WO1994026213A1

WO1994026213A1 - Vertebral body implant

Info

Publication number: WO1994026213A1
Application number: PCT/EP1994/000728
Authority: WO
Inventors: Hartmut Zippel; Franz Bobst
Original assignee: Plus Endoprothetik Ag
Priority date: 1993-05-11
Filing date: 1994-03-09
Publication date: 1994-11-24
Also published as: EP0697843A1; JPH08509645A; DE4315757C1

Abstract

A vertebral body implant consisting of a spacer (10) which can be fitted between adjacent vertebral bodies comprising an upper (11) and a lower (12) cover plate and a flexible intermediate component (13) arranged between said two cover plates (11, 12). Vertebral body securing components (14, 15, 16) are fitted on the outsides of the cover plates (11, 12). The flexible intermediate component (13) takes the form of a U, S or W-shaped curved plate (17) of bio-compatible material, especially titanium.

Description

Vertebral body implant

description

The invention relates to a vertebral body implant according to the preamble of claim 1. Such a vertebral body implant is generally known. In this regard, reference is made to a special print "Spinal Surgery II - Operative Treatment of Chronic Low Back Pain, Symposium Augsburg 1991, published by Klaus A. Matzen, Georg Thieme Verlag Stuttgart, New York 1992". This special print summarizes the development of artificial intervertebral discs and the current state of development. Accordingly, the current state of the art is a three-part modular intervertebral disc prosthesis consisting of two concavely hollowed metallic end plates made of a chrome-cobalt alloy and an interposed central lenticular poly- ethylene (chirules) sliding core. A low sliding friction of the movement elements should be ensured with the metal / polyethylene material pairing. The end or upper and lower cover plates are anchored via spines arranged in a ring or row on the bony vertebral end plates. The constructive design of the biconvex sliding core with a circular ring wall is intended to enable both segmental movements in the extension-flexion plane, sideways inclination and rotation.

At the same time, however, movement deflections going beyond 10 to 15 ° and a luxation of the polyethylene lens in extreme movement positions are to be prevented. The aforementioned intervertebral disc prosthesis is described, inter alia, in EP-0 176 728-B1. The problem with this known construction is the limited elasticity of the polyethylene sliding core, which decreases over time due to cold flow and embrittlement. In addition, it has been shown in practice that the polyethylene sliding core is destroyed after a relatively short period of time, especially when it comes to the edge. This in turn leads to a post-operation that should be avoided as far as possible.

The object of the present invention is to create a vertebral body implant which is structurally considerably simpler than the prior art and which comes as close as possible to the function of the natural intervertebral disc and which, on the other hand, has the advantage of being wear-free and therefore correspondingly long-lasting . Wear-related follow-up operations should therefore be avoided with the vertebral body implant according to the invention.

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

Accordingly, the vertebral body implant according to the invention is essentially reduced to a single essential component, namely to a specially shaped spring element. In the extreme case, namely according to claim 2, the vertebral body implant consists practically exclusively of the spring element designed according to the invention. This is wear-free. It consists of only a single, ie uniform, biocompatible material. The construction according to the invention is characterized by the extreme reduction of components, their extremely simple construction and thus their manufacture, and by their extremely simple handling during implantation.

The operative handling of the implant according to the invention can additionally be made considerably easier by the measures according to one of the claims δ to 10.

Experiments have shown that the vertebral body implant according to the invention surprisingly has a recurrence curve which largely corresponds to that of the natural intervertebral disc. This applies to both the extension-flexion level and the sideways inclination. In contrast, the construction according to the invention does not permit rotation. In practice, this slight disadvantage does not present itself as a disadvantage, since the rotation deflections are only slight even when the intervertebral disc is intact, so that the limitation according to the invention does not become noticeable as an actual disadvantage.

Further advantageous constructive details of the vertebral body implant according to the invention are described in the subclaims. The constructive solution according to claim 6 is also emphasized. In this, the spring element according to the invention is encapsulated on all sides. The implant therefore represents a closed system.

