Tibia tray with tibia tray shaft structure and artificial knee joint

Abstract

The invention relates to a tibial tray (20) having a distal surface (D), in which a tibial tray shaft structure (21) extends away from the distal surface (D) in a distal direction (DD), in which the tibial tray structure (21) comprises at least three shaft wall elements (22, 23, 24, 25), the at least three shaft wall elements (22, 23, 24, 25) are arranged relative to each other in such a way that a cross-section of the at least three shaft wall elements (22, 23, 24, 25) in a plane perpendicular to the distal direction (DD) is at least a T-shaped, Y-shaped or X-shaped cross-section, and an area (F) of the cross-section decreases strictly monotonically from the distal surface (D) in the distal direction. The invention further relates to an artificial knee joint.

Description

[0001] The invention relates to a tibial shaft with a shaft structure having the features of claim 1 and to an artificial knee joint having the features of claim 27.

[0002] Joint replacement, in particular artificial knee joint replacement, has been known for quite some time. In the case of an artificial knee joint, it is known that a tibial tray part is connected with the proximal end of the tibia of a patient. The connection is made by means of a distal part of the tibial tray, namely the tibial tray shaft.

[0003] The femoral part is connected with the distal end of the femur of the patient. The tibial insert is connected with 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 part and the proximal surface of the distal tray.

[0004] Tibial trays and tibial inserts of this type are described, for example, in EP 3 626 209 B1.

[0005] In order to ensure a good joint connection between the proximal end of the tibia and the tibial tray shaft, a suitably shaped geometry, such as a form-fit design, is required. This is important, in particular when ceramic materials are used for the tibial tray and its tibial tray shaft.

[0006] The tibial tray with the features of claim 1 solves these problems.

[0007] The tibial tray comprises a distal surface, wherein the tibial tray shaft structure extends in a distal direction away from the distal surface. The tibial tray structure forms a protrusion which is inserted into the tibial bone.

[0008] In order to fix the tibial tray well to the bone, the tibial tray structure comprises at least three shaft wall elements which are arranged relative to one another such that their cross-section in a plane perpendicular to the distal direction is T-shaped, Y-shaped or X-shaped. The T-shaped structure comprises three shaft wall elements, two of which form the stem of the T and one of which forms the handle. The stem and the handle are positioned at an angle of 90°.

[0009] The Y-shaped structure also comprises three shaft wall elements, but the three angles can differ from 90°. In one possible embodiment, the shaft wall elements are equally spaced apart by 120°. Alternatively, two of the shaft wall elements can be spaced apart by 90°, then the remaining third shaft wall element is each spaced apart from the other shaft wall elements by 135°.

[0010] The X-shaped structure comprises four shaft wall elements. The shaft wall elements are positioned around a central axis, with angles between the shaft wall elements. It is possible, for example, that each of two groups of angles between the shaft wall elements comprises angles of the same size (for example, two angles of each 110° and two angles of each 70°).

[0011] Furthermore, the area of the cross section strictly monotonically decreases in the distal direction from the distal surface. This means that the tibial tray structure is generally tapered in the distal direction from a wide base. This facilitates the tibial tray to be effectively inserted into the tibia. The tapering is continuous with the section parallel to the distal surface.

[0012] In one embodiment, the outer rim of the at least three axial wall elements strictly monotonically converges in the distal direction and towards the axis of the tibial tray structure. Again, this is another aspect of the tapering which facilitates the tibial tray to be effectively inserted into the tibia.

[0013] The shape of the outer rim can for example be curved with a uniform curvature direction (e.g. exponential shape). But in one embodiment, the outer rim of the at least three axial wall elements has at least one inflection point, in particular three inflection points. This means that the direction of the curvature - not just the amount - changes at least once.

[0014] The curvature of the outer rim should not change too quickly such that any change in the tangent angle at the outer rim of the at least three axial wall elements, in particular any tangent angle of the outer rim of the at least three axial wall elements within one third of the height of the tibial tray structure measured from the distal surface, should be less than 30° over a change of 10% in the distal direction. In the third of the tibial shaft structure closest to the distal surface, the change in slope should be even less.

[0015] In another embodiment, at least 50% of the volume of the tibial tray structure is located within one third of the height of the tibial tray structure measured from the distal surface.

[0016] At least one of the axial wall elements can have a wall thickness of between 1 mm and 6 mm, in particular between 2 mm and 5 mm, for ceramic materials between 1 mm and 5 mm, measured at the point furthest from the axis and on the distal surface.

[0017] It is also possible that the radius at the transition from the outer rim of at least one of the at least three axial wall elements to the side wall of at least one of the at least three axial wall elements is in the range of 0.5 mm to 4 mm.

[0018] For effective bonding with bone cement, at least one of the at least three axial wall elements comprises at least one cement holding structure, in particular at least one recess structure, for holding bone cement. Those cement holding structures can preferably be positioned on the anterior and / or posterior side of the tibial tray.

[0019] The transition from the outer rim into the tibial shaft structure in the distal surface is located at least 5 mm from the lateral and / or posterior side of the distal surface. This ensures a proper distance to the edge of the distal surface and ensures that the tibial shaft structure is positioned within the spongiosa and outside the corticalis. The distance is measured in a straight line from the end of the outer rim to the edge of the distal surface.

[0020] In one embodiment, the tibial tray structure comprises a surface extending between at least two of the outer rims of the at least three shaft wall elements or between two of the lateral walls of the at least three shaft wall elements.

[0021] Since a rounding of the edge can be relevant, the radius at the transition from the distal surface to at least one of the at least three shaft wall elements and / or to the smooth surface can be in the range of 1 mm to 4 mm.

[0022] Furthermore, the axis of the tibial tray shaft structure can be located on the distal surface at one third of the distance measured from the anterior rim to the posterior rim. This means that the axis of the tibial tray shaft is located slightly closer to the anterior side than to the posterior side. The axis of the tibial tray shaft is defined for X-shaped, Y-shaped and T-shaped tibial tray shaft structures since the at least three shaft wall elements converge strictly monotonically towards this axis. In specific embodiments, the axis of the tibial tray shaft structure is at a distance of 5 mm, 5.67 mm, 6.33 mm or 7 mm from the center of the distal surface. In combination with this or alternatively, embodiments can have a tibial shaft tray structure with a height of 35 mm, 40 mm, 45 mm or 55 mm from the distal surface. In combination with this or alternatively, the thickness of the shaft wall elements can be 3 mm, 3.75 mm, 4.25 mm or 5 mm.

[0023] The angle between the shaft wall elements is between 90° and 180° on the anterior side and between 30° and 120° on the posterior side. For example, a T-shaped tibial tray structure with three shaft wall elements will have an angle of 180° on the anterior part and two angles of 90° on the posterior side. The shape of the X-shaped and Y-shaped tibial tray structures can vary in the stated regions.

[0024] To ensure a good mechanical connection between the tibial tray and the tibia, the tibial tray shaft structure comprises at least one cement holding structure, in particular a hole, a groove and / or a recess without any undercut. This allows the cement to effectively enter the cement holding structure. In particular, the at least one cement holding structure is located within the vertical two thirds, in particular the anterior third, of the tibial tray shaft structure measured in the distal direction from the distal surface. This means that the at least one cement holding structure is preferably located towards the distal surface and not towards the distal end of the tibial tray shaft structure.

[0025] In another embodiment, the tibial tray comprises at least one anterior fixation element, in particular exactly one anterior fixation element, which is positioned at the anterior side of the proximal surface, the posterior side of the at least one anterior fixation element comprising a wall which is perpendicular to a median plane of the proximal surface in a plane parallel to the proximal surface. In particular, the at least one anterior fixation element comprises at least one form-fit element for a corresponding form-fit element of the tibial insert, in particular at least one cavity in the posterior wall of the at least one anterior fixation element and / or at least one passage through the at least one anterior fixation element, the at least one form-fit element of the at least one anterior fixation element being in particular positioned in a region in which the load transmission is less than 70%, in particular less than 50%, of the maximum load transmission.

