DE3005264C2 - - Google Patents

Description

The invention relates to a method for producing a Prosthesis.

In US-PS 37 89 029 is a method for manufacturing a special bone cement described which poly methyl methacrylate (PMMA) as a plastic base material, ground bone material, a foaming agent and N-Tribu contains tylphosphat. Such a bone cement can also used for coating metallic body become. After hardening of the applied bone cement at a temperature of about 415 K in about 30 minutes and after removing the surface skin of the bone cement By sandblasting you get a total of a prosthesis, which on its outer surface high porosity having. This facilitates the ingrowth into human Tissue.

Metals that make up prosthetic bases commonly are made Cr-Co-Mo alloys, stainless Steel and titanium alloys. As further starting materials for prosthesis basic body also polymers, eg. B. Ultra high polymer polyethylene (UHMWPE = ultra high molecular weight polyethylene) are used.

As a rule, shaft prostheses are using Bone cement attached in a bone, this one Cement a mixture of PMMA polymer and methyl methacrylate Monomer is and additionally a styrene copolymer of PMMA may contain.

In practice it turns out that the adhesive bond between Denture stem and bone cement can break. Around  To reduce this risk, one can use the mechanical To improve adhesion to improve, for. B. by swallows tail-like design of the shaft or small addition pencils. But these solutions lead to a Spannungsver division in the bone, not the physiological force distribution corresponds. Also, the strength of the bone Cement is overwhelmed.

It has now been recognized that the strength of the compound between an implanted prosthesis and the bone cement is limited by mechanically weak boundary layers, which due to the material composition of the prosthesis or due to the prosthesis manufacturing process the prosthesis surface arise. In the case of metallic Prosthesis basic body has mechanically weak resilient Boundary layers on impurities and metal oxides are based on the surface of the prosthesis basic body. For denture basic bodies made of plastics are weak Boundary layers attributed to monomers, only partially polymerized or low molecular weight having Polymers and introduced by mold release agent Impurities. Finally, it also plays a role that a prosthesis with air, blood and water in contact comes before it is inserted into a bone. Also This leads to mechanically only weakly resilient boundary layers.

The problem of creating a solid connection between Denture and bone previously conditioned such a design of the prosthetic part implanted in the bone, that a good mechanical gearing with the bone is obtained. This means that you can restore a damaged one Joint, z. B. become become unusable due to arthritis Hip joint, not just the damaged joint surface can repair. Rather, you have the whole  Remove the condyle of the bone to allow a prosthesis can attach, which in terms of a good mecha Niche anchoring necessary shaft. By Improvement of the direct mechanical connection between a flat prosthesis and underlying this bone material only about a bone cement layer would be against it possible to repair the articular surface on its own.

The present invention is therefore a method for producing a prosthesis, in which no mechanically weak boundary layers after implantation the total load capacity of the composite bone cement / Impair denture body.

This object is achieved by a manufacturing according to the invention Method according to claim 1.

In the method according to the invention is based on that of The purified bodies did not polymethylate much as compared to bone cement lacquer coated with methacrylate. The paint layer So it gets thin. Because the paint at a temperature of more when cured at 70 ° C contains the cured varnish layer at most, still small residual amounts of unpolymerized or low molecular weight fractions. Due to the slow Cooling of base body and lacquer layer from the hardening temperature down to at least 80 ° C is ensured that in the cured lacquer layer no large thermal Tensions occur that lead to cracking or partial cracking Abolish the paint film could result.

When produced by the process according to the invention Prosthesis forms the hardened applied in a thin layer Lack for an excellent bonding agent for the bone cement applied later during the implantation. It also protects the body against oxidation  and pollution. Impurities, which after the Production on the surface of a fiction invention come prosthesis manufactured according to the method Surprisingly, only a very small influence the mechanical strength of the connection between Bone cement and prosthesis.

Advantageous developments of the invention are in sub specified claims.

