Prosthesis, especially knee prosthesis or joint stem prosthesis

Abstract

To provide a prosthesis that develops the lowest possible restoration forces but at the same time has sufficiently high stability.SOLUTION: Embodiments are relating to a prosthesis (10), in particular a knee prosthesis or hip stem prosthesis, including a shaft (12) for arrangement and mounting in a long bone. The shaft has shaft sections ( 30, 32) extending parallel to shaft axes (18) that are separated from one another by a slotted intermediate space (28). The shaft portions are deformable by bending loads starting from an undeformed resting state such that the slotted intermediate space decreases. A first shaft portion includes a first projection provided on a side of the first shaft portion facing a second shaft portion and that forms a first constriction of the intermediate space. The first shaft portion also includes a first boundary surface for alignment against the second shaft portion. The first boundary surface is spaced at a distance from the second shaft portion in the undeformed resting state.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a prosthesis, in particular a knee prosthesis or a hip stem prosthesis, comprising a shaft for placement and installation in a long bone, the shaft being insertable into the long bone and extending longitudinally along a shaft axis between a proximal end and a distal end, the shaft having a first, in particular solid, cross section starting from the proximal end along a first partial length, the shaft having a second cross section deviating from the first cross section along a second partial length including the distal end of the shaft, the shaft comprising shaft portions extending parallel to the shaft axis along the second partial length, the shaft portions being separated from one another by slotted intermediate spaces, the shaft portions being deformable by bending load such that starting from an undeformed rest state the slotted intermediate spaces are reduced.

[0002] A prosthesis of the aforementioned type is known, for example, from EP 0 966 928 A2. To fix the shaft in the long bone, the distal end of the shaft is inserted into the medullary cavity of the long bone. The purpose of the slot-type intermediate space is to allow the shaft part to be elastically deformed radially inwards during insertion into the medullary cavity, the slot-type intermediate space decreasing in the process. After being fully inserted into the medullary cavity, the shaft part rests under pretension against the border of the medullary cavity. Summary of the Invention [Problem to be solved by the invention]

[0003] It has been shown that in at least some patients, so-called shaft pain can also occur as a result of this pretension, even long after the prosthesis has been inserted. It is therefore necessary to provide a shaft section that can be deformed with small forces in order to reduce the elastic restoring forces in this way. However, at the same time, a problem is presented in that an excessively unstable fit of the shaft section can lead to undesirable plastic deformation or even breakage of the shaft section.

[0004] On this basis, a fundamental object of the present invention is to provide a prosthesis which exhibits the lowest possible restoring forces and at the same time has a sufficiently high stability. [Means for solving the problem]

[0005] This object is achieved according to the invention by a prosthesis of the type described above, in which the first shaft portion comprises a first protrusion, which is provided on a side of the first shaft portion facing the second shaft portion, forming a first narrowing of the intermediate space and is arranged at a distance from a first partial length of the shaft, as viewed along the shaft axis, and the first protrusion comprises a first interface surface for alignment with the second shaft portion, which first interface surface is arranged at a distance from the second shaft portion in an undeformed, resting state.

[0006] The prosthesis according to the invention defines at least one first shaft section, the maximum bending deformation of which is limited by a protrusion having a first interface surface aligned with the second shaft section in the maximum deformation state of the first shaft section. In the undeformed rest state, the cross section of the slot-type intermediate space is narrowed in the region of the first protrusion. In the undeformed rest state of this first shaft section, the first interface surface of the protrusion is arranged at a distance from the second shaft section. This allows the first shaft section to be deformed also at the height of the first protrusion (height seen along the shaft axis) when a bending load is applied. However, the deformation path of the first shaft section at the height of the first protrusion is limited to a state in which the first interface surface of the first protrusion of the first shaft section is aligned with the second shaft section.