[0026] The at least one anterior fixation element can comprise at least one guide surface for the tibial insert, in particular the guide surface having a curved portion and / or a planar portion in the proximal direction of the at least one form-fit element. When the tibial insert is to be brought together with the tibial tray, a protrusion of the tibial insert contacts the guide surface and slides along the guide surface such that its movement during the bringing together is guided and the protrusion can snap into the at least one form-fit element. In one embodiment, the at least one guide surface comprises a planar portion or the at least one guide surface is a planar surface inclined by an angle in the range between 5° and 45°, in particular 30°, with respect to a horizontal plane.

[0027] In some embodiments, the tibial surface comprises at least two, in particular exactly two, central fixation elements for enabling a connection with a tibial insert being another part of an artificial knee joint, wherein the at least two central fixation elements are protrusions protruding in the proximal direction from the proximal surface and the 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 in the middle between two outermost points of the proximal surface. In particular, the at least two central fixation elements are positioned symmetrically with respect to a frontal plane perpendicular to the median plane, the frontal plane in particular passing through the outermost points of the proximal surface. The at least two central fixation elements can comprise central fixation element recesses for providing a better fit with the tibial insert. The at least two central fixation elements or exactly two central fixation elements can be configured as form-fit elements and / or press-fit elements.

[0028] Furthermore, embodiments of the tibial tray can comprise at least one, in particular exactly one, posterior fixation element positioned symmetrically with respect to a midplane of the proximal surface, the at least one posterior fixation element comprising a posterior wall flush with a posterior rim of the tibial tray and / or comprising a front wall positioned substantially parallel to the posterior wall of the at least one anterior fixation element. The side wall and / or the front wall of the at least one posterior element can in particular be inclined by an angle between 0 and 45°, in particular between 0 and 30°, more particularly by an angle of 10°, with respect to a plane perpendicular to the proximal plane, and / or the side wall and the front wall of the at least one posterior element comprise an undercut. This enables for example to form a posterior block with an inwardly inclined side wall, i.e. a side wall with an angle greater than 0°, and a side wall or a tongue and groove system (undercut) converging to the front side. Such a posterior fixation element can serve as a fulcrum when attaching a tibial insert.

[0029] The tibial tray can be manufactured completely or partially from ceramic, polymeric material or metal.

[0030] Further embodiments of the tibial tray can comprise a proximal surface for realizing at least two, in particular exactly two, central fixation elements for the connection with a tibial insert being another part of an artificial knee joint. The central fixation elements are protrusions protruding from the proximal surface which can be connected to the tibial insert as a form fit and / or force lock.

[0031] The at least two central fixation elements are designed as protrusions protruding in proximal direction from the proximal surface, i.e. the central fixation elements are generally directed away from the proximal surface in direction of the tibial insert.

[0032] The at least two central fixation elements are positioned symmetrically and / or parallel to a midplane of the proximal surface, the midplane being perpendicular to the proximal surface and intersecting the proximal surface in the middle between two outermost points of the proximal surface. The midplane divides the proximal surface into two lateral halves. The at least two central fixation elements are oriented symmetrically and / or parallel to the midplane. In another embodiment, the at least two fixation elements are oriented asymmetrically with respect to the midplane. This can mean different angles with respect to the midplane and / or different distances from the midplane.

[0033] The at least two central fixation elements are configured as cylindrical protrusions or linear protrusions, in particular designed for a press fit and / or form fit. Cylindrical means that the protrusions have for example a circular cross section, an elliptical cross section. Linear means that the protrusions extend linearly on the proximal surface. At least one of the central fixation elements can for example have a linear or cylindrical shape.

[0034] In one embodiment, the at least two central fixation elements are positioned symmetrically with respect to a frontal plane perpendicular to the median plane. The frontal plane divides the proximal end surface into an anterior portion and a posterior portion. In particular, the frontal plane can pass through the outermost points of the proximal end surface.

[0035] In order to better insert the tibial insert and in order to better fix in the body, the posterior wall of the at least one anterior fixation element and / or the anterior wall of the at least one posterior fixation element can comprise an undercut.

[0036] In one embodiment, the height of the at least two central fixation elements, of the at least one anterior fixation element and / or of the at least one posterior fixation element extending from the proximal end surface is in the range of 1 mm and 6 mm, in particular 3 mm and 4 mm, 3 mm and 5 mm, and / or wherein the anterior end and / or the posterior end of the at least two central fixation elements is rounded. In particular, the height of the at least two central fixation elements above the proximal end surface, the height of the at least one anterior fixation element above the proximal end surface and / or the height of the at least one posterior fixation element above the proximal end surface is constant or varies by a maximum of 10% from a minimum height. These features help to provide a firm connection with the tibial insert and / or allow an efficient assembly.

[0037] This problem is also solved by a tibial insert designed or configured to mate with the claimed tibial tray.

[0038] In order to ensure a good connection with the tibial tray, the tibial insert can comprise one recess in the distal end surface for mating with the at least one posterior fixation element, the recess comprising at least one stress relief notch at the junction of the two walls of the recess. This prevents the formation of a mechanical stress sharp corner where the two walls of the recess meet.

[0039] The firm connection can be achieved by at least one form-fit element of the tibial insert for engaging at least one form-fit element of the at least one anterior fixation element of the tibial tray. The connection can also be achieved by a press-fit connection or a combination thereof.

[0040] This problem is also solved by an artificial knee joint comprising the claimed tibial tray and the claimed tibial insert, wherein there is a light press-fit connection between the tibial insert and the at least two central fixation elements, between the tibial insert and the at least one anterior fixation element and between the tibial insert and the at least one posterior fixation element, in particular with a press-fit in the range of 0 μm to 450 μm, in particular in the range of 0 μm to 250 μm.

[0041] In another embodiment of the artificial knee joint there is at least one press fit area between the posterior fixation element and the tibial insert, in particular at least one press fit area resulting from an angle mismatch between two walls. This allows to improve the assembly of the joint and to reduce micro-motions in the posterior part of the joint.

[0042] Embodiments of the application are shown in the drawings,

[0043] FIG. 1 A perspective view of an embodiment of a tibial tray is shown,

[0044] FIG. 2 A perspective view on the distal surface of an embodiment of a tibial tray with a tibial tray structure with three axis wall elements (Y-shaped structure) is shown,

[0045] FIG. 3 A perspective view on the distal surface of an embodiment of a tibial tray with a tibial tray structure with four axis wall elements (X-shaped structure) is shown,

[0046] FIG. 4 A view on the distal surface of another embodiment of a tibial tray with a tibial tray structure with three axis wall elements (T-shaped structure) is shown,

[0047] FIG. 5 A view on the distal surface of an embodiment of a tibial tray is shown, FIG. 4 with a cross-sectional plane in the proximal third of the tibial tray structure (T-shaped structure);

[0048] FIG. 6 A perspective view on the distal surface of an embodiment shown in FIG. 4 and FIG. 5 is shown (T-shaped structure);

[0049] FIG. 6A A view on the distal surface of an embodiment with an indication of the radius of the circumference is shown;

[0050] FIG. 7 A perspective view from the side of an embodiment of a tibial tray with a tibial tray structure with three axis wall elements (T-shaped structure) and a recess structure for bone cement is shown,

[0051] FIG. 8 A perspective view on the distal surface of an embodiment of a tibial tray with a tibial tray structure with three axis wall elements (T-shaped structure) is shown,

[0052] FIG. 9 A perspective view of an embodiment of a tibial tray is shown,

[0053] FIG. 9A shows the same view as FIG. 9 with the reference system highlighted;

