JPH0898850A - Artificial intervertebral disk - Google Patents

Abstract

PURPOSE: To improve impact absorbability and torsional rigidity by interposing an intermediate layer of a polyvinyl alcohol between a pair of fiber meshes consisting of titanium, etc., and forming this intermediate layer by providing the inner side of an outside layer part having a specific Young's modulus with internal nucleus parts having the Young's modulus smaller than this Young's modulus. CONSTITUTION: This artificial intervertebral disk 1 is constituted by interposing the intermediate layer 4 of PVA including an impregnated part 3 in which the polyvinyl alcohol PVA is held within a part of fiber meshes 2 between a pair of the fiber meshes 2 consisting of the titanium or titanium alloy. The intermediate layer 4 is constituted by starting from the same PVA material and adequately controlling the degree of polymn. thereof, thereby forming the internal nucleus parts 5 of the Young's modulus of 10 to 50MPa on the inner side of the outside layer part 6 having the Young's modulus of 50 to 130MPa. The ratio of the thickness in the radial direction of the internal nucleus layer 5 of such intermediate layer 4 to the outside layer part 6 is preferably set in a range of 1:1 to 3:1.

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 which replaces a natural intervertebral disc in a living body having a defect such as a functional disorder due to a disease or an injury.

[0002]

2. Description of the Related Art When replacing a natural intervertebral disc having inconvenience such as dysfunction due to illness or injury with an artificial material, mechanical properties close to that of a healthy natural intervertebral disc and fixation with upper and lower bones are not achieved. desired.

Conventionally, as an artificial intervertebral disc as described above, as in the invention of JP-A-4-303444, a part of a poly mesh held between the pair of fiber meshes made of titanium or titanium alloy is held in the fiber mesh. An artificial intervertebral disc having an intermediate layer of vinyl alcohol, or an elastic polymer disc sandwiched between two ceramic discs as in the invention of JP-A-5-277141, and each elastic polymer disc has a Young's modulus. And artificial intervertebral disc composed of inner and outer layers having different Poisson's ratios
There is known an artificial intervertebral disc in which silicon rubber is sandwiched between a pair of titanium plates coated with glass as in the invention of No. 407.

[0004]

However, the above-mentioned prior art has the following problems.

That is, the artificial intervertebral disc formed by interposing a middle layer of polyvinyl alcohol (hereinafter abbreviated as PVA) partially held in the fiber mesh between a pair of fiber meshes made of titanium or titanium alloy. In the case of, it is possible to obtain a material that is firmly fixed to the upper and lower bones with a fiber mesh and has a relatively close elastic modulus to a natural intervertebral disc, but shock absorption and durability may be slightly inferior. understood.

In the case of the artificial intervertebral disc in which an elastic polymer disc is sandwiched between two ceramic discs, and the elastic polymer disc is composed of an inner layer and an outer layer having different Young's modulus and Poisson's ratio, firstly, There is a problem that the ceramic disk and the bone cannot be completely bonded, and thus the disk easily falls off from a predetermined position. Further, the Young's modulus of the inner layer and the outer layer of the elastic polymer disk is 0.1 to 5 MPa and 7 to, respectively. 20M
Since it is about Pa, its mechanical characteristics are far from those of a healthy natural intervertebral disc.

Further, in the case of an artificial intervertebral disc in which a silicone rubber is sandwiched between a pair of glass-coated titanium plates, there is a problem in the bondability between the titanium plate and the bone, and the intermediate silicone rubber has in vivo safety and durability. There was a problem that it was very inferior.

[0008]

In order to solve the above-mentioned problems, the present invention provides an artificial intervertebral disc having a PVA intermediate layer interposed between a pair of fiber meshes made of titanium or titanium alloy. As the same PVA
It is intended to provide an artificial intervertebral disc formed by forming an inner core portion having a Young's modulus of 10 to 50 MPa inside the outer layer portion having a Young's modulus of 50 to 130 MPa by starting from a material and controlling the degree of polymerization thereof appropriately.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an artificial intervertebral disc 1 according to the present embodiment, and the artificial intervertebral disc 1 is partially sandwiched between a pair of fiber meshes 2 made of titanium or titanium alloy.
An artificial intervertebral disc 1 having an intermediate layer 4 of PVA containing an impregnated portion 3 in which PVA is retained, wherein the intermediate layer 4 is made of the same PV as shown in the sectional view of FIG. 2 and FIG.
The outer layer portion 6 having a Young's modulus of 50 to 130 MPa can be obtained by starting from the material A and controlling the degree of polymerization appropriately.
The inner core portion 5 having a Young's modulus of 10 to 50 MPa is formed on the inside.

