Tibial tray, tibial insert and artificial knee joint

Abstract

The invention relates to a tibial tray (20) having a proximal surface (P) comprising at least two, in particular exactly two, central fixation elements (1) for effecting a connection to a tibial insert (30) as another part of an artificial knee joint, the at least two central fixing elements (1) are projections projecting from the proximal surface (P) in the proximal direction, and the at least two central fixing elements (1) are positioned symmetrically and / or parallel to a median plane (M) of the proximal surface (P), the median plane (M) is perpendicular to the proximal surface (P) and intersects the proximal surface (P) in the middle between the two outermost points (L1, L2) of the proximal surface (P). The invention also relates to a tibial insert (30) and an artificial knee joint.

Description

[0001] The invention relates to a tibial tray having the features of claim 1 and a tibial insert having the features of claim 13 and an artificial knee joint having the features of claim 16 .

[0002] Joint replacement, in particular artificial knee replacement, has been known for quite some time. In the case of artificial knee joints, it is known that a tibial tray portion is connected to the proximal end of the patient's tibia. A femoral portion is connected to the distal end of the patient's femur. A tibial insert is connected to the proximal surface of the tibial tray so that after the surgical procedure is completed, the tibial insert is positioned between the distal surface of the femoral portion and the proximal surface of the distal tray.

[0003] A tibial tray and a tibial insert of this type are described, for example, in EP 3 626 209 B1.

[0004] In order to ensure a good connection between the proximal end of the tibia and the tibial tray shaft, a properly shaped geometry, such as a form-fitting design, is required. This is important, especially when ceramic materials are used for the tibial tray and its tibial tray shaft.

[0005] It is also a challenge to provide a combination of a tibial tray and a matching tibial insert such that the locally occurring mechanical loads do not exceed certain design limits. In particular, this is important when using ceramic materials for the tibial tray.

[0006] A tibial tray having the features of claim 1 solves these problems.

[0007] The tibial tray comprises a proximal surface, which comprises at least two, in particular exactly two, central fixing elements for connection with a tibial insert as another part of an artificial knee joint. The central fixing element is a protrusion protruding from the proximal surface that can be connected to the tibial insert as a form fit and / or force lock.

[0008] The at least two central fixation elements are designed as projections which protrude from the proximal surface in the proximal direction, ie the central fixation elements point generally away from the proximal surface in the direction of the tibial insert.

[0009] At least two central fixation elements are positioned symmetrically and / or parallel to a median plane of the proximal surface, the median plane being perpendicular to the proximal surface and intersecting the proximal surface midway between the two outermost points of the proximal surface. The median plane divides the proximal surface into two lateral halves. At least two central fixation elements are oriented symmetrically and / or parallel to the median plane.

[0010] At least two central fixing elements are configured as cylindrical protrusions or linear protrusions, particularly designed for press fit. Cylindrical means that the protrusion has, for example, a circular, oval cross section. Linear means that the protrusion extends linearly on the proximal surface. At least one of the central fixing elements can, for example, have a linear or cylindrical shape.

[0011] In one embodiment, at least two central fixing elements are positioned symmetrically relative to a frontal plane perpendicular to the median plane. The frontal plane divides the proximal surface into a front portion and a rear portion. In particular, the frontal plane may pass through the outermost point of the proximal surface.

[0012] In addition to the central fixation element, the proximal surface may include other structures.

[0013] In one embodiment, at least one front fixation element, in particular exactly one front fixation element, is positioned at the front side of the proximal surface, the rear side of the at least one front fixation element comprising a wall which is perpendicular to the median plane of the proximal surface in a plane parallel to the proximal surface.

[0014] In addition, at least one front fixing element comprises at least one form-fitting element for the corresponding form-fitting element of tibial insert, particularly at least one cavity in the rear wall of at least one front fixing element and / or at least one channel through at least one front fixing element. This means that cavity or channel are examples of form-fitting elements, and the form-fitting element can be matched with the corresponding form-fitting element (e.g., protrusion) of the tibial insert to be connected to the tibial tray. At least one form-fitting element of at least one front fixing element can be, for example, positioned in a region where load transfer is less than 70%, particularly less than 50% of the maximum load transfer. Load transfer (pressure, torque, etc.) can be calculated under various conditions. Typically, certain regions in the structure will show a higher load than other regions. A region will show a clearly defined maximum load transfer. The region experiencing a load transfer less than 50% of the maximum value is a potential position for at least one form-fitting element.