[0054] FIG. 9B shows a modification of the embodiment in FIG. 9 ;

[0055] FIG. 10A shows a view of the proximal surface of an embodiment of the tibial tray;

[0056] FIG. 10B shows a view of the distal surface of a tibial insert that matches the tibial tray shown in FIG. 10A ;

[0057] FIG. 11 shows a view of the proximal surface of the embodiment shown in FIG. 10A , indicating the interference region;

[0058] FIG. 12A shows the insertion of the tibial insert into the tibial tray in perspective view;

[0059] FIG. 12B shows the insertion of the tibial insert into the tibial tray in FIG. 12A cross-sectional view;

[0060] FIG. 13A shows a detailed front view of a first embodiment of the tibial insert;

[0061] FIG. 13B shows a detailed front view of a second embodiment of the tibial insert;

[0062] FIG. 14 shows a perspective view of a modification of the embodiment shown in FIG. 9 ;

[0063] FIG. 15A is a perspective view of the distal surface, seen from the anterior side of the tibial shaft structure;

[0064] FIG. 15B is a perspective view of the distal surface, seen from the posterior side of the tibial shaft structure;

[0065] FIG. 15C is a view in the proximal direction on the distal surface;

[0066] FIG. 16A is a perspective view from the posterior side of the proximal surface of the tibial tray with the first embodiment of the central fixation element;

[0067] FIG. 16B is a perspective view from the anterior side of the proximal surface of the tibial tray with the first embodiment of the central fixation element;

[0068] FIG. 17 is a perspective view from the posterior side of the proximal surface of the tibial tray of the second embodiment with central fixation elements;

[0069] FIG. 18A is a cross-sectional view through the embodiment of the tibial tray in the forward direction;

[0070] FIG. 18B shows a cross-sectional view through the embodiment of the tibial tray in the backward direction;

[0071] FIG. 19 shows a schematic view of the line elements to create a smooth outer rim for the wall elements;

[0072] FIG. 20A shows a perspective view of the anterior side of the embodiment of the tibial tray with cement holding structures;

[0073] FIG. 20B shows a perspective view of the posterior side of the embodiment shown in FIG. 20A with cement holding structures;

[0074] FIG. 21A shows a perspective view of the anterior side of the embodiment, where the geometry at the wall elements of the tibial tray shaft structure is illustrated;

[0075] FIG. 21B shows a perspective view of the posterior side of the embodiment shown in FIG. 20A ;

[0076] FIG. 20B shows a perspective view on the proximal surface of another embodiment of the tibial tray with guiding surfaces on the anterior fixation elements;

[0077] FIG. 15A shows details of the connection between the posterior fixation elements in one embodiment.

[0078] In FIG. 15B , an artificial ceramic knee joint 100 is shown in a perspective view from a posterior position. In FIG. 15C , the femoral part 40, the tibial insert 30 and the tibial tray 20 of the artificial knee joint without metal are shown. Alternative embodiments are not without metal.

[0079] Here, the whole artificial knee joint 100 is without metal, e.g. a combination of ceramic and polymer material. The tibial tray 20 can be made of ceramic, for example, and the tibial insert 30 can be made of a polymer material.

[0080] At a proximal position of the artificial knee joint, a femoral part 40 is shown, wherein two bone segments fit into matching recesses in a proximal surface of the tibial insert 30 at a distal end of the femoral part 40.

[0081] The tibial insert 30 is connected with the tibial tray 20, a distal surface D of the tibial insert 30 facing a proximal surface P of the tibial tray 20.

[0082] In combination FIG. 21B , embodiments of the tibial tray 20 are described. In FIG. 21A , embodiments of the tibial tray 10 and the tibial insert 30 are described, which can be used in combination with the embodiments of the tibial tray 20 described herein.

[0083] In FIG. 21B , a perspective view of a distal side of an embodiment of the tibial tray 20 is shown. The shape of the distal surface D is roughly shaped like the proximal side of the tibial tray 20 (see for example FIG. 22 5). The tibial shaft structure 21 is located in the center of the distal surface D, i.e. in the middle of the lateral width between point L1 and point L2. In the shown embodiment, the tibial shaft structure 21 is essentially Y-shaped (i.e. referring to a cross section in a plane parallel to the distal surface D), with the axis A being in the center. The tibial tray structure 21 comprises three shaft wall elements 22, 23, 24 arranged around the axis A, with an angle of 120° between them. One shaft wall element 22 of the Y is oriented to the front side of the tibial tray 20, the other two shaft wall elements 23, 24 are oriented to the back side of the tibial tray 20.

[0084] The tibial tray structure 21 extends away from the distal surface D in a distal direction DD (as for example FIG. 9 indicated), which is essentially pointing out of the plane of the figure in FIG. 16A .

[0085] At the rim of the distal surface D, a raised rim R is provided, which extends away from the distal surface D. The width in a plane parallel to the distal surface D is between 1 mm and 4 mm.

[0086] The three shaft wall elements 22, 23, 24 of the tibial tray shaft structure 21 each comprise an outer rim 26. The outer rim 26 is a thin face of the shaft wall element 22, 23, 24. The thickness T of the shaft wall element 22, 23, 24, measured at the end point (i.e. the point on the distal surface D furthest away from the axis A), is between 2 mm and 5 mm.

[0087] The outer edges 26 converge toward axis A from their wide base at the distal surface D in the distal direction. The convergence is strictly monotonic, meaning there are no segments of the outer edges 26 parallel to the distal surface D. FIG. 12A In the embodiment shown, the slope of the outer edge 26 increases from the base, i.e., the distal surface D, toward the axis. The change in slope is smooth and without kinks.

[0088] In the opposing space between the axial wall elements 22, 23, and 24, the outer edge 26 is connected by a smooth surface S, which is curved inward (i.e., toward axis A). Surface 13 itself has no kinks or edges to allow for good insertion into the tibia. The transition from the smooth surface 13 to the outer edge 26 is also smooth, i.e., without kinks or edges. In the illustrated embodiment, the radius R2 of this transition is between 1 mm and 4 mm, depending particularly on the size of the tibial tray structure 21.

[0089] The transition from the distal surface D to the shaft wall elements 22, 23, 24 and / or from the distal surface D to the smooth wall 13 is rounded, wherein the radius R1 is in the range of 1 mm to 4 mm.

[0090] If it will still be in FIG. 12B As shown in more detail in the context, the cross-sectional area of ​​the tibial axial structure 21 in a plane C parallel to the distal surface D is largest at the base of the distal surface D. As the tibial axial structure 21 extends distally DD, the cross-sectional area decreases (particularly by strictly monotonic means).

[0091] The thickness of the base plate with distal surface D is in the range of 2 mm to 6 mm, particularly 4.5 mm.

[0092] exist FIG. 23 The image shows an embodiment of a tibial tray 20, which includes four axial wall elements 22, 23, 24, and 25 arranged in an X-shaped pattern. Two of the axial wall elements 24 and 25 are oriented toward the anterior side of the tibial tray 20, and two of the axial wall elements 22 and 23 are oriented toward the posterior side.

[0093] In addition, the geometry of the outer edge 26, the smooth surface 13 in the angled space between the axial wall elements 22, 23, 24, 25, and especially the convergence of the outer edge 26 toward the axis A in the distal direction D, are similar to a combination. FIG. 23 The embodiments shown are therefore described in the text.

[0094] FIG. 23 The implementation method shown in the three-dimensional diagram is FIG. 1 and FIG. 1 Further variations of the embodiments shown are also applicable. Therefore, the description given above is also applicable.

[0095] Here, the tibial tray structure 21 has a T-shaped cross section in a plane parallel to the distal surface D. The shaft wall elements 22, 24 forming the stem of the T are positioned essentially parallel to the anterior side, one shaft wall element 25 forming the handle of the T is oriented perpendicular to the posterior side of the tibial tray 20.

