DE9000094U1 - Intervertebral disc endoprosthesis - Google Patents

Description

MECRON 02. January 19 90

nsedizinische Produkte GmbH
&Oacgr;-1000 Berlin
MS39.G17

Endoprosthesis of the intervertebral disc

Description

The invention relates to an endoprosthesis of the type specified in the preamble of claim 1.

From DE-Al-35 29 761 (Figures 11 to 14) a durable intervertebral disc prosthesis is known, in which a cylindrical intermediate element with concavely shaped

ME39.G17 Sheet 2

Front surfaces are supported between appropriately shaped convex surfaces of two non-integrated Dc-plates that are adjacent to adjacent vertebral bodies. This Banci disc replacement allows the vertebrae to rotate mutually around a central axis. The other movement options are limited because the intermediate element is limited by the flanged cover surfaces or by the vertebral bodies themselves during any other movement, i.e. parallel displacement or inclination.

Another disadvantage is that the distance between the two vertebral bodies is also rigidly fixed and therefore the conditions differ greatly from the natural physiological conditions.

As a result, the force is introduced into the vertebral bodies very unevenly, so that the bearing surfaces between the intermediate element and the cover plates are exposed to strong local mechanical stress. This can cause material particles to detach, which can be dangerous for the patient and reduce the service life of the endoprosthesis. The possible local one-sided stress promotes bone loss.

In another embodiment described in the aforementioned document (Figures 1 to 3) ^, the intermediate element is convex, whereas the outer cover plates have concave counter surfaces.

Here too, it is not possible for the cover surfaces to give way in the axial direction. In addition, no movement in the direction of a parallel displacement of the cover surfaces is possible.

MF-: 3 9 . f J1 7 üliil.t

Furthermore, an endoprosthesis of the intervertebral disc is known from the German utility model G 88 07 485.4, which is filled with elastic material and provided with frontal cover plates, whereby a circular or elliptical corrugated tube is provided surrounding the viscoelastic material, which is closed off by cover plates.

The disadvantage of this prosthesis is that all A's
equal movements must be absorbed exclusively by the corrugated pipe.

The invention is based on the object of specifying an endoprosthesis of the type mentioned at the beginning with improved mobility and increased load-bearing capacity, while at the same time preventing material particles from becoming detached under frequent alternating loads.

This object is achieved with the characterizing features of claim 1.

A particularly advantageous feature of this endoprosthesis is the large range of motion of the viscoelastic intermediate element with both ball joints and the resulting necessary flexibility in the face of bending, torsion, shear and pressure stresses. This avoids stresses caused by opposing transverse forces acting on adjacent vertebral bodies, which could lead to the elastic intermediate element of the endoprosthesis breaking. It also reliably prevents material particles from becoming detached and wandering around the patient's body as a result of surfaces rubbing against one another.

ME39. GI 7 BIaLt; &Lgr;

The invention is based on the knowledge that only by combining an elastic intermediate element with an articulated mounting of its concavely shaped ends, which interact with corresponding convex counterparts on the end plates (V) , can maximum mobility be achieved, which allows minimal wear and maximum durability under all loads that occur. This type of mounting also enables, for example (in contrast to a mounting with ^concave ends of the intermediate element), a displacement of the two cover plates on a parallel path relative to one another. Compressive forces are absorbed by the elastic intermediate element.

The casing area of the intermediate element is subject to a particular load, which is absorbed by deformation. In the endoprosthesis according to the invention, the flexible casing area of the intermediate element is not reduced by components of the two front ball joints, so that sufficient space is available for the casing of the intermediate element. The casing of the interior, which consists of viscoelastic plastic, is designed as a corrugated tube. Because the corrugated tube can take up its full height, it has a large range of elasticity and can therefore follow all conceivable movements.

The inclination of the elastic intermediate element enables the cover plates connected to the bones to move transversely relative to each other in a favourable manner. The sliding surfaces of the ball socket-like formations

ME39 . ,17 Sheet 5

The ends of the intermediate element are preferably covered with a friction-reducing plastic layer, in particular made of (high molecular weight) polyethylene.

