DE3005265A1 - PROSTHESIS - Google Patents

Description

DR.ULRICH OSTERTAG 9 DR.REINHARD OSTERTAQ

ElBENWEG 10, 70OO STUTTGART 70, TELEPHONE 0711/70 08 40, CABLE: OSPAT

prosthesis

Applicant: Simon Raab

5872 Westbury Avenue Montreal, Quebec, Canada

Priorities: 1. British Patent Application No. 79/05445

February 15, 1979

2. U.S. Patent Application Ser.No. 63,434 August 3, 1979

Legal file: 903

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Bone connection prosthesis with a reinforcement part which is coated with plastic, the plastic layer being variable over its extension Has modulus of elasticity

The invention relates to prostheses which are firmly inserted into the bone with the aid of bone cement will. In particular, this invention relates to prostheses that are adapted to provide strength and durability of the prosthesis / bone-cement bond is maximized.

In the field of orthopedic surgery, ZIMALOY, a chrome-cobalt-molybdenum alloy, stainless steel, titanium alloys, and high strength plastics such as ultra high polymer polyethylene (hereinafter referred to as UHMWPE) used to close the ends of long bones, joints, including hip joints substitute. However, there are serious limitations here

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in orthopedic surgery, mainly in the connection of prostheses with the bones. By the action various factors, such as mechanical stress, material fatigue, corrosion, etc. are the prosthesis / bone-cement connections very prone to malfunction. As in the same time, on June 5, 1979 (registration number ) submitted a patent application entitled "Bone Connection Prosthesis with Maximized Strength and durability of the bone-prosthesis intermediate layer and method of manufacturing this prosthesis " is described, an improved bone joint prosthesis can be achieved by pretreating the solid prosthesis part, by coating it with polymethyl methacrylate, and using bone cement in the bone itself be fixed. Prosthesis parts coated with polymethyl methacrylate, as described in the parallel application specified, the prosthesis parts can be connected more easily with bone cement and result in a better one and more permanent connection.

Another problem when connecting prosthesis parts to the bone tissue arises from the differences between the strength of a prosthesis part and the bone cement surrounding this part. Prosthetic parts, which are intended to be firmly connected to the bone, for example prostheses with an in The pin or shaft inserted into the bone is usually made of a material with high strength, for example from alloyed metals or, if it is a plastic prosthesis, for example from UHMWPE. On the other hand, there is a bone cement, which is usually made from a mixture of polymethyl methacrylate

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and methyl methacrylate monomer, which can additionally contain a styrene copolymer of methyl methacrylate, is typically a less rigid porous material. If one of these is now fixed in the Bone inserted prosthesis together with the bone, which is now a unit, exposed to a force, for example stress from walking in the case of a hip joint replacement, the less firm bone cement interlayer becomes exposed to high mechanical stress. Even more, because of the non-physiological Distribution of forces (in the bone) can be much greater or extreme in the area of the prosthesis-cement structure local loads occur. The consequences of this are bone atrophy, bone weakening, and regression Loss of bone strength with subsequent tendency to fracture. In addition, these forces can cause fatigue or embrittlement with consequent crumbling of the bone cement cause when the bone cement, as it usually happens, defective areas such as voids, Has cavities or bubbles, which of course leads to malfunction of the prosthesis.

It is therefore the object of the invention to create a prosthesis whose properties better match the physiological ones Meet the requirements and largely exclude the disadvantages described above.

The object is achieved by attaching a prosthetic part that is to be connected to bone tissue to the essential contact points is coated with a polymer, the polymer layer being designed so that this layer has different moduli of elasticity, for example in such a way that the

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returned surface has less strength, i.e. a lower modulus of elasticity, and that on the prosthesis part adjacent surface shows greater strength, i.e. a greater modulus of elasticity. Between On the named surfaces, the modulus of elasticity in the polymer coating changes gradually and continuously. The modulus of elasticity should preferably change through the layer in such a way that the on the prosthesis part resting surface has a modulus of elasticity which is approximately the modulus of elasticity of the material of the prosthesis part is the same and changes through the layer in such a way that the other, with the Bone cement coming into contact surface has a modulus of elasticity which is approximately the modulus of elasticity of the bone cement is the same. This results in a more even distribution of the load, since the attacking Forces tend to be distributed through the polymer layer rather than largely locally at the bone cement intermediate layer to attack. As specific designs for solving the problem, the polymer layer can be a have continuously changing modulus of elasticity over their layer thickness or the modulus of elasticity changes gradually or the function of the change in the modulus of elasticity shows the problem specifically adapted complex course.

