ES2363331T3 - PROTESTIC DEVICES THAT USE OXIDIZED ZIRCONY CONTACT SURFACES. - Google Patents

Abstract

A joint prosthesis, comprising: a prosthetic body formed of zirconium or zirconium alloy comprising an implant portion for inserting into the patient's body tissue, a support surface; and a counter-support surface formed by zirconium or zirconium alloy and adapted to cooperate with the support surface, where the support surface and the counter-support surface have a thin blue-black or black oxidized zirconium coating.

Description

Field of the Invention

This invention is generally framed in the field of prosthetic devices, and more specifically in the field of prosthetic devices that have operating surfaces made of oxidized zirconium.

Background of the invention

This invention relates to orthopedic metal implants with load bearing surfaces coated with a thin, dense, low friction oxidized zirconium coating and high wear resistance. The devices of the present invention have two or more oxidized zirconium surfaces in which the oxidized zirconium surfaces are in contact with each other in an articulated manner (i.e., load bearing). Because these high hardness coatings are resistant to friction and rubbing wear, they are particularly useful in the articulated portions of these prostheses. Typically such prostheses with articulated surfaces have been constructed with materials of different hardnesses. By having a "yielding" surface, such prior art devices eventually achieve an optimum fit, that is, an adjusted tolerance, so that wear due to rubbing, friction, as well as other erosive phenomena is minimized, resulting in devices more durable prosthetics. An example of these first-generation devices is the femoral head of a hip-stem prosthesis that engages with a surface in an acetabular cup that is often made of a softer material, such as ultra-high molecular weight polyethylene. However, the use of contact surfaces of varying hardness has disadvantages that are avoided due to the unique properties of the present invention. The softest surface is, by nature, sacrificial; eventually it will fail, achieving as a counterpart a global increase in the life of the prosthesis. Additionally, friction wear on the softer surface results in debris that may have harmful effects on the patient's health. The invention described herein is a particular type of ceramic-ceramic prosthesis; Its unique composition achieves the traditional advantages of ceramic-over-ceramic systems, while avoiding its greatest disadvantage.

Although efforts have been made to manufacture prosthetic devices with contact surfaces of the same material, these efforts have had limited success in solving the shortcomings of the prior art. By taking advantage of the unique characteristics of blue-black or black oxidized zirconium, the present invention discloses a prosthetic device that has contact surfaces of the same material, thus avoiding the need for a sacrificial or "yielding" surface, while maintaining wear to a minimum. The basic technology on which the improvement described herein is based is described in US Patent 5,037,438 to Davidson. US 5,258,022 describes a non-articulated prosthesis in the form of a heart valve prosthesis made of zirconium or zirconium with alloys. The prosthesis comprises a valve body and a flow control component. These two components comprise a thin coating of black or black blue zirconium oxide on the surfaces that will be subject to friction wear when the valve is in use.

The invention also relates to medical implants that have oxidized zirconium contact surfaces and also have oxidized zirconium coatings on the non-articulated surfaces of an orthopedic implant where these latter oxidized zirconium surfaces provide a barrier between the metal prosthesis and the tissue of the body, thus preventing the release of metal ions and corrosion of the implant. Additionally, this oxidation process and the associated increase in surface oxygen content and hardness increases the strength of the metal substrate and improves the fatigue resistance properties of the implant.

The lifespan of medical implants is of paramount importance, since it is desirable for the implant to function throughout the patient's life. This is particularly true if the patient is young and the number of surgical reviews should be kept to a minimum, and preferably zero. For this purpose, orthopedic implant materials should preferably combine high strength, corrosion resistance and compatibility with body tissues. One of the variables that affects the longevity of implants that support loads, such as hip joint implants, is the rate of wear of articulated surfaces and the long-term effects of metal ion release. A typical hip joint prosthesis includes a stem, a femoral head and an acetabular cup against which the femoral head is articulated. The wear of a

or both articulation surfaces result in an increase of worn particles and the appearance of a "play" between the femoral head and the cup against which it is articulated. Wear debris can contribute to an adverse reaction of the tissue that leads to bone resorption, and ultimately the joint must be replaced.