[0096] Likewise, the three shaft wall elements 22, 23, 24 of the tibial tray structure 21 have a cross-sectional area which strictly monotonically converges in the distal direction DD towards the axis A. The outer edges 22, 23, 24 have a slope which is always greater than 0° (measured with respect to the distal plane), i.e. the outer edges do not have a plateau. But the outer edge 26 has three inflection points 27 where a change in curvature exists.

[0097] Any change in the tangent angle over a 10% height distance of the tibial tray structure means that there is no sharp bend in the outer edge 26. The change in slope is smaller in the first third of the height of the tibial tray structure 21 measured from the distal surface. In combination FIG. 2 to FIG. 8 Another definition of the outer edge 26 is described.

[0098] FIG. 9 to FIG. 14 The rear view shows FIG. 2 an embodiment. Here, the cross-sectional plane C parallel to the distal surface D is shown. The cross-sectional plane C separates the lower third from the upper two-thirds of the tibial tray structure 21. For a good mechanical load distribution, at least 50% of the volume of the shaft wall elements 22, 23, 24 is located between this cross-sectional plane C and the distal surface D, i.e. in the third closest to the distal surface D. This is also FIG. 9 to FIG. 1 and FIG. 5 the case for the other embodiments shown in

[0099] FIG. 2 The same embodiment as shown in FIG. 2 and FIG. 5 is shown, i.e. a tibial tray structure 21 having a T-shaped structure. In this view, the shape of the outer edge 26 and the rounded transition from the distal surface into the tibial tray structure 21 can be clearly seen in the drawing.

[0100] In FIG. 3 , some geometrical shapes of the periphery of the tibial tray 20 are described. The anterior radius Rant is between 30 mm and 60 mm. The lateral radius Rlat is between 15 mm and 30 mm, and the posterior radius Rpost is between 10 mm and 20 mm, in particular 16 mm.

[0101] FIG. 2 The same embodiment as shown in FIG. 4The above description applies mutatis mutandis to the embodiments of the tibial tray 20. In addition to the described embodiments, this embodiment comprises one or more anterior and / or posterior cement holding structures, here recess structures 28 in the tibial tray structure 21. When implanting the tibial tray 20 into the tibia, bone cement can enter such undercuts for better fixation. In this embodiment, the recess structures 28 are shaped like grooves substantially parallel to the distal surface. Other shapes are in principle possible. An aspect here is that the cement holding structures 28 should be oriented such that the bone cement is not easily removed when implanting the tibial tray 20.

[0102] In FIG. 2 , a variation of the embodiment shown in FIG. 3 is depicted, namely a T-shaped structure as tibial tray structure 21. The distal surface D comprises recesses 14. Furthermore, it is pointed out that the transition points from the outer rim 26 of the tibial shaft structure 21 in the distal surface D are located at least 5 mm (D1) from the lateral and / or posterior side of the distal surface D. The medial planes of the shaft wall elements 22, 23 extend to the lateral and / or posterior side of the distal surface D, thereby defining the distance D1. This allows for a good placement of the tibial tray structure 21 in the bone.

[0103] In the following, embodiments of the tibial tray 20 and the tibial insert 30, in particular features of the proximal surface P of the tibial tray 20 and the matching distal surface D of the tibial insert 30 are described.

[0104] FIG. 19 , FIG. 5 A perspective view of the proximal surface P of the tibial tray 20 is shown. In FIG. 4 , the tibial tray is shown without reference numerals, but with reference planes M, N which are used in the following to define the position of features on the tibial tray 20 in order to reduce complexity.

[0105] With reference to FIG. 2 , the medial plane M is perpendicular to the planar proximal surface P and intersects the proximal surface P in the middle between the outermost points L1, L2 of the proximal surface P. The frontal plane N is perpendicular to the medial plane M.

[0106] In one embodiment of the tibial tray 20, the dimensions are grouped in different sizes. There are eight different sizes for the distance between the point L1 and the point L2. This is used to allow for artificial knee joints 100 for different sizes of patients. The smallest distance between L1 and L2 is 60 mm. The other seven sizes are 64 mm, 68 mm, 72 mm, 76 mm, 80 mm, 84 mm and 88 mm (i.e. using increments of 4 mm). Other embodiments can use different absolute sizes and / or different increments, which do not have to be the same.

[0107] In the extent of the proximal surface P in the direction perpendicular to the distance between L1 and L2, the corresponding sizes are 38.7 mm, 41.3 mm, 43.9 mm, 46.5 mm, 49.0 mm, 51.6 mm, 54.2 mm and 56.8 mm. Other embodiments can use different absolute sizes and / or different increments, again, the increments need not be identical.

[0108] The proximal surface P of the tibial tray 20 is configured such that a corresponding tibial insert 30 (see e.g. FIG. 3 , Fig. 13) can be securely fastened to the tibial tray 20 (see FIG. 6 , FIG. 4 ). The planar proximal surface P is polished as such with an average roughness of Ra = 1 pm, in particular Ra = 0.1 pm and a uniformity of 0.1. In other embodiments, the average roughness is less than 5 pm, in particular less than 2 pm.

[0109] 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-like fixation elements 1, 2, 3 for the connection of tibial inserts 30 using a press fit or interference fit (see FIG. 5 ).

[0110] In the embodiment shown in FIG. 6A , the proximal surface P comprises two central fixation elements 1. As will be described in the following, these two central fixation elements enable a secure connection with a tibial insert (see FIG. 7 ) as another part of the artificial knee joint 100.

[0111] In the shown embodiment, the two central fixation elements 1 are linear protrusions, which protrude away from the proximal surface P in the proximal direction, such that the two central fixation elements 1 can match corresponding notches (or grooves) 34 (see FIG. 4 to FIG. 6 ) in the tibial insert 30. In other embodiments, the central fixation elements 1 can have a columnar shape. Other shapes and different positions of the central fixation elements 1 will be shown in the following.

[0112] The two central fixation elements 1 are positioned symmetrically and parallel to the middle plane M.

[0113] In the embodiment shown in FIG. 8 , the two central fixation elements 1 are still symmetric with respect to the middle plane M but not completely parallel, as the two central fixation elements 1 are angled with respect to the middle plane M by less than 5°, such that the two linear fixation elements 1 show some convergence towards the anterior side.

[0114] In other embodiments, the two central fixation elements 1 can also be asymmetric with respect to the median plane M but parallel to each other.

[0115] As FIG. 4 to FIG. 7 illustrated in the different embodiments, more than two central fixation elements 1 can be used. In addition thereto, FIG. 9 the embodiments described in connection with FIG. 9A are quite comparable.

[0116] In the embodiment illustrated in FIG. 9A , the two central fixation 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.

[0117] The two central fixation elements 1 have the form of a parallelepiped, the front end and the rear end of the central fixation elements 1 being rounded.

[0118] In the illustrated embodiment, the two central fixation elements 1 have a height H of 3.8 mm extending 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 illustrated embodiment, the height H of the central fixation elements 1 is constant. In other embodiments, the height H can vary with respect to the proximal surface P. In other embodiments, the height H of at least two central fixation elements 1 on the proximal surface varies by a maximum of 10% from a minimum height.

[0119] In the embodiment illustrated in FIG. 9A , the distance between the two central fixation 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 fixation elements 1 are parallel to each other, the width of each of the central fixation elements is 2.5 mm. The distance between the central fixation elements is chosen here to be as large as possible in order to provide a large torque and to prevent the polyethylene material from being sheared off from the tibial insert 30. If the distance between the two central fixation elements 1 is always the same, different sizes of tibial inserts 30 can be used when assembling the artificial knee joint 100.

