Zirconium-coated implant components and their use

Description

TECHNICAL AREA

[0001] The present disclosure relates to an implant component with a connecting section for connecting to another implant component, wherein the implant component is a prosthesis stem and wherein the connecting section is coated at least partially with a zirconia coating, as well as an implant with at least one implant component. The present disclosure further relates to the use of a zirconia coating for corrosion prevention. STATE OF THE ART

[0002] Endoprostheses, such as hip endoprostheses, can have a modular design, meaning they are composed of at least two separately selectable components. This design gives the prostheses a high degree of adaptability to the individual requirements of a patient.

[0003] A patient's individual requirements can include specific dimensions, geometries, material combinations, and / or attachment mechanisms. The use of modular prostheses allows for the consideration of these diverse requirements without the need to stock implants for every possible combination or to manufacture them individually.

[0004] Individual implant components of a modular endoprosthesis can be assembled into a complete endoprosthesis or implant using connecting sections. Conical connections have proven particularly effective in this regard. A conical connection can, for example, have a substantially conical projection (male cone) and an opening with a tapered cross-section (female cone). Both the male and female cones have a conical axis that aligns when the projection is inserted into the opening (i.e., when connecting the implant components). The conical connection is therefore also self-centering.

[0005] When the male cone is inserted into the female cone, and the implant components are subjected to a force in the direction of the cone axis, this leads to an elastic expansion of the female cone radially oriented with respect to the cone axis and a compression of the male cone. The resulting recoil forces from expansion and compression, in turn, generate a clamping force which, if self-locking occurs, leads to a frictional connection of the implant components.

[0006] Such conical connections are used, for example, in hip endoprostheses. Simple modular hip endoprostheses have such a connection, for instance, between a prosthetic stem and a femoral head (articular head). Furthermore, multi-modular hip endoprostheses are known that have an intermediate piece positioned between the prosthetic stem and the femoral head to allow for better adaptation of the endoprosthesis to the patient's anatomy. In this case, for example, the prosthetic stem and the intermediate piece and / or the intermediate piece and the femoral head can be connected with a conical connection as described above.

[0007] However, it has been shown that crevice corrosion and / or fretting corrosion can occur in the conical connection of the modular endoprostheses described above (technical term: fretting or fretting corrosion). This phenomenon particularly affects the contact surfaces of the implant components, i.e., the outer surface of the male cone and the inner circumferential surface of the female cone.

[0008] Such corrosion can sometimes lead to fatal implant failure. This failure manifests itself particularly as the breakage of the male cone. Micromovements between the interfaces of two implant components and the resulting stresses are sometimes considered the cause of the corrosion. The corrosion can manifest itself as cracks and / or abrasion of a passive layer on the surface of the implant material. It should be noted that corrosion can occur not only in metal-on-metal pairings but also in metal-on-ceramic pairings, such as hip endoprostheses with a metal stem and ceramic head.

[0009] Furthermore, it is assumed that while such conical joints function according to the principle described above, the connection does not occur along the entire length of the cone due to manufacturing processes. It has been observed that the conical joint primarily forms in the proximal region, i.e., at the end of the tapered cone. This results in higher stresses on its surface, which promote the corrosion phenomena described above. This effect is further intensified by the fact that conical joints are typically manufactured by machining, particularly turning. This process creates a characteristic wavy surface on the micrometer scale. This, too, can cause stress peaks and local deformations in a conical joint.

[0010] In addition to the material failure described above, the corrosion phenomena described above also regularly lead to the release of metal ions, metal oxides, metal organophosphates and / or small metal particles, which in turn intensify the mechanical abrasion phenomena.

[0011] This can lead to pain, aseptic loosening of the endoprosthesis, and / or negative consequences for the surrounding tissue in patients. In particular, metallosis can develop, meaning an abnormal presence of wear particles in the tissue. A possible consequence of this is the formation of so-called pseudotumors. Allergic reactions are also possible, which may also necessitate revision of the prosthesis.

[0012] To counteract the problems described above, various design and manufacturing measures have been implemented. For example, efforts have been made to reduce the extent of corrosion through more precise manufacturing processes or adapted contact surface geometries. Furthermore, DE 102014206151 A1 discloses a conical connection with a TiNb coating that exhibits lower susceptibility to corrosion compared to uncoated connections.