The method for producing such an artificial intervertebral disc 1 is as follows. First, the degree of polymerization 1500-5000
At 100 ° C. or above to prepare a PVA solution, which is rapidly cooled at a cold temperature to form a gel, and then DISMO and water are washed with ethanol, and vacuum heat treatment is performed to form an inner core portion 5 of the intermediate layer 4. To get

Next, this is placed in the center between a pair of fiber meshes 2 obtained by integrating and compressing a wire rod of titanium or titanium alloy, and the degree of polymerization 50 which is separately facilitated in that state.
The PVA solution of 0 to 18000 is impregnated only in the periphery of the inner core part 5 and the opposite ends of the pair of fiber meshes 2, and this is rapidly cooled at a cold temperature to gel, and then DISMO and water. Is washed with ethanol and vacuum heat treated to add the intermediate layer 4.

[0012] Then, after surplus PVA is cut off and fibers are stretched, the trowel is immersed in water to swell the gel PVA gel with water to produce the artificial intervertebral disc 1.

The artificial intervertebral disc 1 produced as described above and constructed as described above has an intermediate layer of PVA partially held in the fiber mesh 2 between a pair of fiber meshes 2 made of titanium or titanium alloy. Since it has a structure in which 4 is interposed, it is safe in vivo, its mechanical properties are relatively close to those of the natural intervertebral disc, and since bone growth occurs in the fiber mesh 2, it firmly bonds with bone.
In such a structure, the same PV is used as the intermediate layer 4.
Starting from material A, the central part is formed by controlling the degree of polymerization appropriately, and Young's modulus is 10 to 50MP.
By forming the outer layer portion 6 having a Young's modulus of 50 to 130 MPa on the outer periphery of the inner core portion 5a of a, the impact is mainly transmitted to the inner core portion 5 having a small Young's modulus, so that the outer layer portion having a large Young's modulus is excellent. According to No. 6, the torsional rigidity is remarkably large, and thus the durability is excellent.

When the Young's modulus of the inner core portion 5 and the outer layer portion 6 is less than 10 MPa and 50 MPa, respectively, the torsional rigidity is inferior. On the other hand, when the Young's modulus of the inner core portion 5 and the outer layer portion 6 is greater than 50 MPa and 130 MPa, respectively. It tends to have poor absorbency.

The ratio of the radial thickness of the inner core portion 5 to the outer layer portion 6 is preferably 1: 1 to 3: 1.
That is, when this ratio is smaller than 1: 1, the apparent Young's modulus of the mid layer 4 tends to be large and the shock absorption tends to be poor, while when it exceeds 3: 1, the apparent Young's modulus tends to be small and the torsional rigidity tends to be poor. There is.

Example 1 P having a polymerization degree of 1750 was added to a mixed solution of DMSO: water = 8: 2.
VA was melted at 130 ° C to make a PVA solution. This was rapidly cooled to −20 ° C. to gel, then DMSO and water were washed with ethanol and vacuum heat treated at 140 ° C. for 48 hours. With this PVA as the core, diameter 40 mm, thickness 10 mm
It is placed between the two titanium fiber meshes 2 and is immersed in a separately prepared PVA solution having a polymerization degree of 5000 and a temperature of 130 ° C., and then rapidly cooled to −20 ° C. to gel, and then D
MSO and water were washed with ethanol and vacuum heat-treated at 140 ° C. for 48 hours.

Next, after the excess PVA was cut and washed, it was immersed in water for 48 hours or more to make the PVA portion into a middle gel. The Young's modulus of the inner core portion 5 is 4 by the above process.
5 MPa (moisture content 40%), Young's modulus of the outer layer portion 6 is 10
An artificial intervertebral disc 1 having 0 MPa (water content 35%) was produced.
Table 1 shows the dimensions and mechanical characteristics of each part.

[0018]

[Table 1]

Example 2 P of a polymerization degree of 5000 was added to a mixed solution of DMSO: water = 8: 2.
VA was melted at 130 ° C to make a PVA solution. This was rapidly cooled to −20 ° C. to gel, then DMSO and water were washed with ethanol and vacuum heat treated at 60 ° C. for 24 hours. With this PVA as the core, diameter 40 mm, thickness 10 mm
Placed between the two titanium fiber meshes 2 of No. 1 and immersed in a separately prepared PVA solution having a degree of polymerization of 11000 and a temperature of 130 ° C., followed by rapid cooling to −20 ° C. for gelation, followed by washing DMSO and water with ethanol, Vacuum heat treatment was performed at 60 ° C. for 24 hours.