Hereinafter, the invention with reference to Ausführungsbei play with reference to the drawing explained in more detail. In this show:

Fig. 1 shows a longitudinal section through a complete Hüftge Lenk prosthesis, wherein provided in the implantation with bone cement in contact surface portions with a PMMA-film;

Figure 2 is a greatly enlarged section through the edge region of the femoral prosthesis according to Figure 1 as well as adjacent regions of the bone cement and the femur after implantation;..

Fig. 3 is a side view of a human femur having an affected articular surface;

Fig. 4 is a perspective view of a shaft-free articular surface prosthesis, which serves to restore the condyle of the femur of Fig. 3, and

Fig. 5: a greatly enlarged section through the shaft-free prosthesis of FIG. 4 and underlying bone material after implantation of Gelenkflä chen prosthesis.

Fig. 1 is a longitudinal section through a complete hip joint endoprosthesis, which consists of a femoral shaft prosthesis 1 and a hip joint socket 4 .

The femoral shaft prosthesis 1 has a base body 2 with a shaft for insertion into a bone canal, which is made of a metal alloy or a polymer material such as UHMWPE. Over the main body 2 , a high-strength PMMA film 3 is placed. The acetabular cup 4 has a dome-shaped basic body 5 of a solid, prosthetic material on the inner surface of a PMMA film 6 is applied.

The prosthesis basic body 2 and 5 , z. Example of titanium alloys, stainless steel, cobalt-chromium or cobalt-chromium-molybdenum alloys, MP-35 (protozole) or from a polymeric Ma material such as very high molecular weight polyethylene (UHMWPE = ultra high molecular weight polyethylene) made become.

Order a high-strength PMMA film now To apply the prosthesis basic body, this must first be pretreated for it. This pretreatment includes the removal of impurities, which can act as mechanically weak boundary layers. For metal These weak boundary layers are at the top surface sticking dirt and oil and then additionally still caused by fine metal oxide layers. at  Plastic are for the weak boundary layers typically Verun purifications such as residual monomer, antioxidants and mold release agents. Also low molecular weight fractions of the plastic have a similar effect.

The removal of weak boundary layers in metal Primary bodies includes degreasing as a first step. The fine oxide layers are in another Removed step by means of acid. Then follows a cleaning and passivation of the metal. there treatments can also be used the impurities and light oxide layers of the metal remove.

The degreasing treatment can be carried out with aqueous, alkali shear solution, such as an aqueous solution of sodium hydroxide. It is the Body in a heated to the boiling point 1 N aqueous solution of sodium hydroxide for 30 min. immersed. In a further degreasing treatment, the Basic body be exposed to trichlorethylene fumes. To check if the degreasing is complete or not, the so-called "water pearl test" be performed. This is the degreased body rinsed with distilled water. runs soaking up the water in less than 30 seconds the surface is not clean enough. The water layer on the surface must not tear, nor tingling or frowning.  

Subsequent to the degreasing treatment is at metallic basic bodies the o. a. Säureätz Treatment performed to lightly bound metal remove oxide. This is done by On dive into a sulfuric acid-water mixture at he elevated temperature, for example 60 ° C over a period of time about 30 min. Other treatment lungs are immersed of the main body into an aqueous chromium Sulfur solution or in solutions of others Acids.

The etching treatment terminates before major surface changes occur or become visible. In the case of alloyed bodies, which for example, in a sulfuric acid solution as above described, can be etched by the etching reaction the surface will be stained black. The reason for this is the remaining of carbon, which is a com component of the metal alloy. The becoming visible of carbon shows that the surface enough is etched. To a larger surface change too  should avoid the body within 10 seconds after occurrence of the surface carbon are removed from the bath. He Can then use a Hobsyn tally surfaces profiles or with a SEM to be sure to go that no major surface changes occurred.

Coals remaining on the surface fabric must be cleaned with the help of a cleaning and passivation be removed treatment, for. B. by Immersion in one aqueous, heated to about 60 ° C hydrofluoric acid / nitric acid Mixture. But there can be others, too oxidizing reagents are used. If the etched basic body is immersed in this solution, so within seconds a reaction takes place indicated by a effervescence of the solution and in the Carbon is dissolved away. A subsequent, further effervescence in the solution shows a second Reaction to. At this point, the main body should be removed from the solution. This treatment not only removes the visible on the surface Carbon, in addition, a well-adherent, uniform, heavy-duty oxide surface.

