EP2217176A2

EP2217176A2 - Magnetically mounted artificial joint

Info

Publication number: EP2217176A2
Application number: EP08846627A
Authority: EP
Inventors: Georg Gradl
Original assignee: Universitaet Rostock
Current assignee: Universitaet Rostock
Priority date: 2007-11-06
Filing date: 2008-11-05
Publication date: 2010-08-18
Also published as: WO2009060007A3; DE102007053362B4; US8273130B2; US20100331993A1; WO2009060007A9; WO2009060007A2; DE102007053362A1

Abstract

The invention relates to a prosthesis for replacing a joint connection in which identically polarized magnetic fields of the condyle (10), joint cavity (12), and joint collar (14) are superimposed on each other in such a way that the repulsive forces generate a suspended state of the condyle (10) in the bearing and the damping effect is maximized. The invention also relates to a method for replacing a bone joint of a mammal. In said method, the prosthesis is fastened to the joint bone, and repulsive forces generate a levitated state of the condyle (10) under load.

Description

MAGNETICALLY BASED ARTIFICIAL JOINT

The invention relates to a prosthesis for replacement of a joint in which the magnetic fields of the same type of condyle 10, joint socket 12 and joint collar 14 are superimposed so that the repulsive forces produce a floating state of the condyle 10 in the camp and the damping effect is maximum. The invention is also a

A method for replacing a bone connection of a mammal, in which the prosthesis to the

Fixed joint bone and repulsive forces cause a state of levitation of the joint head 10 during exercise.

Joint prostheses and disc prostheses used in orthopedics and trauma surgery suffer from the problem of abrasion of the corresponding joint components. It comes to asymmetrical load peaks, which can laxate the implant faster or it is caused by abrasion material, a foreign body reaction of the tissue.

In the prior art it is attempted to penetrate the hardest possible substances which form the articular surfaces, e.g. Ceramics to reduce abrasion, but only insufficiently successful.

The patent application US 2006/0149386 A1 teaches a prosthetic device comprising a component for fixation in the bone and a receiving part, the latter having reservoirs and magnets and either the fixation component or the receiving part having magnetic properties. The design uses magnetic forces only to absorb the resulting abrasion, which must be magnetic, in the magnetic reservoirs and to prevent migration into the surrounding tissue, while the abrasion itself is not prevented.

It is further known from US 2006/0247782 A1 a prosthetic device for an intervertebral disc whose end regions generate magnetic fields which repel each other and thereby both keep the end regions apart and produce a supporting structure for two vertebrae. The disc prosthesis has built-in solenoids and external control and operating devices. The magnetic forces cause only a stabilization and / or change in length of the prosthesis, but no levitation and thus low-wear storage. US 4,024,588 discloses an artificial joint for implantation into the body having a head portion and a pedestal having magnetic elements in a polarization that produces either attractive or repulsive forces. The case of attracting magnets is aimed at preventing the dislocation of the joint, while for repulsive magnets a damping effect is to be achieved, since the effective bearing force is weakened. The design is incapable of building the magnetic fields necessary for a floating state because the areas involved are far too small. In addition, the specified magnetic materials are unable to build up the high permanent magnetic fields required for effective damping. Their use in the present design would force the joint unnaturally far apart at rest and without load.

Another problem is that the interface between bone and anchoring of the artificial joint by the walking and standing load of the patient must withstand high pressures. Over time, it comes inevitably to Auslockerungsphänomenen at the interface bone-joint.

The invention has for its object to overcome the disadvantages of the abrasion and the loosening indicated in the prior art and to develop a device that ensures a nearly contactless joint guidance.

The object of the invention is achieved according to the independent claims. The subclaims contain preferred embodiments. According to the invention, there is provided a prosthesis comprising a head 10 and a cup 12 of complementary spatial shape to one another and a collar 14, the head 10, the cup 12 and the collar 14 each comprising a permanent magnet layer 18 and a shielding layer 20, and wherein the Permanent magnet layers 18 of head 10, pan 12 and collar 14 have a like polarization, so that the head 10 and the pan 12 and the head 10 and the collar 14 are separated by a gap 24.

Surprisingly, it has been found that by providing a magnetic field through the additional prosthetic component of the collar 14, the magnetic fields generated by the permanent magnets in head 10, pan 12 and collar 14 can be dimensioned and arranged so that a balance of repulsive forces on the head 10 is caused, as a result, a state of levitation (floating state) of the condyle 10 is reached in the warehouse. As a result of the magnetic joint guidance a non-contact and thus low-abrasion storage is achieved in the joint. In addition to the significant reduction of abrasion, the magnetic bearing also causes an attenuation against mechanical peak loads.

