WO1995025483A1

WO1995025483A1 - Implant with a mechanical protective device and use thereof

Info

Publication number: WO1995025483A1
Application number: PCT/EP1995/001058
Authority: WO
Inventors: Klaus Draenert
Original assignee: Klaus Draenert
Priority date: 1994-03-22
Filing date: 1995-03-21
Publication date: 1995-09-28
Also published as: DE4409836A1

Abstract

The invention concerns a mechanical protective device for an implant or transplant. The device comprises a preferably cylindrical casing (2) which surrounds the implant (1) at least partially. The advantages of the invention reside in the reliable protection of the implant (1) against fracture or shearing off.

Description

Implant with mechanical protection device and its

use

The invention relates to a mechanical protective device for an implant or graft for protection when being introduced into and / or remaining in a living body, an implant having the protective device and its use, preferably for bone replacement or for bone stabilization.

If the term "implant" is used in the present patent, this should be understood to mean both an implant and a transplant.

The use of artificial implants is known in the surgery of the musculoskeletal system, be it as a joint replacement, as a bone replacement or as a method for stabilizing bones or interconnected bone sections.

Such implants are either anchored with a self-curing plastic, the so-called bone cement, or directly press-fit. By enlarging the surface, by hollowing out the solid implant body and / or perforating the mostly metal implant surface, a direct anchoring in the bone and subsequent bone ingrowth should be achieved. However, the pure metal surfaces have the disadvantage that the bone does not adhere to these surfaces. This was shown in the scientific work "Research and further training in the surgery of the musculoskeletal system 3" (Draenert and Draenert, Art and Scierce, Munich, 1992). By roughening the surfaces with roughnesses of 50-100 μm it is possible to considerably improve the transfer of the deformation energy from the implant to the bones and to convert these deformations. reduce or cancel formation energy into a harmful relative movement; In this study, however, it could be shown that surfaces other than metal surfaces interfere with the bone far more favorably. These are, for example, ceramic surfaces and, above all, the hydroxylapatite in its dense form or as a dense coating, as can be achieved with the so-called "HIP process" (hot isostatic pressing) on implants. The HIP-coated surfaces showed tangential adherence of the bone around the implant, which made it possible to completely avoid relative movements in the interface between the implant and the bone.

So far it has not been possible to combine the advantages of a metallic implant in terms of mechanical strength and the advantages of a ceramic implant in terms of interaction with the bone, because the coating of metal surfaces has not yet been satisfactorily solved; the weak point lies in the transition from metal to ceramic.

On the other hand, all massive implants - this could be proven in long-term studies - could not lead to permanent anchoring in the bone. This was only possible with very light and delicate designs. Surprisingly, the rigidity of the implant was of little importance for the long-term result in these results.

From DE-A 40 33 201 and German patent application P 44 03 509.8, to the disclosure of which express reference is made, porous materials for implants are known which consist, for example, of ceramic. In their so-called "positive structure", these materials consist of a three-dimensional framework made up of trellis-like or shell-like structures which enclose interconnectable and predeterminable adjustable cavities which form an interconnecting pore system. This Positive material can be produced, inter alia, by the shell-like structures being formed around shaped bodies which serve as placeholders for the cavities. In their so-called "negative structure", the materials consist of a conglomerate of molded bodies which are firmly connected to one another via webs. The shape of the negative material essentially corresponds to the pore system of the positive material. Investigations have shown that such materials offer excellent healing conditions both in the described positive structure and in the described negative structure, both as a splint for the bone ingrowth and also because of the chemistry, as a result of which there is a tangible adhesion of the bone cells and thus the bone fibers on the implant is made possible. Histological studies have shown that such ceramic implants with certain surfaces and macro and micro porosity are completely grown through by bones. Particularly positive results can be achieved with ceramic implants made from hydroxyapatite.

Good values for the compressive strengths depending on the porosity of the materials can be achieved with these materials. These materials can also be produced synthetically at reasonable prices. Satisfactory flexural strengths can, however, hardly be achieved with these brittle materials, which creates problems if the implant produced therefrom is subjected to increased bending stress in the bone.