The wear rate of the surfaces of the acetabular cup and the femoral head of the artificial hips is dependent on several factors, including the relative hardness and surface finish of the materials that constitute the femoral head and the acetabular cup, the coefficient of friction between the cup and head materials, the applied load and the stresses generated on the articulation surfaces. The most commonly used combinations of material in the manufacture of hip joint implants include femoral heads of cobalt, titanium or zirconium alloys that articulate against acetabular cups coated with polymers or organic compounds such as polymers, including, for example, polyethylene of ultra-high molecular weight (UHMWPE) and polished alumina femoral heads in combination with acetabular cups coated with an organic polymer or a polished alumina compound or alumina.

Of the factors that influence the wear rate of a conventional hip joint implant, the most significant are the patient's weight and activity level. Additionally, it has been shown that the heat generated by friction during normal implant use causes deformation and wear of the polyethylene cup. In addition, there is a correlation between the frictional moment that transmits the torque load to the cup and the coefficient of friction between the femoral head and the surface of the acetabular cup against which the head is articulated. The pair of the cup is associated with the loosening of the cup. Therefore, in general, the higher the coefficient of friction for a given load, the higher the level of torque generated. Ceramic support surfaces have been shown to produce significantly lower frictional torque levels. It is also worth commenting that two of the three commonly used hip joint systems, as indicated above, include a metal femoral head against a UHMWPE coating inside the acetabular cup. UHMWPE, which is a polymeric material, is more susceptible to deformation when heated than commonly used metal alloys or metals due to its relatively lower melting point, and consequently is more susceptible to wear than alloys or ceramics.

It has also been discovered that metal prostheses are not completely inert within the body. Body fluids act on metals, causing them to corrode slowly due to an ionization process, thus releasing metal ions within the body. The release of metal ions from the prosthesis is also related to the articulation and the wear rate of the load bearing surfaces, as expected, when a metal femoral head, for example, articulates against a UHMWPE, the passive sheet of oxide that forms on the femoral head is constantly removed. The repasivation process constantly releases metal ions during this process. In addition, the presence of wear of a third body (cement or bone remains) accelerates this process and micro-friction metal particles can increase friction. Consequently, the UHMWPE coating inside the acetabular cup, against which the femoral head is articulated, is subject to accelerated levels of deformation, wear and torque.

Several attempts to correct these problems were the subject of a large part of the first works in this area. US Patent 4,145,764 of Suzuki disclosed a metal prosthesis sprayed with plasma with a bonding agent which, in turn, is coated with a porous ceramic coating that allows the growth of bone spicules in the pores. However, the Suzuki patent does not take into account the problem of friction or wear of the orthopedic implant support surfaces, but is confined to the sole problem of biocompatibility of the metal prosthesis and solves the problem of dimensional changes that they occur when the coating is applied. US Patent 3,677,795 to Bokros is directed to the application of a carbide coating on a metal prosthetic device. This method is said to produce a prosthetic device that has "excellent compatibility with body tissue and is non-thrombogenic." However, Bokros does not solve the problems related to friction, heating, deformation and wear of the support surfaces of the orthopedic implant, or the induced changes in the mechanical properties of the underlying metal due to this high temperature treatment.

The aforementioned problems of the prior art were partially solved by Davidson in US Patent 5,037,438. In the ‘438 patent, Davidson describes a zirconium metal alloy prosthesis or one containing zirconium coated via an in-situ oxidation with a blue-black or black oxidized zirconium layer. The oxidized zirconium coating gives the prosthesis of the invention '438 a thin, dense, low friction and wear-resistant biocompatible surface suitable for use on joint surfaces of joint prostheses where one surface or surface of the joint pivots , moves or rotates against other complementary articulation surfaces. The oxidized zirconium coating of the ‘438 patent can therefore be used on the femoral heads or internal surfaces of acetabular cups of hip joint implants or on the joint surfaces of other types of prostheses, such as knee joints. Notably, the oxidized zirconium coating of the ‘438 patent was a specific type of oxidized zirconium. Oxidized zirconium has many forms, among which is white, beige and blue-black. The white variety is particularly unfavorable for the present invention, since it has to be separated from the substrate and easily broken. Conventional surfaces of oxidized zirconium formed, for example, by simple oxidation of air are not of the blue-black or black variety, and will not possess the superior properties thereof described in the '438 patent. The most important of these properties is the high hardness and low friction, which result from the presence of surface oxide.