The invention will now be described in detail below with reference to the drawings.

Fig. 1 shows the "side view of a longitudinal section by a hip bone prosthesis, in which a reinforcement element for the bone pin according to of the invention was coated.

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-ff-

FIG. 2 shows the enlargement of a transverse section along the line 2-2 in FIG to show the changing porosity of the polymer layer in FIG.

Fig. 3 shows a diagram in connection with the enlargement of a section through an inserted Implant, as shown in FIG. 1, by the moduli of elasticity assigned to the various layers to show.

Fig. 4 shows the side view of a longitudinal section through a hip joint prosthesis, in which the Polymer coating made of different, individual polymer layers with different moduli of elasticity consists.

Fig. 5 shows the transverse section along the line 5-5 of Fig. 4.

Fig. 6 shows in a diagram the course of the modulus of elasticity over the various layers of an inserted Implant, as indicated in Figures 4 and 5.

Fig. 7 shows a further embodiment of a coated Hip joint prosthesis and

8 shows the perspective view of a partially sectioned human knee joint.

In accordance with the present invention, one becomes capable be able to manufacture prostheses which are made with the help of

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Bone cement are attached in or on the bone, whereby under load the distribution of forces between bones, Bone cement and prosthesis are more evenly distributed than with prostheses such as were previously produced. These prostheses contain a reinforcement element made of a solid material such as chrome-cobalt-molybdenum alloy, for example ZIMALOY, or titanium alloy or stainless steel or a polymer Substance such as UHMWPE, with at least part of the reinforcement element covered by a polymer layer is. This polymer layer, which can also be composed of individual layers, has predetermined characteristics Changes in the modulus of elasticity.

In the case of a prosthesis part with a coating that has a continuously changing modulus of elasticity can consist of a single continuous layer or a discrete coating different polymer layers with different moduli of elasticity. A prosthesis with a single continuous polymer layer on the reinforcement element is applied is shown in Fig. 1. In this longitudinal section of a bone pin hip prosthesis 10, which a reinforcing element 11 with a high-strength polymer layer 12 which is of sufficient thickness and preferably consists of polymethyl methacrylate. This layer contains the voids or bubbles 14 in its interior.

In Fig. 2 is.a transverse section through the prosthesis shaft 1, the reinforcing element 10 of the fixed prosthesis part is located in the center a metal alloy or UHMWPE and in concentric form the polymer layer 12 with the voids or bubbles 14a, 14b and 14c. From the outside to the inside against that

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The voids gradually become smaller towards the center, i.e. the voids 14a closer to the covered prosthesis part has smaller dimensions than the bubble 14c. the outside of the polymer coating facing the bone. The vacancy 14b, which lies linearly between the vacancies 14a and 14c, receives a middle dimension. Accordingly, it can be seen that the strength of the polymer layer increases continuously changes from a relatively high strength inside the encapsulation, where the degree of porosity is practically zero is, to a low strength in the outer region of the polymer capsule · where the degree of porosity is substantial is bigger. In reality, the strength of the polymer layer is not determined solely by the dimensions of the individual emptiness, but also by the The number or density of voids in a given region of the film. If now a certain percentage ■ of vacancies over a certain volume in a given region of the polymer capsule is large, this is it also the part in which the coating is relatively flexible This means that macroscopically, this region has a small modulus of elasticity. On the other hand is the Percentage of vacancies low or almost zero ·, one finds one at this point in the polymer layer high strength and thus also seen macroscopically a high modulus of elasticity.