[0013] From US patent 2016 / 278928 A1, a prosthesis is known that comprises: a femoral stem with a frustoconical femoral neck; a femoral head with an articular bearing surface having an outer diameter of 26 mm or more and a frustoconical internal recess; and a sleeve comprising a frustoconical body for insertion into the recess of the femoral head and a frustoconical internal recess for receiving the frustoconical femoral stem. One surface of the recess of the sleeve is made of oxidized zirconium or an oxidized zirconium alloy to resist or minimize mechanically assisted crevice corrosion.

[0014] Another possibility considered was the use of nitride coatings to improve the wear resistance of implant components. These are used, for example, for the bearing surfaces of endoprostheses. However, it has been found that different wear conditions prevail there than in a connecting section. This may be one reason why nitride coatings have not yielded satisfactory results in this area.

[0015] Since neither premature failure nor interactions with abrasive material can be ruled out in connection sections with or without coating, the aim remains to further reduce corrosion phenomena beyond the level achieved so far. SUMMARY OF THE INVENTION

[0016] The object of this disclosure was to counteract the problems described above and to achieve improvements in an implant component with a connecting section, and in particular improvements with regard to crevice corrosion and / or fretting corrosion. This object is achieved by an implant component according to claim 1, a modular endoprosthesis according to claim 10, or a use according to claim 13. Preferred embodiments are specified in the dependent claims.

[0017] An implant component according to the present disclosure has at least one connecting section which is coated, at least partially, with a zirconia (Zr) coating. Preferably, the entire connecting section is coated with a zirconia (Zr) coating. Particularly preferably, at least those surfaces of the connecting section which are designed to come into contact with surfaces of a connecting section counterpart of another implant component are coated with a zirconia (Zr) coating.

[0018] The Zr coating has a thickness between 1 µm and 20 µm, preferably between 1 µm and 6 µm. For the purposes of this disclosure, Zr refers to elemental zirconium (element with atomic number 40 in the periodic table), but not to zirconium (Zr[SiO₄]) or other zirconium-based minerals or ceramics. Zirconium-based oxides that may form on the surface of a Zr coating in the form of a passive layer are also referred to as Zr coatings according to this disclosure.

[0019] The implant component described above exhibits a significantly reduced susceptibility to crevice corrosion and / or fretting corrosion in the connection area compared to the prior art. This property is primarily due to the choice of coating material (Zr) in combination with the coating thickness.

[0020] The measurement method described below has shown that a connection section with a Zr coating (with a layer thickness as disclosed) has a significantly lower susceptibility to crevice corrosion and / or fretting corrosion than, for example, a connection section with titanium-niobium (TiNb) or a connection section formed with a cobalt-based alloy (e.g., CoCrMo).

[0021] Due to its lower susceptibility to crevice corrosion and / or fretting corrosion, the passive layer on the surface of the Zr coating is assumed to be significantly more stable than the passive layer of other metallic coatings or materials. Furthermore, previous studies indicate a high degree of biocompatibility, which particularly helps prevent allergic reactions.

[0022] Furthermore, it is assumed that the low susceptibility of the Zr coating to corrosion is due to its mechanical properties. In particular, the coating possesses sufficient ductility. As a result, a more uniform contact at the joint is achieved, thus reducing stress peaks. This is advantageous, for example, in the case of the aforementioned, manufacturing-related wavy surface structure.

[0023] The layer thickness of the Zr coating of an implant component according to the present disclosure is preferably between 3 µm and 6 µm, and particularly preferably between 3 µm and 5 µm.

[0024] The aim is to select a layer thickness sufficient to achieve a coating that can withstand mechanical stress. At the same time, the coating should not be too thick to ensure a stable frictional connection between the surfaces of the joint.

[0025] Producing a thick Zr layer is associated with higher costs. Conversely, with a layer that is too thin, the desired effect (reduced susceptibility to crevice corrosion and / or fretting corrosion) may not be achieved permanently and reproducibly. The (particularly) preferred layer thicknesses listed above are associated with reasonably low production costs and simultaneously allow for a reduction in the susceptibility of the joint section to crevice corrosion and / or fretting corrosion compared to known coatings. The layer thicknesses mentioned above can therefore also be considered the solution to a multidimensional optimization problem regarding production costs and the achievement of the desired effect.

