BALL JOINT ENDOPROTHESIS

Description

[0001] The invention relates to a ball joint endoprosthesis, in particular a hip endoprosthesis, with a ball joint head having a convex articulation surface and with a ball joint socket having a concave articulation surface, wherein the convex articulation surface and the concave articulation surface interact in a slidable manner in a ball-joint manner.

[0002] Such a ball-and-socket joint prosthesis is known in the form of a hip endoprosthesis from US 2008 / 0228282 A1 and comprises a ball-and-socket joint head and a ball-and-socket joint socket. The ball-and-socket joint head has a convex articulation surface. The ball-and-socket joint socket has a concave articulation surface. The two articulation surfaces interact in a sliding manner, articulated in a ball-and-socket manner. In the known ball-and-socket joint prosthesis, the ball-and-socket joint head has notches. These notches are introduced as narrow groove-like cuts into the convex articulation surface and are intended to reduce friction. US 2003 / 171817 A1 discloses the technical features of the preamble of claim 1.

[0003] The object of the invention is to provide a ball joint endoprosthesis of the type mentioned above which has improved wear properties compared to the prior art.

[0004] This object is achieved in that the ball joint head has a plurality of adjacently arranged and radially flattened flattened surfaces, whereby the convex articulation surface is designed in the form of a modified spherical surface which - in comparison to an imaginary non-modified spherical surface - has a surface area for articulation with the concave articulation surface that is reduced by the flattened surfaces. The invention is based on the consideration that friction-induced abrasion between the ball joint head and the ball joint socket depends, among other things, on the size, i.e. surface area, of the contact surface effective during articulation and the prevailing friction coefficient. The solution according to the invention reduces the effective contact surface of the ball joint head in size, i.e. surface area. For this purpose, the ball joint head is provided with the said flattened surfaces.In the area of ​​the flattened surfaces, there is no contact between the ball joint head and the ball joint socket. In other words, the effective contact area between the ball joint head and the ball joint socket is reduced by the flattened surfaces compared to a design without flattened surfaces. This allows friction-related wear to be reduced in a surprisingly simple and effective manner and improves the wear properties of the ball joint endoprosthesis. With regard to wear properties, the radially flattened shape of the flattened surfaces has an additional advantageous effect. In contrast to the groove-shaped incisions known from the prior art, the flattened surfaces do not form sharp-edged recesses. Instead, the flattened surfaces merge seamlessly and / or without sharp edges into adjacent surface sections of the convex articulation surface of the ball joint head.The inventors have recognized that this seamless and / or non-sharp-edged transition has a comparatively abrasion-reducing effect. This allows for improved wear behavior compared to the aforementioned groove-shaped incisions by means of the flattened surfaces. "Smooth" specifically means that the flattened surfaces are not offset inward and / or outward in the radial direction relative to the convex articulation surface. In other words, the flattened surfaces transition seamlessly and / or without offset into the convex articulation surface and vice versa. Such a step, offset, or step is present in particular in a notch, groove, indentation, and / or incision, but not in the flattened surfaces.The ball joint head has a consistently convex curvature along its longitude and / or latitude, with the curvature having a larger radius of curvature in the area of ​​the flattened surfaces than in the area of ​​the convex articulation surface. In one embodiment, the radius of curvature approaches infinity in the area of ​​the flattened surfaces, i.e. the flattened surfaces are flat in one direction of extent. To form the flattened surfaces, the ball joint head or its spherical surface is radially flattened in sections. In terms of manufacturing technology, this can be done using an abrasive or non-abrasive process. For example, the ball joint head can be ground flat in sections at several adjacent points. In this case, the flat-ground points or sections form the said flattened surfaces.The flattened surfaces are each flat, planar, and / or non-concave in a first direction of extent and curved in a second direction of extent oriented perpendicular to the first direction of extent in accordance with the spherical shape of the ball joint head. The plurality of flattened surfaces are arranged adjacent to one another and can be spaced from one another, in particular uniformly, in the circumferential direction and / or in the polar direction of the ball joint head. Preferably, the plurality of flattened surfaces are uniformly designed and / or oriented in the same direction with regard to their extent on the ball joint head. The plurality of flattened surfaces can, in principle, have any desired surface shape. Preferably, the flattened surfaces are each longitudinally extending in a strip-like manner and thus each form a capillary gap between the ball joint head and the ball joint socket.Such a design is particularly advantageous, but not considered absolutely necessary and / or essential with regard to the present invention. The ball-and-socket joint endoprosthesis is preferably a hip endoprosthesis. Alternatively, the ball-and-socket joint endoprosthesis can be a shoulder joint endoprosthesis. Preferably, the ball-and-socket joint head does not have any grooves, incisions, depressions, and / or notches, particularly those designed to reduce friction.