[0007] In particular, the first shaft part has a relatively small surface moment of inertia, i.e. it can only be deformed with low deformation forces when the prosthesis is surgically inserted into the long bone, and can develop a relatively low restoring force after insertion into the medullary cavity. Nevertheless, the first shaft part cannot be further deformed as a result of the alignment of the first interface with the second shaft part, so that undesirable plastic deformation or even failure with breakage of the first shaft part can be prevented. The maximum deformation path of the first shaft part is limited to the extent to which the protrusion narrows the slot-shaped intermediate space. This extent is determined by the height of the first protrusion extending beyond the base surface of the first shaft part extending in the direction towards the second shaft part.

[0008] The prosthesis of the present invention may use proven materials such as titanium and steel alloys.

[0009] Particular advantages arise when the second shaft portion has a second protrusion, which is provided on a side of the second shaft portion facing the first shaft portion, forming a second narrowing of the intermediate space and is arranged at a distance from the first partial length of the shaft as viewed along the shaft axis, and the second protrusion has a second interface surface for alignment with the first shaft portion, which second interface surface is arranged at a distance from the first shaft portion in the undeformed, rest state.

[0010] The first and second shaft portions are preferably arranged on opposite sides of the central shaft axis, and if the second shaft portion also comprises a second protrusion, the deformation path of the second shaft portion can also be limited when a second interface surface of the second protrusion is aligned with the first shaft portion.

[0011] The first protrusion and the second protrusion can be positioned offset from one another along the shaft axis such that when a bending load is applied, one of the two interface surfaces is aligned with one of the two shaft portions, and the other interface surface is aligned with the other shaft portion only thereafter.

[0012] However, it is also possible that the first and second protrusions are arranged at the same height along the shaft axis, viewed along the shaft axis, and the bending deformations of the shaft parts in the region of the first and second protrusions are limited by the alignment of the first interface surface relative to the second interface surface. This is particularly advantageous if the shaft parts have cross sections which are mirror-symmetrical to one another with respect to the shaft axis, with the result that when the distal ends are inserted into the long bone, the two shaft parts deform symmetrically with respect to the shaft axis and exert opposite and equal restoring forces on the opposing parts of the interface of the medullary cavity when the prosthesis is in the inserted state.

[0013] It is further preferred if the first and second interface surfaces are oriented parallel to each other in the undeformed rest state of the shaft section or in the deformed state of the shaft section. In the case of parallel orientation of the interface surfaces in the undeformed rest state of the shaft section and in the deformed state of the shaft section, the two interface surfaces initially only contact each other along a contact line. In the case of further deformation, this contact line expands to a state in which the interface surfaces are aligned with each other along their extent (i.e. over their surface area). In this state, the two shaft sections can be braced against each other in a stable manner, i.e. by avoiding locally increased surface pressure. This is especially true if in the undeformed rest state the interface surfaces are arranged at a slight angle to each other, which angle is selected such that in the maximum deformation state of the shaft section, the two interface surfaces are aligned with each other simultaneously and over their entire extent.

[0014] It is particularly preferred that the first and / or second interface extends along the shaft axis to the distal end of the shaft, so that the deformation path of the shaft section or sections can be limited in the region of the shaft section that has the maximum deformation path under bending load. It is also advantageous that the slot-type intermediate space at the distal end of the shaft has a narrowed cross section as a result of the protrusion, so that the distal end can be particularly easily inserted into the medullary cavity.

[0015] The invention further proposes that the first and / or second interface has an interface area of ​​5% to 45%, in particular 15% to 35%, of the second part length in the longitudinal direction along the shaft axis. In other words, 95% to 55%, in particular 85% to 65%, of the second part length of the shaft part is preferably free of protrusions, i.e. has a slot-type intermediate space that is not limited by at least one protrusion. This "protrusion-free" second part length of the shaft part makes it possible to provide a large volume of intermediate space, which is accompanied by a corresponding reduction in the cross section of the shaft part and therefore a low deformation resistance.

