JP2004530526A - Orthopedic joint prosthesis - Google Patents

Abstract

An orthopedic joint prosthesis including a first joint component and a second joint component. Each of the components is formed by a metal body portion and has a support surface portion that engages a corresponding support surface portion of each other component when the prosthesis is implanted. . Each of the metal body portions has a ceramic coating provided on the support surface portion, the coating including a chromium compound and being at least about 5 μm thick. These coatings may be different, for example, such that the difference between the hardness of the material of each coating supplied to the first and second joint components is less than about 5000 MPa. Preferably, the metal from which at least one of the first and second joint components is made has a constant modulus of at least about 150 GPa.

Description

Disclosure of the content of the invention
[0001]
The present invention is directed to an orthopedic joint prosthesis, the prosthesis comprising a first joint component and a second joint component, each of which supports a corresponding support of another component when implanting the prosthesis. It has a support surface portion that engages the surface portion.
[0002]
Various orthopedic joint prostheses are known for the replacement of natural joints such as certain hip, knee, tarsal and shoulder joints. Joint replacement generally involves the removal of tissue from each of the various articulating bones in the joint, and the implantation of prosthetic components in these bones.
[0003]
Since wear debris can adversely affect various physiological responses, it is important to minimize the wear of each component of a prosthetic joint. Thus, the choice of materials for the various joint components is made in a manner that minimizes their wear and ensures that the physiological response to the resulting wear debris is minimized.
[0004]
It is common for certain joint prostheses to have mating mating surface portions that include a metal and a polymer, respectively (a “metal-on-polymer” type). joint). For example, the support surface portion in one of the components could be a cobalt-chromium-molybdenum alloy and the corresponding support surface portion in another component could be a high molecular weight polyethylene. . The surface portions of both parts have been finished to make them smooth. During such articulation, the polymeric component is subject to gradual wear, forming fine particles of the polymer.
[0005]
Attempts to manufacture both of the joint surface portions from metal (certain "metal-on-metal" type joints) have been made to form various joint prostheses. Even in the case of very fine finishing processes to produce a smooth support surface part, wear on the prosthesis cannot be avoided. In addition, this abrasion necessarily results in the formation of various metal particles. Thus, the wear characteristics of such metallic prosthetic components have been improved by the application of various ceramic coatings. One advantage arising from the use of certain ceramic coatings is that the relatively high hardness available allows for reduced wear. Previously used ceramic materials for such applications include titanium nitride and diamond-like carbon. This titanium nitride is particularly preferred as a coating material for use in various prosthetic components made of titanium due to the compatibility of the respective material of the component body and coating.
[0006]
Various difficulties are encountered when attempting to form thick ceramic coatings on various joint prosthesis components. For example, it has been found that the resulting parts are inadequate due to the lack of bonding of the coating. Therefore, the maximum thickness of the applied ceramic coating is limited to 2-3 μm. However, this has the disadvantage that in the case of use over an extended period of time, such coatings can wear to the extent that the underlying metal is exposed. This is particularly disadvantageous when the part is made of titanium, due to its high susceptibility to titanium wear.
[0007]
The present invention provides an orthopedic joint prosthesis, wherein each joining prosthetic component has a metallic body portion, the body portion having a support surface. The portion has a ceramic coating applied thereto, the coating comprising a chromium compound and being at least 5 μm thick.
[0008]
Accordingly, in one aspect, the invention provides an orthopedic joint prosthesis, the prosthesis having a first joint component and a second joint component, each component having a fixed joint. Each of the metallic body portions is formed by a metallic body portion and has a supporting surface portion that engages a corresponding supporting surface portion on each other's parts when the prosthesis is implanted. Has a ceramic coating provided on said support surface portion, said coating comprising a chromium compound and having a thickness of at least about 5 μm.
[0009]
The prosthesis of the present invention has the advantage that it can reduce the likelihood of defects due to insufficient bonding of the coating as compared to prostheses where each support surface portion is provided by a material other than a ceramic-chromium compound. . This advantage is useful despite the increased thickness when compared to conventionally used thin coatings having a thickness of, for example, 2-3 μm or less. This property is believed to be caused by the properties of the chromium compound described above. The advantage resulting from the effect of such relatively low bond strength is a slightly reduced hardness (hence, when compared to certain other ceramic materials used to coat each supporting surface portion of the prosthesis. (Potentially slightly increased wear rate).
[0010]
