WO1991003266A1

WO1991003266A1 - Prosthesis

Info

Publication number: WO1991003266A1
Application number: PCT/EP1990/001424
Authority: WO
Inventors: Jochen Pauls
Original assignee: Böhler Ag
Priority date: 1989-08-31
Filing date: 1990-08-25
Publication date: 1991-03-21
Also published as: DE3928845A1; AU6291290A

Abstract

Disclosed ia a prosthesis implantable without the need for adhesive cement and which has a main body (34) cast from Co-Cr-Mo alloy and, applied to this, a thin protective metal-oxide film (36) produced by plasma spraying and subsequently made non-porous by hot isostatic pressing or mineral sealing (42). Applied to this protective film (36) by plasma spraying is a hydroxyapatite adhesive film (44).

Description

prosthesis

description

The invention relates to a prosthesis according to the preamble of claim 1 and a method for producing such.

For prostheses, e.g. Hip joint prostheses, a rough distinction is made between prostheses that can be implanted using bone cement and prostheses that can be implanted without cement. The first type of prosthesis has a smooth fastening shaft that is positively bonded to the hard outer layer of the bone (Compacta) using PMMA-based bone cement. In contrast, the cementless implantable prostheses have a surface structure on which newly formed cancellous bone material can get caught and anchored.

In order to improve the adherence of the cancellous bone material to a metallic prosthesis base, it is also known to provide its surface with a mineral coating, e.g. with a layer of hydroxyalpatite.

Cementlessly implantable prostheses are well tolerated and resilient.

Since cementlessly implanted prostheses come into contact with living tissue, they also come into contact with body fluids. These could chemically attack the metal of the base body over very long periods of time, as can be achieved in the case of cementlessly implanted prostheses, since the tissue surrounding them is stimulated by the mechanical alternating loads to undergo permanent new formation. The present invention is therefore intended to develop a prosthesis according to the preamble of claim 1 in such a way that its metallic base body is not chemically attacked even in very long periods of time.

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

The prosthesis according to the invention has a liquid-impermeable thin metal oxide layer, which is the metallic

Protects base body reliably against electrolytic body fluids. Since the layer is thin, it can also follow sharp changes in direction of the surface of the base body, so that one still has the desired mechanical embedding areas for cancellous material growing against the prosthesis. Since the thermally sprayed metal oxide layer is mineral sealed to form a liquid barrier and / or is compacted without pores by isostatic hot spitting, it is also possible to access areas of prostheses with a complicated surface structure that are difficult to access, such as e.g. is described in DE-OS 36 16 665, provided with this liquid-tight coating. The production of a uniform and dense protective layer of this type is to be carried out in the manner specified in claim 1 even at reasonable costs. The protective layers are distinguished by good adhesion to the metallic base and good elasticity and impact resistance. They also grow quickly and permanently with cancellous material.

Advantageous developments of the invention are specified in the subclaims.

The developments of the invention according to claims 7 and 8 are particularly economical in terms of Manufacture of the prosthesis is an advantage. Mineral seals can be produced very easily starting from an aqueous solution of a gel or by melting a glass or the like that melts at low temperatures, including prostheses that have complex surface geometries. The impregnation is applied to the porous metal oxide layer simply by dipping or spraying with a spray gun, if appropriate with the addition of a carrier medium or volatile binder. A seal according to claim 7 or 8 is also well suited to those metal oxide layers which have a large porosity (greater than 5%).

The development of the invention according to claim 9 facilitates the penetration of the melt impregnation even into fine-pored metal oxide layers.

If, according to claim 11, the temperature at which the hot isostatic pressing is carried out is selected at about 1400 ° C. and the pressure for the production of the prosthesis

Pressing at about 2000 bar, the individual particles that form the thermally sprayed metal oxide layer are melted sufficiently on the surface to ensure that these particles can be displaced in the layer to form a continuous pore-free layer, but on the other hand the metallic base body has not yet seriously compromised its strength and retains its surface geometry, which specifies a large number of small anchoring surfaces.

The invention is explained in more detail below on the basis of an exemplary embodiment with reference to the drawing, in which:

Figure 1: a side view of the upper end of a Femur with a cementless implanted prosthesis, part of the compacta and spongiosa having broken away in order to be able to show the anchoring structure of the prosthesis;

Figure 2 is a greatly enlarged view of a portion of an anchoring pillar of the prosthesis shown in Figure 1; and

FIG. 3: a further greatly enlarged section through the edge layer structure of an anchoring pillar which has been surface-treated in a special way.

FIG. 1 shows the upper end section of a thigh bone 10. The solid outer layer of the thigh bone 10 has broken away in such a way that a window 12 similar to that which is sawn out by the surgeon for inserting the prosthesis is obtained.

Underneath the compacta lies spongiosa material 14, indicated by dotting, which in reality has a fibrous structure with trabeculae 16 following the force transmission lines, which are shown in an uppermost, non-broken-off partial layer of the spongiosa material.