The object of the invention is to provide a device which mechanically protects an implant or transplant and in particular absorbs laterally acting forces, such as bending or shear forces. Another object of the invention is to improve a porous and brittle implant in such a way that satisfactory bending strengths are achieved. These objects are achieved with the features of the claims.

In the solution, the invention is based on the basic idea of at least partially surrounding an implant with a jacket or a sleeve, which absorbs the bending stresses acting on the implant. The jacket protects the implant both when it is introduced into the bone and also in the bone itself when bending stresses act on the implant. This jacket is preferably cylindrical and has an upper and lower open or closed end surface.

The protective device for implants according to the invention is manufactured with a precise fit around the implant, in the simplest case in the form of a cylindrical sleeve around a cylindrical implant.

The modulus of elasticity of the protective device as an overall construction can be adjusted by either perforating it in various ways or by manufacturing it from a corresponding material with suitable elasticity. The perforations can be designed, for example, as round windows with a diameter of approximately 0.8 to 15 mm, preferably approximately 1 to 2.5 mm. The stiffness of the casing and thus also of the entire implant to be inserted into the body can be specifically adjusted for a given casing material by suitable choice of the size, number and arrangement of the windows. There can also be additional insertable or screw-in fillings for the windows, for example made of a resorbable material, in order to enable a further range of variation in the elasticity of the casing. The sheath as mechanical protection, which has to absorb the bending and shear forces on the implant, is preferably made from a high-strength material, for example from plastic, a high-strength ceramic material, a composite material or from metals; particularly stressed titanium is preferred. The modulus of elasticity can be influenced by adjusting the alloy, but also by the overall construction of the jacket, for example in the form of perforated, closed or open cylinders, or slotted cylinders with slots in the transverse, axial or diagonal direction , or a combination of these measures.

The implant itself forms a kind of inlet in the jacket. If the implant consists of a ceramic material in the described positive or negative structure, for example of tricalcium phosphate or hydroxyapatite, but also of another calcium phosphate or calcium carbonate compound, it has very high compressive strength and can therefore exert pressure on the implant take up very well. The jacket surrounding the implant insert makes it possible to permanently protect the brittle inlet against bending and shear stresses. The pressure loads, on the other hand, should be absorbed by the implantletlet itself, because bony growth of the implants preferably takes place where there is mechanical stress on the implant. Since the mechanical stress is identical to the mechanical resistance of the implant, the ceramic implants can only be stressed optimally under pressure. The implant insert preferably projects beyond the jacket or the mechanical protection on its end face, so that compressive forces are absorbed by the implant itself, while the bending forces are absorbed by the jacket of the composite implant consisting of implant and jacket.

In order to be able to absorb the bending stresses even better, the jacket of the implant can have stiffeners, for example in the form of transverse, longitudinal or diagonal stiffeners, it also being possible to combine different types of stiffeners with one another. The stiffeners are preferably in the form of struts on the outer surface of the Coat trained. If the jacket has the shape of a hollow cylinder, the struts can run, for example, along the circumference, in the axial direction or at an angle over the jacket surface.

The mechanical protective device according to the invention can ideally also be used temporarily, namely around brittle implants, e.g. to protect pure ceramic implants in their positive or negative structure, mechanically against bending and shear forces. This temporary mechanical protection can be used as an applicator for brittle implants. The applicator consists of a mechanical protective sleeve or jacket, a lid and a plunger. The applicator is a packaging required according to the GMP standard, in which the implant can be delivered to the clinics in a single or double welded manner. The implant can also be sterilized in this applicator.

In a special embodiment of this applicator, the plunger or stamp has a continuous cannula, so that after removal of the cover by suction through the stamp or plunger, blood and bone marrow can be sucked into the porous implant. In this way, bone ingrowth into the implant can be accelerated.