These blue-black or black oxidized zirconium coatings were known in the art of mechanical bearings, since they had been described by Watson in US Patent 2,987,352. Watson describes an oxidation method at 371-593 ° C (700-1100 ° F) to produce the specific blue-black or blue oxidized zirconium coating. A subsequent Haygarth patent (US Patent 4,671,824) describes an alternative method based on a salt bath to produce the desired coating. The blue-black or black oxidized zirconium of the present invention that possesses the necessary properties is mainly of monolithic crystalline structure. This has been

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characterized by Hunter et al.

The ‘438 patent did not contemplate and does not describe anywhere the use of oxidized zirconium surfaces directly in contact with other oxidized zirconium surfaces. To our knowledge, no such prosthetic device or medical implant has been manufactured. Initially, it was generally believed that the hardness of two contact surfaces was required to be different. Thus, imperfections in the tolerances between the surfaces would disappear when the first contact occurred, achieving a device of a long useful life relatively free of corrosion problems or rubbing wear, as well as other erosive problems. Although efforts have been made to develop prosthetic devices having contact surfaces with the same or very similar materials, the success in overcoming the problems of prior art devices without incurring other deficiencies has been limited.

The inventors of the present invention have discovered that the unique properties of oxidized zirconium eliminate the general need for one of the contact surfaces to be of a lower hardness to extend the overall life of the device. The characteristics of superior hardness, low friction, wear resistance and compatibility characteristics of the blue-black or black oxidized zirconium are sufficient in themselves to significantly slow down and possibly avoid the wear degradation processes to which the prosthetic devices have been subjected of the prior art.

It is expected that the removal of surfaces of a lower hardness will also have other beneficial effects. This is particularly true in the case of the most commonly used joint component, polyethylene; the most common type being ultra high molecular weight polyethylene (UHMWPE). The original motivation for the inclusion of such surfaces was that they would be sacrificial; they would fail slowly and fail before the harder surface, allowing a global extension of the device's life. Additionally, it was thought that polyethylene absorbed impacts better than harder surfaces, thus mimicking real cartilage. Although the advance of the technique that was achieved through the use of oxidized zirconium surfaces that articulated against UHMWPE surfaces was a decrease in deformation and weakening of the cup due to the heat generated between the surface of the metal component and the UHMWPE, the problem was not It was completely removed. Therefore, the present invention represents another advance in the art, namely the elimination of the problem of deformation associated with prior art prostheses comprising articulated polyethylene surfaces.

In addition, it was eventually discovered that the UHMWPE has additional problems in addition to the eventual failure of the prosthesis. In some patients with prosthetic implants, osteolysis has been observed and was originally believed to be due to metallic remains. As a result, metal-against-polyethylene prostheses were replaced by ceramic-against-polyethylene systems, such as alumina-against-polyethylene and zirconia-counter-polyethylene. When it was suspected that the polyethylene moieties also contributed to the osteolysis observed, the first systems were introduced using contact surfaces of the same material. The first of these devices was the ceramic-anti-ceramic type. For example, Ceratec produced an alumina-counter-alumina device, while Norton-Desmarquest produced a zirconia-counter-zirconia system. Although ceramics have the advantage of low wear rates and low friction, it has its own disadvantages, the most important being its tendency to fracture. More recently, metal-against-metal systems have been introduced. For example, Sulzer introduced a cobalt / chromium-cobalt / chromium device. Although metal-to-metal systems are expected to have low wear rates, they remain unknown regarding the ion release characteristics of such systems and the health risks of the patient.

The present invention of oxidized anti-zirconium zirconium prosthetic devices, in which both surfaces are of the blue-black or black variety, represents a special type of ceramic-counter-ceramic device, which has the advantages of low wear rate and low friction of ceramic systems, but without the high risk of fracture. By eliminating polyethylene, the risk of osteolysis and other problems related to debris due to polyethylene wear are eliminated. Finally, the disadvantages associated with the release of metal ions from metal-to-metal designs are also eliminated. The unique properties of oxidized zirconium make it possible to eliminate or minimize the disadvantages of prior art systems without sacrificing the advantages thereof.

There is a need for an orthopedic implant based on a metal alloy that has low friction load bearing surfaces and high wear resistance, which can be implanted for the entire life of the recipient, has a low risk of brittle breakage, and Low risk of metal ion release. There is also a need for an orthopedic implant based on a metal alloy that is not prone to corrosion by the action of body fluids, so that it is biocompatible and stable throughout the life of the recipient. These needs must be met while maintaining a long service life, to minimize the frequency and perhaps eliminate the need for surgical check-ups in implant patients.