A total of 18 prosthesis is inserted into the upper end of the bone. This includes a support wall 20, which essentially has the shape of a double-angled part, with a wall section 22, which runs to the minor trochanter, and with a second wall section 24, which creates a flush connection to the Adam's arch. The supporting wall 20 thus represents a cap which replaces the compacta at the upper end of the bone and surrounds the cancellous material 14. A pin 26 is formed on the upper side of the support wall 20, to which a joint ball 28 made of ceramic and polished on the outside is fastened. This works together with an acetabular cup to be implanted in the pelvis, which is not shown in the drawing.

From the underside of the supporting wall 20, a large number of integrally formed anchoring posts 30 run inwards into the spongiosa material 14. The basic direction of extension of the anchoring pillars 30 is essentially parallel to the

Axis of the pin 26 and thus lies in the main direction of loading. The individual anchoring pillars 30 are somewhat curved in accordance with the course of the trabecular trajectories. The free ends of the anchoring pillars 30 end at a distance from the Compacta.

The anchoring pillars 30 each have a plurality of axially successive anchoring collars. ^' 2 on. These are distributed essentially at the same distance in the cancellous material 14, which after the implantation of the prosthesis 18 has grown between the anchoring pillars 30 and thus fulfills elongated columnar spaces.

The annular end faces of the anchoring collars 32, their axial spacing, the thickness of their core section and the length, number and spacing of the anchoring posts 30 are so dimensioned overall that the local stresses in the cancellous bone after the prosthesis has healed are not so are large that permanent damage to the cancellous bone occurs, but on the other hand are not so small that the mechanical stimuli desired for the constant renewal of the cancellous bone fail to materialize.

The prosthesis part 18 is produced in such a way that first a Co-Cr-Mo organic alloy blank is poured and this after removal of the casting mold in a conventional manner, first so that the surfaces are clean, especially grease-free.

This cleaning is done e.g. by heating the blank to 420 ° C. in an air circulating oven for about an hour. In this way, impurities on the surface are oxidized and loosened mechanically.

The base body is then blasted mechanically using sharp-edged Al ₂ O ₃ blasting material with a particle size of approximately 0.1 mm. The blasting material is directed at 3 bar from an 8 mm blasting nozzle with a cone opening angle of 35 ° against the casting from a distance of 30 cm.

An approximately 50μ to approximately 350μ thick ceramic mixed layer of 60% by weight A1 ₂ .0 and 40% by weight Ti0 _{2 is} sprayed onto the surface of the casting thus prepared by plasma spraying in a high-speed plasma spraying system. The sprayed powder is agglomerated and has a grain size of approximately 45 μ with a diameter of the individual particles of 5.6 μ.

Plasma spraying is carried out using an argon / hydrogen mixture. The porosity of the sprayed-on layer is 2% by volume and its density is 3.6 g / cmη.

The ceramic layer can also be applied by flame shock spraying instead of plasma spraying.

Loose particles are then removed from the base body provided with the ceramic layer, for example by ultrasound cleaning or repeated blasting with fine Al ₂ O particles. As can be seen from FIG. 3, the ceramic layer 36 has individual grains 38 sintered together and the pores 40 remaining between them. The pores 40 are exaggerated in size and in practice take up considerably less space, for example the 2 vol. %.

A porous ceramic layer soaks up after the implantation of the prosthesis due to the capillary effect with body fluid, which can thus reach the previously extremely cleaned surface of the metallic base body 34. This can then be attacked electrolytically in the long term, which is disadvantageous on the one hand with regard to the migration of metal ions back into the body's own tissue and on the other hand with regard to the infiltration of the ceramic layer. To counter this, the pores 40 remaining between the grains 38 are closed by a barrier layer 42. This barrier layer can be formed by a kiesel impregnation, a melt impregnation or by compacting the outermost grain layers by hot isostatic pressing, as will now be described in more detail below.

For silicification impregnation, the base body 34 carrying the ceramic layer 36 is immersed in an aqueous silicate solution (eg water glass solution). This can additionally contain a physiological wetting agent such as porin. When immersed, the silicate solution penetrates into the pores 40 due to the capillary effect. The base body 34 with the ceramic layer 36 now soaked with silicate solution is then treated for about 5 minutes at 100 ° C. in wet steam. The silicates harden through silicification. The barrier layer 42 is then examined for freedom from holes, for example by immersing the prosthesis in an electrolyte and the current between the metallic base body 34 and one that is also immersed in the electrolyte Counter electrode measures. If the barrier layer 42 is not error-free, the step of forming the barrier layer can simply be repeated again.

It goes without saying that the silicate solution is used instead of through

Can also bring diving by spraying with a spray gun on the ceramic layer 36.

