slightly. The cutout 110 closer to the end 82 has a smaller radius 114 than the cutout 108. For example, the radii 112 and 114 can be 12 mm and 8.5 mm, respectively. A radius 116 of the femoral joint surfaces 62 and 64 is preferably at least twice as large as the radii 112 and 114. In the embodiment of a knee joint endoprosthesis schematically illustrated in the figures, the radius 116 can be 24 mm. In other words, the radii of curvature 112 and 114 of the second stabilization surface 94 correspond to approximately 0.25 to 0.55 times the radius of curvature 116 of the femoral articular surfaces 62, 64.

[0044] Due to the inclination of the stabilizing projection 76 relative to the meniscal sliding surface 34, the first stabilizing surface 92 is also inclined at an angle 120 relative to a plane 118 defined by the meniscal articulating surfaces 58 and 60. This angle preferably lies in a range from approximately 70° to approximately 110°. In the exemplary embodiment illustrated in the figures, the angle 120 is approximately 90°. Due to the special design of the stabilizing surfaces 92 and 94, the first stabilizing surface 92 can also be referred to as a third meniscal articulating surface 122 and the second stabilizing surface 94 as a third femoral articulating surface 124.

[0045] The functioning of the knee joint endoprosthesis 10, in particular of its stabilizing device 70, is described below in connection with the Fig. 5 to 10 explained.

[0046] In Fig. Figure 5 schematically shows a section through an extension position of the knee joint endoprosthesis. A flexion angle between the femur 12 and the tibia 16 in this position is approximately -10°, so that one can also speak of slight hyperextension. The first stabilizing element 72 and the second stabilizing element 74 are arranged or configured on the femoral component 14 and the meniscal component 20, respectively, such that they only become active at a predetermined contact angle 126 of approximately 70°, as schematically shown in Fig. 6, can come into contact with each other. Preferably, the contact angle 126 is in a range of approximately 60° to approximately 80°. For flexion angles smaller than the contact angle 126, the stabilizing elements 72 and 74 do not touch each other. They also do not cooperate to guide a movement of the femoral component 14 relative to the meniscal component 20.

[0047] However, as soon as the stabilizing elements 72 and 74 interact, a rotation of the femoral component 14 about the rotation axis 94 is effected due to the significantly smaller radii of curvature 112 and 114 of the surface 96 compared to the radius 116. With increasing flexion angle, the femoral component 14 tilts further backward and performs an overall superimposed translational movement in the posterior direction. The translational movement is particularly clearly visible in the sequence of the Fig. 7 to 10 show sectional views of the knee joint endoprosthesis 19 with the flexion angles specified above. The guidance is optimized in particular by the fact that the first stabilizing element 72 and the second stabilizing element 74 are in direct contact with each other for each flexion angle that corresponds at least to the contact angle 126, and thereby bear against each other flatly or substantially flatly.

[0048] Not shown in the figures is an alternative configuration of the first and second stabilizing surfaces 92 and 94. These can optionally also be hollow-spherical or spherical and, in turn, have corresponding or substantially corresponding radii of curvature. Even with stabilizing surfaces configured in this way, the guidance of a movement of the femoral component 14 relative to the meniscal component 20 during very strong flexion, as described in connection with the exemplary embodiment illustrated in the figures, can be achieved.

[0049] For the sake of clarity, it should be added that from a rear side 128 of the femoral component 14, which is divided into several flat surface sections 130, 132, 134, and 136, two mutually parallel cylindrical pins 138 protrude perpendicularly from the surface section 134, which, in a zero-degree position between the femur 12 and the tibia 16, runs essentially parallel to the meniscal gliding surface 34. The pins 138 serve to anchor the femoral component to the femur 12. Furthermore, the component can be secured to the femur 12 using conventional bone cement.