[0120] The orientation of the central fixation elements 1 on the proximal surface P enables a linear guidance of the tibial insert 30 during assembly (see FIG. 1 , FIG. 12A ), so that the central fixation elements 1 can also be referred to as central guide rails. In addition, the central fixation elements 1 allow an increased stability against shear forces in the artificial knee joint.

[0121] The proximal surface P also comprises a front fixation element 2 located at the front edge of the proximal surface P. The rear side of the front fixation element 2 comprises a rear wall 4 located perpendicular to the median plane M of the proximal surface P. The rear wall 4 is thus 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. In other embodiments, the height of the front fixation element 2 and the height of the central fixation elements 1 can be different.

[0122] The front fixation element 2 comprises two cavities 5 each in the form of a channel, i.e. a channel open at both ends, having a substantially rectangular cross section. As will be shown in connection with FIG. 12B , FIG. 11 those cavities are shape cooperation elements 5 cooperating with matching shape cooperation elements 31 on the tibial insert 30. The shape cooperation elements 5 in the front fixation element are positioned symmetrically with respect to the median plane M.

[0123] In other embodiments, the front fixation element 2 comprises only one or more than two shape cooperation elements 5. The cross section of the cavities of the shape cooperation elements 5 need not be rectangular, e.g. a circular or polygonal cross section can also be used.

[0124] In the embodiment of FIG. 9 the front fixation element 2 is one continuous element located at the front edge of the tibial tray 20. In other embodiments, the front fixation element 2 can be divided into more than one part, e.g. two elements, each of the two elements comprising shape cooperation elements 5.

[0125] The two shape cooperation elements 5 in the front fixation element 2 are positioned in areas where the mechanical load transfer is less than 50% of the maximum load transfer. This is due to the fact that the channel-like shape cooperation elements 5 slightly weaken the structure of the front fixation element 1.

[0126] Another structure on the proximal surface P is a rear fixation element 3 positioned at the rear edge of the proximal surface P. The rear fixation element 3 is positioned symmetrically with respect to the median plane M and comprises a rear wall 7 flush with the rear edge 8 of the tibial tray 20. The rear wall 7 follows the curved shape of the rear edge 8 of the tibial tray 20. The cross section of the rear fixation element 3 in a plane parallel to the proximal surface P is symmetric with respect to the median plane M. In this embodiment, the rear fixation element 3 has the same height H as the central fixation elements 1. In other embodiments, the height of the rear fixation element 3 and the height of the central fixation elements 1 can be different.

[0127] FIG. 10BThe illustrated embodiment also includes the front wall 9 of the rear fixing element 3 and the rear wall 4 of the front fixing element 2. The respective edges of those walls 4, 9 located at the proximal surfaces of the rear element 3 and the front fixing element 2 are parallel to each other. If the walls 4, 9 do not have undercuts (i.e., the walls 4, 9 are not inclined), then the walls 4, 9 themselves will be parallel. Therefore, the two central fixing elements 1 are oriented perpendicular to both the rear wall 4 of the front fixing element 2 and the front wall 9 of the rear fixing element 3.

[0128] The rear fixation element 3 also includes two side walls 10 angled relative to the front wall 9 of the rear fixation 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 of 0° to 22°, particularly in the range of 15° to 22°. Therefore, the two side walls 10 are oriented to converge in the forward direction. The overall horizontal shape of the rear fixation element 3 is approximately trapezoidal, wherein the long sides of the trapezoid are curved.

[0129] The two sidewalls 10 of the posterior fixation element 3 are inclined inward at an angle between 1° and 45°, particularly between 20° and 30°, relative to a plane perpendicular to the proximal plane P, to form an undercut. Therefore, the top surface of the posterior fixation element 3 is slightly larger than the base cross-section in the plane of the proximal surface.

[0130] The description in this article and FIG. 10B In the preferred embodiment shown, the front wall 9 of the rear fixation element 3 includes an undercut 6 that forms an angle β between 1° and 45°, particularly 30°, 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, in principle, include an undercut 6.

[0131] In the embodiments discussed so far, the height H of the fixing elements 1, 2, and 3 above the proximal surface P is the same. This need not be the case in all embodiments.

[0132] exist FIG. 9B , FIG. 14 The matching tibial tray 20 and tibial insert 30 are shown side by side in the middle. FIG. 14 The implementation of the tibial tray 20 has already been described. FIG. 9 The description is in [the relevant text], therefore you can refer to the corresponding description. FIG. 9 The distal surface D of the tibial insert 30 is shown. A comparison of the two components 20 and 30 shows that the tibial insert 30 can be connected to the tibial tray 20, such that the first fixation element 1 fits into the matching recess 34 in the tibial insert 30.

[0133] The tibial insert 30 includes a recess 32 located in the distal surface D for a matching posterior fixation element 3 for the tibial tray 20 (see [reference]).FIG. 9 ). The recess 32 is open towards the rear side, so that the recess 32 has only a front wall 35 and two side walls 36.

[0134] The side walls 36 of the recess 32 are angled to match the angled side walls 10 of the rear fixation element 3. In the corners 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.

[0135] At the front side of the tibial tray insert 30, two form-fit elements 31 are located which can be inserted into the two cavities of the form-fit elements 5 in the front fixation element 2 (see FIG. 12A ).

[0136] The notches 34 and the recess 32 of the tibial tray 30 also form a certain form-fit connection with the matching structures, namely the central fixation elements 1 and the rear fixation elements 3 of the tibial tray 20. However, the main function of the structures 32, 34 is an aid during assembly, which will be described below in connection with FIG. 12B , FIG. 12A .

[0137] The connection between the tibial tray 20 and the tibial insert 30 is mainly realized by a press-fit connection between the tibial insert 30 and at least two central fixation elements 1, at least one front fixation element 2 and at least one rear fixation element 3, in particular with a press-fit in the front-rear direction in the range of 0 μm to 450 μm, more particularly in the range of 0 μm to 250 μm. In FIG. 12B , surfaces 37 for the press-fit at the rear wall 4 of the front fixation element 2, at the inner side of the central fixation elements 1 and at the front wall 9 of the rear fixation elements 9 are highlighted. All press-fit connections can be dimensioned identically, but this is not necessarily the case for all embodiments. For example, the press-fit between the rear wall 4 of the front fixation element 2 and the front wall 9 of the rear fixation element 3 is in the range of 50 μm to 150 μm and / or the press-fit between the central fixation elements 1 is in the range of 50 μm to 100 μm. The lateral surfaces of the recess 32 provide an interference fit.

[0138] In FIG. 9 and FIG. 9 , the assembly of an embodiment of the tibial insert 30 and the tibial tray is shown in different views.

[0139] FIG. 12B A perspective view from the front is shown, in which the tibial insert 30 is partially connected with the underlying tibial tray 20. FIG. 10A An essentially identical relative position of the tibial tray 20 and the tibial insert 30 is shown, but in a cross-sectional view, in which the front fixation element 2 is located on the right-hand side.

[0140] The tibial insert 30 is first connected with the posterior fixation element 3 (see FIG. 10B , FIG. 10A , FIG. 9 ) which serves as a kind of fulcrum for snapping into place. In the view FIG. 10B a undercut 6 with an angle of about 15° in the front wall 9 is shown which allows a secure positioning of the tibial insert 30. At the front side (see FIG. 10B ) two form-fit elements 31 are shown which snap into the cavities of the form-fit elements 5 (not seen in FIG. 9 ).

[0141] In FIG. 12A a first embodiment of the tibial insert 30 is shown in a front view. In this embodiment the shape of the distal surface D, i.e. the outer rim of the tibial insert 30 is basically a slightly inclined wall which is not suitable for covering. The inclination can be between 0° and 10°. In case of an inclination of 0° the wall is straight.