Compendium of the invention

In this document, the expression "a", "one" or "one" may mean one or more. In the claims of this document, when used together with the word "comprises", the words "a", "one" or "a" may mean one or more than one. In this document, "other" or "other" may mean at least one second or more.

Here, the term "contact surface" refers to any two surfaces of the prosthetic device or medical implant that are in contact with each other, either according to a load-bearing (articulated) mode or without a load-bearing support ( non-articulated).

The present description contains illustrations and examples of preferred embodiments for practicing the present invention. However, they are not limiting examples. Other examples and methods for practicing the present invention are possible.

In this document, "zirconium alloy" is defined as any metal alloy containing an amount of zirconium greater than zero. Therefore, an elation in which zirconium is a minor constituent is considered a "zirconium alloy" herein.

The invention provides a zirconium metal alloy prosthesis or containing zirconium coated in situ by oxidation with blue-black or black oxidized zirconium. The oxidized zirconium coating provides the prosthesis of the invention with a thin, dense, low friction, wear-resistant and biocompatible surface ideal for use on joint surfaces of joint prostheses, where one surface or surfaces of the joint pivots , moves or rotates against complementary articulation surfaces that are also coated with oxidized zirconium. The oxidized zirconium coating can therefore be used on the femoral heads or the inner surfaces of acetabular cups of hip joint implants, or on the articulated surfaces of other types of prostheses, such as knee joints.

In one embodiment of the present invention, there is an articulated prosthesis, comprising a prosthetic body formed of zirconium or zirconium alloy comprising an implant portion for inserting into the patient's body tissue, a support surface and a contracting surface. support formed of zirconium or zirconium alloy and adapted to cooperate with the support surface, where the support surface and the counter-support surface have a blue-black or black oxidized zirconium coating. According to a specific embodiment, the prosthesis is characterized in that the oxidized zirconium coating of said support surface or said counter-support surface or both has a thickness of between 1 and 20 microns. In another embodiment, the prosthesis is characterized in that the oxidized zirconium coating of said support surface or said counter-support surface or both has a thickness of between 1 and 5 microns.

According to an alternative embodiment, the prosthesis is characterized in that the implant portion of the prosthesis body further comprises an irregular surface structure adapted to accommodate growing tissue on a portion of the prosthesis body. According to a specific embodiment, the prosthesis is characterized in that the irregular surface structure is formed by zirconium alloy or zirconium alloy flanges attached to the outer surface of the prosthesis body, where at least a portion of the surface of the flanges is oxidized until rusty zirconium blue-black or black. According to another embodiment, the prosthesis is characterized in that the irregular surface structure is formed by a zirconium wire mesh or zirconium alloy mesh connected to the outer surface of the prosthetic body, where at least a portion of the mesh surface is oxidized to zirconium. Rusty blue-black or black.

In other embodiments that may also comprise some of the features described above, the prosthesis is characterized in that the support surface is part of a femoral component that has at least one condyle and which is further characterized in that the counter-support surface is part of a tibial component, the counter-support surface being adapted to cooperate with the support surface.

In other embodiments that may comprise any of the features described above, the prosthesis is characterized in that the counter-support surface is part of an inner surface of an acetabular cup, said inner surface being adapted to cooperate with the support surface of the portion head

Brief description of the drawings

FIG. 1 is a schematic diagram showing a hip joint prosthesis in position.

FIG. 2 is a schematic diagram showing a typical hip joint prosthesis.

FIG. 3 is a schematic diagram of a knee joint prosthesis in position.

FIG. 4 is a schematic diagram of the parts of a typical knee joint.

Detailed description of the invention

The present invention provides low friction and wear resistant coatings for the articulation surfaces of prosthetic devices. Specifically, the invention provides a prosthetic device in which the contact surfaces comprise blue-black or black oxidized zirconium. Oxidized zirconium comes in many forms, including white, beige and blue-black. The white variety is particularly unfavorable for the present application, since it has to break and separate from the substrate easily. The oxidized zirconium surfaces formed, for example, by simple air oxidation will not be of the blue-black or black variety. The blue-black or black oxidized zirconium of the present invention that possesses the necessary properties is primarily of monolithic crystalline structure and may include tetragonal zirconia. Its microstructure has been characterized by Hunter et al. The specific blue-black or black oxidized zirconium coatings used herein were known in the art of mechanical bearings, having originally been described by Watson in US Patent 2,987,352. Davidson, in US Patent 5,037,428, first described the application of this form of oxidized zirconium to prosthetic devices, but did not describe or suggest its use to make contact directly with other surfaces of oxidized zirconium. Illustrative examples of the use of blue-black or black oxidized zirconium in prosthetic devices are shown in the schematic diagrams, FIGS. 1-4. The following description provides non-limiting examples of the present invention. Although much of the description is centered on hip and knee prostheses, it should be understood that the present invention is not limited thereto and that it is applicable to any articulated prosthetic device where improved wear characteristics are useful on surfaces that cooperate with each other. .