The device according to the invention comprises the three components of head 10, cup 12 and collar 14. The head 10 and the cup 12 are designed so that their spatial structures are complementary to each other, i. the head 10 and the pan 12 fit together like key and lock. The accuracy of fit is dimensioned so that no positive connection arises, the movement, i. Rotation and / or translational movements, would prevent. The interaction of head 10 and pan 12, a joint is formed. A "joint" is understood to mean a movable connection of two or more bones, whereby the anatomy distinguishes between real (provided with a liquid-filled gap 24) and false joints Joints, such as the connection via fibrocartilage, such as discs, are replaced by a true joint prosthesis iSd invention, since the prosthesis according to the invention always generates a gap 24 by the required for levitation abutment of the collar 14.

Both the head 10 and the cup 12 will have other components that allow anchoring in the corresponding joint bones.

By joining head 10 and cup 12, a bearing surface is formed whose size varies depending on the geometric design of the head 10 and pan 12. The geometric design will follow the natural model, i. the existing and to be replaced bone connection, orientate. In most cases, the pan 12 is the

Half ± 30% of the surface of the head 10 enclose, preferably ± 10%. It is particularly preferred that the bearing surface is less than half the surface of the head 10.

The collar 14 in turn is arranged so that the head 10 and the collar 14 form another bearing surface extending from the first bearing surface between the head 10 and pan

12 is locally different and may differ in their spatial extent. For this reason, the collar 14 is also referred to as an abutment. The collar 14 will be So are on the side of the head 10, which faces away from the pan 12 and is not enclosed by it. In other words, the collar 14 lies behind the head 10 and thus at least partially opposite the cup 12, the term "partially" referring both to the fact that parts of the collar 14 can also be arranged elsewhere and / or the bearing surface of the collar 14 only a fraction of the bearing surface of the pan 12. The collar 14 will preferably represent the extension of the cup 12, both components of the prosthesis having an identical shape of equal or differing volume or geometrical shape via a connecting element 28, preferably mechanically.

Head 10, cup 12, and collar 14 have a layered structure, each comprising a permanent magnet layer 18 and a shielding layer 20. In one embodiment of the present invention, head 10, pan 12 and / or collar 14 additionally have a contact layer 16 and / or carrier layer 22. The contact layer 16 is in particular positioned so that it is aligned with the bearing surface, so that the contact layers of the head 10 and pan 12 and / or head 10 and collar 14 are separated by the gap 24.

The arrangement of the layers preferably takes place in the order of permanent magnet layer 18 and shielding layer 20. If, in addition, a contact layer 16 and / or carrier layer 22 are present, the order of contact layer 16,

Permanent magnet layer 18, carrier layer 22 and shielding layer 20 is preferred. It is also possible that on the shielding layer 20 of pan 12 and / or collar 14 a

Outer layer 26 rests, which is biocompatible. This outer layer 26 establishes the contact between pan 12 and bone and can be used as another contact layer 16 in the sense of

Be conceived invention.

However, the aforementioned sequences are not necessarily determined. Nor is the prosthesis according to the invention fixed on the existence of a concrete individual layer, since another layer can also fulfill several functions in the sense of the invention and thus also the function of the physically indistinguishable single layer. In particular, one or more layers may be integrated into another layer or the material underlying a layer may inherently fulfill the function of multiple layers of the invention. Possibly. So the omission of layers is possible. In one embodiment of the invention, the contact layer 16, permanent magnet 18 and / or shielding layer 20 integrated into the carrier layer 22, preferably the permanent magnet layer 18 and the shielding layer 20. In another embodiment of the invention, the permanent magnet layer 18, shielding layer 20 and / or carrier layer 22 are integrated into the contact layer 16. The integration preferably takes place only in adjacent layers without skipping a layer.

In a preferred embodiment of the prosthesis, a stable cup 12 has an outer layer 26, e.g. As a result, this outer layer 26 makes a further shielding layer 20 dispensable, since it already functions as a shielding layer 20. That the shielding layer 20 is not present here as an independent but as a bifunctional layer. In a further embodiment of this embodiment, the permanent magnet layer 18 may be embedded in a subsequent contact layer 16, so that in the end only three layers are present.

In another preferred embodiment of the prosthesis, the head 10 has a contact layer 16, e.g. from a cobalt-chromium alloy, on which the permanent magnet layer 18 comes to rest without an additional carrier layer 22.

