JPH05277141A - Artificial intervertebral disk - Google Patents

Abstract

PURPOSE:To provide the artificial intervertebral disk having adequate rigidity to compression and torsional characteristic. CONSTITUTION:Two sheets of approximately planar bodies 10, 11 consisting of bioactive ceramic materials hold an approximately planar body 14 consisting of a high-molecular elastic material having bioadaptability. The approximately planar body 14 consisting of an elastic high-molecular material is formed of at least two layers; an inside layer 12 having 0.1 to 5MPa Young's modulus and 0.05 to 0.45 Poisson ratio and an outside layer annularly enclosing the circumference thereof and having 7 to 20MPa Young's modulus and 0.35 to 0.49 Poisson ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an artificial intervertebral disc used for treating diseases such as intervertebral disc herniation and damage to the spine due to an accident.

[0002]

2. Description of the Related Art As shown in FIG. 7, the spine of a human body is made up of hard vertebral bodies 1 arranged in a row and a soft disc 2 connecting vertically adjacent vertebral bodies 1. If the above-mentioned spinal disease or damage is severe, vertebral body 1 can be obtained by open surgery.
The surgical treatment is performed by removing all or part of the intervertebral disc and the intervertebral disc 2 and implanting an autogenous bone or an artificial vertebral body in the portion.

As such an artificial vertebral body, conventionally,
As shown in FIGS. 8 (a) and 8 (b), an alumina ceramic molded into a substantially disk shape or a rectangular parallelepiped shape is used. In addition, recently, known bioactive ceramic materials having an apatite crystal phase, materials obtained by blending high density polyethylene or methacrylate resins, and the like have been used.

However, all of these artificial vertebral bodies are merely used as spacers for filling the gap and supporting the load when the intervertebral disc or the like is excised,
It is not as flexible as the vertebral bodies that sandwich the original disc. Therefore, it is not possible to follow the movement of the human body, and an unreasonable load is often applied to the treatment area, and the treatment area or its peripheral area is often damaged again, which is a problem.

Therefore, the present applicant has developed and has already applied for a flexible artificial intervertebral disc that easily follows the movement of the human body (Japanese Patent Application No. 2-74524, filed on Mar. 23, 1990). As shown in FIG. 9, two ceramic plates 3 and 4 made of a bioactive ceramic material are integrally formed on an upper surface and a lower surface of an elastic plate 5 made of a biocompatible polymer elastic material. The upper and lower ceramic plates 3 and 4 freely rotate about the elastic plate 5 to some extent as if the intervertebral disc flexibly connects the upper and lower vertebral bodies.

[0006]

The above-mentioned artificial intervertebral disc has the advantage that it can move flexibly in accordance with the movements such as forward bending and backward bending as compared with the conventional ones, but it has appropriate compressive rigidity and torsion. I have not obtained anything.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an artificial intervertebral disc having appropriate compression rigidity and torsion.

[0008]

In order to achieve the above object, in the artificial intervertebral disc of the present invention, two substantially plate-like bodies made of a bioactive ceramic material are made of a biocompatible polymer elastic material. The polymeric elastic substantially plate-like member is integrally attached to the upper surface and the lower surface of the plate-like member, and has a Young's modulus of 0.1 to 5 MPa and Poisson's ratio of 0.05 to
It is configured to be formed of at least two layers of an inner layer of 0.45 and an outer layer having a Young's modulus of 7 to 20 MPa and a Poisson's ratio of 0.35 to 0.49 surrounding the periphery of the inner layer.

[0009]

In other words, the inventors of the present invention conducted a series of studies to give the artificial intervertebral disc developed previously (see FIG. 9) appropriate compressive rigidity and torsion to give a function closer to that of a human intervertebral disc. went. And in the process, the human intervertebral disc is a composite structure in which a gel-like substance such as a nucleus pulposus exists inside and a fibrous ring rich in anisotropic elasticity surrounds it in a layered manner. Further research was conducted by recalling that the polymeric elastic plate sandwiched by the ceramic plates has a two-layer structure, imitating the two-layer structure of the nucleus pulposus and the annulus fibrosus. As a result, the polymer elastic plate was subjected to Young's modulus of 0.1 to 5 MPa,
An inner layer having a Poisson's ratio of 0.05 to 0.45, a Young's modulus of 7 to 20 MPa surrounding the circumference in an annular shape, and a Poisson's ratio of 0.
If at least two outer layers of 35 to 0.49 are formed, an appropriate compression rigidity force (compression rigidity value of 400 to 60) is obtained.
0KN / m) and torsion (torsional rigidity value 1.0 to 2.0)
N · m / deg. The present invention has been achieved by finding that an artificial intervertebral disc having strength and mobility comparable to that of a human intervertebral disc can be obtained.