The ability to provide a thick ceramic coating in the prosthesis of the present invention has the advantage that the prosthesis is adaptable to its initial wear as the supporting surfaces of its components coincide with each other. That is, slight inconsistencies in the shape of the supporting surface portion of each joining component can result in an initial localized wear of 1-3 μm. This is also true for the overall thickness of conventional thin coatings.
[0011]
Preferably, the thickness of the coating is at least about 6 μm, more preferably at least about 7 μm, especially at least about 8 μm, for example about 10 μm or more. Also, the thickness of the coating is generally about 25 μm or less, for example, about 20 μm or less, or about 15 μm or less.
[0012]
The chromium compound used to provide the coating can include one or more of chromium oxide, chromium nitride, chromium carbide, and chromium carbide. Further, of these, nitrides and carbon nitrides are preferable.
[0013]
Preferably, the difference between the hardness of the coating material supplied to the first and second joint parts is less than about 5000 MPa, more preferably less than about 2500 MPa, especially less than about 1000 MPa. Furthermore, it is particularly preferred that the hardness of the material of the coating is approximately the same. However, it is also conceivable that different chromium compounds could be used at each joining surface portion of the two types of prosthetic components. For example, it is conceivable to coat the supporting surface part of one part with CrN and coat the corresponding supporting surface part in another part with CrCN.
[0014]
Preferably, the material of each coating supplied to the first and second joint parts is the same.
[0015]
Preferably, the metal used in at least one of the above parts, preferably in each of these parts, has a modulus of at least about 150 GPa, more preferably at least about 175 GPa, especially at least about 200 GPa. The use of such a high modulus metal can reduce the imperfect bonding between the material of the supporting surface portion and the metal.
[0016]
Examples of metals that can be used in the body portion include cobalt-chromium based alloys, titanium alloys, and certain stainless steels. Preferably, the metal making up at least one of the first and second joint parts is an alloy containing chromium as a component element. A ceramic coating capable of being applied to a metal prosthesis component formed of a chromium-based alloy with enhanced adhesion interaction between the coating and the alloy in the body portion Is an advantage of the present invention. It is particularly preferred that the material forming at least one of the first and second joint parts is a cobalt-chromium-molybdenum alloy, especially an alloy satisfying ASTM F-1537. preferable. The use of such alloys in orthopedic joint prostheses is well established. This has an advantage due to its low hardness and low wear effects. According to the present invention, by providing a ceramic coating to a prosthesis component formed of a chromium-based alloy, a strong adhesive interaction between the coating and the body portion is provided. And the abrasion resistance can be further improved. Further, if the chromium-based ceramic coating is worn away after long-term use and the alloy is exposed, the hardness characteristics of the alloy make this part the same as a part whose main body is made of titanium. It does not produce moderately high wear rates.
[0017]
Either or both of the above parts can be made of a plurality of parts made of different materials. For example, where the joint prosthesis is for replacement of a hip joint, the femoral component may include separate stem and head components each formed of a different material. Attached to a corresponding supporting surface portion of the acetabular component, the supporting surface portion provided with the ceramic coating is on the head component. Alternatively, or additionally, the acetabular component in a hip prosthesis may include separate shell and inner components, each formed of a different material. Attached to a corresponding supporting surface portion of the thigh component, the supporting surface portion provided with the ceramic coating is on the inner component.
[0018]
Preferably, the surface roughness of the coating supplied to each of the first and second joint parts as measured by a conventional surface profilometer apparatus is about 0.05 μm (R _a ) or less, more preferably about 0.02μm and a (R _a) or less, particularly about 0.01 [mu] m (Ra) below. Preferably, the surface roughness is no greater than about 0.1 μm (R _pm ), and more preferably, no greater than about 0.04 μm (R _pm ). It is an object of the present invention that such ceramic materials can be conveniently finished with such conventional techniques and readily achievable surface finishing techniques using commercially available equipment, with smooth surface properties as described above. An advantage in the use of these ceramic materials in joint prostheses.
[0019]
The present invention can be practiced with certain hip, knee, tarsal and shoulder joints, and joints such as the joints on each finger, arm and elbow, and the like. For example, the invention may be practiced at a hip joint, wherein the first component may include a head portion of the femoral component and the second component may include a cup portion of the acetabular component. Also, when the present invention is implemented in a knee joint, the first component may include the femoral component and the second component may include a tibial component (the component may be implanted into the tibia. May include a movable half-moon part for this part).
[0020]
In general, the coating is applied only to the body part of the part in the region of the bearing surface part which joins with the bearing surface part of another part in the joint.
[0021]