[0015] In one embodiment, at least one, in particular exactly one, rear fixation element may be symmetrically positioned relative to the median plane of the proximal surface, the at least one rear fixation element comprising a rear wall flush with the rear edge of the tibial tray and / or comprising a front wall positioned parallel to the rear wall of the at least one front fixation element. The rear wall may provide some connecting elements for the tibial insert at the front side. In one embodiment, the at least one rear fixation element may comprise two side walls, each having an angle α relative to a plane perpendicular to the front wall, the angle α also being in a plane parallel to the proximal plane. The angle may be in a range between 5 ° and 85 °, in particular in a range between 40 ° and 50 °.

[0016] In one embodiment, at least one rear element has side walls that are inclined at an angle between 1° and 25°, in particular between 3° and 10°, relative to a plane perpendicular to the proximal plane. This makes it possible, for example, to form a rear block with side walls that are inclined inwardly and that converge to the anterior side. Such a rear fixation element can be used as a fulcrum when attaching the tibial insert.

[0017] The rear wall of at least one front fixing element and / or the front wall of at least one rear fixing element may also comprise an undercut, in particular the undercut may form an angle β of between 10° and 30°, in particular 15°, with a plane perpendicular to the proximal surface. Thus, various structures on the proximal surface may have an undercut, in particular an undercut for providing a better hold during assembly.

[0018] In one embodiment, the height of at least two central fixing elements, at least one front fixing element and / or at least one rear fixing element extending from the proximal surface is between 1mm and 6mm, particularly in the range of between 3mm and 4.5mm, and / or wherein, the front end and / or the rear end of at least two central fixing elements are rounded. In particular, the height of at least two central fixing elements above the proximal surface, the height of at least one front fixing element above the proximal surface and / or the height of at least one rear fixing element above the proximal surface is constant or varies up to 10% from the minimum height. These features help to provide a firm connection with the tibial insert and / or allow effective assembly.

[0019] In another embodiment, at least one anterior fixation element comprises at least one guide surface for the tibial insert, in particular, the guide surface has a curved portion and / or a flat portion in the proximal direction of at least the form-fitting element. The guide surface can assist the movement of the tibial insert during assembly, i.e. when the form-fitting portions snap together.

[0020] The at least two central fixing elements may further comprise a central fixing element recess.

[0021] For a secure connection, in one embodiment, the side walls and the front wall of at least one rear element are inclined at an angle between 0° and 25°, in particular between 0° and 10°, relative to a plane perpendicular to the proximal plane, and / or the side walls and the front wall of at least one rear element include an undercut.

[0022] Embodiments of the tibial tray are manufactured entirely or partially from ceramic, polymeric materials, or metal.

[0023] The problem is also solved by a tibial insert designed or constructed to match the claimed tibial tray.

[0024] In order to ensure a good connection with the tibial tray, the tibial insert may include a recess in the distal surface for matching at least one posterior fixation element, the recess including at least one stress relief notch at the junction of the two walls of the recess. This prevents the formation of a mechanically stressful sharp corner where the two walls of the recess meet.

[0025] The secure connection may be achieved by at least one form-fitting element of the tibial insert for engaging at least one form-fitting element of at least one anterior fixation element of the tibial tray.

[0026] The problem is also solved by an artificial knee joint, which comprises a tibial tray as claimed in the claim according to the claimed tibial insert, wherein there is a light press-fit connection between the tibial insert and at least two central fixation elements, at least one anterior fixation element and at least one posterior fixation element, in particular with a press-fit in the range of 0 μm to 250 μm.

[0027] In another embodiment of the artificial knee joint, there is at least one press-fit region between the posterior fixation element and the tibial insert, in particular at least one press-fit region produced by an angular mismatch between the two walls. This allows for improved assembly of the joint and reduced micromotion in the posterior part of the joint.

[0028] In the accompanying drawings, embodiments of the present invention are shown.

[0029] Figure 1 shows a perspective view of an artificial knee joint;

[0030] Figure 2 A perspective view showing an embodiment of a tibial tray;

[0031] Figure 2A is with Figure 2 The same view, which highlights the frame of reference;

[0032] Figure 2B Shows Figure 2 A variation of the embodiment in;

[0033] Figure 3A A view showing a proximal surface of an embodiment of a tibial tray;

[0034] Figure 3B Shown with Figure 3A A view of the distal surface of the tibial insert mating with the tibial tray shown in FIG.