[0005] Compared to the imaginary non-modified spherical surface, the modified spherical surface has a surface area for articulation with the concave articulation surface that is reduced by 25% to 50%, preferably by 40%. The inventors recognized, firstly, that a surface reduction of less than 25% is too small to enable a significant reduction in wear. Secondly, the inventors recognized that a surface reduction of more than 50% excessively reduces the contact area between the ball joint head and the ball joint socket, which is effective for articulation and can also be referred to as the bearing surface. This can, in particular, lead to increased surface pressure, which can be detrimental to the desired wear reduction. In this respect, the aforementioned value range between 25% and 50% has proven advantageous.A surface reduction of 40% represents a particularly advantageous compromise between significant friction reduction on the one hand and sufficient load-bearing capacity on the other.

[0006] In a further embodiment of the invention, the flat surfaces are arranged at equal spacing in the circumferential direction of the ball joint head. Such an arrangement offers particular advantages. "Evenly spaced" means that the flat surfaces are arranged at a constant angular offset in the circumferential direction of the ball joint head. The constant angular offset is the quotient of 360° divided by n, where n represents the number of flat surfaces.

[0007] The ball joint head is flat-ground in sections to form the flat surfaces. Alternatively, the ball joint head can be machined non-abrasively to form the flat surfaces. Reshaping the ball joint head is particularly conceivable. In one embodiment, at least one of the flat surfaces is formed by flat grinding. In other embodiments, more than one, preferably all, flat surfaces are formed by flat grinding.

[0008] The flattened surfaces each extend flat in a first direction of extent and are curved in a second direction of extent oriented perpendicular to the first direction of extent. Preferably, the first direction of extent is parallel to a circumferential direction of the ball joint head. Preferably, the second direction of extent is a main and / or longitudinal direction of extent of the respective flattened surface.

[0009] In a further embodiment of the invention, the flattened surfaces are each continuously elongated, extending from a lower shaft region of the ball joint head to an upper pole region of the ball joint head, thereby forming a continuously elongated capillary gap for the capillary transport of synovial fluid. This is a particularly advantageous embodiment of the invention. The continuous longitudinal extension of the flattened surfaces creates several correspondingly continuously elongated capillary gaps between the ball joint socket and the ball joint head. These capillary gaps are provided for the capillary transport of synovial fluid. The synovial fluid can flow from the shaft region of the ball joint head along the capillary gap to the pole region of the ball joint head.This improves lubrication of the sliding joint between the ball and socket. This leads to reduced wear and ultimately to further improved wear behavior of the ball and socket joint. The shaft region of the ball and socket joint, if the ball and socket joint is a hip joint, is oriented toward the femur. The pole region faces away from the shaft region and can be oriented toward the hip. Due to the continuous longitudinal extension between the shaft and pole regions, the flattened surfaces have a strip-like, track-like, or otherwise elongated shape.

[0010] In a further embodiment of the invention, the flattened surfaces are each flattened by 0.03 mm to 0.3 mm, preferably by 0.1 mm, compared to the imaginary non-modified spherical surface. This embodiment of the invention is particularly advantageous, in particular but not exclusively, with regard to the aforementioned capillary effect. This is because the flattened surfaces within the specified value range allow a sufficient capillary rise of the synovial fluid within the capillary gap to be achieved. This ensures that the synovial fluid can wet essentially the entire convex articulation surface or modified spherical surface of the ball joint head. If the flattened surfaces are continuously elongated according to the preceding embodiment and corresponding capillary gaps are formed, these accordingly have a gap dimension between 0.03 mm and 0.3 mm, preferably 0.1 mm.The flattening surfaces can each be formed with a flattening that is variable or constant along their longitudinal extent.