This state of affairs is shown in Fig. 3, in which in part a a section through an implant, as shown in FIGS. 1 and 2, and which with the aid of bone cement in is fixed to a bone, i.e. to the bone tissue. In part · b there is an associated graph showing the progression of the modulus of elasticity, where the different

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different components reinforcement element / polymer layer / bone cement / bone tissue each have their specific modulus of elasticity. The reinforcement element 10 has a relatively high modulus of elasticity, what is to be shown by the straight line 20. The polymer layer 12 with the continuously variable porosity also shows a continuously changing modulus of elasticity, indicated by the line 22. Im, in this case inside the polymer layer, where the porosity reaches almost zero, one can see that the The modulus of elasticity of the polymer layer is almost the same as that of the reinforcing element. On the outside the polymer layer, where the proportion of voids or bubbles is much larger and thus also the porosity, you can see that the much lower modulus of elasticity is compared to the modulus of elasticity of a cured Aligns bone cement. The hardened bone cement 16 lies between the polymer layer 12 and the bone 18. The modulus of elasticity of hardened bone cement has, so to speak, a constant Value and is represented by line 24. The strength of the polymer layer 12 is then ideally varies so that inside the layer the modulus of elasticity is approximately equal to the modulus of elasticity of the Reinforcement element, while on the outside of the layer which corresponds to the bone fastening layer, the modulus of elasticity approximately equal to the modulus of elasticity of the bone cement, which is determined by the The presence of voids and defects in its structure is naturally low.

As already mentioned, the polymer layer has a certain substantial thickness. With the phrase "substantial

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Thickness is intended to mean that the polymer layer is at least so thick that there is a change in elasticity the layer, as it has been described up to now, is possible at all. Polymer layers, which according to of the invention have a minimum thickness of about 0.1 cm, thicknesses of 0.5 cm are preferred, but the best layers are 0.5 to 1.0 cm thick.

The manufacture of prostheses as shown in Figures 1, 2 and 3, wherein a single-layer Polymer layer with voids is attached to a reinforcing element, and in which the modulus of elasticity changes from the inside out, brought about by the percentage of voids, which changes from the inside to the outside can be produced by various suitable means. One The method that can be used for this is to change the solidification rate of the polymer layer linear from the outside to the inside or from the inside to the outside, while at the same time the degree of porosity of the not changed solid polymer.

The polymer capsule can be made from molten thermoplastic PMMA by controlling the solidification rate of the thermoplastic material with the aid of temperature is controlled. The melted thermoplastic is in a shape that matches the desired bone implant is included. The reinforcement element or the bone pin of the implant, consisting of made of a metal alloy, is included in the center of the same shape. The part of the prosthesis that doesn't is to be coated remains outside the mold.

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The metal alloy exhibits a high degree of thermal conductivity and, taking advantage of this, can be brought into contact are used with cooling devices such as chilled air, liquid nitrogen, etc. Using the arrangement just described, the polymer inside the mold and in contact with the bone pin or reinforcement element cooled, the polymer inside solidifies first while the polymer portion on the outer part of the mold is cooled at a later point in time, so that something here too solidification occurs delayed.

The molten polymer in the mold contains an inert gas, such as nitrogen or carbon dioxide, solved. The amount of dissolved gas is controlled by the pressure, at high pressure practically everything is gas dissolved, while at lower pressure the dissolved gas occurs in individual bubbles or voids. Form is designed so that the pressure inside the mold can be continuously changed. Accordingly, will in such an arrangement the pressure in the form varies continuously as follows. From a higher value the pressure at which all the gas is dissolved in the polymeric substance, at the same time as the thermally conductive bone pin is cooled in the center of the mold, it slowly goes down to a lower pressure value only a small percentage of the gas is still dissolved in the polymer. Will the polymeric substance inside the Form solid, as long as the pressure in the form is so high that all gas is dissolved, it still contains no spaces. If the pressure in the mold is then reduced when the next following region solidifies, so the dissolved gas begins to escape from the substance,

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bubbles form and the solid polymer contains voids in this region.