In FIG. 1 and in FIG. 2 shows a typical hip joint assembly. The stem 2 of the hip joint fits into the femur, while the femoral head 6 of the prosthesis fits into, and articulates against, the inner lining 8 of an acetabular cup 10 which in turn is fixed to the pelvis as it is shown in FIG. 1. A coating of porous metal flanges or wire mesh can be incorporated to allow stabilization of the implant by growing the surrounding tissue into the porous coating. Similarly, said coating can also be applied to the acetabular component. The femoral head 6 may be an integral part of the stem 2 of the hip joint or it may be a separate component mounted on a conical narrowing at the end of the neck 4 of the hip joint prosthesis. This allows the fabrication of a prosthesis that has a metal stem and neck, but a femoral head of a different material. This construction method is often desirable because the use of composite materials allows localized optimization of various parameters, such as weight, strength and wear resistance. Regardless of the materials, however, the femoral head articulates against the inner surface of the acetabular cup, thus causing wear and, in the long run, this involves replacing the prosthesis. This is especially the case when the femoral head is made of metal and the acetabular cup is coated with an organic polymer or a compound thereof. Although these polymeric surfaces provide good, relatively low friction surfaces, and are biocompatible, they are, as explained above, subject to accelerated wear and deformation due to frictional heat and the torque to which they are subjected during ordinary use. In the present invention, the inner lining 8 and the femoral head 6 are coated with a blue-black oxidized zirconium surface

or black Preferably, the surface coatings have a thickness of 1-20 μm, but may be outside this range. Alternatively they can have a thickness of 1-5 μm. The wire mesh or metal flange surface 12 may be at least partially coated with a blue-black or black oxidized zirconium surface to promote tissue or bone growth into the device, thereby stabilizing its position.

In FIG. 3 and FIG 4. a typical knee joint prosthesis is shown in situ. The knee joint includes a femoral component 20 and a tibial component 30. The femoral component includes condyles 22 that provide the articulation surface of the femoral component and spikes 24 to secure the femoral component to the femur. The tibial component 30 includes a tibial base 32 and a spike 34 for mounting the tibial base on the tibia. A tibial platform 36 is mounted on the upper part of the tibial base 32 and is provided with cavities 38 similar to the shape of the condyle 22. The inner surfaces of the condyle 26 are in contact with the cavities 38 of the tibial platform, so that the condyles articulate within these cavities against the tibial platform. Both the condyles 22 and the cavities 38 of the tibial platform are coated with a blue-black or black oxidized zirconium surface. Part or all of the rest of the femoral component 20 and a tibial component 30 may have a blue-black or black oxidized zirconium surface coating. Preferably, the surface coatings have a thickness of 1-20 μm, but may be outside this range. Alternatively, they can be 1-5 μm thick. As in the case of the hip joint, porous overlays or wire mesh can also be applied to one of the tibial or femoral components of the knee, or both. These porous overlays or cable mesh of the knee prosthesis may also be at least partially coated with a blue-black or black oxidized zirconium surface to promote tissue or bone growth into the device, thus stabilizing their position. .

The invention provides orthopedic implants coated with oxidized zirconium or prostheses made of zirconium or metal alloys containing zirconium or a thin coating of zirconium or zirconium alloy on the materials of a conventional orthopedic implant. To form oxidized zirconium coatings that are continuous and useful over the entire surface of the metal alloy substrate of the prosthesis, the metal alloy should preferably contain from 80% to 100% by weight of zirconium, and more preferably from 95% to 100% by weight. However, much smaller amounts of zirconium can also produce an acceptable product. For example, it has been shown that a titanium alloy with 13% zirconium, 13% niobium (Ti13-13) provides an acceptable zirconium surface. Smaller amounts of zirconium are expected to also provide an acceptable oxidized zirconium coating. The results obtained by X-ray Photoelectronic Spectroscopy shown in Tables 1 and 2 for the Ti-13-13 alloy show the atomic concentrations (100% normalized) of the individual elements and of various oxides. Therefore, as an acceptable product is obtained when zirconium and its oxides are present as minor constituents, in the invention a wider range of alloys, which includes those in which zirconium is a minor component, is useful.