The dimensioning of the implant according to the invention is selected such that a segmental mobility of approximately 5 ° is achieved with a disc thickness of approximately 12 mm. With thicker intervertebral discs, segmental mobility can be increased.

Preferred embodiments of the vertebral body implant according to the invention are explained in more detail below with the aid of the attached schematic drawing. Show it: 1 shows a first embodiment of a vertebral body implant designed according to the invention in a perspective view;

FIG. 2 shows the implant according to FIG. 1 in a front view in the direction of arrow II in FIG. 1;

3 shows the implant according to FIG. 1 in a side view in the direction of arrow III in FIG. 1;

FIG. 4 shows a modified vertebral body implant according to the view according to FIG. 3;

5 shows the implant according to FIGS. 1 to 3 in the compressed state before insertion between two adjacent vertebral bodies and in a side view;

6 shows the implant according to FIGS. 1-3 in a compressed state before insertion between two adjacent vertebral bodies in a perspective view;

7 shows a third embodiment of a vertebral body implant designed according to the invention in a schematic longitudinal section, the elastic intermediate element being indicated by a dashed line; and

FIG. 8 shows a capsule for the implant according to FIG. 7 on a greatly enlarged scale, showing the relative mobility of the upper and lower shell of the implant capsule.

The vertebral body implant shown in FIGS. 1-3 consists of a spacer body 10 which can be inserted between adjacent vertebral bodies and not shown here, which comprises an upper cover plate 11 and a lower cover plate 12 as well as a resilient intermediate element 13 arranged between these two cover plates . On the outside or Spike-like vertebral body anchoring elements 14, 15 and 16 are arranged on the sides of the cover plates 11 and 12 facing the vertebral bodies. After insertion of the vertebral body implant, these penetrate between two adjacent vertebral bodies into the vertebral body bones. As a result, the implant is firmly anchored between two adjacent vertebral bodies. The resilient intermediate element 13 is formed by an S-shaped plate 17 made of biocompatible material, in particular titanium, a titanium-coated cobalt-chromium-molybdenum, cobalt-chromium or stainless spring-steel alloy or the like. The wall thickness of the spring plate is approximately 0.2-0.6, in particular approximately 0.35 mm. The top and bottom cover plates 11 and 12 and the spring element 13 arranged between them are approximately oval in plan view. A kidney-shaped contour is also conceivable. Furthermore, in the embodiment according to FIGS. 1-3 and in the embodiment according to FIGS. 4-6 described in more detail below, the upper and lower cover plates 11 and 12 are an integral part of the spring-elastic intermediate element 13 or the S-shape curved plate 17. That is, the upper and lower cover plates 11 and 12 are formed by the two free legs of the S-shaped curved plate 17.

Alternatively, according to FIG. 4, the resilient intermediate element 13 can be formed by a plate 17 bent in a W-shape. The simplest embodiment is a U-shaped spring plate.

As can also be seen in FIGS. 2 and 3, the two cover plates 11 and 12 are each convexly shaped on the outside, both in their longitudinal direction and transversely thereto. This results in better embedding or anchoring on the respectively assigned vertebral bone.

According to FIGS. 3 and 4, the two cover plates 11, 12 close an angle α of approximately 3 to 25 °, in particular in the relaxed state of the spring-elastic intermediate element 13 in a plane perpendicular to their longitudinal extension about 8 °. The implant is then inserted between two adjacent vertebral bodies so that the higher side is at the front. Then the desired elasticity and damping properties are ensured both in the extension-flexion plane and also in the event of a sideways inclination.

7 and 8, the spring-elastic intermediate element, for. For example, according to FIGS. 1-3, encapsulated or enclosed within a capsule 20 formed by an upper shell 18 and a lower shell 19, the upper and lower cover plates then being part of the upper and lower shells 18 and 19, respectively . Accordingly, the spikes 14, 15 and 16 mentioned above are also arranged on the outer sides of the upper and lower shells.