The removal of weak boundary layers is not only possible with chemical agents, as with For example, degreasing and acid etching, including mechanical Funds can lead to success. It is the Basic body z. B. a sandblast treatment with aluminum subjected to miniumoxid. Other mechanical treatments such as grinding,  Honing, polishing can also be applied the.

Subsequent to such a mechanical treatment of the main body immediately, at the latest after 1 min., in a passivation be dipped in solution. These are Sal, for example peteric and hydrofluoric acids, as already described above.

Subsequently, the base body thus treated is rinsed in water, until the water has a neutral pH. Then he will dried, for example in one Drying oven or oven or by blowing the Surface with dry, warm air.

Once the base has dried, it can reach room temperature are cooled to then apply a PMMA film. Care must be taken so that the cleaned Do not touch surfaces again while drying and cooling lens are contaminated. Before the coating must so-called adhesion promoters such as siloxane derivatives to be brought.

Subsequently, the PMMA film is applied to the main body applied. This can be done by painting or spraying a PMMA lacquer or A dive into such a paint done.  

The applied paint mainly consists of PMMA, contains besides, crosslinking agents, free radicals as catalysts, activating agents, Plasticizers, inhibitors, plasticizing co polymers, as well as adhesion promoters in the form of Co polymers, such as acrylic acid or others freely orientable polar molecules.

The PMMA paint is made by dissolving high molecular weight PMMA in a solvent such as dichloro produced methane. A small amount of barium sulfate can be added to the paint to cracking prevent the film, which at the same time the film increased absorbing properties for short-wave receives electromagnetic radiation. The concentration the polymer solution is within the range of 0.01 g per ml to 0.8 g per ml; preferably, a concentration from 0.2 to 0.4 g per ml applied, the best results is obtained with concentrations between 0.25 and 0.35 g per ml.

When dipping, the dive time can be 5 sec. To 60 Min., Are advantageous immersion times between 15 and 60 minutes, preferably those between 25 and 35 minutes  

Contains a modified PMMA paint PMMA, which in methyl methacrylate (MMA), which zu additionally contains a conventional hardener, is solved. A further modified PMMA paint contains PMMA together with MMA and a Kataly sator. In cases where MMA ver is used, is one after application of the paint Curing at higher temperature necessary, such as will be described below.

After completion of the PMMA coating The PMMA film is heated by heating the coated base cured, with temperatures above the conversion temperature of the amorphous region of PMMA For example, at 343 to 363 K (70 ° C to 90 ° C), preferably at 353 K (80 ° C). The hardness treatment is necessary to a Durchpolymerisierung as well as an Ab evaporate the volatile components from the film to back up. Due to increased pressure (more than 7 bar) will blister avoided. When heating the film over the conversion temperature of the PMMA become mechanical Tensions, which develop during the drying in the film form, eliminated.

The cooling rate with which a coated base body after the Curing process is cooled, must be carefully over To ensure that the value of 1.5 K per min. at temperatures above 353 K. is not exceeded. This occurs during cooling only minimal tensions in the film. So it is desired The film can be either chemically or by irradiation be additionally networked.  

The thickness of the film produced is not critical, so long as the preferred minimum thickness of the film is not less than 2.5 x 10 ^-3 mm, preferably 25 x 10 ^-3 mm, or more preferably 50 x 10 ^-3 mm, in thickness should be available.

After completion of the curing of the PMMA film is the coated body ready for use as a prosthesis. Will this prosthesis be a bone implant used, the bone must be eroded accordingly cleaned and then mixed with PMMA bone cement ver will see. Thereafter, the part to be implanted the prosthesis, which as described above coated in the interior of the bone leads. So it may be desired, the coating may be before insertion into the bone with a solvent how MMA monomer softened a bit. This causes, that the PMMA film begins to swell and soften What better, mechanical and chemical Interaction between the coating and the bone cement allowed.