[0035] Figure 4 Shows Figure 3A a view of the proximal surface of the embodiment shown in , indicating a press fit;

[0036] Figure 5A The fitting of the tibial insert to the tibial tray is shown in a perspective view;

[0037] Figure 5B The cross-sectional view shows Figure 5A The tibial insert and tibial tray are matched;

[0038] Fig. 6A is a detailed front view of a first embodiment of a tibial insert;

[0039] Figure 6B is a detailed front view of a second embodiment of a tibial insert;

[0040] Figure 7 yes Figure 2 A perspective view of a variation of the embodiment shown in ;

[0041] Fig. 8A is a perspective view from the posterior side of the proximal surface of the first embodiment of the tibial tray having a central fixation element;

[0042] Figure 8B is a perspective view from the anterior side of the proximal surface of the first embodiment of the tibial tray having a central fixation element;

[0043] Fig. 9 is a perspective view from the posterior side of the proximal surface of a second embodiment of a tibial tray having a central fixation element;

[0044] Fig.10 is a perspective view of a proximal surface of another embodiment of a tibial tray having a guide surface on an anterior fixation element;

[0045] Fig.11 is a detail of the connection between the rear fixing elements in one embodiment.

[0046] exist Figure 1 In FIG. 1 , an artificial ceramic knee joint 100 is shown in a perspective view from a rear position. Figure 1 , the femoral portion 40, the tibial insert 30 and the tibial tray 20 of the metal-free artificial knee joint are shown. The entire artificial knee joint 100 is metal-free, for example, a combination of ceramic and polymer materials. The tibial tray 20 can be made of ceramic, for example, and the tibial insert 30 can be made of a polymer material.

[0047] At the proximal position of the artificial knee joint, the femoral portion 40 is shown with two condyles fitting into matching recesses in the proximal surface of the tibial insert 30 at the distal end of the femoral portion 40 .

[0048] The tibial insert 30 is connected to the tibial tray 20 , with the distal surface D of the tibial insert 30 facing the proximal surface P of the tibial tray 20 .

[0049] Hereinafter, embodiments of the tibial tray 20 and the tibial insert 30 , and in particular features of the proximal surface P of the tibial tray 20 and the mating distal surface D of the tibial insert 30 , are described.

[0050] Figure 2 , Figure 2A A perspective view of the proximal surface P of the tibial tray 20 is shown. Figure 2A In order to reduce complexity, the tibial tray is shown without reference numbers, but with reference planes M, N used hereinafter to define the locations of features on the tibial tray 20.

[0051] Reference Figure 2A The median plane M is perpendicular to the planar proximal surface P and intersects the proximal surface P at the middle between the outermost points L1 , L2 of the proximal surface P. The frontal plane N is perpendicular to the median plane M.

[0052] In one embodiment of the tibial tray 20, the sizes are grouped in different sizes. There are eight different sizes for the distance between point L1 and point L2. This is used to allow for artificial knee joints 100 for patients of different sizes. The minimum distance between L1 and L2 is 60mm. The other seven sizes have distances of 64mm, 68mm, 72mm, 76mm, 80mm, 84mm and 88mm (i.e., using 4mm increments). Other embodiments may use different absolute sizes and / or different increments, which do not have to be the same.

[0053] In the direction perpendicular to the distance between L1 and L2, the corresponding sizes are 38.7mm, 41.3mm, 43.9mm, 46.5mm, 49.0mm, 51.6mm, 54.2mm and 56.8mm. Other embodiments may use different absolute sizes and / or different increments, and again, the increments need not be the same.

[0054] The proximal surface P of the tibial tray 20 is configured so that the corresponding tibial insert 30 (see, e.g. Figure 1 6) can be securely fastened to the tibial tray 20 (see Figure 5A , Figure 5B ). The planar proximal surface P itself is polished, wherein the average roughness is Ra=0.1 μm and the uniformity is 0.1. In other embodiments, the average roughness is less than 5 μm, in particular less than 2 μm.

[0055] In the following, different aspects of the structures 1, 2, 3 on the planar proximal surface P are described. These structures provide a symmetrical flat platform with island-shaped fixation elements 1, 2, 3 for connection of the tibial insert 30 using a press fit (see Figure 4 ).

[0056] exist Figure 2 In the embodiment shown in FIG. 1 , the proximal surface P includes two central fixing elements 1. As will be described below, these two central fixing elements realize the connection with the tibial insert (see FIG. 1 ) as another part of the artificial knee joint 100. Figure 3B ) for a secure connection.

[0057] In the embodiment shown, the two central fixation elements 1 are linear protrusions that protrude away from the proximal surface P in the proximal direction so that the two central fixation elements 1 can match corresponding recesses 34 in the tibial insert 30 (see Figure 3B ). In other embodiments, the central fixing element 1 may have a cylindrical shape.

[0058] The two central fixing elements 1 are positioned symmetrically and parallel to the center plane M.