[0011] In a further embodiment of the invention, the flattened surfaces are each decreasingly flattened in the pole direction of the ball joint head and continuously transition into the modified spherical surface in the pole region of the ball joint head. Accordingly, in this embodiment of the invention, the flattened surfaces have a variable flattening or flattening depth along their main extension direction, which decreases towards the pole region and ultimately approaches zero. This can offer particular advantages. In particular, any impairment of the load-bearing capacity of the pole region can be avoided. This is because, in this embodiment of the invention, the pole region is not provided with flattened surfaces, as these continuously transition into the modified spherical surface there. This ensures an unreduced and thus maximum convex articulation surface in the pole region of the ball joint head.This can offer advantages, particularly with regard to static loading of the ball joint endoprosthesis.

[0012] In a further embodiment of the invention, the flattened surfaces are each longitudinally extended in a straight, angular, or helical manner with respect to the pole direction of the ball joint head. A straight longitudinal extension of the flattened surfaces is particularly easy to manufacture.

[0013] In a further embodiment of the invention, between two and 20, preferably twelve, flattened surfaces are provided. The number of flattened surfaces can be matched, in particular, to a diameter of the ball joint head and / or a material of the ball joint head and / or a material pairing between the ball joint head and the ball joint socket.

[0014] The invention also relates to a ball joint head for a ball joint endoprosthesis according to the preceding description, with a convex articulation surface intended for ball-joint, sliding articulation with a concave articulation surface of a ball joint socket of the ball joint endoprosthesis. According to the invention, the ball joint head has several adjacently arranged and radially flattened flat surfaces, whereby the convex articulation surface is designed in the form of a modified spherical surface, which—compared to an imaginary non-modified spherical surface—has a surface area for articulation with the concave articulation surface reduced by the flat surfaces. For advantages associated with the inventive design of the ball joint head and inventive embodiments, reference is made to the description of the inventive ball joint endoprosthesis and its embodiments.What has been said about the ball joint head there applies mutatis mutandis to the ball joint head according to the invention and its embodiments.

[0015] The invention is defined by claim 1.

[0016] Further advantages and features of the invention emerge from the claims and from the following description of a preferred embodiment of the invention, which is illustrated with reference to the drawings. Fig. 1 shows a schematic perspective view of an embodiment of a ball joint endoprosthesis according to the invention in the form of a hip endoprosthesis, Fig. 2 the ball joint endoprosthesis according to Fig. 1 in a schematic longitudinal section, Fig. 3 in a schematic perspective view of a ball joint head not designed according to the invention according to the prior art for a ball joint endoprosthesis, Fig. 4, 5 in different schematic perspective views an embodiment of a ball joint head according to the invention of the ball joint endoprosthesis according to the Fig. 1 and 2 and Fig. 6 a schematic cross-sectional view of the ball joint head according to the Fig. 4 und 5 along an equatorial section plane.

[0017] According to the Fig. 1 and 2 A ball joint endoprosthesis 1 is intended as an artificial joint replacement for a human ball joint and has a ball joint head 2 and a ball joint socket 3.

[0018] In the embodiment shown, the ball-and-socket joint endoprosthesis 1 is designed in the form of a hip endoprosthesis, which can also be referred to as a hip implant. The ball-and-socket joint head 2 can therefore also be referred to as an artificial femoral head. The ball-and-socket joint socket 3 can accordingly be referred to as an artificial acetabulum.

[0019] With the exception of the inventive design of the ball joint head 2, which will be described in more detail below, the ball joint endoprosthesis 1 has a spatial and physical design and function that is generally known to those skilled in the art, so that a detailed description in this regard can be omitted. In brief, it should be noted that the ball joint socket 3 is intended for fixation on the pelvic side. The ball joint head 2, on the other hand, is intended for fixation on the femur side. For this purpose, the ball joint head 2 is arranged at one end in a manner known to those skilled in the art on a ball joint shaft 4, which can also be referred to as an artificial hip stem. The ball joint shaft 4 is inserted into the patient's femoral shaft in a known manner.

[0020] In the embodiment shown, the ball-and-socket socket 3 is designed in several parts and comprises a shell part 31, which can also be referred to as an acetabular cup, and an inlay part 32, which can also be referred to as an acetabular insert. Such a multi-part design of the ball-and-socket socket 3 is not considered essential with regard to the invention.

[0021] The ball joint head 2 has a convex articulation surface 5, which will be described in more detail and which interacts in a ball-jointed manner with a concave articulation surface 6 of the ball joint socket 3 ( Fig. 2 ).