In Fig. 2, the section of an enlargement of a coated prosthesis, which was fixed by means of PMMA bone cement to the bone, shown. The shaft of the base body 2 is about the PMMA film 3 with the bone cement layer 7 in conjunction. The bone or the bone tissue 8 is intimately adhered to the bone cement layer 7 . The intermediate layer 9 between the PMMA film and the base shows no defects or any weak interlayers due to the treatment of the base before its coating. The intermediate layer 10 between the PMMA film and the bone cement exhibits mechanical as well as chemical adhesion. The bubbles 11 in the bone cement 7 are held by the intermediate layer 9 fernge by the interaction between film and cement.

Be prosthesis body of a polymer, especially made of UHMWPE, so is a slightly different Treatment to remove the weak boundary layers necessary. This treatment contains either an oxidation treatment or treatment with the acronym "Casing" (cross-linking by activated species of inert gases). The oxidation treatment can by corona discharge, flame treatment or acid treatment action, such as chromic acid, etc. durchge be led. The oxidation treatment causes a Removal of contaminants and low molecular polymers, such as polyethylene.

Before oxidation or casing treatment is the plastic or polymer base body degreased, by giving some Seconds immersed in trichlorethylene solution.

When casing treatment one leaves excited by electron beams Noble gases on the surface of the polymer. Once this metastable and ionized gas in contact with the plastic comes, is a splitting off of water atoms and thus the formation of polymer radicals obtained in and on the surface of the polymer. These  Radicals combine crosslinking with unsaturated groups, without losing one cause significant cleavage of the polymer chains. The mechanical strength of the surface region is notable thereby by the formation of a gel matrix elevated. This is a weak boundary layer in one strong boundary layer transferred. The wettability of the Surface is practically not affected. The contact of the activated gas with the plastic surface for less than 1 second. causes a good improvement of adhesion. Longer exposure times may be needed if stronger inert plastics, such as polytetra fluoroethylene, used for the basic body.

If you replace the Casing treatment by one Oxidation treatment is obtained later on the surface a better PMMA movie.

After carrying out the oxidation and / or casing Treatment of the surface of the plastic base body is in the same As previously described, a PMMA layer applied. The PMMA movie will follow Hardened, as it is the metalli rule body was described. Curing at a temperature of about 373 K is at one UHMWPE prosthesis basic body sufficient.

So if a PMMA movie as described above a prosthesis basic body was applied, then arises a prosthesis which, when used with bone cement in Is associated, a striking higher liability has as the same prosthesis without such Coating. The adhesion is also better than one with PMMA coated denture, in which no pre-treatment before coating and no curing after coating was carried out.  

The improved adhesion between Prosthesis and bone cement not only brings an improved fit of an implant in bone tissue, it can also be used in some cases a switching prosthesis be dispensed with. Shafts are usually used to secure steel implants in To fix bones. The real reason for such Implantations are per se degradation symptoms on the upper surface of a joint, for example by arthritis. A restoration of the functioning of the joint Surface is not yet easy to perform, because it is Fixation problems occur.

Recent advances in the application of cements Bones contain a pressure treatment of the cement, to bring him deep into the pores of the bone and so on a good adhesion through mechanical gearing bring about. Nevertheless, the problem remains Applying a metallic surface to a bone, without the help of a shaft. This problem can by PMMA-coated prostheses be solved.

Fig. 3 shows a human femur 21 in a side view, the condyle has a damaged surface 22 . According to the conventional technique, the entire head of the femur is removed and replaced with an artificial head having a shaft.

Fig. 4 shows a shell-shaped prosthesis replacing the destroyed, natural head surface. This has a base body 23 , which may consist of an alloy, and a PMMA film applied to the shell inner surface 24 . This prosthesis, which is coated as described above for the shaft prosthesis, can be fixed firmly on the head of the femur.

Fig. 5 is an enlarged section through the femur head after placing the cup-shaped prosthesis. On the one hand, the bone cement 25 has penetrated deep into the surface of the bone 26 and, on the other hand, has been connected to the PMMA film 24 . An intermediate layer 27 consists of a molecular binding of PMMA / PMMA bone cement. The main body 23 is thus connected via a PMMA film and bone cement surface to be replaced with the bone.