[0059] exist Figure 2B In the embodiment shown in , the two central fixing elements 1 are still symmetrical with respect to the middle plane M but are not completely parallel, because the two central fixing elements 1 are angled less than 5° with respect to the middle plane M, so that the two linear fixing elements 1 show some convergence toward the front side.

[0060] In other embodiments, the two central fixing elements 1 can also be asymmetrical relative to the middle plane M but parallel to each other.

[0061] like Figure 7 As shown in FIG, in different embodiments, more than two central fixing elements 1 can be used. In addition, Figure 7 Implementation and combination of Figure 2 The described embodiments are comparable.

[0062] exist Figure 2 In the embodiment shown in , the two central fixing elements 1 are positioned symmetrically with respect to a frontal plane N perpendicular to the median plane M. In this embodiment, but not necessarily, the frontal plane N passes through the outermost points L1 , L2 of the proximal surface P.

[0063] The two central fixing elements 1 have the form of a parallelepiped. The front and rear ends of the central fixing elements 1 are rounded.

[0064] In the embodiment shown, the two central fixation elements 1 have a height H extending 3.8 mm from the proximal surface P of the tibial tray 20. In other artificial knee joints 100, the height H can be up to 6 mm. In the embodiment shown, the height H of the central fixation elements 1 is constant. In other embodiments, the height H can vary relative to the proximal surface P. In other embodiments, the height H of at least two central fixation elements 1 above the proximal surface varies from a minimum height by a maximum of 10%.

[0065] exist Figure 2 In the embodiment shown in , the distance between the two central fixing elements 1 is 10.5 mm as measured between the inner walls and 15.5 mm as measured between the outer walls. Since the two central fixing elements 1 are parallel to each other, the width of each of the central fixing elements is 2.5 mm. The distance between the central fixing elements is selected to be as large as possible here to provide a large torque and prevent the polyethylene material from shearing off the tibial insert 30. If the distance between the two central fixing elements 1 is always the same, different sizes of tibial inserts 30 can be used when assembling the artificial knee joint 100.

[0066] The orientation of the central fixation element 1 on the proximal surface P enables linear guidance of the tibial insert 30 (see FIG. 5 ) during assembly, so that the central fixation element 1 can also be referred to as a central guide rail. Furthermore, the central fixation element 1 allows increased stability against shear forces in the artificial knee joint.

[0067] The proximal surface P further comprises a front fixation element 2 at the front edge of the proximal surface P. The rear side of the front fixation element 2 comprises a rear wall 4 positioned perpendicular to the median plane M of the proximal surface P. Therefore, the rear wall 4 is also substantially perpendicular to the two linear central fixation elements 1. In this embodiment, the front fixation element 2 has the same height H as the central fixation elements 1.

[0068] The front fixing element 2 comprises two cavities 5, each in the form of a channel (i.e., the channel is open at both ends), which have a substantially rectangular cross section. As will be shown in conjunction with FIG. 5 , those cavities are form-fitting elements 5 that cooperate with matching form-fitting elements 31 on the tibial insert 30. The form-fitting elements 5 in the front fixing element are positioned symmetrically with respect to the median plane M.

[0069] In other embodiments, the front fixing element 2 comprises only one or more than two form-fitting elements 5. The cross section of the cavity of the form-fitting element 5 does not have to be rectangular, for example a circular or polygonal cross section may also be used.

[0070] exist Figure 2In the embodiment of the present invention, the anterior fixation element 2 is a continuous element located at the front edge of the tibial tray 20. In other embodiments, the anterior fixation element 2 can be divided into more than one part, for example two elements, each of which includes a shape-fitting element 5.

[0071] The two form-fit elements 5 in the front fixing element 2 are positioned in a region where the mechanical load transfer is less than 50% of the maximum load transfer. This is due to the fact that the channel-shaped form-fit elements 5 slightly weaken the structure of the front fixing element 1 .

[0072] Another structure on the proximal surface P is a posterior fixation element 3, which is positioned at the posterior edge of the proximal surface P. The posterior fixation element 3 is symmetrically positioned relative to the median plane M and includes a posterior wall 7 that is flush with the posterior edge 8 of the tibial tray 20. The posterior wall 7 follows the curved shape of the posterior edge 8 of the tibial tray 20. The cross-section of the anterior fixation element 3 in a plane parallel to the proximal surface P is symmetrical relative to the median plane M. In this embodiment, the posterior fixation element 3 has the same height H as the central fixation element 1.

[0073] Figure 2 The embodiment shown in also comprises a front wall 9 parallel to the rear wall 4 of the front fixing element 2. Thus, the two central fixing elements 1 are oriented perpendicularly to both the rear wall 4 of the front fixing element 2 and the front wall 9 of the rear fixing element 3.