If permanent magnet layers 18 are used which exhibit brittle material properties, stabilization by integration into the carrier layer 22 is possible. Alternatively or additionally, the carrier layer 22 may also surround the permanent magnet layer 18, wherein the carrier layer 22 may simultaneously serve as a contact layer 16 and / or shielding layer 20, provided that it has the required properties. In the case of the substitution of the contact layer 16 or addition as a contact layer 16, the carrier layer 22 is characterized by body compatibility and abrasion resistance. A suitable material for this embodiment is, for example, titanium.

The arrangement of the head 10 to pan 12 and collar 14 is done in particular such that the layer sequence is contrary. It is understood that this embodiment requires that head 10, pan 12 and collar 14 have the same layers, the absence of one or more layers being harmless. That is, in the region of the bearing, the bearing surface is formed by the contact layers 16, permanent magnet layers 18 or carrier layers 22, depending on which layers represent the outermost layer of the head 10 and the innermost layer of the pan 12 and the collar 14, respectively functionally identical layers are preferred. Preferably, the bearing surface is formed by the contact layers 16.

The contact layers 16 are made of a biocompatible and abrasion resistant material. Depending on the dimensioning of the joint and occurring peak loads, the maximum bearing forces and thus sliding friction between the head 10 and the socket 12 may be exceeded with the consequence of abrasion. The layer thickness is depending on the material 0.1 to 10 mm, preferably 1 to 3 mm. Preference is given here to plastics, steel, titanium, ceramics or other coatings, particularly preferably PE plastics and cobalt-chromium alloys. In particular, the contact layer 16 of the pan 12 made of PE plastic, ceramic or steel, while the contact layer 16 of the head 10 made of ceramic or steel composed. The material pairings of the contact layers 16 are not limited. However, it is preferred that the contact layer 16 from the head 10 has a different material than the contact layer 16 of the pan 12. In particular, there are in the contact layer 16 on the head 10 steel or ceramic and on the contact layer 16 of the pan 12 PE. An exception to this preferred embodiment form steel-steel pairings, in which the same material of the contact layer is preferred. A preferred steel in the context of the invention are cobalt-chromium alloys.

Magnetic layer 18 is preferably located directly underneath contact layer 16. For the purposes of the invention, "magnetic" means that there is a magnetic field which is generated exclusively permanently by a permanent magnet, but not temporarily, such as by the movement of electrical charges Magnetic properties of solids originate in the magnetism of the atoms / ions and electrons of which it is built up.This is magnetic material when the elementary magnetic moments are aligned so that they do not completely compensate each other, so the material For the purposes of the invention, "magnetic" should also be understood as a generic term for the associated terms "magnetizable", "paramagnetic" and "superparamagnetic", unless expressly stated otherwise in the specific context here the own Chaft of a substance, in particular a ferromagnetic material, in the course of the action and the subsequent omission of an external magnetic field to show a remaining magnetization or remanence. "Paramagnetic" involves the tendency of a substance to migrate into a magnetic field, and paramagnetic behavior is found in substances with unpaired ones Electrons, because the spin moments of the electrons align themselves parallel to the external magnetic field and amplify it. The orbital angular momentum of the unpaired electrons also contributes to paramagnetism. "Superparamagnetic" indicates a particularly strong paramagnetic tendency.

The magnetic properties of head 10, cup 12 and collar 14, which are used in the prosthesis according to the invention, can be caused by magnetic materials, which are preferably selected from a group of ceramic oxide materials, preferably barium oxide or iron oxide, or metals of VIII Subgroup or an alloy thereof, preferably iron, cobalt, nickel, whose alloys contain one another or their alloys with platinum or rare earths, particularly preferably neodymium-iron-boron alloys or cobalt-samarium alloys.

The permanent magnet layer 18 can consist of an integral piece or a plurality of individual magnets, which are assembled analogously to what are known as Halbach magnets by means of a multiplicity of correspondingly shaped and aligned individual magnets. The Halbach array has the property of almost canceling out the magnetic flux on one side of the configuration but increasing it on the other.

The permanent magnet layers 18 of head 10, pan 12 and collar 14 have a polynomial of the same name, so that 18 repulsive forces prevail between the magnetic layers. The repulsive forces of the magnets initially lead to, depending on the weight of the patient, the mechanical contact pressure of the condyle 10 is greatly reduced to the socket 12 or even completely disappears. With the reduction of the force acting on the surface between head 10 and cup 12, the sliding friction between the two joint components and the mechanical abrasion decrease linearly. As a consequence, the head 10 is mounted wear in the pan 12 and the collar 14, preferably wear-free.