Another method of making a polymer layer of varying porosity such as this invention teaches, is that a polymerizable material, for example crosslinkable PMMA polymer, a monomer, or a polymer monomer in admixture with a thermosensitive polymer catalyst or initiator is used. In such a case, a gas is again dissolved in the polymerizable material, wherein a closed shape or the like is used. The reinforcement part of the prosthesis can be heated so that the heated material inside the mold, i.e. in the vicinity of the thermally conductive part of the prosthesis, polymerized first. As indicated in the example above, the pressure is inside the mold continuously decreased as a function of the polymerization rate; contains the material inside the mold then no voids, while the material has a higher degree of voids towards the periphery.

In the preceding discussion, polymer dissolved gases and polymerizable solutions were mentioned to make the desired Establish porosity. In the case of some polymerizable solutions, such as a solution of methyl methacrylate monomer and PMMA, inherently forms upon polymerization of such a mixture and porosity even in the absence of pressure. If such a polymerizable mixture is used, so no special precautions are necessary to dissolve a gas in the mixture.

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Another method of producing the desired product involves the use of temperature-sensitive foaming agents. A non-temperature-sensitive, polymerizable material is made with a heat-sensitive flatulence agent and under conditions that polymerization can be triggered, for example the Adding an ambient temperature polymerization catalyst enclosed in the mold. Thermal energy is then introduced into the mixture from the outer part of the mold, making the polymer with the temperature sensitive Foaming agent creates voids while the relatively colder material is inside the mold does not have these voids. It must be taken into account that the heat-sensitive foaming agent and the gas that arises from it can develop an unphysiological activity, which must be avoided Polymer layer can have a negative effect on the bone.

Finally, the process of post-expansion can also be used to create polymer layers with varying porosity to manufacture. A layer of thermoplastic material which contains a foaming agent in solution, for example pentane or nitrogen, is drawn onto the surface of the reinforcement element or bone pin and hardened. The outside of the hardened layer is thermal energy, such as that caused by an infrared source is emitted, wherein the surface of the thermoplastic layer is heated and softened will. At this point the dissolved foaming agent passes into the gas phase and produces in this way Vacancies in the polymer layer. According to what you want

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During the foaming process, the heat source is removed and the polymer layer hardens again.

As previously indicated, a polymer layer with a varying modulus of elasticity can also consist of different individual layers. In this case, the already discussed prosthesis should use the outermost layer of the composite polymer layer has the lowest modulus of elasticity, i.e. a relative Flexibility. Preferably, in this layer, which is also the one to be connected to the bone Layer is selected, a modulus of elasticity which is approximately the modulus of elasticity of hardened bone cement is equivalent to. The innermost layer of the composite polymer layer, which is the layer that rests directly on the prosthesis part should have a high modulus of elasticity or high strength. Preferably the elastic modulus of the innermost layer is selected to be approximately the elastic modulus corresponds to the prosthesis part or the bone shaft to be coated. The subsequent polymer layers have moduli of elasticity that lie between the moduli of the outermost and innermost layers, see above that each further layer arranged in the direction of the periphery has a smaller modulus of elasticity than the adjacent, inner layer. The figures show a prosthesis with such a composite polymer layer 4, 5 and 6. Fig. 4 is a side view of a section through a hip joint prosthesis part, the Bone shaft is coated with a composite polymer layer. The hip joint prosthesis is with the number denotes and includes a reinforcement member 31, coated

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with the multilayer polymer arrangement 32. In this case the layer consists of four individual layers 32a, 32b, 32c and 32d, each having a different modulus of elasticity from the other.

FIG. 5 shows the same prosthesis in cross section along the line 5-5 in FIG. 4, with the individual layers are represented by concentric rings 32. The reinforcing element or the bone pin 31 is either made of a metal alloy or from the polymer UHMWPE, which has a high modulus of elasticity. the innermost polymer layer 32a has a high modulus of elasticity, preferably a modulus of elasticity that corresponds approximately to that of the reinforcement element made of metal or plastic. The outermost polymer layer 32d has the lowest modulus of elasticity, preferably that of a hardened layer of bone cement. The two intermediate polymer layers 32b and 32c preferably have corresponding intermediate layers Modulus values, with each outer layer adjacent to an inner layer having a lower one Has modulus value than the adjacent inner layer.