[0074] The rear fixing element 3 further comprises two side walls 10 which are angled relative to the front wall 9 of the rear fixing element 3. The angle α between the two side walls 10 and the front wall 9 in a plane parallel to the proximal plane P is in the range between 5° and 85°, in particular in the range between 40° and 50°. Thus, the two side walls 10 are oriented to converge in the forward direction. The overall horizontal shape of the rear fixing element 3 is generally trapezoidal, wherein the long sides of the trapezoid are curved.

[0075] The two side walls 10 of the rear element 3 are inclined inwardly at an angle between 1° and 25°, in particular between 3° and 10°, relative to a plane perpendicular to the proximal plane P. Therefore, the top surface of the rear fixing element 3 is slightly smaller than the base cross section in the plane of the proximal surface.

[0076] Described in this article and Figure 5B In the embodiment best shown in , the front wall 9 of the rear fixation element 3 comprises an undercut 6 which forms an angle β of between 10° and 30°, in particular 15°, with a plane perpendicular to the proximal surface P. In other embodiments, the undercut 6 may at least partially have a curved shape. The rear wall 4 of the front fixation element 2 may also comprise an undercut 6 in principle.

[0077] In the embodiments discussed so far, the height H of the fixation elements 1 , 2, 3 above the proximal surface P is the same. This is not necessarily the case in all embodiments.

[0078] exist Figure 3A , Figure 3B The matching tibial tray 20 and tibial insert 30 are shown side by side. Figure 3A The embodiment of the tibial tray 20 in Figure 2 , so you can refer to the corresponding description. Figure 3B The distal surface D of the tibial insert 30 is shown in . Comparison of the two components 20 , 30 shows that the tibial insert 30 can be connected to the tibial tray 20 such that the first fixation element 1 fits into a matching recess 34 in the tibial insert 30 .

[0079] The tibial insert 30 comprises a recess 32 for the matching posterior fixation element 3 of the tibial tray 20 in the distal surface D. The recess 32 is open towards the posterior side, so that the recess 32 has only an anterior wall 35 and two side walls 36 .

[0080] The side walls 36 of the recess 32 are angled to match the angled side walls 10 of the rear fixing element 3. In the corner where the front wall 35 and the two side walls 36 of the recess 32 meet, a stress relief notch 33 is located at the junction of the two walls 35,36.

[0081] At the front side of the tibial tray insert 30 are located two form-fitting elements 31 which can be inserted into the front fixation element 2 (see Figure 2 ) in the two cavities of the shape-fitting element 5.

[0082] The groove 34 and the recess 32 of the tibial tray 30 also form a certain form-fit connection with the matching structure, namely the central fixation element 1 and the rear fixation element 3 of the tibial tray 20. However, the main function of the structures 32, 34 is to assist during assembly, which will be described below in conjunction with Figure 5A , Figure 5B Give a description.

[0083] The connection between the tibial tray 20 and the tibial insert 30 is mainly achieved by a light press-fit connection between the tibial insert 30 and at least two central fixing elements 1, at least one front fixing element 2 and at least one rear fixing element 3, in particular with a press-fit in the range of 0 μm to 250 μm in the anterior-posterior direction. Figure 4In the embodiment, the surfaces 37 for press fit at the rear wall 4 of the anterior fixation element 2, at the medial side of the central fixation element 1 and at the front wall 9 of the rear fixation element 9 are highlighted. All press fit connections can be dimensioned identically, but this need not be the case for all embodiments. For example, the press fit between the tibial insert 30 and the rear wall 4 of the anterior fixation element 2 and the front wall 9 of the rear fixation element 3 is in the range of 25 μm to 125 μm, and / or the press fit between the tibial insert 30 and the central fixation element 1 is in the range of 0 μm to 100 μm.

[0084] exist Figure 5A and Figure 5B , the assembly of an embodiment of a tibial insert 30 and a tibial tray is shown in different views.

[0085] Figure 5A A perspective view from the front is shown with the tibial insert 30 partially connected to the underlying tibial tray 20 . Figure 5B Essentially the same relative position of the tibial tray 20 and the tibial insert 30 is shown, but in a cross-sectional view with the anterior fixation element 2 located on the right-hand side.