In the case of melt impregnation, a mineral blocking agent that is curable at low temperatures is introduced into a carrier material in finely divided form. Examples of this are: a melting glass type such as solder glass in the form of a fine frit suspended in water; Dry gels of aluminum oxide, magnesium oxide, spinel, zirconium oxide or titanium oxide suspended in water; finely ground frits of the aforementioned oxides or glass frits suspended in a gas stream. These blocking agents, to which wetting agents and / or fluxing agents (finely ground) can also be added, are again applied to the ceramic layer 36 by dipping or spraying or powder coating processes. At a

The base body carrying the impregnated ceramic layer 36 is treated for about 30 minutes at a temperature sufficient to split off the residual water of the dry gel or to melt the mineral blocking agent. Typical treatment temperatures for frits made from finely ground glass are around 300 to 320 ° C, typical temperatures for curing metal oxide dry gels are around 220 to 230 ° C. Also during melt impregnation, the blocking agent penetrates into the pores 40 by capillary effect closes the pores on the surface. Whether the barrier layer 42 is free of holes is again checked as described above. If the barrier layer contains 42 errors, the step of forming the barrier layer can simply be repeated.

In hot isostatic pressing, the barrier layer 42 produced by compacting the ceramic layer 36 itself, which has the advantage that no additional material component is introduced. In a first step, which takes place at a relatively low temperature, the surface of the ceramic layer 36 is "provisionally" closed, e.g. B. by the silicification impregnation described in more detail above. The layer structure obtained in this way is compacted by hot isostatic pressing at 1400 ° C. and 200 bar in an autoclave, an inert gas such as argon or helium being used as the protective gas. Pressure and temperature are maintained in the autoclave over a period of about 60 minutes, and one is obtained after slow cooling and removal of the prosthesis from the autoclave on the casting base body designated 34 in FIG. 2 from the Co-Cr-Mo alloy compacted ceramic layer 36, which is free of pores and has a density of 99.7% of the theoretical density that can be obtained by complete compaction. After the hot isostatic pressing, the "provisional" working seal produced by dip impregnation is removed again, for example by blasting with fine, sharp-edged aluminum oxide particles.

Whichever of the three sealing methods described above is used, the ceramic layer 36 permanently electrically and chemically insulates the surface of the base body 34.

A highly porous adhesive layer 44 made of hydroxyapatite is then sprayed onto the ceramic layer 36 by plasma spraying. With its large surface area, this promotes the growth of cancellous bone.

The thickness of the hydroxyapatite layer is 5 to 150μ, preferably 30 to 50μ. The coated prosthesis thus obtained is sterilized in superheated steam and then packaged sterilized.

Since the ceramic layer 36 is impact-resistant due to its thickness and the special choice of material, the liquid barrier formed by it is retained even if the prosthesis is improperly stored or transported or falls to the floor.

Claims

1. A prosthesis with a metallic base body and with a mineral coating applied thereon, characterized in that the mineral coating has a metal oxide protective layer (36) with a thickness of approximately 50μ to approximately 350μ, preferably 70μ to 120μ points that by thermal spraying, for example Plasma spraying or flame shock spraying, on which the base body (34) is applied and in which the porosity is eliminated at least on the surface by a mineral seal (42) and / or hot isostatic pressing.

2. Prosthesis according to claim 1, characterized in that the metal oxide protective layer (36) is a mixture as aluminum oxide and titanium dioxide.

3. Prosthesis according to claim 2, characterized in that the metal oxide mixture about 60 wt.% Alumina and

40% by weight of titanium dioxide.

4. Prosthesis according to claim 1, characterized in that the metal oxide protective layer (36) is a mixture of zirconium dioxide and cerium dioxide.

5. A prosthesis according to claim 4, characterized in that the mixture has at least 85% by weight, preferably more than 92% by weight of zirconium dioxide, the rest of cerium dioxide.

6. A prosthesis according to any one of claims 1 to 5, characterized ge indicates that the density of the metal oxide protective layer (36) compacted by hot pressing is over 99%, preferably about 99.7%, of the density of the ideally solid ceramic material.

7. Prosthesis according to one of claims 1 to 6, characterized ge indicates that the mineral seal (42) has a silicified impregnation based on silicate or metal oxide.

8. Prosthesis according to one of claims 1 to 7, characterized ge indicates that the mineral seal (42) has a melt impregnation based on silicate or metal oxide.

9. A prosthesis according to claim 8, characterized in that a flux is added to the melt impregnation.

10. Prosthesis according to one of claims 1 to 9, gekenn¬ characterized by a on the metal oxide protective layer (36) by thermal spraying, preferably plasma spraying, applied porous adhesive layer (44) made of hydroxyapatite.

11. A method for producing a prosthesis according to one of claims 1 to 10, characterized in that the hot isostatic pressing takes place at about 1400 ° C and about 2000 bar.

12. The method according to claim 11, characterized in that the Metalloxid¬ powder used for thermal spraying is agglomerated and preferably has a grain size of approximately 40 to 50 μ, the diameter of the individual metal oxide particles approximately 5 to 6 μ, preferably approximately 5.6 μ is.