The moduli of elasticity of the various individual layers can be determined by the amount of plasticizer in each individual layer can be determined. For example, the layer 32a consists of polymethyl methacrylate without Plasticizers. The layer 32b also consists of polymethyl methacrylate, with a small amount of plasticizer is included. The layer 32c, also made of polymethyl methacrylate, has a larger amount of soft

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more than the layer 32b and finally in the polymethyl methacrylate layer 32d of all layers contain the largest amount of plasticizers.

In another way, the modulus of elasticity of each layer can be varied by using different Amounts of reinforcing filler material are added, these in fibrous or granular form. Usually causes the inclusion of reinforcing filler materials an increase in the modulus of elasticity and thus also an Stiffness of such a composition. The degree of increase depends on numerous factors, one of which is the applied polymer mixture, the chemical make-up of the filling materials and the physical properties of the Fillers, such as size, shape and density, in the case of a particulate filler and in the case of a fibrous filler material, the length, diameter and stiffness of the individual fibers are just some of them. Further information regarding the inclusion of reinforcing fillers in polymers and the result in stiffness or elasticity can be found in Reinforced Thermoplastics, author W.V. Titow and B.J. Lanham; Halsted Press, a Division of John Wiley & Sons, Inc. (New York 1975), referring specifically to pages 9-16 and 111-116 will be read.

Fibrous reinforcements, either aligned or dispersed, are for example glass fibers, carbon fibers, Boron fibers, etc. Special reinforcements offer filling materials such as glass or metal in the form of microspheres and flakes, talc, wallastonite, chalk, clay powder, etc.

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Since usually the modulus of elasticity or the stiffness of a polymer with the amount of added As the filler material increases, the composite polymer layer as shown in FIG. 5 can be made from individual layers are composed, the filling amount of which is different in each individual layer. as well a different filler can also be selected for each layer. The amounts of Fillers, as well as the fillers themselves in each layer in combination, either as desired with a constant amount or also varying amount of plasticizer used in each individual layer will.

In addition, the modulus of elasticity of each layer can be changed by changing its chemical components be brought about. The innermost layer 32a can be made of a relatively hard polymer, such as polymethyl methacrylate or that is melamine formaldehyde resin. The subsequent layer 32b can consist of a softer polymer or copolymer, for example made of polymethyl methacrylate, which is replaced by a softer copolymer, such as polybutyl acrylate, modified. The layer 32c is formed from one even more elastic polymer or copolymer and finally the layer 32d is made of the most elastic polymer or copolymer formed. An equally effective method of inducing increased polymer strength is that Networking. Thus the innermost layer can be fully crosslinked with intermediate layers of different degrees of crosslinking, the outermost layer practically not being crosslinked is.

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In Fig. 6 again a diagram is shown which in relation of the individual layers of an inserted implant indicates the course of the modulus of elasticity. in the The upper part of FIG. 6 is an enlargement of a section through an inserted implant, as shown in FIG Figures 4 and 5 show shown. The course of the various moduli of elasticity extends over the composition of the prosthesis part / composite polymer layer / bone cement / down to the bone tissue. Included shows the reinforcement element 31 a constant modulus of elasticity, which is relatively high and by which Line 34 is shown. The composite polymer layer shows four individual layers 32a, 32b, 32c and 32d, each one having its own constant modulus of elasticity extending in the direction of 32a gradually decreases to 32d, which is intended to be represented by lines 36a, 36b, 36c and 36d. The hardened one Macroscopically, bone cement 16 has a constant modulus of elasticity that is relatively low is represented by line 4. At the transition points of the outermost layer to the bone cement and of the innermost layer to the prosthesis part, the modulus of elasticity shows an incontinuity, which is supposed to show that the moduli of elasticity of the layers 32a and 32b as close as possible to the values of the moduli of elasticity Prosthetic part 31 or the bone cement 16 should come up. In doing so, the innermost layer 32a becomes again around the highest and the outer layer 32b have the lowest modulus of elasticity.