[0086] The tibial insert 30 is first attached to the posterior fixation element 3 (see Figure 2 , Figure 3A , Figure 3B ) connection, the rear fixing element 3 acts as a kind of fulcrum for snapping into place. Figure 5B In the view of FIG. 1 , an undercut 6 having an angle of about 15° is shown in the anterior wall 9, which allows a secure positioning of the tibial insert 30. In the anterior side (see FIG. 1 ), an undercut 6 having an angle of about 15° is shown in the anterior wall 9, which allows a secure positioning of the tibial insert 30. Figure 5A ) shows two form-fitting elements 31, which snap into the form-fitting element 5 ( Figure 5A not seen in the cavity.

[0087] exist Fig. 6A In the figure, a first embodiment of a tibial insert 30 is shown in a front view. In this embodiment, the shape of the distal surface D, i.e. the outer edge of the tibial insert 30 is basically a slightly inclined wall that is not suitable for covering. The inclination can be between 0° and 10°. In the case of an inclination of 0°, the wall is straight.

[0088] exist Figure 6B , a second embodiment of a tibial insert 30 is also shown in a front view. Here, the shape of the distal surface D, ie the outer wall, is slightly inclined outwardly and is suitable for covering.

[0089] In with Figure 2 In a different embodiment than the one shown in the figure, the central fixing element 1 has a shape with two axes of symmetry, one along the longitudinal axis and one perpendicular to this axis. Fig. 8A , Figure 8B , an embodiment of a tibial tray 20 that deviates from this pattern is shown.

[0090] exist Fig. 8A , Figure 8B , an embodiment is shown in which the central fixation element 1 has a wider lateral cross-section toward the front side than toward the rear side. Thus, the long side walls of each of the central fixation elements 1 converge toward the front side. The medial side walls of the central fixation elements 1 are not parallel and diverge toward the rear of the tibial tray 20, while the lateral side walls are substantially parallel.

[0091] exist Fig. 9 In FIG. 2 , a variant embodiment of a tibial tray 20 is shown, because the central fixing element 1 is shaped differently. Here, the outer side walls of the central fixing element 1 are parallel to each other and as in FIG. Figure 2 As in the embodiment shown in FIG. , there are two axes of symmetry. Fig. 9 In the embodiment, the inner side wall is not linear over the entire length. Towards the front side and the rear side, the side wall converges and there is a divergence towards the middle.

[0092] Fig. 8A , Fig. 9 B and Fig. 9 The front fixing element 2 of the embodiment shown in FIG. 1 is shaped as follows Figure 2 However, Fig. 8A , Figure 8B and Fig. 9 The rear fastening element 3 of the embodiment shown in FIG. 1 is shaped differently.

[0093] The side walls of the rear element 3 are inclined at an angle between 0° and 25°, in particular between 0° and 10°, relative to a plane perpendicular to the proximal plane P. Additionally or alternatively, the side walls and the front wall of at least one rear element comprise undercuts.

[0094] exist Fig.10 , a proximal surface P of a tibial tray 20 is shown, which comprises a variation of the design of the anterior fixation element 2 with respect to the embodiment described above. The central fixation element 1 and the posterior fixation element 3 have been described, for example, in Figure 2 or Fig. 8A The present invention has been described in one way or another in the specification and therefore reference can be made to the above description.

[0095] The anterior fixation element 2 comprises a corresponding portion for receiving a tibial insert 30 (not shown here, see Figure 5A , Figure 5B , for example for the clip-in process of a tibial tray). The form-fit elements 5 are essentially holes with a rectangular cross section.

[0096] When the tibial insert 30 is inserted from the top using its posterior portion and the posterior fixation device 3 as a fulcrum, the form-fitting element 31 for anterior fixation has a shape corresponding to the form-fitting element 5 (eg, a rectangular hole).

[0097] In order to facilitate the insertion of the tibial insert 30 (not shown here), a guide surface 11 is provided on the proximal surface of the anterior fixation device 5. The guide surface 11 is a plane inclined 5° to 45°, in particular 30°, relative to the horizontal plane.

[0098] The form-fitting element 31 of the tibial insert 30 protrudes into the forward direction. When the tibial insert 30 is to be snapped in, the form-fitting element 31 first rests on the upper part of the guide surface 11. When pressure is applied in the distal direction in the tibial insert 30, the form-fitting element 31 is guided downward along the guide surface 11 and finally snaps into the hole of the form-fitting element 5 forming the anterior fixation element for a secure fit. The guide surface 11 prevents lateral sliding and makes secure snapping in easier.

[0099] The lateral width of the guide surface is the same or approximately the same as the lateral width of the form-fit element 5 in the front fixing element 2 .

[0100] exist Fig.11 , a detail of the rear fixing element 3 is shown in a top view, ie in the direction of the proximal surface P.