Next, the present invention will be described in detail.

The artificial intervertebral disc of the present invention is shown, for example, in FIG.
As shown in (a) and its sectional view (b), hard discs 10 and 11 made of ceramics are provided on the upper and lower sides, and an inner layer 12 and an outer layer 13 are concentrically formed between them. The elastic polymer disk 14 is sandwiched. The outer peripheral surface of the elastic polymer disc 14 is recessed in a concave shape so that the whole is easily bent in a dogleg shape.

The upper and lower ceramic discs 10 and 11 are required to have bioactivity that chemically binds to bone and cannot be separated, and is made of a bioactive ceramic material. Be done. Examples of the ceramic material include hydroxyapatite, bioglass, glass ceramics and the like. Among them, glass ceramics containing apatite-wollastonite, which is a crystallized glass, is suitable.

On the other hand, the upper and lower ceramic discs 10,
Both the inner layer 12 and the outer layer 13 of the elastic polymer disk 14 sandwiched between 11 need to have biocompatibility and a certain elasticity. For example, a biomedical silicone elastomer or a biomedical urethane elastomer is used. Is preferred.

The Young's modulus of the inner layer 12 is 0.
The outer layer 13 should have a Young's modulus of 7 to 20 MPa and a Poisson's ratio of 0. 1 MPa and a Poisson's ratio of 0.05 to 0.45.
It is necessary to use a material having a material of 35 to 0.49. That is, by limiting the materials of the inner layer 12 and the outer layer 13 as described above, it is possible to provide characteristics similar to those of a human intervertebral disc.

As described above, in order to set the Young's modulus and the Poisson's ratio of the inner layer 12 and the outer layer 13 to the preferable values, even if the same rubber and resin are used, the vulcanization degree (crosslinking degree) of the same rubber or resin may be changed, or foaming may occur. Giving or changing the thickness in the circumferential direction is performed.

The elastic polymer disk 14 having the above-mentioned two-layer structure is used.
To obtain, for example, an unvulcanized (uncrosslinked) inner layer material is filled in a mold capable of shaping the inner layer shape, and this is vulcanized (crosslinked).
After curing and curing, it is further placed in the center of the mold capable of shaping the outer layer shape and unvulcanized (uncrosslinked) around it.
The elastic polymer disk 14 having a two-layer structure can be obtained by filling the outer layer material of (3) and vulcanizing (crosslinking) and curing the material. Alternatively, the outer layer material may be applied around the pre-vulcanized inner layer 12 in a predetermined thickness and then vulcanized. On the other hand, the outer layer 13 may be formed by extrusion molding into a tubular shape, and then the inner layer material may be filled inside the outer layer 13 and cured to integrate them.

The artificial intervertebral disc of the present invention can be obtained by integrally joining the three members by placing the elastic polymer disc 14 at the center and sandwiching it between the ceramic discs 10 and 11 from above and below. A biocompatible adhesive is used for the joining. Examples of such an adhesive include silicone coupling agents, titanium coupling agents, aluminum coupling agents, and the like.
Silicone-based coupling agents are preferred.

The artificial intervertebral disc thus obtained exhibits compressive and torsional stiffness values close to those of human intervertebral discs, and has the strength to receive the load in the vertical direction and the mobility to follow the motion such as twisting of the waist. It is also an excellent one.

In the artificial intervertebral disc of the present invention, the shapes and thicknesses of the ceramic discs 10 and 11 and the elastic polymer disc 14 are individually set according to the patient's physique and balance with other spinal functions. be able to. For example, in the above example, the outer peripheral surface of the elastic polymer disk 14 is recessed in a concave shape, but conversely, as shown by a chain line in FIG.
A convex roundness may be provided to show a strong resistance to the load applied in the above direction. The planar shape is not limited to the disk shape, but may be an appropriate shape such as an elliptical shape or a quadrangular shape.

Further, protrusions (or streak-like grooves) as shown in FIG. 2 may be formed on the outer surfaces of the ceramic disks 10 and 11. This way,
When it is embedded in a living body, the joint area between the vertebral body (see FIG. 7) and the ceramic discs 10 and 11 is increased, and the artificial intervertebral disc is firmly fixed.