Such shaft-free, shell-shaped prostheses can not only be destroyed Ball joints and joints with sockets used be, but also generally for any damaged Articular surfaces, for example a knee joint.

The following examples show the preparation of PMMA-coated prostheses in more detail:

Example 1 Pretreatment and coating of a metallic base body Production of a PMMA lacquer

30 g high molecular weight PMMA beads in 100 ml of dichloromethane with stirring solved. Once all the beads have dissolved, 1 g Barium sulfate added. The barium sulfate is suspended and clouds the solution. This Approach is standing for half an hour let, with the barium sulfate settles to the bottom. After half an hour, the solution with the suspen  decanted barium sulfate from the sediment.

Pretreatment of a cobalt-chrome prosthesis basic body with shaft

The surface of a dry sandblasted cobalt Chromium prosthesis basic body should be coated. The Body is first immersed in a boiling water for about 30 minutes 1 N sodium hydroxide solution degreased. He is then rinsed with warm water for so long, until the draining water is neutral.

The main body is then in a 50 vol .-% etched aqueous, sulfuric acid solution. The temperature is 333 Kelvin. If after about 30 minutes through remaining carbon blackens the surface, the main body is removed from the acid solution and rinsed with distilled water.

Then the main body is in a cleaning given solution, which consists of a mixture of 15 vol .-% a 52% hydrogen fluoride solution and 45% by volume a 40 vol .-% aqueous nitric acid solution be stands. The temperature of this solution is between 323 and 333 Kelvin. About 10 seconds after immersion of the body appears a torrent of bubbles, which indicate that the carbon has been released. Immediately after, a sudden second barrage of Bubbles, indicating a second reaction. At this Point is the main body of the cleaning solution taken out and immediately rinsed vigorously with distilled water,  until the draining water shows a neutral reaction. Then the main body is in an oven at a temperature of 383 K during dried for about 5 to 10 minutes. Then he will outside the oven to room temperature cooled.

Applying the coating

The thus pretreated base body is in the manner described above submerged PMMA paint prepared. After 30 minutes will be he took it out again and in an oven with heated at a temperature of 333 K for 2 hours.

hardening

The coated body is then subsequently held in an oven at 433 K for 18 hours. After this time it is taken out of the oven and cooled at a cooling rate of 1.5 K per minute up to a temperature of 343 K. Subsequently, the body can be cooled down at ambient temperature. It is important that the coated body is not cooled too quickly as this will cause differences in thermal contraction between the coating and the substrate. The PMMA film produced in this way has a thickness of between 25 to 40 × 10 ^-3 mm.

example 2 Pretreatment and coating of a polyethylene base

A UHMWPE prosthesis base body should be coated. The The main body is initially so by a butane-oxygen flame pulled out that whole surface of the flame is set. Then the main body activated argon gas, which with the help of a High voltage discharge in a vacuum chamber has been activated. The thus treated polyethylene body is then cooled to room temperature and with Coated PMMA paint, as described in Example 1. The coated body is placed in an oven at a temperature of 333 K for 2 hours dried. Then the coating is heated by heating coated body in an oven at 373 K during Hardened for 2 hours. Finally, the body is slowly starting cooled, as described in Example 1.

The importance of pretreatment and coating of the reason Body according to Example 1 and 2 illustrate the following Comparative tests:

Trial 1 (metallic base body: with / without PMMA film)

A shaft test body is according to Example 1 prepared. This test body and a corresponding uncoated test bodies are under room conditions on the surfaces Equally provided with bone cement. The shear strength of Interlayer is using a cylinder shear force tests were measured for both test bodies. You get:

PMMA film Shear strength (MPa) uncoated 2.1 according to Example 1 15.2

The cylinder shear force test is performed as follows guided: A cylindrical test body is in a ring shaped mold containing PMMA / MMA bone cement done. The cement is cured, and the form is then taken away. The cylindrical one Test body now carries a ring of bone cement. The test piece is clamped over the cement ring in a clamping device. Then, on the remote from the cement ring end of the specimen an axial force exercised, and the magnitude of the force is measured, which is necessary is to the connection between the cylindrical test body and the ring of bone cement break.