Table 1. Atomic concentration of the elements on the near surface of the oxidized surface determined by X-ray photoelectronic spectroscopy. Analysis (XPS).

Depth Å O Ti N Nb Zr C

Surface 36.2 7.4 1.0 0.2 0.1 55.1 50 65.7 29.7 0.0 0.6 0.6 3.4 200 62.1 32.7 0.0 1.5 1.7 2.0 1000 59.8 27.3 0.0 5.6 5.5 1.9 2000 58.4 29.9 0.0 5.6 5.0 1.1 5000 55.4 32.3 0.0 6.0 5.3 1.0 10000 37.2 43.5 0.0 8.3 6.3 4.6 15,000 23.5 51.9 0.0 10.0 7.3 7.2 20,000 14.0 59.7 0.7 13.1 8.4 4.1

Table 2. Oxide concentrations of Ti, Nb and Zr contained in the superficially oxidized mixed oxide layer Ti-13-13

Depth Å TiO2 TiOx TiO Nb2O5 NbOx ZrO2 ZrOx

50 28.7 67.3 0.0 2.0 0.0 2.0 0.0 200 23.6 51.1 16.4 0.0 4.0 4.4 0.6 1000 14.6 36.7 22.1 0.0 15.0 12.0 2.0 2000 13.8 32.1 18.3 0.0 14.0 10.3 1.7 5000 13.6 36.6 22.9 0.0 14.0 9.6 2.4

Oxygen, niobium and titanium are common alloy elements in the alloy, often also with the presence of hafnium. Although such alloys containing zirconium can be formulated with conventional methods known in metallurgy, there are multiple commercially available alloys. Illustrative examples of these commercial alloys include, among others, Zircadyne 705, Zircadyne 702, and Zircalloy.

Base alloys containing metal alloys are molded or machined using conventional methods to shape and give the desired size to obtain the substrate of a prosthesis. The substrate then undergoes conditions that cause the natural formation (in situ) on its surface of an oxidized zirconium coating strongly adhered by diffusion bonds. The conditions of this process include, for example, oxidation to air, steam or water or oxidation in a salt bath. These processes ideally provide a thin, hard, dense, blue-black or black, low-friction and wear-resistant oxidized zirconium layer or coating, typically thick in the order of several microns (10-6 meters) above the surface of the prosthesis substrate. Under this coating, the oxygen diffused in the oxidation process increases the hardness and resistance of the underlying metal substrate.

Representative methods for the formation of the blue-black or black oxidized zirconium surface coating have been previously described in US Patent 5,037,428 to Davidson. Preferably, the thickness of the coating is 1 to 5 microns. Useful conditions for the manufacture of surfaces of different thicknesses are described in US 5,037,428. Methods to control the uniformity of the oxidized zirconium coating are described in the application of several pending holders S / N 09 / 381,217.

These oxidized zirconium coatings fixed by diffusion, low friction and high wear resistance are applied to the contact surfaces of orthopedic implants subject to wear conditions. Such surfaces include the articulation surfaces of knee, elbow and hip joints. As mentioned above, in the case of hip joints, the femoral head and the stem are typically made of metal alloys, while the acetabular cup can be made of ceramic. The only requirement is that the contact surface of the device must be made of zirconium or zirconium alloy, so that when surface oxidation takes place under appropriate conditions, measurable surface concentrations of oxidized zirconium are formed.

