SE457692B - IMPLANT PROTECTION PROVIDES WHOLE OR PARTIAL REPLACEMENT OF A SENA, A LIQUOR OR A CROSS BAND - Google Patents

Description

'457 692 10 15 20 25 30 35 2 U.S. Patent 3' +63,158 discloses the use of polyglycolic acid composites and non-absorbable fibrous materials as implants for tissue repair or replacement, the composites being designed so that the new tissue will be surround the non-absorbable fibrous material.

However, no completely successful results with these types of prostheses have been reported so far. Carbon fiber structures have also been tested as a replacement for damaged tendon or ligament tissue. However, it has been found that over time the carbon fiber structure is mechanically degraded and that the carbon fiber fragments then tend to migrate out into the body from the surgical site. To overcome this problem, U.S. Patent 4,411,027 proposes encapsulating the carbon fiber structure with a layer of a bioabsorbable polymer in order to both protect the structure from external mechanical influences and to keep the fragments in place at least in the early healing stage. However, it has been shown that carbon fiber fragments from the prosthesis still migrate out into the body.

U.S. Patents 3,297,033, 3636,595 and 3982513 propose only purely general use of tubular structures of bioabsorbable polymers in the form of polyglycolic acid, lactide polymers resp. copolymers of lactic acid and glycolic acid for the repair of various body parts, including tendons, without further description of the proposed applications.

The present invention aims to provide an improved prosthetic element which can completely or partially replace a tendon, a ligament or a cruciate ligament and which lacks the above-mentioned disadvantages of the hitherto known prostheses. The new prosthetic element should thus stabilize the tendon, ligament or cruciate ligament throughout the healing process. Furthermore, the structure of the prosthetic element should be such that it controls the build-up of collagen in the new tissue to mimic as much as possible the original tissue that it is to replace. In the case of ligaments and cruciate ligaments, bones must also be able to grow into the new structure. Finally, the prosthesis material as a whole must be able to disappear from the body without residue. These objects, as well as other objects and advantages, are achieved by a prosthetic device having the features set forth in the appended claims and explained in more detail below.

According to a basic idea of the invention, the prosthesis element consists entirely of bioresorbable material (the meaning of which will be explained later) and also has a special structure which must be able to provide the required strength (especially important at cruciate ligaments) and promote and control the growth of new tissue in suitable focus.

This structure is characterized in its broadest aspect by the fact that it has longitudinal grooves or channels intended to serve as initial growth guides for new fibrous tissue. The expressions trace resp. channels are here to be understood in a broad sense and the structure may, in order to fulfill the objects of the invention, be arranged in a large number of different ways, as will appear from the following.

Thus, in one embodiment, it can simply consist of a single, or possibly several, elongate elements, which are each provided with several longitudinal grooves or channels. These grooves or channels can in this case be arranged on the outside of the element or also extend inside the element, possibly in combination. As an example, in the former case the prosthesis element can be designed directly during manufacture with the required grooves, e.g. by spraying, but it can also consist of an initially sheet-shaped piece of material which has been folded into a suitable configuration. An example of such a prosthetic element with internal channels or cavities is a sheet rolled into a helical cross-section.

According to another embodiment, the prosthetic element structure according to the invention is built up of a plurality of elongate elements, which delimit longitudinal channels or cavities between them. Preferably, these elongate elements are arranged to be able to be substantially individually load-bearing during the application of the prosthesis. For example, they may consist of threads or fibers, the assembly thereof being straight or also braided, twisted or rotated. They can also consist of a plurality of parallel lamella, leaf or band-shaped elements.

Another alternative is a plurality of concentrically arranged cylinders or tubes. The individual elements can in these cases be whole, possibly perforated pieces of material, but can e.g. may also consist of nets or be knitted, woven or braided structures, etc. A pleated structure can also be covered by this embodiment, whereby e.g. in the case of a fabric, the load-bearing elements correspond to the warp threads.

As indicated above, the design and dimensions of said grooves or channels of the prosthesis element structure can vary considerably, but in order for the desired penetration of cells to take place in Lex. internal ducts or cavities, these should have a minimum cross-sectional dimension of about 10 μm.

The resorption time of the prosthetic element structure according to the invention must be long enough to be able to constitute a stabilizing replacement, until the new tissue has been regenerated sufficiently to be able to absorb loads itself.

This time of course depends on the type and extent of tissue to be replaced but can generally be said to be about six months to about two years.

In the same way, the strength requirements vary according to the tissue to be replaced, so the strength requirements are, for example, relatively high at a cruciate ligament, while they can of course be relatively low for, for example, a finger tendon.