The upper shell 18 and lower shell 19 consist of biocompatible material, in particular titanium sheet. They are connected to one another, in particular, in accordance with FIGS. 7 and 8, hooked together at the edges such that they can follow the movement of the spring-elastic intermediate element 13 without play. The relative mobility between the upper and lower shell is shown schematically in FIG. Accordingly, the segmental mobility should be approximately 5 °. This corresponds to an implant height of approximately 12 mm.

7, the upper and lower shells 18, 19 are each convexly curved. This curvature gives the half-shells 18, 19 additional inherent stability, with the result that they can be made from thinner sheet metal without the risk of breakage. Above all, it is possible with this embodiment to make the central region of the upper and lower shell extremely thin-walled, while the wall thickness of the upper and lower shell is selected to be larger in the region of the peripheral edge. In the central area of the upper and lower shells, the maximum wall thickness when using a titanium sheet is approximately 0.05 to 0.25 mm, in particular approximately 0.10 mm. The wall thickness then preferably increases continuously by approximately 25-50% towards the peripheral edge.

In the embodiment according to FIG. 8, the wall thickness of the upper and lower shells 18 and 19 is approximately 0.10-0.30 mm, in particular approximately 0.15 mm.

The embodiment according to FIGS. 7 to 8 represent a closed system. A different spring element than that according to FIGS. 1-3 or according to FIG. 4 can also be arranged within the capsule 20. In principle, the arrangement of a coil spring package is also conceivable. Above all, cone pressure springs have proven to be advantageous with regard to their spring characteristic.

It should also be pointed out that in all of the embodiments, the length of the spikes 14 and 15 lying at the front in the inserted state is greater than the length of the rear spike or spikes 16. This is related to the space available between two adjacent vertebral bodies.

In order to avoid a complicated tool for implantation, it is advantageous that the described vertebral body implants before insertion between two adjacent vertebral bodies by means of a compression band 21 that can be removed after insertion, a compression wire, a compression clip or the like in the effective direction the resilient intermediate element is compressed. In this regard, reference is made to FIGS. 5 and 6. By means of the compression band 21, the implant can be compressed by about 1/4 of its maximum height plus the height of the vertebral body anchoring elements (spikes 14, 15, 16) before insertion between two adjacent vertebral bodies. The implant can thus be inserted between two adjacent vertebral bodies without an expanding tool or forceps. The compensation band is then opened and removed. The implant expands in the axial direction of the spine under the pretension of the spring-elastic intermediate element. The spikes 14, 15 and 16 penetrate the bone of the associated vertebral body. The implant accordingly anchors itself.

6 is arranged within a groove 22 which extends around the implant 10, in particular within a groove 22 formed on the outside on the upper and lower cover plates 11, 12. The depth and width of this groove 22 corresponds approximately to the thickness and width of the compression band 21. Instead of a compression band, a compression wire or the like can also be used. In the present case, the two ends of the compression band 21 are attached to one another on the front side of the implant 10 (solder connection or the like). This connection is released after inserting the implant, e.g. B. opened by means of a side cutter. When using a compression wire, this can be twisted on the front side of the implant 10. After inserting the implant, the twisting is released and the wire around the implant is pulled out to the front.

In principle, it is also possible to provide recesses or openings on the top and bottom of the implant in which the tines of a pair of pliers can be inserted in order to press the implant together between two adjacent vertebral bodies. However, the aforementioned solution with a compression band or the like is more elegant in that the relatively high compression pressure can already be applied during the manufacture of the implant. This corrosive pressure then only needs to be released after inserting the implant by opening the compression band or the like. Of course, the compression band is also made of biocompatible material.

Instead of convexly arching the upper and lower cover plates 11 and 12 in the embodiment according to FIGS. 1-3, it is also conceivable to attach convexly arched cover plates provided with spikes to the legs of the spring element 13, z. B. to screw. This version rungεfor has the advantage that the curvature of the cover plates 11 and 12 can be selected individually for the patient.