The protective device for brittle implants according to the invention is very simple to construct and very efficient in its effect on the implant. According to the invention, implants can be produced which, due to the lack of strength, could not previously be produced technically for clinical use, for example implants for connecting two vertebral bodies to one another, as described in the article "Help for the lumbar spine" (newspaper "Die Welt") dated 01/21/94). However, femoral shafts and socket components can also be constructed in a similar way by using hollow shafts or hollow implants or channel-shaped implants with a suitable positive or negative tiv-ceramic implant are connected and thus lead to permanent bony anchoring of the implant in the bone. In particular on the spine, implants can also be temporarily provided with mechanical protection according to the invention. For this purpose, the implant jacket must be constructed in such a way that the cuff around the implant can be removed again after the implant has grown through and the bony connection between two vertebral bodies. If in such a case the implant consists, for example, of a ceramic implant made of highly porous tricalcium phosphate in its negative structure, this can also be absorbed so that a restititio ad integrum with respect to the bone is produced. The cuff can be removed in a simple manner by connecting a cuff ring in the form of a blind with pins or a hinge. This hinge is then opened and the metal sleeve can be pulled out again via a slit opening. However, it is also possible to provide the sheath with an external screw thread or to form a spiral, so that after the implant has been waxed in, it can be removed from the bone again by screwing it out without the Bone bridge between the implant and the surrounding bone is lost. Even if the implant with the jacket remains permanently in the bone, bone can grow in through the perforations which are preferably provided in the jacket of the implant and establish a connection between the implant and the surrounding bone.

In a further embodiment of the invention, the mechanical protection for an at least partially porous implant is produced in that the cavities of the implant are at least partially filled with a reinforcing material in the vicinity of the outer surfaces of the implant; this reinforcing material forms a thin layer in the form of a jacket on the implant surface. There is a composite of implant and reinforcement material in massive Form before. Such reinforcement can be produced both for a porous implant, which consists of a three-dimensional framework made of shell-like structures, and for an implant made of interconnected molded bodies. In the "positive structure" of the three-dimensional framework, the reinforcing material occupies the cavities of the interconnecting pore system, while in the "negative structure" it is in the form of shell-like structures between the molded bodies. The thickness of the layer of the reinforcing material on the surface of the implant preferably corresponds to approximately one to two layers of the shaped bodies in the case of the negative structure or the pores in the case of the positive structure. The layer thickness is between approximately 200 and 3000 μm, preferably between approximately 500 to 2000 μm, particularly preferably between approximately 1000 to 1200 μm.

In this embodiment too, the implantletlet, which has no additional reinforcing material, preferably projects somewhat beyond the outer part, into which the reinforcing material is introduced, in order to ensure that the porous implant itself is pressurized. For this purpose, either a ring of the implant filled with the reinforcing material is milled off or this part is covered during manufacture so that no reinforcing material enters there.

In this embodiment of the invention, an at least partially porous implant is preferably provided first and then a layer is poured out on the surface of the implant with the reinforcing material. This casting is particularly advantageously carried out by centrifugal casting, the implant rotating and the reinforcing material being fed in from the outside, the centrifugal force only penetrating into the surface layer of the porous implant. During manufacture, however, a larger cylinder of the porous implant can first be completely poured out with the reinforcing material, then drilled out and then the bore be filled with a porous implant. Here, the outer diameter of the porous implant preferably corresponds to the inner diameter of the bore, so that the porous implant fits snugly in the outer hollow cylinder filled with the reinforcing material. In this embodiment, the implant itself preferably consists of ceramic, for example tricalcium phosphate or hydroxylapatite. The reinforcing material preferably consists of a high-strength, easily castable metal alloy, for example a CoCrMo cast alloy. Suitable alloys are, for example, Protasul 2, Vitallium and Endocast.

According to the invention, the implant itself, the implant jacket and / or the reinforcement material cast in at the edge of the implant can contain an active ingredient which can be released quickly or in a protracted manner. An antibiotic, a cytostatic or a tissue hormone, such as a growth factor, are used as such an active ingredient.

The advantage of the invention is, in particular, reliable protection of an implant against breakage or shearing and simple and inexpensive assembly.

The invention is explained in more detail below with reference to the drawings. Show it:

1 is a plan view of an embodiment according to the invention,

2 shows a partially sectioned side view of the embodiment according to the invention according to FIG. 1,

3 shows a partially sectioned side view of another embodiment according to the invention with a perforated jacket,

4 shows a further embodiment according to the invention with a plunger,

5 shows the embodiment according to FIG. 4 in an exploded view, 6 and 7 embodiments of the invention with covers firmly connected to the jacket,

8 shows an embodiment according to the invention with a spiral jacket;

FIG. 9 the embodiment according to the invention according to FIG. 7 implanted in a spine, and

10 shows an embodiment according to the invention with a cast outer layer.