With regard to the cross-sectional dimensions of the prosthesis element itself, for example, about one to two millimeters can be mentioned for smaller tendons up to two centimeters 457 692 10 l5 20 25 30 35 4 (Achilles tendon), and e.g. for cruciate ligaments about 4-5 millimeters.

In use, the prosthetic elements according to the invention will function as a load-bearing replacement for the tendon, ligament or cruciate ligament they are to replace, so that loading of the body part in question can take place immediately after the surgical procedure. Such immediate loading has been shown to accelerate the healing process and have a beneficial effect on cell differentiation. As the new tissue grows, the prosthetic material is slowly broken down and resorbed in the body, whereby the new tissue gradually takes over the load absorption. The special structure according to the invention has thereby been found to function as an effective climbing frame for the new fabric while successively aligning it along the elongate elements, so that the finally formed new fabric will at least to a very large extent resemble the original fabric.

In an advantageous design of the prosthesis structure, the different individual elements have two or more different resorption times, which can for instance easily be achieved by varying the thickness of the elements and / or by the choice of material.

The individual elements of the prosthesis structure may consist of a single material, but in order to achieve the desired resorbability and strength of the prosthesis as a whole, it may be necessary to use a combination of different materials. For example, each individual element may have a core of high strength but relatively rapidly resorbable material and an outer shell of low strength material but with a longer resorption time.

According to a preferred embodiment of the invention, the prosthetic element structure is surrounded by a porous outer casing of bioresorbable material, partly in order to be able to coalesce the inner structure if necessary but above all to reduce the supply of body fluids to the inner structure and thus suitably delay the chemical attack on it to prolong the resorption time. Furthermore, the outer casing will advantageously serve as a climbing frame for blood vessels and from the outside penetrating fibroblasts.

However, the porosity of the outer layer should be sufficient to allow penetration of blood cells and veins and is suitably such that at least half of the pores are in the range between about 10 and about 200 μm, but they are preferably not larger than 150 μm.

The outer layer, which is essentially not load-bearing, can consist of a separate casing structure, e.g. mesh-shaped, but may also be a layer coated or coated on the inner structure in an appropriate manner.

As a suitable resorption time on the outer layer, mention may be made of about 3 to about 12 weeks, which, depending on the choice of material, usually gives a layer of the order of 0.1 to 0.5 mm.

The external shape of the prosthesis element is not per se critical and is adapted to the structure to be replaced.

The term "bioresorbable material" as used herein means substantially water-insoluble, non-toxic, tissue-friendly materials which can be degraded and completely resorbed in the body without giving rise to scar tissue or toxic degradation products.

Suitable bioresorbable materials for the purposes of the present invention can be readily selected by those skilled in the art, e.g. among those that are either commercially available or have been described in the literature or will be available in the future. Examples of such bioresorbable materials are polymers based on polyglycolic acid (PGA), copolymers of glycolic acid and lactic acid, copolymers of lactic acid and ε-aminocaproic acid, and various lactide polymers. PGA esters are available e.g. described in U.S. Patent 3,463,658, while copolymers between glycolic acid and lactic acid are described e.g. in U.S. Patent 3,982,543. Homo- and copolymers of lactic acid are described e.g. in U.S. Patent 3,636,956. Examples of now commercially available materials are Vicry (a copolymer of 90% glycolic acid and 1096 lactic acid sold by Ethicon, Sommerville, NY, USA - also known as Polyglactin) and Dexon (Davies d: Geck, Pearl River, NY, USA). Further examples are polydesoxazone (PDS) (Ethicon, USA), polyhydroxybutyric acid (PHB), copolymers of hydroxybutyric acid and hydroxyvaleric acid (P1-IB-PHV), polyesters of succinic acid, and crosslinked hyaluronic acid. As indicated above, mixtures of the above-mentioned materials can of course also be considered. Those skilled in the art should readily be able to modify such bioresorbable materials according to the current needs, e.g. in terms of porosity, resorption time, strength, etc.

Optionally, growth factors may be incorporated into the prosthesis structure, either deposited in the indicated cavities or also incorporated into the resorbable material for slow release of growth factor. In the following, the invention will be described in more detail with reference to a special embodiment of the invention for replacing a cruciate ligament, reference being made to the accompanying drawings, in which: Fig. 1 is a schematic perspective view of an embodiment of a prosthetic element according to the invention Fig. 2 schematically shows application as a cruciate ligament replacement of three prosthetic elements according to Fig. 1 in a knee joint, and Figs. 3 to 10 show schematic cross-sections of alternative embodiments of the prosthetic element according to the invention.