[0026] An implant component according to the present disclosure can have a connecting section formed with a female and / or male cone. Preferably, the female and / or male cone is rotationally symmetrical.

[0027] A tapered connection can be considered self-stabilizing due to its interlocking properties. Furthermore, it is characterized by relatively low manufacturing costs and allows for precise production of the mating surfaces (for example, with a runout tolerance of less than 0.1 mm, less than 0.05 mm, or less than 0.01 mm). As a result of the high manufacturing precision achievable with such geometries, the amount of free volume between mating surfaces can be reduced to a minimum. This ensures that the forces transmitted via the tapered connection are distributed evenly, preventing stress concentrations.

[0028] If the conical connection is rotationally symmetrical, the operating surgeon has an additional degree of freedom available for aligning the implant during insertion, namely a rotational degree of freedom around the conical axis. This rotational degree of freedom allows, with certain implants, the implant geometry to be quickly and easily adapted to the patient's anatomy.

[0029] As an alternative to a conical connection, the connecting section can, for example, be designed as an axially parallel cylinder and / or an axially parallel bore. If the connecting section is connected to another implant component, the axially parallel cylinder and / or bore can be part of a fitting system, such as an interference fit or a transition fit (e.g., H7p6 or H7n6).

[0030] The connecting section can further comprise a stop with a stop surface, wherein the stop surface can, for example, be substantially perpendicular to the cone or cylinder axis or form an angle with it. The stop surface is preferably substantially rotationally symmetrical with respect to the cone or cylinder axis.

[0031] An implant component according to the present disclosure can comprise a metal alloy, for example, a titanium-based alloy or a cobalt-based alloy. Preferably, the implant component is formed substantially from a metal alloy, for example, a titanium-based alloy or a cobalt-based alloy. In other words, the Zr coating is preferably applied to a connecting section of an implant component formed substantially from one of the aforementioned alloys. In particular, an implant component according to the disclosure can comprise a CoCr casting alloy containing, for example, approximately 62-66 wt.% cobalt, approximately 27-31 wt.% chromium, and 4-5 wt.% molybdenum. However, such an alloy can also contain small amounts of carbon, silicon, manganese, iron, and / or other accompanying elements (e.g., according to ISO 5832-4, ASTM F75).Other examples of metal alloys that can be used in an implant component are CoCr forging alloys (e.g. according to ISO 5832-12), steel alloys (e.g. according to ISO 5832-1) or titanium alloys (e.g. according to ISO 5832-3 or ISO 5832-11).

[0032] The implant component can also be made of other materials, such as ceramics or plastics, or be essentially composed of one or more of these materials. Examples of ceramic materials that can be used include aluminum, titanium, zirconium, and / or magnesium-based ceramics. Examples of plastics that can be used include UHMW-PE, PP, PEEK, or POM.

[0033] The aforementioned metallic materials offer, for example, high mechanical strength combined with excellent biocompatibility. Furthermore, titanium alloys in particular are known for their excellent ingrowth properties in bone tissue. The ceramic materials mentioned can offer advantages in terms of fatigue strength. The plastics listed above can exhibit advantageous sliding properties, favorable impact strength, advantageously high ductility, and / or excellent strength-to-weight ratios.

[0034] An implant component according to the present disclosure can be, for example, a prosthetic stem, an intermediate piece, or a joint component, in particular a joint head. The implant component can, for example, be designed to be used as part of a hip replacement prosthesis, a knee replacement prosthesis, an elbow replacement prosthesis, a shoulder replacement prosthesis, or a foot, hand, or finger joint replacement prosthesis.

[0035] In a patented implant component, the zirconia (Zr) coating can, for example, have a Zr content of at least 90 at.%. Preferably, the Zr coating has a Zr content of at least 94 at.%, and particularly preferably at least 99.5 at.%. These values ​​are to be understood as mole fractions. With a high purity of the coating, for example, at the Zr contents mentioned above, a reduction in susceptibility to crevice corrosion and / or fretting corrosion can be particularly pronounced.