[0016] The shaft section comprises, in the region of the second shaft section length adjacent to the first shaft section length and in the undeformed rest state of the shaft section, a shaft section distance which corresponds to the width of the slot-shaped intermediate space. This ("without protrusions") shaft section distance is preferably at least 20%, in particular at least 25%, of the maximum diameter of the circumferential surface of the shaft. For example, this maximum diameter is 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, 22 mm or 24 mm. In the example of a shaft with a diameter of 10 mm, taking into account a symmetrical design with respect to the shaft axis, it is preferred that the aforementioned shaft section distance is at least 2 mm, so that the radial extent of the shaft section is at most 4 mm.

[0017] The first projection has a first height, measured perpendicularly to the first boundary surface, by which it extends beyond the base surface of the first shaft part. If present, the second projection has a second height, measured perpendicularly to the second boundary surface, by which it extends beyond the base surface of the second shaft part. Said base surface forms the opposing boundary surface of the slot-type intermediate space, viewed along the shaft axis, in the area where no projections are arranged. The invention proposes that the first height and / or the second height is at least 0.5 mm. This means that, in comparison with prostheses known from the prior art which only have opposing base surfaces and no inventive projections, the slot-type intermediate space is limited by a deformation path of at least 0.5 mm in the area of ​​at least one projection.

[0018] When two protrusions are provided which are arranged at the same height along the shaft axis, the slot-type intermediate space is narrowed by at least 1 mm compared to the prior art and the common deformation path of the shaft parts is therefore shortened by at least 1 mm compared to the prior art.

[0019] It is particularly preferred when the ratio between the first height and the ("no protrusion") shaft distance or the ratio between the second height and the ("no protrusion") shaft distance or the ratio between the sum of the first height and the second height and the ("no protrusion") shaft distance is at least 10%, in particular at least 20%, which entails a shortening of the deformation path of at least 10%, in particular at least 20%, based on the "no protrusion" prior art.

[0020] It is further advantageous if the shaft has a circumferential surface with longitudinal grooves running parallel to the shaft axis. Such a design of the circumferentially closed surface of the shaft can also be described in that the shaft has a "Wagner profile". The longitudinal grooves support a secure fixation at the border of the medullary cavity, but when viewed by themselves they form a locally weakened area of ​​the cross section of the shaft part. The prosthesis according to the invention is able to compensate for this weakening.

[0021] Further features and advantages of the present invention are within the following description of preferred exemplary embodiments. [Brief description of the drawings]

[0022] As shown in the drawing: [Figure 1] 1 is a cross-sectional view of a prosthesis known from the prior art; [Diagram 2] 1 is a side view of one embodiment of a prosthesis according to the present invention. [Diagram 3] FIG. 3 is an enlarged view of the part marked III in FIG. 2 . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] A prosthesis known from the prior art (EP 0 966 928 A2) is shown in Figure 1 and is designated by the reference number 10. The prosthesis comprises a shaft 12 connected at one end to an articulation part 14, for example by arranging a connection part 16 between them.

[0024] The shaft 12 extends along a shaft axis 18, i.e., between a proximal end facing the articular portion 14 and a free distal end 22 which is inserted first into the medullary cavity when the shaft is placed in the medullary cavity of a long bone.

[0025] Beginning at the proximal end 20, the shaft 12 has a first, particularly solid, cross-section along a first partial length 24. Along a second partial length 26, which includes the distal end 22 of the shaft 12, the shaft 12 has a second cross-section that deviates from the first cross-section.

[0026] A slot-shaped intermediate space 28 extending parallel to the shaft axis 18 is provided along the second partial length 26. The intermediate space 28 is bounded on opposite sides by a first shaft portion 30 and a second shaft portion 32 spaced apart from the first shaft portion 30.

[0027] For the following description of an exemplary embodiment of the prosthesis 10 of the invention, reference is made to the above description of Fig. 1. It goes without saying that the prosthesis 10 according to Fig. 2 can be adapted, for example, as a knee prosthesis or a hip stem prosthesis, and that, if necessary, the prosthesis 10 can also be provided with an articulation section 14 (not shown) by using an intermediate section 16.