The prosthetic element of Fig. 1, generally designated by the reference numeral 457 692 10 15 20 25 30 35 6 1, comprises an internal structure in the form of a plurality of threads 2 of suitable bioresorbable material or material combination, which are twisted into a multifilament strand of desired thickness and provided with in the case shown net-shaped outer casing or cover 3 of suitable bioresorbable material.

By way of example, the wires 2 may be composites consisting of a core and an outer layer of PHB, which are bundled and twisted and then provided with a coating of PHB and PHV. The cover can e.g. applied by dipping the twisted filament bundle first in a solution of PHB and PHV in dimethylacetamide (DMA), and then in water. A suitable porous outer layer of PHB - PHV is then deposited on the twisted structure.

The prosthetic element 1 is in the illustrated case intended to be used as a cruciate ligament replacement, in which case three such elements are used, but the structure as such can generally be used for all kinds of tendons and ligaments.

Vicry For the cruciate ligament application, in the lower end of the prosthesis element 1, the wires 2 and the outer casing 3 are attached to an end sleeve 11 threaded on the outside, in which each wire 2 is individually fixed. A lower fixing sleeve 5 threaded on the inside with an end flange 6 is arranged to be able to be screwed onto the end sleeve 1i. An upper fixing sleeve 7 is slidably arranged on the prosthesis element 1 and has an end flange 8 provided with inwardly pointed points or tags 9. The end sleeve 11 as well as the fixing sleeves 5, 7 can be made of bioresorbable material or of suitable non-absorbable tissue-friendly material, such as titanium. A guidewire 10 extends from the lower end of the prosthesis element.

Fig. 2 shows schematically the application of three prosthetic or cruciate ligament elements in the knee joint which are provided with suitably arranged bores 11 in the two joint portions 12, 13.

The arrangement of the cruciate ligament elements 1 shown in the figure is intended to be isometric, i.e. that the cruciate ligament elements 1 on the basis of the known movement patterns of the joint are placed with their fiber or wire directions so that loads are absorbed and the joint is stabilized in three different main directions during the joint movement.

When applying the cruciate ligament prosthesis in Fig. 2, each cruciate ligament 1 is inserted into its respective bore 11 by means of the guide wire 10. The length of the cruciate ligament is then adjusted with the upper fixing sleeve 7, which is then fixed on the cruciate ligament, e.g. by clamping, and at the same time in the bore opening via the projections 9. The application is completed by screwing the inner fixing sleeve 5 onto the end sleeve 4 while simultaneously adjusting the tension in the cruciate ligament.

Almost immediately after the surgery, the cruciate ligament prosthesis shown is ready to absorb loads. New ligament tissue grows into the spaces between the threads 2 and has an advantageous gradual orientation in the longitudinal direction.

At the same time, the prosthesis material will be slowly subjected to hydrolysis and / or enzymatic degradation, which at least in the initial period of the healing process is suitably delayed by the outer structure 3, which also serves as a climbing frame for e.g. blood vessels. The ability to load the knee joint from the beginning contributes to an efficient regeneration of the ligament tissue, as the natural movements promote the differentiation of the new cells. As the prosthesis material is resorbed, a gradual regeneration of the ligament tissue takes place to eventually result in a collagen-rich tissue oriented in parallel bundles and very similar to a normal cruciate ligament.

Of the examples schematically illustrated in Figs. 3-10 of various alternative embodiments of the prosthetic element according to the invention, Figs. 3 and 4 refer to prosthetic elements, which, like that in Fig. 1, are built up of a plurality of sub-elements, while Figs. 10 shows those based on a single element.

The prosthetic element structure in Fig. 3 consists of a schematically illustrated assembly of a plurality of concentrically arranged tube or cylinder elements 11: of bioresorbable material, the outermost tube element 11a-a being surrounded by or coated with an outer casing or layer 15, also of bioresorbable material .

The elements lll delimit annular, in the figure greatly exaggerated channels or cavities 16 between them, whereby in practice the elements lll can abut against each other and still leave the required spaces. In the embodiment according to Fig. 4, the inner structure consists of a plurality of slats or strips 17 of bioresorbable material held together by an outer casing or layer 18 of bioresorbable material. The bands 17 define channel-shaped passages or cavities 19 in the figure which are greatly exaggerated in the figure. Here, too, in practice, the bands 17 can abut against each other.

The embodiments according to Figs. 5-8 all consist of a solid elongate element 20, which is formed into different configurations having external grooves or channels 21, which are to serve as growth guides for the new tissue.