In one embodiment of the invention, the permanent magnet layers 18 of head 10 and pan 12 have a flux density B of at least 0.4 Tesla. The minimum flux density depends on the type and position of the joint, which results in both the resting load and the load limit. The "resting load" in the sense of the invention is that proportion of the body weight that makes up the body components above the joint, ie the body components, their weight force the joint squeezed or pulled apart, this proportion of body weight can be distributed over several joints and reduces the resting load accordingly.

It is understood, for example, that a knee joint has a higher resting load compared to a shoulder joint, as a result of which they are also dimensioned for different peak load limits, which in turn entail different minimum flow densities. In the embodiment of a hip joint, the permanent magnet layers 18 of head 10 and cup 12 have a flux density B of at least 0.5 Tesla, preferably at least 0.7 Tesla, more preferably at least 1.0 Tesla. It is further preferred that the flux densities B of the permanent magnet layers 18 of head 10 and pan 12 are approximately equal, more preferably with a maximum deviation of 10%. Most preferably, the flux densities B of the permanent magnet layers 18 of head 10 and pan 12 are the same size. It is also understood that the implementation of a certain flux density B and thus the effective repulsive force effect on the geometry of the magnetic layers 18 is dependent. By specifying a magnetic bearing pressure to be achieved, the design of a particular geometry and flux density is independent, so that any combinations of bearing surface and flux density can be selected, which are within a preferred bearing pressure and thus solve the object of the invention. It is preferred that the permanent magnet layers 18 of head 10 and pan 12 build up a maximum magnetic bearing pressure of at least 150000 N / m ² , more preferably of at least 300000 N / m ² , most preferably of at least 400000 N / m ² .

Since the repulsive magnetic forces cause the condyle 10 is pushed out of the pan 12, by a counter bearing (collar 14) to build up a corresponding back pressure. The permanent magnet layer 18 of the collar 14 has a flux density which corresponds at most to the flux density of the permanent layers 18 of head 10 and pan 12, the higher flux density being decisive. In one embodiment of the invention, the permanent magnet layer 18 of the collar 14 has a flux density of at most 1, 0 Tesla. Taking into account a minimum depth of the gap 24 between head 10 and cup 12 and the resting load of the prosthesis, which corresponds to the patient, possibly proportionate body weight, the permanent magnet layer 18 of the collar 14 has a flux density at least 40% lower than the flux density of the permanent magnet layer 18 the pan 12, preferably at least 20% lower flux density, more preferably at least 10% lower flux density. It goes without saying for the person skilled in the art Instead of the flux density and the design of the joint, in particular the storage area, can be used to set a limbo.

In a preferred embodiment of the prosthesis according to the invention, the depth of the joint gap 24 at resting load is between 1 and 10 mm, preferably between 3 and 6 mm, in order to be able to realize a damping effect under peak loads. The damping effect is characterized in that the depth of the gap 24 between the head 10 and cup 12 is reduced during the load, but without reaching the value zero and thus contact and abrasion of the contact layers 16 of the head 10 and pan 12. The case of contact corresponds to the maximum load limit, which is to endure at least a 1, 5-fold rest load, preferably at least three times the rest load, more preferably at least five times the rest load. Assuming that a patient has a body weight of 80 kg and the distribution of this weight on two joints, e.g. two knee or hip joints results in a resting load of less than 40 kg of torso, thighs, arms and head, which has to support each prosthesis, so that the maximum load limit, expressed by the load mass, is at least 60 kg, preferably at least 80 kg, more preferably at least 120 kg.

The shielding layer 20 serves to shield the magnetic field lines. The static magnetic field lines caused by the permanent magnet layer 18 exert a force on charge carriers, such as, for example, ionic conduction in nerve tracts, dissolved salts in body fluids, etc., within the body of a patient and, as a result, cause small electrical currents. Possible influences on the body are therefore to be found in the field of conduction systems, with insufficient evidence of the effects of long-term exposures due to static magnetic fields. In addition, the permanent magnets 18 act on metallic objects in the vicinity of the joint prostheses. It is therefore essential that the magnetic fields of the condyle 10, acetabulum 12 and abutment 14 are directed inwardly of the bearing surface and shielded outwardly so as to comply with the limits for static magnetic fields in the patient's surrounding tissue. There is no complete shielding of the magnetic field necessary because a residual magnetic field can even stimulate bone healing. Thus, when this residual magnetic field still comes into play on the socket 12 on the bone side, the healing of the prosthesis in the bone is stimulated. The The size of a stimulating residual magnetic field can be determined by a person skilled in the art in routine experiments.