[0028] The shaft 12 has a circumferential surface 34 which is provided, at least cross-sectionally, with longitudinal grooves 36 distributed, in particular regularly distributed, over the circumference of the shaft 12 when viewed along the shaft axis 18. For example, a total of ten longitudinal grooves 36 are provided, offset from one another in the circumferential direction.

[0029] The shaft 12 has a maximum diameter 38, for example between 10 mm and 24 mm.

[0030] For further explanation, please refer to FIG.

[0031] The first shaft portion 30 has a base surface 40 facing the second shaft portion 32 in a region adjacent the first partial length 24 of the shaft 12. The second shaft portion 32 has a second base surface 42 facing the first base surface 40. The base surfaces 40 and 42 are spaced apart from one another over a shaft portion distance 44 and form the boundary of the slot-shaped intermediate space 28.

[0032] On the side facing the second shaft part 32, the first shaft part 30 has a protrusion 46 with a first interface surface 48 facing the second shaft part 32. The distance between the first interface surface 48 and the base surface 40 corresponds to a height 50 of the first protrusion 46. The first protrusion 46 is in particular formed integrally with the first shaft part 30.

[0033] On the side facing the first shaft part 30, the second shaft part 32 carries a second protruding part 52 having a second interface surface 54 facing the first shaft part 30. The distance from the second interface surface 54 of the second shaft part 32 to the base surface 42 corresponds to a second height 56 ​​of the second protruding part 52. The second protruding part 52 is in particular formed integrally with the second shaft part 32.

[0034] The first height 50 is at least 0.5 mm and the second height 56 ​​is at least 0.5 mm.

[0035] The projections 46 and 52 form respective constrictions of the slot-type intermediate space 28. In the region of the boundary surfaces 54, 48, the slot-type intermediate space 28 is limited by the sum of the heights 50, 56 of the projections 46, 52.

[0036] Interface surfaces 48 and 54 are specifically oriented parallel to one another in the undeformed, resting state of shaft 12 .

[0037] The interfaces 48 and 54 are disposed relative to the shaft axis 18 on opposite sides of the shaft axis 18 and are mirror images of each other with respect to size and position relative to the shaft axis 18 .

[0038] Interfaces 48 and 54 preferably extend along the same interface length 58 along shaft axis 18 .

[0039] Starting from the undeformed rest state of the shaft portions 30 and 32 shown in the drawings, the distal end 22 can be inserted into the medullary cavity of a long bone, in particular the tibia or femur, in which case the diameter 38 of the shaft 12 is selected in relation to the diameter of the medullary cavity so that the shaft can be inserted into the medullary cavity, preferably with the extension of the longitudinal groove 36, and so that the radially outwardly facing faces of the shaft portions 30 and 32 are aligned under pretension against the respective borders of the medullary cavity after said insertion.

[0040] Starting from an undeformed starting state, and referring to Figure 3, shaft portions 30 and 32 can be deformed by bending until interfaces 48 and 54 move towards one another, i.e., until interfaces 48 and 54 are aligned with one another at least cross-sectionally, and preferably over a surface area. This alignment defines a maximum deformation path of shaft portions 30 and 32 over interface length 58.

[0041] Assuming the same shaft distance 44 as in the prior art (see FIG. 1), assuming the same material and the same dimensions of the shaft portions 30 and 32, and assuming the same second portion length 26, the deformation path of the shaft portions 30 and 32 is thus shortened in the region of the distal end 22 by a measure corresponding to the sum of the heights 50 and 56 of the projections 46 and 52. As a result, the shaft portions 30 and 32 can be bent with low deformation forces and accordingly only low restoring forces arise after insertion into the long bone, while at the same time preventing breakage accompanied by undesirable plastic deformation or fracture of the shaft portions 30 and 32.