The prosthesis of the present invention has advantages in several applications. Hip prostheses constitute a comparatively simple mechanical system, consisting of a spherical head, a spherical cavity and a simple narrowing of the stem. The range of mechanical load states in this configuration is comparatively low. Therefore, one can design the head so that a brittle material such as ceramic can be used while maintaining a relatively low risk of brittle fracture. In contrast, a knee joint constitutes a joint that has a greater range of mechanical loading states. The knee joint presents a higher risk of suffering "point loads", that is, highly localized stress levels. Therefore, in applications for knees, a brittle material over another brittle material, such as conventional ceramic-counter-ceramic, presents a high risk of fracture. For this reason, it has been found that it is particularly important to design such prostheses as "hard-versus-soft" systems, such as ceramic-counterpolyethylene. Although ceramic-anti-ceramic prostheses have the advantages of low friction and low wear rates, they suffer the disadvantage of a high risk of brittle fracture. Therefore, such ceramic-anti-ceramic systems (and in fact all "hard-against-soft" systems, to some extent) are problematic in both knee prostheses and hip prostheses, but are particularly unsuitable for knee prosthesis Although it is a ceramic-anti-ceramic system, the oxidized zirconium of the present invention has advantages over them, that is, low friction and high wear resistance, but does not suffer the main disadvantage of such systems consisting of a high risk of brittle fracture Therefore, the present invention can generally be applied in different prostheses, allowing to achieve the advantages of ceramic-counter-ceramic and avoiding its disadvantages.The oxidized anti-zirconium zirconium prostheses of the present invention have general applicability in both prostheses used in "hard-against-hard" applications and in traditional "hard-against-bland" applications or". It is suitable for use in a wide variety of prosthetic devices that are subjected to a wide range of mechanical loading states.

Because the oxidized zirconium coating is firmly attached to the zirconium alloy prosthesis substrate, it provides a barrier between the body fluids and the zirconium alloy metal, thus preventing corrosion of the alloy due to the ionization process and the associated release of metal ions. Additionally, the diffusion of oxygen in the metal substrate during oxidation also increases the strength of the metal. Consequently, it is expected that a rusted zirconium coated prosthesis has a longer shelf life.

Zirconium or zirconium alloy can also be used to provide a porous surface of flanges or wire mesh to which the surrounding bone or other tissue can be integrated to stabilize the oxidized anti-zirconium zirconium prosthesis. These porous coatings can be treated simultaneously by the oxidation treatment in a manner similar to the oxidation of the base prosthesis for the removal or reduction of the release of metal ions. In addition, zirconium or zirconium alloy can also be used as a surface layer applied on conventional implant materials before oxidation in situ and formation of the oxidized zirconium coating.

References

All patents and publications mentioned in the description are indicative of the level of an average expert in the field to which the invention belongs.

US Patent 5,037,438 8/1991 Davidson

US Patent 4,145,746 3/1979 Suzuki et al.

US Patent 3,677,, 795 7/1972 Bokros et al.

US Patent 2,987,352 2.1958 Watson

US Patent 4,671,824 6/1987 Haygarth

Application US S / N 09 / 381,217 filed 11/1999 Hunter et al.

Hunter, G. et al., Mat. Res. Soc. Symp. Proc. 1999, 550, 337

Claims (8)

1. A joint prosthesis, comprising: a prosthetic body formed of zirconium or zirconium alloy comprising an implant portion for inserting into the patient's body tissue, a support surface; Y a counter-support surface formed by zirconium or zirconium alloy and adapted to cooperate with the support surface, where the support surface and the counter-support surface have a thin blue-black or black oxidized zirconium coating.

2.

The prosthesis of claim 1, characterized in that the oxidized zirconium coating on said support surface or said counter-support surface or both has a thickness of between 1 to 20 microns.

3.

The prosthesis of claim 1, characterized in that the oxidized zirconium coating on said support surface or said counter-support surface or both has a thickness of between 1 to 5 microns.

Four.

The prosthesis of claim 1, characterized in that the implant portion of the prosthesis body further comprises an irregular surface structure adapted to accommodate an internal growth of tissue over a portion of the prosthesis body.

5.

The prosthesis of claim 4, characterized in that the irregular surface structure is formed of zirconium or zirconium alloy flanges attached to the outer surface of the prosthetic body, where at least a portion of the surface of the flanges is oxidized to blue oxidized zirconium -black or black.

6.

The prosthesis of claim 4, characterized in that the irregular surface structure is formed by a zirconium wire mesh or zirconium alloy mesh connected to the outer surface of the prosthetic body, where at least a portion of the mesh surface is oxidized to rusty zirconium blue-black or black.

7.

The prosthesis of any of claims 1-6, characterized in that the support surface is part of a femoral component having at least one condyle and further characterized in that the counter-support surface is part of a tibial component, the surface being adapted of counter-support to cooperate with the support surface.

8.

The prosthesis of any of claims 1-6, characterized in that the support surface is part of a femoral component having a head portion and further characterized in that the counter-support surface is part of an internal surface of an acetabular cup, said internal surface being adapted to cooperate with the support surface in the head portion.