Claims

[1] Knee joint endoprosthesis (10) with a tibial component (16), a meniscal component (20) mounted on the tibial component (16) and formed in one piece, and a femoral component (14) cooperating with the meniscal component (20), which femoral component (14) comprises two femoral articulation surfaces (62, 64) and which meniscal component (20) comprises two meniscal articulation surfaces (58, 60), wherein in each case a femoral articulation surface (62, 64) and a meniscal articulation surface (58, 60) are cooperating with one another, wherein furthermore a posterior stabilization device (70) with first and second cooperating stabilization elements (72, 74) is provided, wherein the first stabilization element (72) is arranged or formed on the meniscal component (20) between the meniscal articulation surfaces (58, 60), wherein the second stabilization element (74) on the femoral component (14) in the region of a posterior end (82) of the femoral articular surfaces (62,64) is arranged or formed between them, wherein the first stabilizing element (72) has a first, concave stabilizing surface (92) pointing in the posterior direction, wherein the second stabilizing element (74) has a second, convexly curved stabilizing surface (94) cooperating with the first stabilizing surface (92), , characterized bythat the meniscus component (20) is mounted on the tibial component (18) so as to be rotatable about a rotation axis (36), that the tibial component (18) has a flat tibial sliding surface (30), that the meniscus component (20) has a flat meniscus sliding surface (34) and that the tibial sliding surface (30) and the meniscus sliding surface (34) bear against one another, that the rotation axis (36) runs perpendicular to the tibial sliding surface (30), that the first stabilizing element (72) is designed in the form of a stabilizing projection (76) which extends from an upper side (56) of the meniscus component (20) transversely to the meniscus sliding surface (34), and that the stabilizing projection (76) is arranged or designed offset in the posterior direction relative to the rotation axis (36), that the knee joint endoprosthesis (10) has a pivot bearing (38) for rotating the meniscus component (20) relative to the tibial component (14) about the rotation axis (36),that the pivot bearing (38) comprises a guide element for the meniscus component (20), that the guide element protrudes beyond the tibial sliding surface (30), that the pivot bearing comprises a bearing pin (40) which can be screwed into the tibial component (18) and has a cylindrical head (42) and a head receptacle (54) formed on an underside (32) of the meniscus component rotationally symmetrically to the axis of rotation (36) for positively receiving the head (42), and that the head (42) forms the guide element. [2] Knee joint endoprosthesis according to claim 1, characterized by that the bearing bolt (40) is rotationally symmetrical and comprises a bolt section (46) provided with an external thread (44), and that a blind hole (50) is formed on the tibial component (18) which is provided with an internal thread (48) to the external thread (44) and is open in the direction of the meniscus component (20). [3] Knee joint endoprosthesis according to one of the preceding claims, characterized bythat the first stabilizing surface (92) is inclined by an angle (120) relative to the meniscal articular surfaces (58, 60), which angle (120) lies in a range of approximately 70° to approximately 110°. [4] Knee joint endoprosthesis according to one of the preceding claims, characterized by that the first stabilizing surface (92) defines a third meniscal articular surface (122) and that the second stabilizing surface (94) defines a third femoral articular surface (124). [5] Knee joint endoprosthesis according to one of the preceding claims, characterized by that a cross-section of the second stabilizing element (74) in a sectional plane defining a sagittal plane has a kidney-shaped or substantially kidney-shaped contour (84). [6] Knee joint endoprosthesis according to one of the preceding claims, characterized bythat a radius of curvature or radii of curvature (112, 114) of the second stabilizing surface (94) corresponds approximately to 0.25 times to approximately 0.55 times a radius of curvature (116) or radii of curvature of the femoral joint surfaces (62, 64), preferably approximately 0.3 times to approximately 0.5 times. [7] Knee joint endoprosthesis according to one of the preceding claims, characterized by that the stabilizing projection (76) comprises the first stabilizing surface (92). [8] Knee joint endoprosthesis according to one of the preceding claims, characterized by that the stabilizing projection (76) comprises a posterior side surface (77) pointing in the posterior direction and that the posterior side surface (77) comprises or defines the first stabilizing surface (92). [9] Knee joint endoprosthesis according to one of the preceding claims, characterized bythat the femoral component (14) comprises a lateral and a medial condyle (66, 68), each of which comprises one of the femoral articular surfaces (62, 64), that anterior ends (86) of the condyles (66, 68) are directly connected to one another, that posterior ends (82) of the condyles (66, 68) are connected to one another via the second stabilizing element (74), and that the femoral component (14) has a recess (88) delimited by the condyles (66, 68) and the second stabilizing element (74), into which recess the first stabilizing element (74) projects or engages. [10] Knee joint endoprosthesis according to claim 9, characterized by that the recess (88) is designed in the form of an opening (90). [11] Knee joint endoprosthesis according to one of the preceding claims, characterized bythat the first stabilizing element (72) on the femoral component (14) and that the second stabilizing element (74) on the meniscal component (20) are arranged or designed in such a way that they only come into contact with one another from a predetermined contact angle (126), which corresponds to a flexion angle between the tibial component (18) and the femoral component (14). [12] Knee joint endoprosthesis according to claim 11, characterized by that the contact angle (126) is in a range of about 60° to about 80°. [13] Knee joint endoprosthesis according to one of the preceding claims, characterized by that the first stabilizing element (72) and the second stabilizing element (74) are in direct contact with each other for each flexion angle which corresponds at least to the contact angle (126). [14] Knee joint endoprosthesis according to one of claims 11 to 13, characterized bythat the first stabilizing surface (92) and the second stabilizing surface (94) lie flatly or substantially flatly against one another for each flexion angle which corresponds at least to the contact angle (126). [15] Knee joint endoprosthesis according to one of the preceding claims, characterized by that a first radius of curvature (100) of the first stabilizing surface (92) and a second radius of curvature (112, 114) of the second stabilizing surface (94) correspond to one another or substantially correspond to one another. [16] Knee joint endoprosthesis according to one of the preceding claims, characterized by that the first stabilizing surface (92) is designed in the form of a hollow spherical or substantially hollow spherical surface (96). [17] Knee joint endoprosthesis according to one of the preceding claims, characterized by that the first stabilizing surface (92) defines a center of rotation. [18] Knee joint endoprosthesis according to claim 17, characterized by that the center of rotation is offset in the posterior direction relative to the first stabilizing element (72). [19] Knee joint endoprosthesis according to claim 17 or 18, characterized by that a distance of the center of rotation from the meniscus sliding surface is smaller than a distance of a free end of the first stabilizing element (72) from the meniscus sliding surface (34). [20] Knee joint endoprosthesis according to one of claims 1 to 15, characterized by that the first stabilizing surface (92) is designed in the form of a hollow cylindrical or substantially hollow cylindrical surface (96). [21] Knee joint endoprosthesis according to one of claims 1 to 15, characterized by that the first stabilizing surface (92) defines an axis of rotation (98). [22] Knee joint endoprosthesis according to claim 21, characterized by that the axis of rotation (98) is offset in the posterior direction relative to the first stabilizing element (72). [23] Knee joint endoprosthesis according to claim 21 or 22, characterized by that a distance (102) of the rotation axis (98) from the meniscus sliding surface (34) is smaller than a distance (104) of a free end (106) of the first stabilizing element (92) from the meniscus sliding surface (34). [24] Knee joint endoprosthesis according to one of claims 21 to 23, characterized by that the rotation axis (98) runs parallel to the meniscus sliding surface (58). [25] Knee joint endoprosthesis according to one of claims 21 to 24, characterized by that the axis of rotation (98) runs in a medial-lateral direction.

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