[0142] In FIG. 12B a second embodiment of the tibial insert 30 is also shown in a front view. Here the shape of the distal surface D, i.e. the outer wall is slightly inclined outwards which is suitable for covering.

[0143] Although the above described ceramic knee joint 100 with a tibial tray 20 which is free of metal, in particular ceramic, is a preferred embodiment, the tibial tray 20 or the whole knee joint 100 can also be made of metal or polymeric material or they can comprise these materials.

[0144] FIG. 11 , FIG. 12A and FIG. 12B show the distal surface D of the tibial tray 20. FIG. 12A shows a view as seen from the front side, FIG. 12B shows a view as seen from the back side. FIG. 9 shows a top view of the distal surface D.

[0145] The tibial tray structure 21 is basically an X-shaped structure, wherein the angle γ1 between the first and second shaft wall elements 22, 23 is different from the angle γ2 between the third and fourth shaft wall elements 24, 25. The angle γ1 between the first and second shaft wall elements 22, 23 facing the back side is smaller than the angle γ2 between the third and fourth shaft wall elements 24, 25. In the shown embodiment the angle γ1 between the first and second shaft wall elements 22, 23 is smaller than 90°, i.e. 80° (see FIG. 10A) ; the angle y2 between the third axial wall element 22 and the fourth axial wall element 23 is greater than 90°, namely 120°. In one embodiment, the angles y1, y2 are 110° and 70°, respectively.

[0146] In other embodiments, as shown for example in FIG. 10B , the central fixation element 1 has a shape with two axes of symmetry, one along the longitudinal axis and one perpendicular to this axis. In FIG. 12B , FIG. 12A , embodiments of the tibial tray 20 are shown which deviate from this pattern.

[0147] In FIG. 12A , FIG. 13A , embodiments are shown in which the central fixation element 1 has a wider lateral cross section towards the front side than towards the rear side. Thus, the long side walls of each of the central fixation elements 1 converge towards the front side. The inner side walls of the central fixation element 1 are not parallel and diverge towards the rear of the tibial tray 20, while the outer side walls are essentially parallel.

[0148] In FIG. 13B , a variant embodiment of the tibial tray 20 is shown, since the central fixation elements 1 are differently shaped. Here, the outer side walls of the central fixation elements 1 are parallel to each other and there are two axes of symmetry as in the embodiment shown in FIG. 15A . In the embodiment of FIG. 15B , the inner side walls are not linear over the entire length. Towards the front side and the rear side, the side walls converge, there is a divergence towards the middle.

[0149] FIG. 15C , FIG. 15A and FIG. 15B , the front fixation elements 2 of the embodiments shown are shaped as in the embodiment shown in FIG. 15C . However FIG. 15B , FIG. 9 and FIG. 16A , the rear fixation elements 3 of the embodiments shown are differently shaped.

[0150] The side walls of the rear element 3 are inclined with respect to a plane perpendicular to the proximal plane P by an angle between 0° and 45°, in particular between 0° and 30°. Additionally or alternatively, the side walls and the front wall of at least one rear element 3 comprise an undercut.

[0151] In FIG. 16B , FIG. 16A , a cross section in the frontal plane N (see for example FIG. 16B ) of one embodiment is shown. FIG. 17A view in forward direction is shown, i.e. the anterior fixation element 2 can be seen behind the central fixation element 1 shown in cross section. FIG. 9 A view in the same frontal plane N but in backward direction is shown.

[0152] The cross section of the central fixation element 1 shows that they comprise a central fixation element recess 12 (undercut) at the transition to the proximal surface P and along the inner lateral wall. The central fixation element recess 12 is here a groove with constant radius. In different embodiments not shown here, the central fixation element recess 12 can also be located on the outer lateral wall of the central fixation element 1 or only on the outer lateral wall.

[0153] FIG. 17 , FIG. 16A Also shown is the cement holding structure 28 which will be described in more detail in connection with FIG. 16B and FIG. 17 .

[0154] FIG. 9 A schematic view of a view in forward direction is shown, wherein the tibial tray structure 21 (here a T-shaped structure) points in distal direction upwards. This representation does not show a specific embodiment of the tibial tray 20, but is meant to indicate how the shape of the outer rim 26 of the lateral wall can be generated (e.g. as in FIG. 16A and FIG. 16B ). In this exemplary embodiment, the outer rim 26 follows a strictly monotonic curve with an inflection point. The possible generation of this curve is described in the following by using a plurality of line segments M1, M2, M3, M4, M5 connecting the distal plane D with a distal tip of the tibial tray axis structure 21.

[0155] The first line segment M1 connects the distal plane D with a first point P1 in the distal plane D. The first point P1 is laterally positioned at about 68% of the distance from the middle plane M (see FIG. 17 ) and the outermost point of the lateral rim. The inclination of the first line segment M1 is about 20° as measured from the distal plane D. In alternative embodiments, the first point P1 is laterally positioned in the range of 55% to 75% of the distance from the middle plane M to the outermost point of the lateral rim. In alternative embodiments, the inclination of the first line segment M1 can also be in the range of 15° to 30° as measured from the distal plane D. Embodiments can be combined.

[0156] A second line segment M2 connects the first point PI with a second point P2 above the distal end plane D. The second point P2 is positioned vertically at about 15% of the distance from the distal end plane D to a plane parallel to the distal-most point of the tibial tray shaft structure 21. The inclination of the second line segment M2 is about 40° as measured from the distal end plane D. In alternative embodiments, the second point P2 is positioned vertically in a range of 10% to 20% of the distance from the distal end plane D to a plane parallel to the distal-most point of the tibial tray shaft structure 21. In alternative embodiments, the inclination of the second line segment M2 can also be in a range of 30° to 50° as measured from the distal end plane D. Embodiments can be combined.

[0157] A third line segment M3 connects the second point P2 with a third point P3 above the distal end plane D. The third point P3 is positioned vertically at about 33% of the distance from the distal end plane D to a plane parallel to the distal-most point of the tibial tray shaft structure 21. The inclination of the third line segment M3 is about 60° as measured from the distal end plane D. In alternative embodiments, the third point P3 is positioned vertically in a range of 25% to 40% of the distance from the distal end plane D to a plane parallel to the distal-most point of the tibial tray shaft structure 21. In alternative embodiments, the inclination of the third line segment M3 can also be in a range of 45° to 70° as measured from the distal end plane D. Embodiments can be combined.

[0158] A fourth line segment M4 connects the third point P3 with a fourth point P4 above the distal end plane D. The fourth point P4 is positioned vertically at about 50% of the distance from the distal end plane D to a plane parallel to the distal-most point of the tibial tray shaft structure 21. The inclination of the fourth line segment M4 is about 50° as measured from the distal end plane D. In alternative embodiments, the fourth point P4 is positioned vertically in a range of 40% to 60% of the distance from the distal end plane D to a plane parallel to the distal-most point of the tibial tray shaft structure 21. In alternative embodiments, the inclination of the fourth line segment M4 can also be in a range of 40° to 60° as measured from the distal end plane D. Embodiments can be combined.

[0159] A fifth line segment M5 connects the fourth point P4 with a point at the center structure of the tibial tray shaft 21. The inclination of the fifth line segment M5 is about 75° as measured from the distal end plane D. In other embodiments, the inclination of the fifth line segment M5 is in a range of 50° to 80° as measured from the distal end plane D. Embodiments can be combined.

[0160] The line segments Ml, M2, M3, M4, M5 have varying inclinations such that generally in the middle, the inclination of the fourth line segment M4 is steeper than the inclination of the third line segment M3.

[0161] The points defining the line segments can be fitted with a smooth curve such as a polynomial or a spline curve to generate a smooth profile of the outer edge 26 of one of the tibial tray shaft structures 21, i.e. of one of the two lateral shaft wall elements in the T-shaped structure shown in FIG. 18A .