Claims

1. A prosthesis (10), in particular a knee prosthesis or a hip stem prosthesis, a shaft (12) for placement and attachment within a long bone; The shaft (12) is insertable into the long bone and extends along a shaft axis (18) between a proximal end (20) and a distal end (22); The shaft (12) has a particularly solid cross-section along a first partial length (24) beginning at the proximal end (20); The shaft (12) has a second cross-section along a second portion length (26) that deviates from the first cross-section; the second cross section includes the distal end (22) of the shaft (12); The shaft (12) has shaft portions (30, 32); The shaft portions (30, 32) extend along the second portion length (26) parallel to the shaft axis (18) and are separated from one another by a slot-type intermediate space (28); the shaft portions (30, 32) are deformable by bending loads such that, starting from an undeformed rest state, the slot-shaped intermediate space (28) decreases; The first shaft portion (30) includes a first protrusion (46); the first protrusion (46) is provided on a side of the first shaft portion (30) facing the second shaft portion (32), forms a first narrowing of the intermediate space (28) and is spaced apart from the first partial length (24) of the shaft (12) as viewed along the shaft axis (18); The prosthesis (10), wherein the first projection (46) has a first interface surface (48) for alignment with the second shaft portion (32), the first interface surface (48) being positioned at a distance from the second shaft portion (32) in the undeformed, resting state.

2. the second shaft portion (32) includes a second protrusion (52); the second protrusion (52) is provided on a side of the second shaft portion (32) facing the first shaft portion (30), forms a second narrowing of the intermediate space (28) and is arranged at a distance from the first partial length (24) of the shaft (12) as viewed along the shaft axis (18); 2. The prosthesis (10) of claim 1, wherein the second protrusion (52) comprises a second interface surface (54) for alignment with the first shaft portion (30), the second interface surface (54) being positioned at a distance from the first shaft portion (30) in the undeformed, resting state.

3. 3. The prosthesis (10) of claim 2, characterized in that the bending deformation of the shaft portion (30, 32) is limited in the region of the first protrusion (46) and the second protrusion (52) by alignment of the first interface surface (48) with respect to the second interface surface (54).

4. 4. The prosthesis (10) of claim 3, wherein the first interface (48) and the second interface (54) are oriented parallel to one another in the undeformed, resting state of the shaft portions (30, 32) or in the deformed state of the shaft portions (30, 32).

5. 3. The prosthesis (10) of claim 2, wherein the first interface (48) and / or the second interface (54) extend, as viewed along the shaft axis (18), to the distal end (22) of the shaft (12).

6. The prosthesis (10) according to claim 2 or 5, characterized in that the first interface (48) and / or the second interface (54) have an interface length (58), viewed along the shaft axis (18), of 5% to 45%, in particular 15% to 35%, of the second portion length (26).

7. the shaft portions (30, 32) have, in the region of the second partial length (26) of the shaft (12) adjacent to the first partial length (24) of the shaft (12), a shaft portion distance (44) from one another which corresponds to a width of the slot-shaped intermediate space (28) in the undeformed, rest state of the shaft portions (30, 32); 2. The prosthesis (10) according to claim 1, characterized in that the shaft distance (44) is preferably at least 20%, in particular at least 25%, of the maximum diameter (38) of the circumferential surface (34) of the shaft (12).

8. 8. The prosthesis (10) according to claim 7, characterized in that the first projection (46) has a first height (50) measured perpendicular to the first interface (48) and / or the second projection (52) has a second height (56) measured perpendicular to the second interface (54), preferably the first height (50) and / or the second height (56) being at least 0.5 mm or more.

9. 9. The prosthesis (10) according to claim 8, characterized in that the ratio between the first height (50) and the shaft distance (44), or the ratio between the second height (56) and the shaft distance (44), or the ratio between the sum of the first height (50) and the second height (56) and the shaft distance (44) is at least 10%, in particular at least 20%.

10. 2. The prosthesis (10) of claim 1, wherein the shaft (12) comprises a circumferential surface (34) having a longitudinal groove (36) extending parallel to the shaft axis (18).

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