[0036] In the case of a disclosed implant component, the coating can be applied by a physical vapor deposition (PVD) process or by an electroplating process. An electroplating process can offer cost advantages over other methods. A PVD process is characterized by high accuracy in maintaining the desired layer thickness. For example, deviations of no more than ±20% (relative to a target layer thickness) can be achieved with a PVD process. In particular, very uniform layer thicknesses can be produced with PVD processes, even with complex geometries. Furthermore, a coating applied by a PVD process adheres significantly better to the surface of the coated workpiece than a coating applied by another method.

[0037] According to the present disclosure, a modular endoprosthesis is further provided, comprising at least one, but preferably exactly one, of the implant components described above. Preferably, the modular endoprosthesis further comprises a second implant component with a connecting section counterpart, wherein the connecting section counterpart is configured to engage with the connecting section of the implant component as disclosed. In other words, the connecting section and the connecting section counterpart are complementary. The connecting section counterpart preferably does not have a Zr coating.

[0038] It has been shown that a reduction in susceptibility to crevice corrosion and / or fretting corrosion occurs when the connecting section of a first implant component of a modular endoprosthesis has a Zr coating as described in the disclosure, while a connecting section counterpart of a second implant component connected to the connecting section does not have a Zr coating. However, in a modular endoprosthesis as described in the disclosure, both the connecting section and the connecting section counterpart of a second implant component connected to the connecting section can also have a Zr coating.

[0039] In a modular endoprosthesis as disclosed, the first implant component may, for example, be a prosthetic stem in which the connecting section is a male cone, and the second implant component may, for example, be a joint component, in particular a joint head in which the connecting section counterpart is designed as a female cone.

[0040] Furthermore, the use of a Zr coating for corrosion prevention at a connection point of an implant component is also disclosed, wherein the coating has a thickness of 1-20 µm, preferably 1-6 µm, and particularly preferably 3-5 µm, and wherein the implant component is preferably one of the implant components described above according to the disclosure. This use has the same or comparable advantages or effects as a disclosed implant component or a disclosed modular endoprosthesis. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Fig. 1 shows an embodiment of a modular endoprosthesis according to the present disclosure in the disassembled state; Fig. 2 shows the embodiment of the modular endoprosthesis made of Fig. 1 in a connected state. Fig. 3a shows the current profile measured during cyclic loading of an endoprosthesis with a known implant component; Fig. 3b shows the current profile measured during cyclic loading of an endoprosthesis with an implant component according to the present disclosure. DETAILED DESCRIPTION OF PREFERRED EXECUTION FORMS

[0042] The preferred embodiments described below are merely examples and are not to be considered limiting. Identical reference numerals appearing in different figures denote identical, corresponding, or functionally similar elements.

[0043] Fig. 1Figure 1 shows an embodiment of a modular endoprosthesis according to the present disclosure in a disassembled state. The modular endoprosthesis comprises a prosthetic stem (10) as the first implant component and a joint head (20) as the second implant component. The prosthetic stem (10) has a connecting section designed as a male cone (30). The male cone (30) has an end face (40) and an outer circumferential surface (50). The male cone (30) is coated, at least partially, with a zirconia coating, wherein the zirconia coating has a thickness of 1-20 µm, preferably 1-6 µm. Preferably, at least the entire outer circumferential surface (50) of the male cone (30) is coated with a zirconia coating. Furthermore, the end face (40) of the male cone (30) can also be coated with a zirconia coating.The transition from the outer circumferential surface (50) of the male cone (30) to the end face (40) of the male cone (30) can, for example, be formed as a chamfer or edge rounding. This transition (i.e., the chamfer or edge rounding) can also have a Zr coating as disclosed.

[0044] The joint head (20) has a connecting section counterpart designed as a female cone (60). The female cone (60) has an inner circumferential surface (70) and a base surface. The joint head (20) further has a ball joint (80). The ball joint is preferably designed as a spherical segment with a substantially spherical surface, which serves as the articulating surface of this joint component. Figures 1 and 2The female cone (60) is formed in a connection area substantially opposite the ball joint. This connection area, with the female cone (60) formed therein, projects from the side of the ball joint that defines the ball segment. The female cone (60) can extend into the area of ​​the ball segment. Alternatively, the connection area may be formed not as a projection, but as a surface that defines the ball segment and thus the joint surface. In this case, the female cone (60) is formed within the ball segment.