[0101] The cross section of the posterior fixation element 3 includes two side walls 10 that are inclined toward the median plane M. Each of the side walls 10 is angled at about 20° relative to the median plane M. In the illustrated embodiment, there is an intentional angular mismatch between the side walls 10 of the posterior fixation element 3 and the corresponding side walls of the tibial insert 30 (not shown here).

[0102] For example, if the sidewall of the tibial insert 30 that is intended to contact or form-fit with the sidewall 10 of the posterior fixation element 3 has a slightly different inclination than the sidewall 10, an angular mismatch occurs, resulting in a tighter contact or force fit at some portions along the sidewall 10 and a looser fit at other portions.

[0103] exist Fig.11 In the embodiment shown in , the angle of the side wall of the posterior fixation element 3 is wider (e.g., about 1° wider) than the corresponding angle in the recess in the tibial insert 30. This results in a form fit, ie a tighter fit, in the posterior region. Fig.11 A press fit area 38 in this region is indicated in . This angular mismatch not only enables easier assembly, but it also reduces micro-movements in the rear region.

[0104] In other embodiments, the press-fit region 38 is formed by widening the rear portion of the rear fixing element 3 .

[0105] Although the ceramic knee joint 100 described above with a metal-free, in particular ceramic, tibial tray 20 is a preferred embodiment, the tibial tray 20 or the entire knee joint 100 may also be made of metal or polymer materials or they may include these materials.

[0106] Reference numerals

[0107] 1 Central fixing element

[0108] 2 front fixing elements

[0109] 3 Rear fixing element

[0110] 4 Rear wall of the front fixing element

[0111] 5Form-fitting element of the front fixing element

[0112] 6 Undercut in the wall of the rear fixing element

[0113] 7 Rear wall of rear fixing element

[0114] 8 Posterior edge of tibial tray

[0115] 9 Anterior wall of the rear fixing element

[0116] 10 Side wall of rear fixing element

[0117] 11Guide surface

[0118] 12Central fixing element recess

[0119] 20 Tibia Tray

[0120] 30 Tibial Insert

[0121] 31 Form-fitting element for front fixing element

[0122] 32 Recess for rear fixing element

[0123] 33 Release notch

[0124] 34 Recess for linear central fixation element in tibial insert 35 Anterior wall of recess

[0125] 36 side wall of the recess

[0126] 37 Press fit surface

[0127] 38 Press fit area

[0128] 40 Femoral part

[0129] 100 Artificial knee joint

[0130] D Distal surface of tibial insert

[0131] H Height of the fixing element

[0132] Lateral point on the proximal surface of L1

[0133] Lateral point on the proximal surface of L2

[0134] M Midplane of the proximal surface of the tibial tray

[0135] N is the frontal plane perpendicular to the midplane

[0136] PProximal surface of the tibial tray

[0137] α The angle between the side wall and a plane perpendicular to the anterior wall of the anterior fixation element, in a plane parallel to the proximal surface

[0138] β Angle of undercut

Claims

1. A tibial tray (20) having a proximal surface (P), said proximal surface (P) comprising at least two, in particular exactly two, central fixing elements (1) for achieving a connection with a tibial insert (30) as another part of an artificial knee joint, wherein: The at least two central fixing elements (1) are protrusions protruding from the proximal surface (P) in the proximal direction, and the at least two central fixing elements (1) are positioned symmetrically and / or parallel to a middle plane (M) of the proximal surface (P), the middle plane (M) being perpendicular to the proximal surface (P) and intersecting the proximal surface (P) in the middle between the two outermost points (L1, L2) of the proximal surface (P).

2. The tibial tray (20) according to claim 1, wherein: At least one of the at least two central fixing elements (1) is a cylindrical or linear protrusion protruding from the proximal surface (P), in particular designed for a press fit.

3. The tibial tray (20) according to claim 1 or 2, wherein: The at least two central fixing elements (1) are positioned symmetrically with respect to a frontal plane (N) perpendicular to the median plane (M), the frontal plane (N) in particular passing through the outermost points (L1, L2) of the proximal surface (P).

4. The tibial tray (20) according to any one of the preceding claims, wherein: At least one front fixing element (2), in particular exactly one front fixing element (2), is positioned at the front side of the proximal surface (P), and the rear side of the at least one front fixing element (2) includes a wall (4), which is perpendicular to the middle plane (M) of the proximal surface (P) in a plane parallel to the proximal surface (P).

5. The tibial tray (20) according to claim 4, wherein: The at least one anterior fixation element (2) comprises at least one form-fitting element (5) for a corresponding form-fitting element (31) of the tibial insert (30), in particular at least one cavity in the posterior wall (4) of the at least one anterior fixation element (2) and / or at least one channel passing through the at least one anterior fixation element (2), the at least one form-fitting element (5) of the at least one anterior fixation element (2) being in particular positioned in an area in which the load transfer is less than 70%, in particular less than 50%, of the maximum load transfer.