1 shows a top view of a porous, cylindrical implant 1, which is surrounded by a jacket 2 according to the invention. The jacket 2 is cylindrical with upper and lower open end surfaces 2a, 2b (only the upper open end surface 2a is visible in FIG. 1). Preferably, the inlet of the implant 1 consists of a material as described in the two German patent applications mentioned. The material preferably consists of interconnected spherical shaped bodies 10 made of e.g. Tricalcium phosphate or hydroxylapatite, in a size of preferably approximately 1000 to 2000 μm, which are surrounded by cavities 12. When the implant is inserted into a bone, bone grows against the ceramic and into the cavity system of the porous implant. A further ingrowth of the bone is also favored by the osteoconductive effect of the ceramic. The disadvantage of the brittleness of such ceramic materials is eliminated by the covering with the cylindrical jacket 2. This jacket 2 can consist of metal, preferably titanium, plastic, a composite material or a resorbable material. But it can also be made by knitting or weaving carbon, glass or textile fibers.

FIG. 2 shows a side view of the embodiment according to the invention according to FIG. 1, the jacket being cut in half. It can be seen that the implant 1 projects beyond the jacket 2 at the upper and lower open ends 2a and 2b, for example around a shaped body layer. To this In this way, better contact is achieved with the bone mass to be waxed in, and pressure can act on the implant. The jacket 2 has a concavely curved structure, which increases its strength, and is press-fit connected to the implant insert.

3 shows the side view of an embodiment according to the invention with perforations of the casing 2, which are designed as round windows 3. The left open side of the jacket shows that the windows 3 allow contact between an external bone mass and the implant, which facilitates the ingrowth of bone into the implant. If the implant e.g. is used as a vertebral body replacement, bone ingrowth occurs through the perforation. In addition, the stiffness of the implant can be adjusted through the size, number and arrangement of the windows. A further possibility for increasing the rigidity are insertable or screw-in window panels made of a suitable material. The diameter of the round window 3 is in the range of 0.8 to 15 mm. The diameter is preferably in the range from 1 to 2.5 mm.

A further possibility for increasing the rigidity of the implant are external stiffeners on the jacket 2. These can be transverse, longitudinal or diagonal stiffeners or combinations of them, e.g. in the form of outer reinforcing ribs.

4 shows a further embodiment according to the invention. In this embodiment, a cover 4, which closes the cover, and a plunger 5 are provided in addition to the casing 2. The arrangement of the casing 2, cover 4 and plunger 5 serves for the sterile transport of the implant. With the plunger 5, the implant 1 can be pressed out of the jacket 2. If, for example, the implant 1 is to be inserted into a bone, it can be completely or partially inserted into a cavity in the bone prepared for this purpose by the plunger 5. be pressed. The dimensions of the cavity preferably correspond to the external dimensions of the implant 1, so that a tight contact is formed between the implant and the bone after the implant has been inserted into the bone. The jacket 2 mechanically protects the implant 1 during insertion into the bone and prevents undesirable bending stresses on the implant.

5 shows an exploded view of the embodiment of FIG. 4 according to the invention. The implant 1 is slidably arranged in the jacket 2. Therefore, a difference between the outer circumference of the implant and the inner circumference of the casing 2 of approximately 0.02 mm is provided in this embodiment. Guide ribs 5a are preferably provided on the plunger in order to guide the plunger when the implant 1 is pressed out and thus avoid tilting and uneven loading of the implant, which could lead to breakage.

Furthermore, the plunger 5, as shown in FIG. 4, or the cover can have at least one cannula 6. When a vacuum is applied to the end of the cannula 6, bone marrow can be sucked into the implant, as a result of which the bone ingrowth is accelerated after the implant has been introduced into the bone.

In contrast to guiding the implant 1 with tolerances in a jacket 2 with a plunger 5 (applicator) for temporarily protecting the implant, there is preferably a coherent contact between the implant 1 and the jacket 2 when the implant 1 together with the jacket in the bones is introduced.