[0022] The sliding articulation between the ball joint head 2 and the ball joint socket 3, more precisely between the convex articulation surface 5 and the concave articulation surface 6, is inherently subject to friction. Accordingly, abrasion and the associated wear cannot be completely avoided.

[0023] To counteract this, the ball joint head 2 has several adjacent and radially flattened flattening surfaces 7a to 7l ( Fig. 4, 5 , 6 ). As a result, the convex articulation surface 5 of the ball joint head 2 is designed in the form of a modified spherical surface K. The modified spherical surface K has a surface reduced by the flattened surfaces 7a to 7l for articulation with the concave articulation surface 6 of the ball joint socket 3. The modified spherical surface K is smaller than a non-modified spherical surface K' of a ball joint head 2' which is identically designed except for the flattened surfaces 7a to 7l, as is known from the prior art and exemplified with reference to Fig. 3 is shown.

[0024] As can be seen in particular from Fig. 6 As can be seen, the flattened surfaces 7a to 7l do not form grooves, incisions, or other concave notches on the ball joint head 2. Instead, the flattened surfaces 7a to 7l are flat, level, and / or non-concave. This is at least with respect to a circumferential direction of the ball joint head 2. This avoids recesses and / or sharp edges on the convex articulation surface 5. This is in contrast to groove-shaped notches of the ball joint head known from the prior art. With respect to their respective main direction of extension, the flattened surfaces 7a to 7l are curved longitudinally in accordance with the spherical contour of the ball joint head 2 or the modified spherical surface K. Fig. 6 It is also evident that the ball joint head 2 is designed with a radius R. The flattened surfaces 7a to 7l - at least with respect to the section plane shown - have no radius and thus neither a convex nor a concave curvature.

[0025] In the embodiment shown, the modified spherical surface K has, in comparison to the non-modified spherical surface K' of the non-flattened and thus usual ball joint head 2' ( Fig. 3 ) has a surface area for sliding articulation with the concave articulation surface 6 that is reduced by 40%. In other words, there is no sliding contact between the flattened surfaces 7a to 7l and the concave articulation surface 6, whereby the effective contact area of ​​the ball joint head 2 is correspondingly reduced.

[0026] In embodiments not shown in the drawing, the modified spherical surface is comparatively reduced by 25% to 50% compared to a non-flattened spherical surface with identical diameter.

[0027] In the present case, the flattened surfaces 7a to 7l are arranged at equal distances in the circumferential direction U of the ball joint head 2 ( Fig. 4, 5 , 6 ). In an embodiment not shown in the drawing, uneven spacing is provided instead.

[0028] In addition, the flattened surfaces 7a to 7l are each longitudinally extending from a lower shaft region 21 of the ball joint head 2 to an upper pole region 22 of the ball joint head 2. As a result, the flattened surfaces 7a to 7l, in cooperation with the concave articulation surface 6, each form a continuously longitudinally extending capillary gap S ( Fig. 1 ). Fig. 1 For reasons of clarity, only one of the several capillary gaps is designated by the reference symbol "S." It is understood that, corresponding to the number of flattened surfaces 7a to 7l, several capillary gaps are formed adjacent to each other in the circumferential direction of the ball joint head 2. In the implanted state of the ball joint endoprosthesis 1, capillary transport of synovial fluid takes place along the capillary gaps.

[0029] This allows for improved lubrication of the sliding joint between the ball joint head 2 and the ball joint socket 3. This reduces friction-related abrasion and thus wear of the ball joint endoprosthesis 1.

[0030] The capillary transport of the synovial fluid is enabled by appropriately dimensioning the flattening of the flattening surfaces 7a to 7l. To ensure a sufficient capillary rise of the synovial fluid within the capillary gap, the flattening surfaces 7a to 7l in the illustrated embodiment are each flattened by 0.1 mm compared to the imaginary non-modified spherical surface K'. This achieves a sufficiently small gap in the capillary gap. If the flattening is too severe, exceeding a few tenths of a millimeter, a gap is achieved that produces no, or at least insufficient, capillary effect.

[0031] In embodiments not shown in the drawing, the flattening of the flattening surface varies between 0.03 mm and 0.3 mm.