[0162] FIG. 18B and FIG. 9A An embodiment of the tibial tray 20 is shown in perspective view. Essentially, this embodiment has the features as described above, but here the tibial shaft structure 21 which is a T-shaped structure comprises cement holding structures 23 relatively close to the distal surface D. The front side, best observed in FIG. 18A , comprises a groove as cement holding structure 28 spanning the two wall elements. The rear side, best observed in FIG. 18B , comprises two grooves as cement holding structures 28, each extending over the two wall elements, i.e. through the rounded corner between the wall elements.

[0163] The cement holding structures 28 are here designed as rounded grooves which are easy to manufacture. In other embodiments, they can also comprise or consist of other shapes, for example grooves with sharp corners or holes with a circular or polygonal cross section.

[0164] In FIG. 18A , FIG. 18B , an embodiment of the tibial tray 20 is shown which is a variation of the above described embodiments, such as those shown in FIG. 20A , FIG. 20B , but here without cement holding structures 23. The tibial tray shaft structure 21 comprises a vertical cylindrical base shaft structure 29 extending around the axis A of the tibial tray shaft structure 21. The diameter of this base shaft structure 29 is between 5 mm and 8 mm, in particular depending on the size of the tibial tray 20. The diameter can vary in discrete steps such as 5 mm, 6 mm, 7 mm and 8 mm. The cross section of the base shaft structure 29 does not have to be circular. Other shapes, like for example elliptical or polygonal, are also possible.

[0165] As discussed above, the three wall elements 22, 23, 24 (Y-shaped structure, T-shaped structure) or four wall elements 22, 23, 24, 25 (X-shaped structure) extend radially away from the base shaft structure 29. The angle between the wall elements 22, 23, 24, 25 is for example described in connection with FIG. 19 , FIG. 4 , FIG. 5 . The angle space between the wall elements 22, 23, 24, 25 is smoothly filled with curved surfaces 13, for example connecting adjacent wall elements 22, 23, 24, 25.FIG. 9A A rear view of the T-shaped structure of the tibial tray 20 is shown. The radius of the curved surface 13 near the base shaft structure 29 is between 1 mm and 9 mm, in particular between 3 mm and 5 mm. Similar curved surfaces with the same radius will be used between the wall elements in the X-shaped or Y-shaped structure.

[0166] FIG. 19 A front view of the T-shaped structure shown in FIG. 20A The cylindrical base shaft structure 29 here extends in the forward direction beyond the two front wall elements 22, 23. The curved surface 23 at the front side here is between 10 mm and 30 mm, in particular 20 mm.

[0167] Those curved surfaces 13 prevent sharp corners, which in particular improves the insertability of the tibial tray.

[0168] In FIG. 20B , a proximal surface P of the tibial tray 20 is shown, which comprises a design of the front fixation element 2 that is a variant with respect to the embodiments described above. The central fixation element 1 and the rear fixation element 3 have been described in one way or another, for example in FIG. 20A or FIG. 20B , so reference can be made to the above description.

[0169] The front fixation element 2 comprises two form-fit elements 5 for receiving a corresponding part of the tibial insert 30 (not shown here, see FIG. 21A , FIG. 21B , for example for the snap-in process of the tibial tray). The form-fit elements 5 are essentially holes with a rectangular cross-section.

[0170] The form-fit elements 31 for the front fixation have a shape that corresponds to the form-fit elements 5 (for example, rectangular holes) when the tibial insert 30 is inserted from the top using its rear part and the rear fixation 3 as a fulcrum.

[0171] To facilitate the snap-in of the tibial insert 30 (not shown here), a guide surface 11 is provided on the proximal surface of the front fixation 5. The guide surface 11 here is a plane that is inclined by 5° to 45°, in particular by 30°, with respect to the horizontal plane. In other embodiments, this is not shown here. The guide surface is curved or has a planar portion.

[0172] The form-fit element 31 of the tibial insert 30 protrudes into the forward direction. When the tibial insert 30 is to be snapped in, the form-fit element 31 first rests on the upper portion of the guide surface 11. When pressure is applied in the distal direction in the tibial insert 30, the form-fit element 31 is guided along the guide surface 11 and finally snaps into the hole of the form-fit element 5 forming the front fixation element for a secure fit. The guide surface 11 prevents damage to the form-fit element 5 during insertion and makes a secure snap-in easier.

[0173] 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 fixation element 2.

[0174] In FIG. 20A , a detail of the posterior fixation element 3 is shown in a top view, i.e. in the direction of the proximal surface P.

[0175] The cross-section of the posterior fixation element 3 comprises two side walls 10 which are inclined towards the mid-plane M. Each of the side walls 10 is angled at about 20° with respect to the mid-plane M. In the shown 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).

[0176] For example, if the side walls of the tibial insert 30 which are intended to come into contact or form-fit with the side walls 10 of the posterior fixation element 3 have a slightly different inclination than the side walls 10, an angular mismatch is created, which leads to a tighter contact or force fit at some portions along the side walls 10 and a looser fit at other portions.

[0177] In the embodiment shown in FIG. 20B , the angle of the side walls 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 leads to a form-fit, i.e. a tighter fit, in the posterior region. In FIG. 15A FIG. 15B FIG. 15C FIG. 21B FIG. 21A FIG. 21B FIG. 22 FIG. 9 FIG. 16A FIG. 12A FIG. 12B FIG. 23 FIG. 23 FIG. 23 , the press-fit region 38 in this region is indicated. This angular mismatch not only makes assembly easier, but also reduces micro-movements in the posterior region.

[0178] In other embodiments, the press-fit region 38 is formed by widening the posterior portion of the posterior fixation element 3. List of reference signs 1 central fixation element 2 front fixation element 3 posterior fixation element 4 rear wall of the front fixation element 5 form-fit element of the front fixation element 6 undercut in the wall of the posterior fixation element 7 rear wall of the posterior fixation element 8 rear edge of the tibial tray 9 front wall of the posterior fixation element 10 side wall of the posterior fixation element 11 guiding surface for the tibial insert on the anterior fixation element 12 central fixation element recess 13 curved surface between the shaft wall elements 14 recess in the distal surface 20 tibial tray 21 tibial tray shaft structure 22 first shaft wall element of the tibial tray shaft structure 23 second shaft wall element of the tibial tray shaft structure 24 third shaft wall element of the tibial tray shaft structure 25 fourth shaft wall element of the tibial tray shaft structure 26 outer edge of the shaft wall element 27 inflection point on the outer edge of the shaft wall element 28 cement holding structure, recess structure for bone cement in the shaft wall element 29 base shaft structure 30 tibial insert 31 form fit element for the anterior fixation element 32 recess for the posterior fixation element 33 release notch 34 notch / groove for the linear central fixation element in the tibial insert 35 front wall of the recess 36 side wall of the recess 37 press fit surface 38 press fit area due to angular mismatch 40 femoral part 100 artificial knee joint A axis of the tibial tray shaft structure C cross-sectional plane D distal surface of the tibial tray DD distal direction D1 distance H height of the fixation element L height of the tibial tray structure measured from the distal surface L1 lateral point of the proximal surface L2 lateral point of the proximal surface M midplane of the proximal surface of the tibial tray M1 first line segment defining the outer edge of the shaft element M2 second line segment defining the outer rim of the shaft element M3 third line segment defining the outer rim of the shaft element M4 fourth line segment defining the outer rim of the shaft element M5 fifth line segment defining the outer rim of the shaft element N frontal plane perpendicular to the median plane P proximal surface of the tibial tray P1 first point between the line segments defining the outer rim of the shaft element P2 second point between the line segments defining the outer rim of the shaft element P3 third point between the line segments defining the outer rim of the shaft element P4 fourth point between the line segments defining the outer rim of the shaft element R edge of the distal surface R1 radius R2 radius Rant anterior radius Rlat lateral radius Rpost posterior radius S smooth surface T thickness of the shaft wall element a angle between the side wall and the front wall of the anterior fixation element in a plane parallel to the proximal surface b angle of the undercut g1 angle between the first wall structure and the second wall structure of the tibial tray structure g2 angle between the third wall structure and the fourth wall structure of the tibial tray structure

Claims

1. A tibial tray (20) having a distal surface (D), wherein, The tibial tray shaft structure (21) extends in a distal direction (DD) away from the distal surface (D), wherein The tibial tray structure (21) comprises at least three shaft wall elements (22, 23, 24, 25) arranged relative to each other such that a cross-section of the at least three shaft wall elements (22, 23, 24, 25) in a plane perpendicular to the distal direction (DD) is T-shaped, Y-shaped or X-shaped, and The area of the cross-section strictly monotonically decreases in the distal direction (DD) from the distal surface (D).