Preferably, the coating is applied to each of the support surface portions by a deposition technique. It is particularly preferred to use physical vapor deposition techniques with constant evaporation. An example of a suitable deposition apparatus is available from IonBond AG of Olten, Switzerland, such as, for example, a cathodic arc coating system sold under the trademark PVD-3344. . The apparatus uses a water-cooled, stainless steel, cylindrical chamber 84 cm in diameter and 112 cm in height containing nine 5.4 kW arc sources.
[0022]
The invention is described below on the basis of various embodiments.
[0023]
Coating Technique Each part was coated using an IonBond 3344 arc-deposited PVD coating system available from IonBond AG, Industry Strasse 211, CH-4601, Olten, Switzerland. Coated. These parts were prepared for the coating process by washing with a widely available aqueous cleaner and then drying with hot air. The components were then mounted on a fixture that allowed them to operate in the coating chamber. Fixtures that accommodate convex parts, such as the head of a femoral component, etc., in a hip prosthesis allow for dual rotation planetary motion. On the other hand, a fixation device corresponding to a concave part such as a cup part in a certain acetabular part performs a single rotation operation with the mouth of the cup part facing outward toward the deposition source. enable. Note that the minimum distance between each component and the evaporation supply source is 180 mm.
[0024]
The coating chamber is evacuated to 2 × 10 ⁻⁵ mTorr (2.66 × 10 ⁻³ Pascal). Thereafter, the parts to be coated are adjusted by glow discharge in a fixed mixture of argon and hydrogen. This is followed by a bombardment treatment with chromium ions accelerated by a constant negative voltage of about -1000 V which is emitted by the deposition source and applied to each part. Thereafter, a vapor deposition process is performed at a chamber pressure of 48 mTorr (6.4 Pascal) of nitrogen gas (99.999% purity) with a negative voltage of about -300 V applied to each component.
[0025]
The thickness of the coating applied to each of the above components is at least 10 μm.
[0026]
Test Results The parts were tested for wear rate and ion concentration after coating with the techniques described above. These components were femoral and acetabular components in a hip prosthesis formed of a cobalt-chromium-molybdenum alloy. This thigh had a spherical head with a constant diameter of 28 mm. After coating the supporting surface portions of the above femoral and acetabular components with a layer of a 10 μm thick ceramic material, the radial clearance between each supporting surface portion was 30 μm. Further, each of these supporting surface portions was finished to _a surface roughness Ra of 0.02 μm.
[0027]
Femoral and acetabular components in a hip prosthesis were prepared with ceramic coatings on the respective TiN, CrN and CrCN bearing surface portions. A certain hip joint simulator that reproduces the load and movement of these parts during a certain normal walking process (J. Eng Med, 215H, pp. 119-121, (2000) ). Calf serum (25% (vol / vol)) was used to lubricate the supporting surface portion of each part during each test. In addition, the wear volume was determined by gravimetric analysis. In addition, the amount of metal ions from the main body of each prosthesis component was determined by atomic absorption spectroscopy. These tests were performed with the exposed (uncoated) metal support surface portion on both parts, the TiN coating on the support surface portion on both parts, the CrN coating on the support surface portion on both parts, and the support surface on both parts. This was performed on a portion of the CrCN coating.
[0028]
FIG. 1 shows the average wear rate from a wear test using a fixed hip joint simulator.
[0029]
FIG. 2 shows the ion concentration in the joint serum lubricant by a test using the hip joint simulator.
[0030]
The amount of wear and the ion concentration in the serum after 2 million walking steps were significantly less in each of the coated samples than in the uncoated metal samples. In addition, the volume of wear debris generated from the three sets of coated parts after 2 million steps (measured in units of mm ³ / million steps) has varied significantly. Less than in each case about 0.1 mm ³ / million steps (compared to about 1.3 mm ³ / million steps in the uncoated metal control). Each of the components coated with CrN and CrCN described above produced only nanometer-sized small particles, whereas the components coated with titanium nitride showed relatively large debris consistent with the nanometer-sized small particles and surface damage. Had also occurred.
[0031]
After 5 million steps, the parts coated with CrN and CrCN described above showed a 30-fold reduction in their wear rate compared to the metal in the metal counterpart. In addition, no damage was seen in the CrN and CrCN coatings during these relatively long test periods. On the other hand, 5 million process tests could not be completed on each part coated with TiN due to surface damage caused by lack of bond strength of the coating.
[0032]
Both CrN and CrCN described above show a substantial reduction in wear and ion release compared to uncoated metal joint prosthesis parts. These materials can be supplied as thick coatings that are stable in long-term testing and do not show a tendency for lack of cohesion as indicated by the formation of debris. In addition, the expected time for these thick coatings to wear down in their entirety is likely to be more than 50 years.
[0033]
In addition, separate in vitro cell culture studies of wear particles for CrN and CrCN described above have shown to be at least 10 times less toxic than cobalt-chromium wear debris at equivalent volume concentrations. Thus, the CrN and CrCN support surface portions described above exhibit extremely low wear, low ion release and low biological activity.
[Brief description of the drawings]
[0034]
FIG. 1 is a diagram showing an average wear rate by a wear test using a certain hip joint simulator.
FIG. 2 is a diagram showing the ion concentration in joint serum lubricant obtained by a test using the hip joint simulator.