[0032] In the present case, the above dimensional information refers to a maximum flattening of the flattening surfaces 7a to 7l. In the embodiment shown, the maximum flattening is provided at one end, at a front end region of the respective flattening surface 7a to 7l adjacent to the shaft region 21. Starting from there, the flattening of the flattening surfaces 7a to 7l increases in the pole direction P ( Fig. 6 ) of the ball joint head 2 decreases continuously and merges into the modified spherical surface K in the pole area 22 of the ball joint head 2. This is clearly visible from Fig. 5 In other words, the flattening of the flattened surfaces 7a to 7l decreases starting from the shaft region 21 along the respective main extension direction and approaches zero in the pole region 22. As a result of the continuously decreasing flattening, the flattened surfaces 7a to 7l have a variable width along their respective main extension direction. This width is maximum in the shaft region 21 and minimum in the pole region 22. In this case, the said width approaches zero in the pole region 22.

[0033] In the embodiment shown, the flattened surfaces 7a to 7l are straight longitudinally extended with respect to the pole direction P ( Fig. 6 ).

[0034] In embodiments not shown in the drawing, however, an angular or helical longitudinal extension of the flattened surfaces is provided.

[0035] In the present case, the ball joint head 2 has a total of twelve flattened surfaces 7a to 7l. These are offset from each other by 30° in the circumferential direction of the ball joint head 2.

[0036] In the embodiments shown in the drawings, the ball joint head 2 has between two and 20 flattened surfaces.

[0037] The flattened surfaces 7a to 7l can be formed on the ball joint head 2 using abrasive or non-abrasive manufacturing processes. For this purpose, section-by-section grinding, in particular surface grinding, of the ball joint head 2 has proven particularly advantageous.

Claims

1. Ball joint head (2) having a convex articulation surface (5), which is provided for spherical sliding articulation with a concave articulation surface (6) of a ball joint socket (3) of a ball joint endoprosthesis (1), wherein the convex articulation surface (5) has a plurality of adjacently arranged and radially flattened flat surfaces (7a to 71), as a result of which the convex articulation surface (5) is designed in the form of a modified spherical surface (K), which - compared to an imaginary non-modified spherical surface (K') - has a surface, reduced by the flat surfaces (7a to 71), for articulation with the concave articulation surface (6), characterized in that the modified spherical surface (K) has, compared to the imaginary non-modified spherical surface (K'), a surface reduced by 25% to 50%, preferably by 40%, for articulation with the concave articulation surface (6), wherein the flat surfaces (7a to 71) each extend in a planar manner in a first direction of extent and extend in a curved manner in a second direction of extent oriented perpendicular to the first direction of extent.

2. Ball joint endoprosthesis (1), in particular a hip endoprosthesis, having a ball joint head (2) according to Claim 1 and having a ball joint socket (3), which has a concave articulation surface (6), wherein the convex articulation surface (5) and the concave articulation surface (6) interact with spherical sliding articulation.

3. Ball joint endoprosthesis (1) according to Claim 2, wherein the flat surfaces (7a to 71) are arranged uniformly spaced apart in the circumferential direction (U) of the ball joint head (2).

4. Ball joint endoprosthesis (1) according to either of Claims 2-3, wherein the flat surfaces (7a to 71) each extend longitudinally continuously from an underside shaft region (21) of the ball joint head (2) as far as an upper pole region (22) of the ball joint head (2), as a result of which in each case a continuously elongate capillary gap (S) is formed for the capillary transport of synovial fluid.

5. Ball joint endoprosthesis (1) according to any one of Claims 2-4, wherein the flat surfaces (7a to 71) are flattened in each case by 0.03 mm to 0.3 mm, preferably by 0.1 mm, compared to the imaginary non-modified spherical surface (K').

6. Ball joint endoprosthesis (1) according to any one of Claims 2-5, wherein the flat surfaces (7a to 71) are each flattened decreasingly in the pole direction (P) of the ball joint head (2) and transition continuously into the modified spherical surface (K) in the pole region (22) of the ball joint head (2).

7. Ball joint endoprosthesis (1) according to any one of Claims 2-6, wherein the flat surfaces (7a to 71) each extend longitudinally straight or at an angle or helically with respect to the pole direction (P) of the ball joint head (2).

8. Ball joint endoprosthesis (1) according to any one of Claims 2-7, wherein between two and 20, preferably twelve, flat surfaces (7a to 71) are provided.