According to an advantageous development of the invention, the cover plates are pot-shaped, with the opening areas facing each other. This creates stops or limits against transverse movements of the elastic intermediate element in the event of lateral displacement or compression, so that overloading of the intermediate element, and in particular of the corrugated pipe surrounding a viscoelastic filling, is reliably avoided.

The two cup-shaped cover plates of the vertebral body are initially braced against each other using wires welded to the cover plates, which on the one hand stabilizes the configuration for transport and storage and on the other hand facilitates the implantation process. The tension wires can be easily cut and removed after implantation.

In another advantageous development, the spherical cap-like formation consists of a complete sphere, which in turn is mounted in a further convex formation of the cover plate.

Advantageous further developments of the invention are characterized in the dependent claims or are presented in more detail below together with the description of the preferred embodiment of the invention with reference to a figure.

ME39.C17 Sheet (&igr;

The figure shows a sectional view of a design of the endoprosthesis according to the invention with the transverse displacement of the cover plate indicated by a dot-dash line.

The intervertebral disc endoprosthesis shown in the figure consists essentially of two cover plates 1 and 2 connected to adjacent vertebral bones, an elastic intermediate element 3 and two ball-joint-like bearings 4 and 5 arranged between the cover plates 1, 2 and the intermediate element 3. The bearings 4 and 5 each have a (convex) element connected to the cover plate 1 or 2 and formed as a ball cap 6 or 7, respectively, and a (concave) element connected to the intermediate element 3 and formed as a ball socket 8 or 9, respectively. The ball socket and ball cap can be rotated against each other and can also be tilted towards each other. The joint connections enable both an inclination of the cover plates relative to each other - corresponding to a bending movement - and a parallel sliding movement of the cover plates.

2ü Leu uuLör SchiöföLölluny of the intermediate school opening.

The intermediate element 3 is designed as a metal corrugated tube 10 which is filled with viscoelastic material. The casing consists of corrugated metal sheet. The ^{biocompatible} metal in the endoprosthesis is either titanium or stainless steel.

It is evident that the off-axis shell area 11 of the intermediate element is formed by the two front-side ball

3C pans 8 and 9 are not shortened or reduced in size. The jacket 10 has a maximum length available. The

ME39.G17 Sheet 7

The mobility of components 1 and 2, 3 and 4 and 5 of the endoprosthesis therefore corresponds as far as possible to the mobility of a natural intervertebral disc. Even extreme movements of the vertebral bones and thus of the cover plates 1 and 2 against each other are possible without risk of breakage and without particle abrasion. The dash-dotted contour 1' illustrates such a movement corresponding to a lateral parallel displacement. The cover plate 1 is displaced laterally up to position l ¹ , whereby any height displacement can be compensated by the viscoelastically filled intermediate element 3. In order to follow this movement, the ball socket 8 connected to the intermediate element 3 slides on the ball cap 6 in the opposite direction. At the same time, the ball socket 9 slides on the ball cap 7 of the cover plate 2 in the direction of displacement of the cover plate 1. Due to these sliding movements in opposite directions, the intermediate element 3 assumes an inclination 3' to the starting position, indicated by a straight line 3' inclined to the vertical direction.

The sliding surfaces 12 and 13 of the ball sockets 8 and 9 are coated with a thin sliding layer of high molecular weight polyethylene to reduce friction, which is mechanically fixed to a grooved surface.

The two cover plates 1 and 2 have pot-shaped outer contours, where the opening areas are opposite each other and are provided with ring-shaped edge projections 14 and 15. Due to the pot-shaped cover plates 1 and 2

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In the event of extreme compression, excessive compression of the intermediate element 3 is avoided. Maximum compression is reached when the edges of the pot-shaped cover plates 1 and 2 abut against one another. The opening width is selected so that in the event of transverse movements (dash-dotted line), a lateral guide stop is formed for the corrugated pipe 10 of the intermediate element 3, so that the lateral deflection is prevented and additional stabilization is thus provided.