The jacket of the device according to the invention preferably consists of titanium if it remains in the body. If the jacket is part of an applicator, it is preferably made of plastic. The invention Applicator makes it possible to use brittle materials, such as ceramics, which are particularly well tolerated by bones, without fear of breakage or shearing.

FIGS. 6 and 7 show embodiments according to the invention in which one or two covers 6 are firmly connected to the casing 2 on the upper and lower end faces. The cover 6 according to FIG. 7 has a recess for an Allen screw for screwing into the bone. In these embodiments, the jacket 2 also only partially surrounds the peripheral surface of the implant 1 and is preferably web-shaped or spiral-shaped. The implant, e.g. made of ceramic, is inserted into the jacket with a precise fit and is implanted together with the jacket.

FIG. 8 shows an embodiment in which the casing 2 is of spiral shape. Such an embodiment allows the sheath 2 to be removed again after the implant has been inserted, in that it can be subsequently screwed out of the bone like a bone screw, even when the ceramic has grown through the bone. In this embodiment, the jacket 2 can either be applied to the outside of the implant 1, or it can be inserted into corresponding spiral millings in the implant 1, so that the peripheral surfaces of the implant 1 and the jacket 2 are approximately flush.

A preferred use of the covered implant according to the invention in a cervical spine is shown in FIG. 9. The implant 1 is surrounded with a jacket 2 with firmly connected lids. The vertebrae are firmly connected to one another by ingrowth of bone mass from the two adjacent vertebrae into the implant.

The embodiment according to FIG. 10 shows an implant 1 'with a framework 12 made of shell-like structures (shown hatched in FIG. 10), between which approximately spherical is formed (shown in white in FIG. 10) which form an interconnecting pore system. Such an implant is also referred to as a "positive implant". The implant 1 'according to FIG. 10 is cylindrical, a part of the cylinder being cut out in FIG. 10 for clarification. On the peripheral surface of the cylinder, the pores are filled with a reinforcing material 16, which is shown in black in FIG. 10. The reinforcing material forms a jacket-shaped reinforcing layer on the outer surface of the implant 1 ', which is solid there. The framework 12 is preferably made of ceramic, such as hydroxylapatite or tricalcium phosphate, and the reinforcing material 16 is a metal, preferably a CoCrMo cast alloy. The implant l ¹ of FIG 10 is preferred wise manufactured by centrifugal casting, wherein the metal 16 is cast from outside onto the rotating implant. Due to the centrifugal force that occurs, the metal 16 only penetrates into the outer jacket layer into the cavities 14. The thickness of the layer into which the metal 16 enters for reinforcement is preferably about 1 to 1.5 times the diameter of the cavities, ie preferably about 1000 to 1200 μm. The implant 1 'according to FIG. 10 has a high flexural strength due to the reinforcing material 16. In addition, for rapid bone ingrowth, it is advantageous that a large contact area is formed between the bone and the ceramic of the framework 12 both on the end faces and on the lateral surface of the implant 1 '.

Claims

Patent claims

1. Mechanical protection device for an implant (1), which has a jacket (2) which at least partially surrounds the implant (1).

2. Device according to claim 1, wherein the jacket is designed such that it protects the implant (1) when it is inserted into and / or remains in a living body, preferably bone.

3. Device according to claim 1 or 2, wherein the shape of the jacket (2) is adapted to the shape of the implant (1) in such a way that the jacket (2) at least partially coherently surrounds the implant.

4. Device according to one of claims 1 to 3, wherein the implant (1) essentially has the shape of a full cylinder and the jacket (2) has essentially the shape of a hollow cylinder, the inside diameter of which corresponds approximately to the outside diameter of the implant.

5. Device according to one of claims 1 to 4, wherein the jacket (2) has at least one open end and the implant (1) projects beyond the jacket (2) at at least one of the open ends (2a, 2b).

6. Device according to one of claims 1 to 4, wherein the jacket (2) is closed at one or both of its ends (2a, 2b) with a cover (4).

7. The device according to claim 6, wherein the lid (4) has at least one cannula.

8. Device according to one of claims 1 to 7, wherein the jacket (2) is perforated.

9. The device according to claim 8, wherein the perforations are windows (3).

10. The device according to claim 9, wherein the number and arrangement of the windows (3) is selected such that the rigidity of the implant (1) surrounded by the jacket (2) is specifically adjustable.