In the embodiments according to Figs. 9 and 10, the prosthesis element is formed of a film or foil 22, which in Fig. 9 is folded and in Fig. 10 rolled. Growth conductive grooves or channels 23 are formed in Fig. 9 by the folds, while those in Fig. 10 are formed between adjacent rolling turns.

The prosthetic elements of Figs. 5-10 may, like the embodiments of Figs. 1-1; provided with a cover (not shown) or coating of porous bioresorbable material.

An animal experiment is described below, in which a cruciate ligament prosthesis according to Figs. 1 and 2 has been applied to sheep. In Example A cruciate ligament prosthesis according to Fig. 1 was made of bundles of P1-IB-P1-IV-457 692 10 15 20 25 8 coated VicryQ wire, which was twisted into strands of about 3 mm thickness and provided with a cohesive knitted sock of Vicryl ®. I de. the individual threads have the Vicry material high strength with relatively fast resorption, which is balanced by the outer layer of P1-lß -PHV with long resorption but lower strength.

In 10 adult sheep, anesthetized with sodium pentothal, oxygen / nitrous oxide and Fluothane, the anterior cruciate ligament was recessed. Two or three cruciate ligament prostheses described above were inserted either isometrically via drill channels or anti-isometrically. The latter attachment was made to ascertain the sensitivity of the method in case of incorrect attachment. After the reconstruction, all knees were stable. Four months later, half of the animals were killed and after another two months, the rest of the animals were killed. Macroscopic photo-documentation was performed, after which the preparations were filtered in Wó-ig formalin. The bone attachment was sawn off, after which the bone substance was decalcified and the cruciate ligaments were cut for microscopic analysis. A regenerated was taken for strength test.

As a result, all cruciate ligaments showed good regeneration. There was no difference between isometrically implanted and antiisometric implanted cruciate ligament prostheses. However, varying degrees of osteoarthritis were found in antiisometric implantation.

The microscopic analysis showed excellent regeneration of collagen-rich tissue oriented in parallel bundles and very similar to the image of a normal cruciate ligament. The invention is of course not limited to the embodiments specifically described above and shown in the drawings, but many variations and modifications are possible within the scope. for the basic idea of the invention and the subsequent claims.

Claims (11)

1. Implantable prosthesis for implanting a tendon, a ligament or a cruciate ligament in whole or in part, characterized by a structure (1) of a substantially water-insoluble, non- toxic, tissue-friendly bioresorbable material selected from polymers based on polyglycolic acid, copolymers of glycolic acid and lactic acid, copolymers of lactic acid and α-aminocaproic acid, lactide polymers, homopolymers of lactic acid, polydesoxazone, polyhydroxamic acid butyric acid hydrochloric acid hydrochloric acid and combinations thereof, wherein the structure (1) has longitudinal grooves or channels H6; 19; 21; 23) intended to serve as initial growth leaders for new fibrous tissue. 2. A prosthesis according to claim 1, characterized in that the structure comprises a plurality of elongate elements (2; lll; 17), which delimit at least a part of said grooves or channels (16; 19). 3. A prosthesis according to claim 1, characterized in that the structure comprises one or more elongate elements (20; '22), each of which is provided with said grooves or channels (21; 23). 'll. A prosthesis according to any one of claims 1 to 3, characterized in that the structure comprises a porous outer casing or layer (3; 15; 18) with sufficient porosity to allow penetration of blood cells. A prosthesis according to any one of claims 2-11, characterized in that said elongate elements (2; 11ll; 17) are arranged to be able to be substantially individually load-bearing. Protea according to any one of claims 2, 11 and 5, characterized in that the elongate elements are filaments or threads (2), which are optionally twisted or braided into a thread or filament strand. A prosthesis according to any one of claims 2, 1: 5 and 5, characterized in that the elongate elements are substantially parallel blades or bands (17) or concentrically arranged tubular elements (III). Prosthesis according to one of Claims 2 to 7, characterized in that at least some of the individual elongate elements (2; 11 +; 17) have different resorption times with one another. A prosthesis according to any one of claims 2-8, characterized in that the outer sheath or sheath O; 15; 18) has a shorter resorption time than the internal structure (2; 14; 17). A prosthesis according to any one of claims 2-9, characterized in that said elongate elements (2; 14; 17; 20; 22) comprise a core with a shorter resorption time and an outer layer with a longer resorption time, or vice versa. Prosthesis according to any one of claims 1-10, characterized in that the bioresorbable material is selected from polyhydroxybutyric acid, copolymers of hydroxybutyric acid and hydroxyvaleranoic acid, homopolymers of lactic acid, and combinations thereof.