In the illustrated embodiments, the lateral flexibility of the implant is somewhat less than in the plane perpendicular to the longitudinal extension of the implant. Accordingly, the implant is also used in such a way that the plane extends transversely to the longitudinal extent parallel to the patient's extension-flexion plane. The implant is accordingly highly flexible at this level. Towards the side, i.e. H. the implant is harder for sideways inclination. In this respect, the implant approaches the effect of the natural intervertebral disc. For the right or left sideways movement, a maximum of about half the mobility forwards and backwards should be estimated. The implants described meet this requirement.

For the rotation of the individual vertebrae against each other, the segmental movement deflections lie between 2 and 4 °. These are therefore generally negligible for the construction of an implant. Accordingly, no rotation of the implants is provided in the described embodiments. This allows the construction to be simplified considerably.

All of the features disclosed in the application documents are claimed as essential to the invention, insofar as they are new or in combination with respect to the prior art.

Claims

Vertebral implant patent claims

1. Vertebral body implant, consisting of a spacer that can be inserted between adjacent vertebral bodies

(10), which comprises an upper (11) and a lower (12) cover plate and a spring-elastic intermediate element (13) arranged between these two cover plates, with the outer or the vertebral bodies facing On the sides of the cover plates, vertebral body anchoring elements (14, 15, 16) are provided, characterized in that the spring-elastic intermediate element (13) is formed by a plate (17) made of biocompatible material, which is bent into a U, S or W shape, in particular titanium, a titanium-coated cobalt-chromium-molybdenum, cobalt-chromium or stainless spring steel alloy or the like.

2. Implant according to claim 1, characterized in that the upper and lower cover plate (11, 12) are integral components of the U, S or W-shaped spring plate (17), or the upper and lower cover plate through the two free legs of the U, S or W-shaped spring plate ( 17) are formed.

3. Implant according to claim 1 or 2, characterized in that the top and bottom (11, 12) cover plate is each oval or kidney-shaped in plan view.

4. Implant according to one of claims 1 - 3, characterized in that the two cover plates (11, 12) are respectively convexly shaped or curved on the outside.

5. Implant according to one of claims 1-4, characterized in that the two cover plates (11, 12) in the relaxed state of the resilient intermediate element (13) in a plane perpendicular to it

Include an extension (α) of approximately 3 to 25 ^β , in particular approximately 8 ^β , in the longitudinal extent or in the extension-flexion plane.

6. Implant according to one of claims 1 and 3-5, characterized in that the spring-loaded intermediate element is enclosed within a capsule (20) formed by an upper (18) and lower (19) shell, the upper and lower cover plate are part of the upper (18) and lower (19) shell.

7. Implant according to claim 6, characterized in that the upper (18) and lower (19) shell made of biocompatible material, in particular titanium sheet and connected to each other, in particular εind hooked on the edge, that they are free of play ¬ can follow the spring-elastic intermediate element (13).

8. Implant according to one of claims 1-7, characterized in that it is inserted between two adjacent vertebral bodies by a removable compression band after insertion (21), a compression wire, a compression clip or the like in the direction of action of the resilient before insertion Intermediate element (13) is compressed.

9. Implant according to claim 8, characterized in that it is compressible before insertion of two adjacent vertebral bodies by about 1/4 of the maximum height plus height of the vertebral anchoring element (14, 15, 16).

10. The implant according to claim 8 or 9, characterized in that the compression band (21) or the like is located within an area around the implant (10), in particular within an outer side of the top and bottom cover plates (11, 12). formed groove (22), whose depth and width corresponds approximately to the thickness and width of the compression band (21) or the like.

11. Implant according to claim 6, characterized in that the wall thickness of the upper (18) and lower (19) shell is approximately 0.10-0.30 mm, in particular approximately 0.15 mm.

12. Implant according to claim 6 or 11, characterized in that in the region of the peripheral edge of the upper (18) and lower (19) shell the wall thickness of the same is larger than that in the central area, where the wall thickness is a maximum of about 0.05. Is 0.25 mm, in particular approximately 0.10 mm.