11. The apparatus of claim 9 or 10, wherein the windows

(3) are round and have a diameter of approximately 0.8 to 15 mm.

12. The apparatus of claim 11, wherein the windows (3) have a diameter of 1 to 2.5 mm.

13. Device according to one of claims 9 to 12, wherein the windows (3) have screw-in window panels.

14. Device according to one of claims 1 to 13, wherein the jacket (2) has stiffeners.

15. The apparatus of claim 14, wherein the stiffeners are transverse, longitudinal and / or diagonal stiffeners.

16. The apparatus of claim 14 or 15, wherein the stiffeners are outer struts which are arranged on the jacket (2) circular, in the longitudinal direction and / or obliquely.

17. The device according to one of claims 2 to 16, wherein the jacket (2) and / or the implant are designed such that the jacket (2) can be screwed into the body together with the implant (1).

18. The apparatus according to claim 17, wherein threaded means are provided for screwing in,

19. The device according to one of claims 2 to 18, wherein the jacket (2) is designed in such a way that it can be removed from the body again after being inserted together with the implant (1) into the body.

20. The apparatus of claim 19, wherein the jacket (2) can be unscrewed from the body.

21. Device according to one of claims 1 to 20, wherein the jacket (2) is designed to be removable.

22. The apparatus of claim 21, wherein the jacket has elements which are connected in the form of a blind with pins or with a hinge.

23. The device according to one of claims 1 to 22, which further comprises a plunger (5) with which the implant (1) can be pressed out of the jacket.

24. The device according to claim 23, wherein the plunger (5) has at least one continuous cannula (6).

25. The method of claim 23 or 24, wherein the implant

(1) by the jacket, the lid (4) and the plunger (5) is closed sterilizable.

26. Mechanical protective device for an implant, the implant being at least partially porous and the cavities of the implant being at least partially filled with a reinforcing material.

27. Device according to claim 26, wherein the cavities of the implant are filled in a layer on the surface of the implant, so that the implant has a jacket made of the reinforcing material.

28. The apparatus of claim 26 or 27, wherein the cavities are filled by pouring.

29. Device according to one of claims 1 to 28, wherein the jacket (2) or the reinforcing material as a positive or negative structure made of metal, spongiosa metal, plastic, a composite material or a resorbable material.

30. The device according to claim 29, wherein the jacket or the reinforcing material consists of titanium.

31. The device according to claim 29, wherein the jacket or the reinforcing material consists of a high-strength and easily castable metal or a metal alloy.

32. The apparatus of claim 31, wherein the high-strength and easily castable metal alloy is a CoCrMo casting alloy.

33. Device according to one of claims 1 to 28, wherein the jacket (2) consists of carbon, glass or textile fibers.

34. Device according to one of claims 1 to 33, wherein the implant consists of ceramic.

35. Apparatus according to claim 34, wherein a tri-calcium phosphate or hydroxylapatite or another calcium phosphate or calcium carbonate compound is used as the ceramic.

36. Device according to one of claims 1 to 35, wherein the implant has a three-dimensional framework of shell-like structures and an interconnecting pore system.

37. Device according to one of claims 1 to 35, wherein the implant has a conglomerate of interconnected moldings.

38. Device according to one of claims 1 to 37, wherein the implant, the jacket and / or the reinforcing material contain an active ingredient that can be released quickly and / or protracted.

39. The apparatus of claim 38, wherein the active ingredient is an antibiotic, a cytostatic, a tissue hormone or a growth factor. *

40. Implant with a mechanical protective device according to one of claims 1 to 39.

41. A method for producing an implant according to claim 40, comprising the following steps:

Providing an at least partially porous implant and

Pour a layer on the surface of the implant with a reinforcing material.

42. The method according to claim 41, wherein the pouring takes place by centrifugal casting and the reinforcing material only penetrates into the surface layer of the porous implant due to the centrifugal force and forms a jacket.

43. The method of claim 42, wherein the thickness of the jacket is about 500 to 2000 microns, preferably about 1000 to 1200 microns.

44. Use of the implant according to claim 40 as bone replacement or for stabilizing bones.

45. Use of the implant according to claim 40 for connecting two vertebrae.