The application of a multilayer polymer coating to a bone pin can be carried out with various suitable Means can be carried out, such as immersion in a polymer solution or the use of a

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Number of shapes after treatment of the part to be coated to ensure a secure adhesion of the Achieve polymer layer. Such pretreatments of the prosthetic part, including removal of weak boundary layers are contained in the above-mentioned parallel application no. (filed June 5, 1979).

The reinforcement element of the prosthesis part has a relatively simple shape, as for example in FIG. 4 shown, the multilayer coating can easily be produced by immersion. In addition For example, four containers of molten polymer such as polymethyl methacrylate are required. The molten polymer in the first container does not contain a plasticizer. The molten polymer the second container contains a small amount of plasticizer. The molten polymer in the third container contains a larger amount of plasticizer while the molten polymer is in the fourth and final container has the highest amount of plasticizer. The reinforcement part or the bone pin is melted into the Immersed the polymer of the first container and removed it again. After the polymer has cured the part is re-immersed in the first container. This continues until a Thickness of the coating of about 0.125 cm is reached. So the reinforcement part of the prosthesis has its first coating and is then immersed in the second container. This dipping and letting it harden is again continued until the second layer also reaches a thickness of approximately 0.125 cm and thus the one composed of two layers

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Polymer coating has a thickness of 0.250 cm. In the same way, the two-layer coating is now applied in dipped the third container to apply a third layer approximately 0.125 cm. Achieved with it the coating composed of three layers 0.375 cm. Finally, the coating is in the fourth container brought to a total thickness of 0.50 cm.

The composite polymer coating can be composed of more or less four individual polymer layers and, as shown in Figure 5, it is not necessary that each individual polymer layer be the same Having thickness. Sometimes in certain circumstances it is desirable that these layers not be of the same thickness exhibit.

In a further procedure for the production of a multi-layer cover on a prosthesis part in turn uses a number of different forms in such a way that starting from a smallest form, each next shape is bigger than the other. The reinforcement part of the prosthesis is now in the first and smallest Given the shape, this shape is to be understood as a casting mold, this casting mold is now made with a polymer material filled with a relatively high modulus of elasticity with a value as close as possible to the modulus of elasticity of the reinforcing element and in this way the first layer applied to the prosthesis part. This part with the first layer is now in the second, somewhat larger Brought into shape and in turn poured with a polymer material of a lower modulus of elasticity to produce a to form second layer. The lower modulus of elasticity is brought about by adding a little more plasticizer

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or that a smaller amount of solidifying filler material is used. The polymer material for this second layer can be a thermoplastic or a thermosetting resin. The one that now has two layers The bone shaft is provided with polymer material a third time, again in an even larger shape, the is poured with a less solid polymer material. By dimensioning the different shapes the desired thickness can thus also be given to the individual layers of the coating.

The application of polymer layers to a prosthesis part according to the present invention also allows coatings on substrates with significantly more complex shapes. In Fig. 7 is an example of such a prosthesis part, the reinforcing element by physiological More adapted design has taken a more complex shape, like the simple bone pins previously described demonstrate. In order to distribute the applied forces through the prosthesis on the bone in case of stress To distribute in a controlled manner, such more complex forms are often necessary; in this example takes the finished coating has an almost truncated cone-like shape, which is very well suited to be placed in a bone cavity to be attached. Fig. 7 shows the view of a longitudinal section a partially polymer-coated femoral hip joint prosthesis 40. The reinforcement element 41 made of high strength material such as metal alloys or UHMWPE shows a finger-like part 41a and a even smaller finger-like approach 41b. These multiple extensions 41a and 41b allow a more uniform Force distribution. This irregular shape of the bone

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However, the prosthesis cannot simply help with the pin be fixed in a bone by bone cement. When encapsulating this irregular shape 41 with a The polymer coating 42 again has a regular shape, as shown in FIG. 7. The irregular Shaped reinforcement elements or bone pins, for example, have a number of indentations and bulges, which is necessary for the implantation by a subsequent coating with the help of different polymer layers take simple form. The expression "regular" means a generally smooth three-dimensional body with a Surface that has no significant concavities or convexities, understood.