Further, by making the central portion of the elastic polymer disk 14 into a cavity 15 as shown in FIG. 3 and forming a ring shape, it is possible to increase the torsional rigidity value while suppressing the compression rigidity value. In this case, the ring-shaped portion is divided into an inner layer 12 and an outer layer 13 to form a multilayer structure.

Further, as shown in FIG. 4, most of the elastic polymer disk 14 is composed of the inner layer 12, and the outer side of the inner layer 12 is formed from a very thin skin layer (thickness of about 1 to 3 mm). You may make it coat | cover with the outer layer 13 which becomes.

Further, the upper and lower ceramic disks 10, 1
The shape of the disk 1 and the elastic polymer disk 14 may be a shape in which one side of a circle is crushed, as shown in FIG. 5, imitating an actual intervertebral disk.

Next, examples will be described together with comparative examples.

[0025]

Examples 1 to 4 and Comparative Examples 1 to 3 The overall shape shown in FIG. 5 and its cross section taken along the line AA ′ in FIG. 6 was used, and the inner layer 12 and outer layer 13 of the elastic polymer disk 14 were circumferentially oriented. The artificial disc having a shape similar to that of a human intervertebral disc was prepared by changing the thickness and material of the disc as shown in Tables 1 and 2 below. Then, the compression rigidity value and the torsional rigidity value of each artificial intervertebral disc were measured, and the results are shown in Tables 3 and 4 below.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

[Table 4]

From the above results, all of the example products have an appropriate compression rigidity force (compression rigidity value of 400 to 600 KN / m).
And twistability (torsional rigidity value 1.0 to 2.0 Nm / de
g. ).

[0031]

As described above, according to the present invention, the elastic polymer disk is sandwiched between the upper and lower ceramic plates, and the elastic polymer disk has at least two inner layers and outer layers having predetermined physical properties. It has a multi-layer structure. Therefore, the artificial intervertebral disc of the present invention is capable of exerting appropriate compressive rigidity and torsion, is strong against vertical compressive loads, and is excellent in that it is easy to follow motions such as twisting of the waist.

[Brief description of drawings]

FIG. 1A is a plan view showing an embodiment of the present invention, and FIG. 1B is a sectional view thereof.

FIG. 2 is a sectional view showing another embodiment of the present invention.

FIG. 3 is a sectional view showing still another embodiment of the present invention.

FIG. 4 is a sectional view showing another embodiment of the present invention.

FIG. 5 is a plan view showing still another embodiment of the present invention.

6 is a cross-sectional view taken along the line AA ′ of FIG.

FIG. 7 is a partial perspective view showing the configuration of the spine.

8A and 8B are perspective views showing an example of a conventional product.

FIG. 9 is a perspective view showing an example of an artificial intervertebral disc developed previously.

[Explanation of symbols]

 10, 11 Ceramics disk 12 Inner layer 13 Outer layer 14 Elastic polymer disk

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[Procedure amendment]

[Submission date] June 9, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

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 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeru Tanno 9-chome, Kita-ku, Nishi-ku, Sapporo-shi, Hokkaido (72) Inventor Hiromasa Ishikawa 3-12, Momiji-Tainan, Atsubetsu-ku, Sapporo, Hokkaido (72) Inventor Takehiro Shibuya 2-41-7 Motomiya, Otsu City, Shiga Prefecture (72) Inventor Yukio Sakuraba Komaki City, Aichi Prefecture Oita Kitayama Yamato 3600 Tokai Rubber Industry Co., Ltd. (72) Inventor Kiyoshi Aiba Prefecture Komaki City, Aichi Prefecture Sotoyama character Otsu 3600 Tokai Rubber Industry Co., Ltd.

Claims (1)

[Claims] 1. Two substantially plate-shaped bodies made of a bioactive ceramic material are integrally attached to an upper surface and a lower surface of the substantially plate-shaped body made of a biocompatible polymer elastic material, respectively. Polymer elastic substantially plate-shaped body has Young's modulus of 0.1 to 5 MPa and Poisson's ratio of 0.05 to 0.45, and Young's modulus of 7 to 20 MP surrounding the inner layer in a ring shape.
a, an artificial intervertebral disc formed by at least two layers of outer layers having a Poisson's ratio of 0.35 to 0.49.