Next, after the excess PVA was cut and washed, it was immersed in water for 48 hours or more to make the PVA portion into a middle gel. Through the above steps, the artificial intervertebral disc 1 in which the Young's modulus of the inner core portion 5 was 45 MPa and the Young's modulus of the outer layer portion 6 was 130 MPa was produced. Table 1 above shows the dimensions and mechanical characteristics of each part.

Example 3 P of a polymerization degree of 5000 was added to a mixed solution of DMSO: water = 8: 2.
VA was melted at 130 ° C to make a PVA solution. This was rapidly cooled to −20 ° C. to gel, then DMSO and water were washed with ethanol and vacuum heat treated at 60 ° C. for 24 hours. With this PVA as the core, diameter 40 mm, thickness 10 mm
Placed between the two titanium fiber meshes 2 of No. 1 and immersed in a separately prepared PVA solution having a degree of polymerization of 11000 at 130 ° C., rapidly cooled to −20 ° C. to gel, and then DMSO and water are washed with ethanol, Vacuum heat treatment was performed at 60 ° C. for 24 hours.

Then, after the excess PVA was cut and washed, the PVA portion was covered with a titanium wire woven fabric and joined to the titanium fiber mesh 2 by arc welding. Then, the PVA portion was immersed in water for 48 hours or more to form a middle gel. Through the above steps, the artificial intervertebral disc 1 was produced in which the Young's modulus of the inner core portion 5 was 45 MPa, the Young's modulus of the outer layer portion 6 was 130 MPa, and the PVA intermediate layer 4 was covered with the titanium wire fabric. Table 1 above shows the dimensions and mechanical characteristics of each part.

Example 4 P of a polymerization degree of 1750 was added to a mixed solution of DMSO: water = 8: 2.
VA was melted at 130 ° C to make a PVA solution. This was rapidly cooled to −20 ° C. to gel, then DMSO and water were washed with ethanol and vacuum heat treated at room temperature for 24 hours.
With this PVA as the core, a diameter of 40 mm and a thickness of 10 mm
It is placed between two titanium fiber meshes 2 and immersed in a separately prepared PVA solution having a polymerization degree of 11000 and a temperature of 130 ° C., and then rapidly cooled to −20 ° C. to gel, and then DM
The SO and water were washed with ethanol and vacuum heat treated at room temperature for 24 hours.

Next, after the excess PVA was cut and washed, it was immersed in water for 48 hours or more to make the PVA portion into a middle gel. Through the above steps, the artificial intervertebral disc 1 having a Young's modulus of the inner core portion 5 of 15 MPa and a Young's modulus of the outer layer portion 6 of 100 MPa was produced. Table 1 above shows the dimensions and mechanical characteristics of each part.

[0025]

As described above, in the artificial intervertebral disc of the present invention, P is partially held in the fiber mesh between a pair of fiber meshes made of titanium or titanium alloy.
Since it has a structure in which the intermediate layer of VA is interposed, it is safe in vivo, its mechanical properties are relatively close to those of the natural intervertebral disc, and bone growth occurs in the fiber mesh, so it firmly bonds to bone. In such a structure, as the intermediate layer, the Young's modulus is 50 to 130 by starting from the same PVA material and controlling the degree of polymerization appropriately.
By forming an inner core portion having a Young's modulus of 10 to 50 MPa inside the outer layer portion of MPa, shock absorption and durability are remarkably improved.

[Brief description of drawings]

FIG. 1 is a perspective view of an artificial intervertebral disc according to an embodiment of the present invention.

2 is a vertical cross-sectional view of the artificial disc of FIG.

3 is a perspective view showing only an intermediate layer of the artificial disc of FIG. 1. FIG.

[Explanation of symbols]

 1 Artificial intervertebral disc 2 Fiber mesh 3 Impregnated part 4 Intermediate layer 5 Inner core part 6 Outer layer part

Claims (1)

[Claims] 1. An artificial intervertebral disc in which an intermediate layer of polyvinyl alcohol is interposed between a pair of fiber meshes made of titanium or titanium alloy, the intermediate layer being inside an outer layer portion having a Young's modulus of 50 to 130 MPa. An artificial intervertebral disc formed by forming the outer periphery of the inner core having a Young's modulus of 10 to 50 MPa.