[0045] In the present embodiment, neither the inner circumferential surface (70) nor the base surface of the female cone (60) has a zirconia coating. However, in a modification of the embodiment described above, the female cone (60) of the articulating head (20) can also have a zirconia coating, while the male cone (30) of the prosthetic stem (10) does not. According to a further modification, both the female cone (60) of the articulating head (20) and the male cone (30) of the prosthetic stem (10) can have a zirconia coating. Preferably, at least the entire outer circumferential surface (50) of the male cone (30) or the entire inner circumferential surface (70) of the female cone (60) is coated with a zirconia coating.

[0046] In a not in the Figures 1 and 2In the illustrated variant of the embodiment described above, the female cone (60) and the male cone (30) can also be reversed. For example, the prosthetic stem (10) can have a female cone, and the joint head (20) can have a male cone.

[0047] In Fig. 2 The embodiment of the modular endoprosthesis as described above is shown in a connected state. Fig. 2It is evident that the inner circumferential surface (70) of the female cone (60) is in contact with the outer circumferential surface (50) of the male cone (30) when connected. To avoid a double fit (which could potentially counteract a wedging effect between the male cone (30) and the female cone (60)), it is preferred that the geometry of the male cone (30) and the geometry of the female cone (60) are matched such that the end face (40) of the male cone (30) and the bottom face of the female cone (60) are not in contact.

[0048] If the end face (40) of the male cone (30) and the bottom face of the female cone (60) (and / or any chamfers, radii, or transition areas) are not in contact with each other, it can be assumed that crevice corrosion and / or fretting corrosion will not occur on these surfaces. Therefore, a Zr coating on these surfaces is not necessary. Nevertheless, a Zr coating may be provided on these surfaces. In particular, it may be advantageous for other reasons to provide a Zr coating on the end face (40) of the male cone (30), on the bottom face of the female cone (60), and / or on any chamfers, radii, or transition areas. If a Zr coating is also provided in these areas, a transition from an uncoated surface to a coated surface can be prevented, which in turn reduces the risk of parts of the coated surface flaking off (e.g., due to chipping).as a result of a notch effect and / or stress concentrations). Furthermore, if the end face (40) of the male cone (30), the bottom face of the female cone (60) and / or any chamfers, radii or transition areas are also coated, the need to mask these surfaces during the coating process is eliminated. This, in turn, can lead to cost advantages.

[0049] The Figures 3a and 3b illustrate (in part) measured values ​​from an experimental investigation in which a known implant component ( Fig. 3a ) and an implant component with a Zr coating as disclosed ( Fig. 3bThe susceptibility of a joint section to crevice corrosion and / or fretting corrosion has been investigated. Qualitative or comparative information about the susceptibility of a joint section to crevice corrosion and / or fretting corrosion can be obtained experimentally, for example, using a measurement method according to ASTM F1875-98 (reapproved in 2014). In this method, femoral shaft and head components are immersed in a medium, such as a saline solution, and subjected to a cyclic load. The shaft and head components are connected by a joint section. Reference electrodes, whose coating material matches that of the shaft and head components under test, are also immersed in the medium. The surface area of ​​the reference electrodes and the surface area of ​​the (submerged) sections of the shaft and head components are also identical.

[0050] The shaft and head components, as well as the reference electrodes, are connected to a current meter that allows the measurement of currents flowing (via the medium) between the shaft and head components on the one hand and the reference electrodes on the other. Since the surface and coating material of the shaft and head components and the reference electrodes are identical, these currents are not due to a potential difference between the shaft and head components and the reference electrodes (galvanic cell / battery effect). Rather, the measurable current flow between the shaft and head components on the one hand and the reference electrodes on the other results from the fact that, due to the aforementioned cyclic force, parts of the passive layer (or layers) on the surface (or surfaces) of the connection section are abraded and reformed.

[0051] From the measured values ​​of the current flow between the shaft and head components and the reference electrodes, the time-averaged current Im and the mean dynamic current Id can be determined. The mean dynamic current Id is the difference between the maximum current Imax and the minimum current Imin measured in a specific time interval (i.e., in the time interval Δt1: Id,Δt1 = Imax,Δt1 - Imin,Δt1).