It should also be noted that the polymer layer 42 in FIG. 7 is made up of four layers 42a, 42b, 42c and 42d is. These individual layers have different moduli of elasticity, although this is also possible if desired is to manufacture this coating from a single polymer layer, whereby the variation of the modulus of elasticity, as already stated, is produced by a constantly changing porosity.

The production of prosthetic parts with complex shapes, in which this shape is achieved by polymer layers is covered so that the ultimately resulting external shape is simple and suitable for implantation be carried out with suitable means, in particular with the means that have been specified so far. It is note that the dipping method of making a multilayer coating is usually not very useful well suited.

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8 shows a perspective, opened view of a vertical section through a human knee joint in which the tibia of the knee joint has been replaced by a prosthesis according to the present invention. A vertical section through the femur of the knee joint is denoted by 51. The damaged part of the knee joint was removed from the tibia 52. The prosthetic portion 50 which is to be connected to the damaged tibia, comprises a fixed reinforcing member 53 and a multi-layer of the four layers 54, 55, 56 and 57 _c formed polymeric film. The reinforcement element 53 in turn consists of a solid material such as a metal alloy or the UHMWPE. This reinforcement element again has a complex shape with two indentations for receiving the condyles of the femur and two corresponding convexities or bulges on the other side of the reinforcement part. Such a complex shape provides an even distribution of the forces acting under load through the prosthesis, but it is very difficult to adequately connect such a complicated shape to the bone. A composite, multi-layer polymer coating made up of layers 54, 55, 56 and 57 ultimately results in a regular, convex surface on its periphery, which serves to connect to the bone. As already described above, the individual layers are again designed in such a way that they have different moduli of elasticity. The polymer layer 54 has the highest modulus of elasticity, while the polymer layer 57 has the lowest. The polymer layer 55 has a modulus of elasticity which is greater than that of the layer 56, but less than that of the polymer layer

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The polymer layer 56 has a modulus of elasticity greater than that of the layer 57, but smaller than that the polymer layer 54. It is also possible here to use a single layer instead of a multi-layer layer to be used with varying modulus of elasticity.

In the context of this invention, other joint upper surfaces replacing implants can be produced. For example, according to the present invention, it is possible to use an acetabalum or an acetabular cup to replace. A hemispherical or cup-shaped prosthetic element can with its concave side cooperate with a femoral head. The part is made of a solid alloy like ZIMALOY or made of a plastic such as UHMWPE. The convex surface of the implant has a polymer layer varying elasticity and is intended to be connected to the bone. The convex side of the solid reinforcement part can be a simple, regular hemisphere or a more complex shape show in which bulges, concavities, entirely in accordance with the engineering ideas can be provided to distribute the forces. So convex, either regular or complex Surfaces of the reinforcement element are then provided with a polymeric coating according to the invention, which has a varying elasticity and whose surface is attached to the bone with the help of bone cement will. The polymer layer can consist of several layers or a single, continuous layer Layer.

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summary

Hip joint prosthesis with bone pin, the shaft of which has a reinforcement part (30) and a multilayer cover (32). The multi-layer cover consists of the layers 32a to 32b, each individual
Layer has a different modulus of elasticity. the
innermost layer (32a) has a modulus of elasticity which is essentially the same as the modulus of elasticity
of the reinforcement part (31), wherein this reinforcement part can consist of a metal alloy or of a highly tough polymer material. The outermost polymer layer (32d) of the prosthesis shaft has a modulus of elasticity that is essentially the same as the modulus of elasticity
of hardened bone cement is the same. The two intermediate polymer layers (32b, 32c) have
Modules of elasticity that lie in between, the
Modulus of elasticity of the layer (32b) is higher than
that of the layer (32c). The multilayer polymer coating with variable modulus of elasticity can by
a single-layer cover with a likewise variable modulus of elasticity can be replaced. As a result of the measure described above, the force acting through the prosthesis is evenly adjusted in the case of load and thus better adapted to the physiological requirements
Distribution of forces on the bone.