Claims (10)

An orthopedic joint prosthesis includes a first joint component and a second joint component, each component being formed by a metal body portion, each of which is a separate component when the prosthesis is implanted. Wherein said metal body portions each have a ceramic coating provided on said support surface portion. A joint prosthesis wherein the coating comprises a chromium compound and is at least about 5 μm thick. The joint prosthesis according to claim 1, wherein the coating comprises at least one of chromium nitride, chromium carbon nitride, and chromium carbide. The joint prosthesis according to claim 1, wherein the thickness of the coating is at least about 8 μm. The joint prosthesis of claim 1, wherein the difference between the hardness of the coating material supplied to each of the first and second joint components is less than about 5000 MPa. The joint prosthesis according to claim 1, wherein the material of the coating supplied to each of the first and second joint parts is the same. The joint prosthesis according to claim 1, wherein the metal from which at least one of the first and second joint components is made has a modulus of at least about 150 GPa. The joint prosthesis according to claim 1, wherein the metal from which at least one of the first and second joint components is made is an alloy containing chromium as a component. The joint prosthesis of claim 5, wherein the metal from which at least one of the first and second joint components is made is a cobalt-chromium-molybdenum alloy. The joint prosthesis according to claim 1, wherein _a surface roughness (R _a ) of _a coating supplied to each of the first and second joint parts is about 0.05 μm or less. The joint prosthesis of claim 1, wherein the first component includes a head portion of a femoral component and the second component includes a cup portion of an acetabular component of a hip prosthesis.

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