The Federal Office for Radiation Protection recommends an upper limit of 0.3 mT for persons who are exposed to a low-frequency magnetic field of 16 2/3 Hz. The current limit in Germany and the recommendation of the IRPA / INIRC (International Commission on Non-Ionizing Radiation Protection) for private individuals (daily, permanent residence) in 50/60 Hz alternating fields is even only 0.1 mT; the maximum limit for permanent working in magnetic fields is 0.5 mT. The Working Group on Electro-Biology e.V. requires a limit value of 0.002 mT even for sleeping places and rest zones. However, based on the geomagnetic field in Central Europe, averaging about 0.045 mT, a limit value of 0.1 to 0.3 mT and therefore twice or even six times the value of the earth's magnetic field appears to be reasonable. Accordingly, the shielding layer 20 must shield the magnetic field of the permanent magnet layer 18 on the side facing away from the gap 24 by a factor of the order of at least 1: 1000, preferably at least 1: 3000, more preferably at least 1: 10000. This shielding factor can be effected only by a combination of different shielding components, which are applied depending on the design of the shield directly to the back of the permanent magnets 18 or at a small distance of 1 to 3 mm.

For this purpose, the permanent magnets 18 are surrounded, inter alia, by a solid so-called shielding cap of magnetically soft material, preferably structural steel, iron, nickel, cobalt, special alloys, so-called mu metals (or μ metals), or combinations thereof. Alternatively or additionally, the use of compensation magnets which are applied opposite pole to the permanent magnet layer 18 on the outside thereof. It is understood that in both cases it is necessary to examine whether there are magnetic short circuits and what effects these in turn have on the inward field. The resulting residual field can be further reduced by magnetically shielding metal-fabric mats. The magnetic field strength decreases quadratically with the distance, so that the field strength in the surrounding tissue reaches the limit. The exact interactions between the permanent magnet layer 18 and the shielding layer 20 and the resulting magnetic fields inside and outside of a prosthesis can be calculated using appropriate programs. The mechanical support layer 22 is able to absorb the forces occurring. The carrier layer 22 is made of a non-magnetic, biocompatible and ductile material such as titanium, alloy thereof or other composites. The term "composite material" refers to a material composed of two or more bonded materials which, in the case of a composite, are fully bonded together and can not be separated by hand The composite material has different material properties than its constituent components, for which the material properties and geometry of the composite material are In particular, size effects often play a role.The connection is made by fabric or form-fitting or a combination of both.The components of a composite material can themselves be composites again.

Depending on the design of the permanent magnets 18 and the shielding layer 20, these layers are either integrated directly into the carrier layer 22 in order to protect them from mechanical loads, or they rest on the carrier layer 22. In a preferred embodiment of the invention, possible materials capable of producing the required high field strengths are neodymium magnets, which materials are typically very brittle and can not withstand high mechanical stresses such as those encountered under peak load conditions. so that the integration of permanent magnet layer 18 and shielding layer 20 in the carrier layer 20 is preferred. So that the permanent magnets 18 do not break under load, several possibilities come into consideration. They are either incorporated in a mechanically loadable, non-magnetic carrier material, such as e.g. Titan, bedded. This variant is preferred in the composition of the permanent magnets 18 made of Halbach magnets. Another embodiment of the invention, during sintering of the permanent magnets 18 into them, is a fibrous web which is resistant to tearing and temperature, e.g. Kevlar or teflon fibers, whereby the fibrous web is able to absorb tensile and compressive stresses. If the permanent magnets 18 still break, the resulting fragments are held together by the fiber fabric. A further embodiment is to manufacture the permanent magnets 18 from a multiplicity of small magnetic microcrystallites which are held together by the fiber fabric.

The object of the invention is also achieved by providing a prosthesis comprising a head 10 and a socket 12 of complementary spatial shape, separated by a gap 24, and a collar 14 resting on one of the socket 12 facing away from the head 10 is arranged, wherein the head 10 and the pan 12 each comprise a permanent magnet layer 18 and a shielding layer 20, and wherein the permanent magnet layers 18 of head 10 and pan 12 have a like polarization.