The re-formations 14 and 15 also serve to attach tension wires 16 and 17, shown in dashed lines, which prevent the elements of the disc from falling apart during transport, ensure precise alignment during implantation and are removed by pinching them off after implantation.

All elements of the intervertebral disc shown, with the exception of the viscoelastic filling of the intermediate element 3, are made of a biocompatible metal alloy. The outer cover surfaces 18 and 19 of the cover plates 2 and 3 are provided with a porous surface or surface coating so that adjacent spongy bone tissue can grow on. To do this, the adjacent vertebrae are milled in such a way that the spongiosa is exposed and adapted to the respective cover plate.

The solution according to the invention ensures that both a lateral displacement and a rotation of the cover plates against each other in relation to all wheel axes can take place with little friction.

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This allows for flexibility when compressed. Furthermore, the movements are limited by fixed stops in such a way that additional stresses are prevented. Furthermore, the casing, which is designed as a corrugated pipe, has a space available outside the area of the convex formations of the cover plates and within the pot-like edge formations, which can be filled by the intermediate element and preferably by the edge areas of the ^intermediate element. This means that the elastic properties can be optimized essentially without any restrictions. In this case, an annular pre-forming space 21 is provided between the ball-capped space 6, 7 and the inner edge of the edge formations 14, 15, into which the edge 22 of the intermediate element 3 can extend during their relative movement, as can be seen from the drawing.

f In the case of a further - not shown in the drawing

- version, the spherical cap-like formation consists of a complete sphere, which in turn is mounted in a further convex formation of the cover plate. In this way, with corresponding advantages,

>■ simplified manufacturability from common components

The convex shapes are each adapted to the ball diameter.

The metal parts of the prosthesis according to the invention are, in preferred embodiments, made either from titanium or steel in the form of biocompatible alloys.

ME39.G17 Sheet

The invention is not limited in its implementation to the preferred embodiment given above. In this context, many variants are conceivable which make use of the solution presented even in fundamentally different embodiments.

Claims (9)

MK S9 .Gl 7 UJ.at Λ η s �r �Pgr; C h P- 1. Endoprosthesis of the cervical vertebral disc with an intermediate element , the front surfaces of which are each connected by means of a spherical-concave - and thus ball-socket-like - formation between two corresponding spherical-convex - and thus ball-cap-like - formations on the inside of two cover plates is rotatably mounted,
10 characterized, that the intermediate element (3) is designed as an elastic element with viscoelastic properties. 2. Endoprosthesis according to claim 1, characterized in that the spherical cap-like formation (6, 7) is higher than the spherical cap-like formation (8, 9). 3. Endoprosthesis according to one of the preceding claims, characterized in that the sliding surfaces (12 and 13) of the ball socket-like formations (8 and 9) and/or the ball cap-like formations (6 and 7) have a friction-reducing plastic layer. 4. Endoprosthesis according to claim 3, characterized in that the friction-reducing plastic layer consists of high molecular weight polyethylene. .CJ17 Sheet .1.2 5. Endoprosthesis according to one of the preceding claims, characterized in that the cover plates (1 and 2) are formed in a topi-like manner by means of edge formations (J ⁴ , 15), the edge formations facing each other. 6. Endurothesis according to claim 5, characterized in that the shaped portions (14 and 15) are secured in a mutually fixed position by means of welded wires (16, 17). 7. Endoprosthesis according to one of the preceding claims, characterized in that the intermediate element (3) is filled with viscoelastic material which is surrounded between the end faces by an elastic corrugated tube (10). 8. Endoprosthesis according to one of the preceding claims, characterized in that between the spherical cap-like formation (6, 7) and the inner edge of the edge formations (14, 15) an annular free space (20, 21) is provided, into which the edge (22) of the intermediate element (3) can extend during their relative movement. 0 9. Endoprosthesis according to one of the preceding claims, characterized in that the ku- ME3 9.UL7 Sheet IJ gel cap-like formation consists of a complete sphere, which in turn is mounted in a further convex formation of the cover plate.