Trial 2 (metallic base body: curing temperature PMMA film)

A metallic stem prosthesis test body is degreased, with PMMA coated and cured, as in Example 1 described. For comparison purposes will be another Test body treated in the same way, except that in place of the cure at 433 K, the PMMA film Room temperature is cured. Subsequently, the Test body under room conditions with bone cement ver see. The interlayer shear strength becomes measured as previously described, for the two test bodies give the following values:

PMMA film Shear strength (MPa) similar to Example 1, but dried at room temperature 3.9 according to Example 1 (hardening at 433 K) 6.2

Trial 3 (PMMA film: protection against impurities)

PMMA-coated prosthesis stem test bodies are, as indicated in Example 1, prepared. One of them is ver under room conditions with bone cement ver bound, while another intermediary substance exposed, washed off with a saline solution and on closing is connected to bone cement. The Interlayer shear strength of both test bodies becomes measured. There will be no statistically significant Deviation of the values found.

The above tests are also carried out on uncoated prosthesis stem Test bodies performed. The interlayer shear strength an uncoated and uncontaminated test specimen is then significantly smaller than that of a be layered test specimen and beyond that is the Interlayer shear strength of a contaminated test specimen 50% smaller than an unbe layered, uncontaminated test body.

This is clear that prostheses, which as described above with a PMMA film are provided by Kontamina tion are not affected, while uncoated Prostheses of Contaminants are greatly affected.

Trial 4 (UHMWPE base body with / without PMMA film)

A UHMWPE test specimen is treated in a flame with PMMA coated, dried and cured, as in Example 2 described. This test body and an unbe layered UHMWPE test body under Raumbe conditions associated with bone cement. The block shear strengths for the test bodies are:  

PMMA film Block shear strength (MPa) uncoated <0.1 according to example 2 5.1

The above-mentioned block shear strengths are measured as follows: A cubic or cuboid shaped test piece is coated on one of its flat surfaces as described, the reference test body remains uncoated. A cube or cuboid of bone cement is using a mold manufactured. The test specimen is with the bone cement block connected by bone cement, and after curing of the bone cement, the force is measured, the up must be used to the bone cement connection zwi the test body and the bone cement block break.

Claims (8)

A method of manufacturing a prosthesis ( 1, 4 ) comprising a base body ( 2, 5 ) and a polymethyl methacrylate film ( 3, 6 ) covering at least part of the surface of the base body ( 2, 5 ) the

• a) the base body ( 2, 5 ) is cleaned of boundary layers,
• b) a polymethyl methacrylate lacquer with 0.01 to 0.8 g of polymethyl methacrylate per ml is applied to the base body ( 2, 5 ),
• c) the paint is cured at a temperature of more than 70 ° C, and
• d) the base body ( 2, 5 ) and lacquer layer is cooled from the curing temperature at least down to 80 ° C at a maximum rate of 1.5 ° C per minute.

2. The method of claim 1, wherein the base body ( 2, 5 ) of the prosthesis ( 1, 4 ) consists of metal, characterized in that is cleaned to clean the body of boundary layers of the body with alkaline agents and subsequent acid treatment. 3. The method according to claim 2, characterized in that degreasing at a temperature between 93 ° C and 104 ° C takes place. 4. The method according to claim 2 and 3, characterized that the acid treatment followed by acid etching from a passivation treatment. 5. The method according to claim 1, wherein the base body ( 1, 4 ) consists of ultra-high molecular weight polyethylene, characterized in that the base body ( 1, 4 ) for the purification of boundary layers on the surface is oxidized. 6. The method according to claim 5, characterized in that the surface oxidation from an acid treatment and a flame treatment or corona discharge treatment consists. 7. The method according to any one of claims 1 to 6, characterized characterized in that the solvent of polymethyl methacrylate varnish is dichloromethane. 8. The method according to claim 7, characterized in that the polymethyl methacrylate paint still barium sulfate added will give.