2. The tibial tray (20) of claim 1, wherein, The outer edges (26) of the at least three shaft wall elements (22, 23, 24, 25) strictly monotonically converge in the distal direction (DD) and towards an axis (A) of the tibial tray structure (21).

3. The tibial tray (20) of claim 1 or 2, wherein, The outer edges (26) of the at least three shaft wall elements (22, 23, 24, 25) have at least one inflection point (27), in particular three inflection points (27).

4. The tibial tray (20) according to at least one of the preceding claims, wherein A tangent angle (γ) at the outer edges (26) of the at least three shaft wall elements (22, 23, 24, 25), in particular any change of any tangent angle (γ) of the outer edges (26) of the at least three shaft wall elements (22, 23, 24, 25) within one third of a height (L) of the tibial tray structure (21) measured from the distal surface (D), is less than 30° over a change of 10% in the distal direction.

5. The tibial tray (20) according to at least one of the preceding claims, wherein, At least 50% of a volume of the tibial tray structure (21) is located within one third of a height (L) of the tibial tray structure (21) measured from the distal surface (D).

6. The tibial tray (20) according to at least one of the preceding claims, wherein At least one of the shaft wall elements (22, 23, 24, 25) has a wall thickness (T) of between 1 mm and 6 mm, in particular between 2 mm and 5 mm, in particular between 1 mm and 5 mm for ceramic materials, measured at a point furthest from the axis (A) and at the distal surface (D).

7. The tibial tray (20) according to at least one of the preceding claims, wherein A radius (γ) at a transition from an outer edge (26) of at least one of the at least three shaft wall elements (22, 23, 24, 25) to a side wall of the at least one of the at least three shaft wall elements is in a range of 0.5 mm to 4 mm.

8. The tibial tray (20) according to at least one of the preceding claims, wherein At least one of the at least three shaft wall elements (22, 23, 24, 25), in particular on a front side and / or a rear side, comprises at least a cement holding structure, in particular at least one recess structure (28), for holding bone cement.

9. The tibial tray (20) according to at least one of the preceding claims, wherein A transition point in the distal surface (D) from an outer edge (26) into the tibial shaft structure (21) is located at least 5 mm from a lateral side and / or a rear side of the distal surface (D).

10. The tibial tray (20) according to at least one of the preceding claims, wherein The tibial tray structure (21) comprises a surface (S) extending between at least two of the outer edges (26) of the at least three shaft wall elements (21) or between two side walls of the at least three shaft wall elements (21).

11. The tibial tray (20) according to at least one of the preceding claims, wherein The radius (R1) at the transition from the distal surface (D) to at least one of the shaft wall elements (22, 23, 24, 25) and / or to the smooth surface (S) is in the range of 1 mm to 4 mm.

12. The tibial tray (20) according to at least one of the preceding claims, wherein The axis (A) of the tibial tray shaft structure (21) is located on the distal surface (D) at one third of the distance between the anterior and posterior edges measured from the anterior edge.

13. The tibial tray (20) according to at least one of the preceding claims, wherein and the angle (y1) between the shaft elements (22, 23) is between 30° and 120° on the posterior side and the angle (y2) between the shaft wall elements (24, 25) is between 90° and 180° on the anterior side.

14. The tibial tray (20) according to at least one of the preceding claims, wherein The tibial tray shaft structure (21) comprises at least one cement holding structure (28), in particular a hole, a groove and / or a recess without any undercut.

15. The tibial tray (20) of claim 14, wherein, The at least one cement (1) holding structure (20) is located within the vertical two thirds, in particular the front third, of the tibial tray shaft structure (21) measured from the distal surface (D) in the distal direction (DD).

16. The tibial tray (20) according to any one of the preceding claims, wherein, At least one, in particular exactly one, anterior fixation element (2) is located at the anterior side of the proximal surface (P), the posterior side of the at least one anterior fixation element (2) comprising a wall (4) which is perpendicular to a median plane (M) of the proximal surface (P) in a plane parallel to the proximal surface (P).

17. The tibial tray (20) of claim 16, wherein, The at least one anterior fixation element (2) comprises at least one form-fit element (5), 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 passage through the at least one anterior fixation element (2), for a corresponding form-fit element (31) of a tibial insert (30), the at least one form-fit element (5) of the at least one anterior fixation element (2) in particular being located in a region where the load transmission is less than 70%, in particular 50%, of the maximum load transmission.

18. The tibial tray (20) of claim 17, wherein, The 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 planar portion in the proximal direction of the at least form-fit element (5).

19. The tibial tray (20) of claim 18, wherein, At least one of the guide surfaces (11) comprises a planar portion or at least one of the guide surfaces (11) is a planar surface inclined by an angle in the range of 5° and 45°, in particular 30°, relative to a horizontal plane.

20. The tibial tray (20) according to at least one of the preceding claims, having a proximal end surface (P) comprising at least two, in particular exactly two, central fixation elements (1) for enabling a connection with a tibial insert (30) being another part of an artificial knee joint, wherein, The at least two central fixation elements (1) are protrusions protruding in the proximal direction from the proximal surface (P) and the at least two central fixation elements (1) are located symmetrically and / or parallel to a median plane (M) of the proximal surface (P), the median 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).

21. The tibial tray (20) according to at least one of the preceding claims, wherein, The at least two central fixation elements (1) comprise a central fixation element recess (12).

22. The tibial tray (20) of at least one of the preceding claims, wherein, At least one, in particular exactly one, posterior fixation element (3) is positioned symmetrically relative to a median plane (M) of the proximal surface (P), the at least one posterior fixation element (3) comprising a posterior wall (7) flush with a posterior rim (8) of the tibial tray (20) and / or comprising a front wall (9) positioned substantially parallel to the posterior wall (4) of the at least one anterior fixation element (2).

23. The tibial tray (20) of claim 22, wherein, A lateral wall (10) and / or the front wall (9) of the at least one posterior element (3) is inclined relative to a plane perpendicular to the proximal plane (P) by an angle between 0° and 45°, in particular between 0° and 30°, more particularly by an angle of 10°, and / or the lateral wall (10) and the front wall (9) of the at least one posterior element (3) comprise an undercut.

24. The tibial tray (20) of at least one of the preceding claims, wherein, The at least two central fixation elements (1) are oriented symmetrically and / or parallel to a median plane (M), or the at least two fixation elements (1) are oriented asymmetrically relative to the median plane (M).

25. The tibial tray (20) of at least one of the preceding claims, wherein, The tibial tray (20) is completely or partially manufactured from ceramic, polymeric material or metal.

26. A knee prosthesis (100) comprising a tibial insert (30) and a tibial tray (20) according to at least one of claims 1 to 23.

27. The artificial knee joint (100) according to claim 25, wherein There is at least one press fit (38) area, in particular at least one press fit (38) area resulting from an angle mismatch between two walls, between the posterior fixation element (3) and the tibial insert (20).

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