It has surprisingly been found that the magnetic fields of head 10 and cup 12 can also be dimensioned so that the resulting gap 24 does not correlate with an unnatural joint strain. Due to the prevailing resting load and the tension of the muscles surrounding and fixing the joint, little or no contact of the condyle 10 with the collar 14 takes place. Friction of the condyle 10 and collar 14 is consequently only in the fully relaxed state, such as e.g. during sleep, or under stress associated with pulling the joint apart. In these cases, the collar 14 functions advantageously as a mechanical barrier. The collar 14 must have the properties already described in the course of the present specification for the contact layer 16, in particular good body compatibility and high abrasion resistance, the latter property being essential only in the region of the bearing surface. That the collar 14 is at least partially formed as a contact layer 16, preferably completely, the preferred materials of which are plastics such as e.g. Polyethylene plastics, or ceramics are. In contrast, this collar 14 has no magnetic properties.

Incidentally, the prior teaching of the invention to the prosthesis with a collar 14 having a permanent magnet layer 18, shielding layer 20 and carrier layer 22 and their configurations are valid and applicable without restriction to the prosthesis having a non-magnetic collar 14 comprising a contact layer 16 if it makes sense.

In the context of the present invention, therefore, a prosthesis for replacing a bone connection is provided for the first time, which addresses a magnetic and thus contactless joint guidance, so that levitation of the condyle 10 exists both in the resting state and in the loaded state. In principle, the magnetic bearing is ideal for a prosthetic joint preservation of any kind, especially for hip joint, shoulder joint and knee joint prostheses and disc prostheses. The loosening occurring, for example, in conventional hip prostheses on the transition points between prosthesis and hip joint fastened with, inter alia, bone cement. or thighbones are significantly reduced by the magnetic damping. The components of the joint prostheses are characterized by a layer structure of different materials, so that in addition to the magnetic properties they also meet the following requirements of a biocompatible and abrasion-resistant coating and a mechanical stability. In addition, it is advantageously achieved by means of a massive and multilayered magnetic shielding that the residual magnetic fields occurring in the patient's body are below the limit value recommended by the Federal Office for Radiation Protection.

Another object of the invention is a method for replacing a bone joint of a mammal by attaching a head 10 of a prosthesis to a joint bone of the mammal, a socket 12 of the prosthesis complementary to the head 10 on another joint bone of the mammal and a collar 14 of the mammal Prosthesis attached to the pan 12 or the mammal, wherein head 10, pan 12 and collar 14 each comprise at least one permanent magnet layer 18 and a shielding layer 20, thereby providing the permanent magnet layers 18 of head 10, pan 12 and collar 14 with the same polarization and the permanent magnet layers 18 is configured so that repulsive magnetic forces cause a gap 24 between the contact layers 16 of head 10 and cup 12 and head 10 and collar 14 during stress on the joint bone and prosthesis.

In a preferred embodiment of the method according to the invention, the replacement of the bone connection of a human takes place.

It should be understood that an existing bone connection must first be removed to create a cavity for the prosthesis. Both the removal and the implantation of the prosthesis are performed by a surgical procedure in accordance with common medical practice. The attachment of the prosthesis at the intersections of joint bone and head 10 or pan 12 can be done eg with bone cement. As an alternative to cementing, the pan 12 can also be held by a rough surface which is pressed in, so-called press-fit pans. The magnetic fields generated by the permanent magnet layers 18 are adjusted so that a depth of the gap 24 of 1 to 10 mm is effected, preferably from 1 to 3 mm. The prosthesis may either be delivered pre-assembled outside the body or assembled in-situ during the operation, as currently preferred in practice, to the individual needs of the patient. Accordingly, the present invention is intended to be used for already prefabricated joint prostheses, such as a duo-head prosthesis on the hip joint or intervertebral disc prostheses, as well as for the joint replacement individually adapted by the surgeon. In the case of the previous assembly, at least the head 10 and the socket 12 of the prosthesis are mounted outside the mammal. In one embodiment of the method, it is preferred that the collar 14 be mechanically secured to the cup 12 so that there is the possibility of complete assembly of the prosthesis prior to the operation. In one embodiment of the present method, however, the complete assembly of the prosthesis does not include the magnetization of the permanent magnet layer 18, which preferably takes place in-situ. That is, after implanting the prosthesis, the permanent magnet layer 18 is exposed to an electric field, for example, so that the magnetization occurs within the mammalian body. The shield layer 20 of the pan 12 preferably causes incomplete shielding of the permanent magnet layer 18 of the pan 12, thereby stimulating the healing process.

The prior teaching of the invention to the prosthesis and its embodiments are valid and applicable without limitation to the method of replacement of a mammalian bone junction, as appropriate.