[0052] If a lower value I m is measured for a first combination of shaft and head components than for a second combination of shaft and head components, this is considered indirect evidence that the first combination of shaft and head components is less susceptible to crevice corrosion and / or fretting corrosion than the second combination of shaft and head components.

[0053] In particular, if a lower value Im and a lower value Id are measured for a first combination of shaft and head components than for a second combination of shaft and head components, this is considered indirect evidence that the first combination of shaft and head components is significantly less susceptible to crevice corrosion and / or fretting corrosion than the second combination of shaft and head components.

[0054] The known implant component of the Fig. 3a and the implant component with the disclosed Zr coating of the Fig. 3bEach implant component was connected to another implant component via a connecting section, thereby forming an endoprosthesis. The geometry of the endoprosthesis with the known implant component and the geometry of the endoprosthesis with the implant component with the disclosed zirconia coating were identical. Furthermore, identical test parameters were chosen for both endoprostheses. As can be seen from the Figures 3a and 3b As can be seen, the endoprostheses were subjected to a cyclic load with a frequency of 1 Hz. The load magnitude varied periodically between 0.04 kN and 2.04 kN. The diagrams in Fig. 3a and Fig. 3bThe load (in kilonewtons) is plotted on the left vertical axis, with the negative sign indicating the load's orientation (compressive load). The horizontal axis of each diagram shows time in seconds. The right vertical axis shows the current (in microamperes) measured between the endoprostheses and the reference electrodes during cyclic loading.

[0055] As demonstrated by Fig. 3a As can be verified, within a specific time interval, the endoprosthesis with the known implant component exhibited a time-averaged current Im = 4.49 µA and a mean dynamic current Id = 3.61 µmA. As demonstrated by Fig. 3bAs can be seen, within a specific time interval, the endoprosthesis with the implant component bearing the disclosed zirconia coating exhibited a time-averaged current Im = 0.49 µA and a mean dynamic current Id = 0.68 µmA. A comparison of the test series suggests that the endoprosthesis with the implant component bearing the disclosed zirconia coating is less susceptible to crevice corrosion and / or fretting corrosion than the endoprosthesis with the known implant component.

Claims

1. An implant component (10) with a connecting section (30), wherein the connecting section (30) is coated at least in sections with a Zr coating and the coating has a thickness of 1-20 µm, preferably 1-6 µm, wherein the Zr coating has a Zr content of at least 90 at%, and wherein the Zr coating comprises at least one of elemental zirconium and zirconium-based oxides, characterized in that the implant component (10) is a prosthesis shaft (10).

2. The implant component (10) of claim 1, wherein the coating has a thickness of 3-6 µm, preferably 3-5 µm.

3. The implant component (10) of any one of the preceding claims, wherein the connecting section (30) has a female and / or a male cone.

4. The implant component (10) of any one of the preceding claims, wherein the connecting section (30, 60) is rotationally symmetrical.

5. The implant component (10) of any one of the preceding claims, wherein the implant component (10) comprises a metal alloy, preferably a titanium-based alloy or a cobalt-based alloy.

6. The implant component (10) of any one of the preceding claims, wherein the implant component (10) comprises a CoCr alloy.

7. The implant component (10) of any one of the preceding claims, wherein the Zr coating has a Zr content of at least 97 at% and preferably at least 99.5 at%.

8. The implant component (10) of any one of the preceding claims, wherein the Zr coating is a physical vapor-deposited Zr coating or a galvanic Zr coating.

9. A modular endoprosthesis with a first implant component (10) according to any one of the preceding claims.

10. The modular endoprosthesis of claim 9, further comprising a second implant component (20) with a connecting section counterpart (60), wherein the connecting section counterpart (60) is designed to engage with the connecting section (30) of the first implant component (10), wherein the connecting section counterpart (60) preferably does not have a Zr coating.

11. The modular endoprosthesis of claim 10, wherein the first implant component is a prosthesis shaft (10) with a connecting section (30) designed as a male cone, and wherein the second implant component is a joint head (20) with a connecting section counterpart (60) designed as a female cone.

12. A use of a Zr coating for preventing corrosion on a connecting section (30) of an implant component (10), wherein the coating has a thickness of 1-20 µm, preferably 1-6 µm and particularly preferably 3-5 µm, characterized in that the implant component (10) is an implant component (10) of any one of claims 1 to 8.