(Fig. 4)

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Claims (21)

Claims Ii prostheses in which a firm connection to the bone is provided by means of bone cement, characterized by a reinforcement part (11, 31, 41), at least part of the surface of the Reinforcing element has a polymer layer and the outer surface of the polymer layer with is connected to the bone, and the inner surface of the polymer layer rests on the reinforcement part, and this polymer layer has a modulus of elasticity that changes in the thickness expansion, such that the modulus of elasticity of parts of this polymer layer adjacent to the inner surface is substantially constant and the modulus of elasticity of the parts of the layer adjacent to the outer surface is essentially constant, and that the modulus of elasticity in the parts adjacent the inner surface is greater than the modulus of elasticity of the parts adjacent to the outer Surface and wherein the modulus of elasticity of the layer increases in the direction from the inside to the outside. 030035/0724 2. Prosthesis according to claim 1, characterized by a modulus of elasticity of the part of the polymer layer adjacent to the outer surface, which is largely the Corresponds to the value of the modulus of elasticity of hardened bone cement. 3. Prosthesis according to claim 1, characterized by a modulus of elasticity of the part of the polymer layer, adjacent to the inner surface, which largely corresponds to the value of the modulus of elasticity of the reinforcement part of the Prosthesis. 4. Prosthesis according to claim 1, characterized in that the modulus of elasticity of the polymer layer continuously decreases in the direction from the inside to the outside. 5. Prosthesis according to claim 4, characterized in that that the polymer layer has voids, these voids through the polymer layer are distributed in such a way that the percentage of the volume occupied by the voids is larger in the neighboring region of the outer surface than in the neighboring region of the inner Surface and that the percentage by volume of the voids continuously in the direction from the inside to the inside outside increases. 6. Prosthesis according to claim 5, characterized in that the percentage by volume of the voids is practically zero in the vicinity of the inner surface. 630035/0724 7. Prosthesis according to claim 5, characterized in that the reinforcement element is essentially made of metal. 8. Prosthesis according to claim 7, characterized in that the polymer layer has a thickness of more than 0.10 cm. 9. Prosthesis according to claim 8, characterized in that the prosthesis is a bone pin prosthesis is. 10. Prosthesis according to claim 1, characterized in that the modulus of elasticity of the polymer layer increases essentially gradually in the direction from inside to outside. 11. Prosthesis according to claim 10, characterized in that the polymer layer is a composition of individual polymer layers with different moduli of elasticity. 12. Prosthesis according to claim 11, characterized in that each individual polymer layer is a different one Has amount of plasticizer. 13. Prosthesis according to claim 12, characterized in that each of an inner layer is adjacent Layer has a larger amount of plasticizer than the inner adjacent layer. 14. Prosthesis according to claim 11, characterized in that each individual layer is a different one Has amount of stiffening filler materials. Θ30Ο35 / 072Α 15. Prosthesis according to claim 14, characterized in that that the stiffening filler material is granular. 16. Prosthesis according to claim 14, characterized in that the stiffening filler material is fibrous is. 17. Prosthesis according to claim 14, characterized in that each individual layer with
adjacent to an inner layer has a smaller amount of stiffening filler material than
this adjacent inner layer. 18. Prosthesis according to claim 1, characterized in that the reinforcement part has an irregular shape and the outer surface
the polymer layer has a simple, largely regular shape. 19. Prosthesis according to claim 18, characterized in that the reinforcement part is made of metal
consists. 20. Prosthesis according to claim 18, characterized in that the prosthesis is a bone pin prosthesis is. 21. Prosthesis according to claim 19, characterized in that the prosthesis _{r is} again a bone pin prosthesis. Θ30035 / 0724