It should be understood that this invention is not limited to the specific methods, devices, and conditions described herein, as such things may vary. It is further understood that the terminology used herein is for the sole purpose of describing particular embodiments and is not intended to limit the scope of the invention. As used herein in the specification including the appended claims, word forms in the singular, such as words, include For example, "a", "an", "an", "the" or "that" are plural equivalents unless the context clearly dictates otherwise. For example, the reference to "a gap" includes a single gap or multiple gaps, which in turn may be identical or different, or the reference to "one method" includes equivalent steps and methods known to those skilled in the art. In the following, the invention will be explained in more detail with reference to a non-limiting example of specific embodiments.

Fig. 1 shows a schematic drawing of a hip joint prosthesis.

The pan 12 and collar 14 have a spherically convex shape and the head 10 has a spherically concave shape, i. the geometric shape of the socket 12 and collar 14 corresponds to the segment of a spherical shell, while the head 10 has the shape of a precisely fitting spherical segment. The collar 14 consists of several spherical shell segments.

2 shows a layer model of the hip joint prosthesis.

Head 10, cup 12 and collar 14 are made of a PE contact layer 16, permanent magnet layer 18, carrier layer 22, shielding shield layer 20 and biocompatible

Outer layer 26 constructed. The spherical shell segments of the collar 14 are by means of

Screw connections connected as a mechanical connection element 28 with the socket 12. They are made to increase the mobility of the joint, e.g. by

Jamming or locking, do not affect. Head 10 and collar 14 thus have a complementary shape to each other. When the condyle 10, the carrier layer 22 goes into the

Shank over, which is implanted in the femur. In the socket 12, the outer layer 26 makes contact with the hip bone.

In condyle 10, cup 12 and collar 14 are spherical convex or spherical concave permanent magnets 18, i. the magnet 18 in the head 10 has the shape of a ball, while the magnets 18 are formed in pan 12 and collar 14 as a spherical shell. Due to the balance of the repulsive magnetic forces of cup 12 and collar 14, the state of levitation (levitation) of the condyle is reached in the camp.

The following calculation determines the magnitude of the required magnetic flux density B of the permanent magnets 18. The basis is the formula for calculating the magnetic

Bearing pressure P _mag in cylindrical geometry:

P - 1 / * D2 mag - '2 μ D, where μ = 4π ^* 10 ^"7 V ^* s / A ^* m represent the permeability of the vacuum in the joint space and B the magnetic flux density.

With the currently strongest, commercially available permanent magnets 18 long-term stable flux densities B on the surface of the magnets 18 are achieved up to 1, 0 Tesla. The theoretically maximum achievable magnetic bearing pressures therefore amount to 400,000 N / m ² .

If the condyle has a radius of r = 0.03 m and the bearing surface is approximated by the lower half of a spherical half-shell, the relevant bearing surface is calculated as A = 0.003 m ² according to the formula:

A = V ₄ ^* 4π ^* r ²

With a maximum possible bearing pressure of 400,000 N / m ² and a bearing surface of 0.003 m ² results in a theoretically possible maximum weight of 1200 N or a maximum load mass of 120 kg per hip joint prosthesis. Assuming an 80 kg patient, each hip joint prosthesis must support a maximum of 40 kg resting load and has additional reserves to cushion up to three times the peak load (120 kg).

LIST OF REFERENCE NUMBERS

10 head

12 pan

14 collar

16 contact layer

18 permanent magnet layer

20 shielding layer

22 carrier layer

24 gap

26 outer layer

28 connecting element of pan 12 and collar 14th

Claims

A prosthesis for replacement of a bone joint comprising a head (10) and a socket (12) of complementary spatial shape to one another and a collar

(14), wherein the head (10), the pan (12) and the collar (14) each comprise a permanent magnet layer (18) and a shielding layer (20), wherein the head (10) and the pan (12) and the Head (10) and the collar (14) are separated by a gap (24), and wherein the permanent magnet layers (18) of head (10), pan (12) and collar (14) have a like polarization and wherein a flux density of the Permanent magnet layers (18) of the head (10) and pan (12) is at least 0.4 Tesla and the permanent magnet layer (18) of the collar (14) has at most the flux density of the permanent magnet layers (18) of the head (10) and pan (12) ,

2. A prosthesis according to claim 1, characterized in that the head (10), the pan (12) and / or the collar (14) have a contact layer (16) and / or a carrier layer (22).

3. A prosthesis according to claim 2, characterized in that the contact layer (16), permanent magnet layer (18), carrier layer (22) and shielding layer (20) are arranged in the above order.

4. A prosthesis according to claim 2, characterized in that the contact layer (16), permanent magnet layer (18) and / or shielding layer (20) at the same time the carrier layer (22).