6. The tibial tray (20) according to at least one of the preceding claims, wherein At least one, in particular exactly one, rear fixation element (3) is positioned symmetrically relative to the middle plane (M) of the proximal surface (P), and the at least one rear fixation element (3) includes a rear wall (7) flush with the rear edge (8) of the tibial tray (20) and / or includes an anterior wall (9) positioned parallel to the rear wall (4) of at least one anterior fixation element (2).

7. The tibial tray (20) according to at least one of the preceding claims, wherein At least one rear fixing element (3) comprises two side walls (10), each of which has an angle (α) with a plane perpendicular to the front wall (9), the angle (α) being in a plane parallel to the proximal plane (P) and in a range between 5° and 85°, in particular between 40° and 50°.

8. The tibial tray (20) according to at least one of the preceding claims, wherein The side wall (10) of at least one rear element (3) is inclined at an angle between 1° and 25°, in particular between 3° and 10°, relative to a plane perpendicular to said proximal plane (P).

9. The tibial tray (20) according to at least one of the preceding claims, wherein: The rear wall (4) of at least one front fixing element (2) and / or the front wall (9) of at least one rear fixing element (3) comprises an undercut (6), in particular, the undercut (6) forms an angle (β) between 10° and 30°, in particular 15°, with a plane perpendicular to the proximal surface (P).

10. The tibial tray (20) according to at least one of the preceding claims, wherein The height (H) of the at least two central fixing elements (1), at least one front fixing element (2) and / or at least one rear fixing element (3) from the proximal surface (P) is between 1 mm and 6 mm, in particular between 3 mm and 4.5 mm, and / or wherein the front end and / or the rear end of the at least two central fixing elements (1) are rounded.

11. The tibial tray (20) according to at least one of the preceding claims, wherein The height (H) of the at least two central fixing elements (1) above the proximal surface (P), the height of at least one front fixing element (2) above the proximal surface (P) and / or the height of at least one rear fixing element (3) above the proximal surface (P) is constant or varies by a maximum of 10% from a minimum height.

12. The tibial tray (20) according to at least one of the preceding claims, wherein: At least one anterior fixation element (2) comprises at least one guide surface (11) for a tibial insert (30), in particular, the guide surface (11) having a curved portion and / or a flat portion in at least the proximal direction of the form-fitting element (5).

13. The tibial tray (20) according to at least one of the preceding claims, wherein: The at least two central fixing elements comprise central fixing element recesses (12).

14. The tibial tray (20) according to at least one of the preceding claims, wherein The side walls (10) and the front wall (9) of at least one rear element (3) are inclined at an angle between 0° and 25°, in particular between 0° and 10°, relative to a plane perpendicular to the proximal plane (P), and / or the side walls (10) and the front wall (9) of at least one rear element (3) include undercut portions.

15. The tibial tray (20) according to at least one of the preceding claims, wherein The tibial tray (20) is made entirely or partially of ceramic, polymer material or metal.

16. A tibial insert (30) designed to mate with a tibial tray (20) according to at least one of the preceding claims.

17. The tibial insert (30) according to claim 16 comprises a recess (32) in the distal surface (D) for matching at least one posterior fixation element (3), said recess (32) comprising at least one stress relief notch (33) at the junction of the two walls (35, 36).

18. The tibial insert (30) according to claim 16 or 17, comprising at least one form-fitting element (31) for engaging at least one form-fitting element (5) of at least one anterior fixation element (2) of the tibial tray (20).

19. An artificial knee joint (100) comprising a tibial tray (10) according to at least one of claims 1 to 115 and a tibial insert (30) according to at least one of claims 16 to 18.

20. The artificial knee joint (100) according to claim 19, wherein: There is a light press-fit connection between the tibial insert (30) and at least two central fixing elements (1), at least one front fixing element (2) and at least one rear fixing element (3), in particular, the press-fit between the tibial insert (30) and the rear wall (4) of the front fixing element (2) and the front wall (9) of the rear fixing element (3) is in the range of 25μm to 125μm, and / or the press-fit between the tibial insert (30) and the central fixing element (1) is in the range of 0μm to 100μm.

21. The artificial knee joint (100) according to claim 19 or 20, wherein: There is at least one press-fit region (38) between the posterior fixation element (3) and the tibial insert (20), in particular at least one press-fit region (38) generated by an angular mismatch between the two walls.

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