5. A prosthesis according to claim 2, characterized in that the permanent magnet layer (18), shielding layer (20) and / or carrier layer (22) at the same time the contact layer (16).

6. A prosthesis according to one of the preceding claims, characterized in that it is a genuine or spurious joint prosthesis.

7. A prosthesis according to claim 6, characterized in that it is a hip, shoulder, knee joint or intervertebral disc prosthesis.

8. A prosthesis according to one of the preceding claims, characterized in that the pan (12) and the collar (14) have a spherically convex shape and the head (10) has a spherical concave shape.

9. A prosthesis according to one of the preceding claims, characterized in that the collar (14) on one of the pan (12) facing away from the side of the head (10) is arranged.

10. A prosthesis according to one of the preceding claims, characterized in that the pan (12) and collar (14) are mechanically connected to a connecting element (28).

1 1. A prosthesis according to one of the preceding claims, characterized in that the head (10) and the collar (14) have a complementary spatial shape to each other.

12. A prosthesis according to one of the preceding claims, characterized in that the prosthesis has a maximum load limit, which corresponds to at least a 1, 5-fold resting load.

13. A prosthesis according to one of the preceding claims, characterized in that the contact layer (16) made of plastic, ceramic, steel or titanium.

14. A prosthesis according to claim 13, characterized in that the contact layer (16) consists of PE plastic or a cobalt-chromium alloy.

15. A prosthesis according to one of the preceding claims, characterized in that the permanent magnet layer (18) consists of a ceramic oxide material or a metal of the VIII. Subgroup or an alloy thereof.

16. A prosthesis according to claim 15, characterized in that the ceramic oxide material is barium oxide or iron oxide.

17. A prosthesis according to claim 15, characterized in that the metal of the VIII. Subgroup iron, cobalt or nickel.

18. A prosthesis according to claim 15, characterized in that the alloy of a metal of the VIII. Subgroup is an alloy of iron, cobalt or nickel with each other or an alloy with platinum or rare earths.

19. A prosthesis according to claim 18, characterized in that the alloy of a metal of the VIII. Subgroup is a neodymium-iron-boron alloy or a cobalt-samarium alloy.

20. A prosthesis according to one of the preceding claims, characterized in that the shielding layer (20) causes a shielding of the magnetic field of the permanent magnet layer (18) on the side facing away from the gap (24) side by a factor of at least 1000.

21. A prosthesis according to one of the preceding claims, characterized in that the shielding layer (20) comprises a magnetically soft material and / or a magnet with unlike polarization to the permanent magnet layer (18).

22. A prosthesis according to claim 21, characterized in that the magnetically soft material is structural steel, iron, nickel, cobalt, mu-metals or a combination thereof.

23. A prosthesis according to one of the preceding claims, characterized in that the carrier layer (22) consists of titanium, alloys thereof or a fiber fabric.

A bone replacement prosthesis comprising a head (10) and a socket (12) of complementary spatial shape separated by a gap (24) and a collar (14) resting on one of the socket (14). 12) facing away from the head (10) is arranged, wherein the head (10) and the pan (12) each have a permanent magnet layer (18) and a shielding layer (20), and wherein the permanent magnet layers (18) of head (10) and pan (12) have a like polarization.

A method of replacing a mammalian bone joint by attaching a head (10) of a prosthesis to a mammalian articular bone, a socket (12) of the prosthesis having a shape complementary to the head (10) on another mammalian articular bone, and a collar ( 14) of the prosthesis attached to the cup (12) or mammal, wherein the head (10), cup (12) and collar (14) each comprise a permanent magnet layer (18) and a shielding layer (20) comprising permanent magnet layers (18) of Head (10), pan (12) and collar (14) provided with the same polarization and configured so that repulsive magnetic forces a gap (24) between the head (10) and pan (12) and head (10) and collar (14 ) during stress on the joint bone and prosthesis.

A method according to claim 25, characterized in that at least the head (10) and the socket (12) of the prosthesis are assembled outside the mammal.

27. The method according to claim 25 or 26, characterized in that the collar (14) on the pan (12) with a connecting element (28) is mechanically fastened.

28. The method according to any one of claims 25 to 27, characterized in that for the gap (24) has a depth of 1 to 10 mm is effected, preferably from 3 to 6 mm.

29. The method according to any one of claims 25 to 28, characterized in that the permanent magnet layer (18) is magnetized in situ.

30. The method according to any one of claims 25 to 29, characterized in that the shielding layer (20) of the pan (12) causes an incomplete shielding of the permanent magnet layer (18) of the pan (12).