Interbody fusion device

Abstract

To provide an intervertebral fusion device that allows its rigidity to be adjusted according to the needs of each patient.SOLUTION: An intervertebral fusion device includes a structural ceramic body. The structural ceramic body has a bottom surface, a top surface, a peripheral surface connecting between the bottom surface and the top surface, and at least one pore channel penetrating the bottom surface and the top surface. The inner surface of the pore channel is either an inward convex curved surface or a funnel-shaped surface. For the pore channel having the inward convex curved surface, the pore diameter of the pore channel gradually expands from the center of the pore channel to the bottom surface and the top surface. The pore diameter may gradually expand from the bottom surface to the top surface. The peripheral surface of the structural ceramic body is wavy or zigzag.SELECTED DRAWING: Figure 2C

Description

[Technical field]

[0001] The present invention relates to devices for implantation between vertebral bodies in the spine, and more particularly to intervertebral fusion devices that have low stiffness and uniform internal stress distribution. [Background technology]

[0002] The spine is the most important bone in the human body. It is made up of 26 vertebrae: 7 cervical, 12 thoracic, and 5 lumbar. The spine, together with muscles and ligaments, supports the body's weight.

[0003] In vertebrates, there are intervertebral discs between the vertebrae. These discs are relatively soft and act as a lubricant for the sliding motion between the vertebrae of vertebrates. The slippage between each vertebra gradually wears down the discs, and in severe cases, the discs can become deformed or collapse, causing pain due to nerve compression. Therefore, implanting an intervertebral fusion device between the vertebrae is one of the most common ways to relieve pain in patients.

[0004] Metals such as titanium alloys and stainless steel have traditionally been used for intervertebral fusion devices, but because stainless steel can release harmful ions (e.g., nickel) into the blood, titanium alloy intervertebral fusion devices are often used in clinical practice. However, the elastic modulus of titanium alloys is about 114 GPa, which is higher than the elastic modulus of bone. To reduce stiffness, titanium alloy intervertebral fusion devices usually have a large through hole running through the center. The through hole can be filled with autogenous bone or bone graft.

[0005] Although the rigidity of titanium alloy intervertebral fusion devices is reduced by the central through hole, all stress is concentrated on the edge of the intervertebral fusion device, which causes the problem of subsidence of the intervertebral fusion device after a certain period of time has passed since it was implanted. In addition, titanium alloy is a metal material that interferes with electromagnetic waves, so when observing an implanted titanium alloy intervertebral fusion device using X-rays, magnetic resonance imaging (MRI), or computed tomography (CT), the image around the intervertebral fusion device becomes blurred, making observation difficult.

[0006] Polymer intervertebral fusion devices have also been developed. Polymer intervertebral fusion devices are typically made of polymethyl methacrylate (PMMA) or polyether ether ketone (PEEK). The elastic modulus of PEEK is approximately 5 GPa, which is close to the stiffness of bone. PEEK also has high strength, but PMMA and PEEK are made of polymer monomers, and after long-term exposure to the body, very small amounts of harmful monomers are released into the body.

[0007] Therefore, the clinical requirements for an intervertebral fusion device are: 1. The stiffness of the fusion device matches the stiffness of the adjacent vertebrae. 2. The intervertebral fusion device is strong enough to support the body weight. 3. A through hole is required to fill the bone filler. 4. Does not interfere with electromagnetic waves such as X-rays, MRI, and CT. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention meets these demands and provides an intervertebral fusion device, particularly one whose stiffness can be adjusted to suit individual patient needs. [Means for solving the problem]

[0009] The intervertebral fusion device of the present invention has a structural ceramic body having a bottom surface, a top surface, a peripheral surface connecting the bottom surface and the top surface, and at least one through hole penetrating the bottom surface and the top surface. The inner surface of the through hole is formed as an inwardly convex curved surface, or the through hole is formed as a funnel shape. When the inner surface of the through hole is formed as an inwardly convex curved surface, the diameter of the through hole gradually increases from the center of the through hole toward the bottom surface and the top surface. When the through hole is formed as a funnel shape, the diameter of the through hole increases from the bottom surface toward the top surface. The peripheral surface of the structural ceramic body is wavy or sawtooth.

[0010] In an embodiment of the present invention, the material of the structural ceramic body includes zirconium oxide (ZrO2), aluminum oxide (Al2O3), cerium oxide (CeO2), yttrium oxide (Y2O3), magnesium oxide (MgO), titanium oxide (TiO2), silicon oxide (SiO2), zinc oxide (ZnO), bioactive glass (Bioglass), silicon nitride, silicon carbide, or a composite material thereof.

[0011] In an embodiment of the present invention, the material of the structural ceramic body includes yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP), cerium-stabilized tetragonal zirconia polycrystal (Ce-TZP), a composite of yttrium-stabilized tetragonal zirconia and aluminum oxide (Y-TZP / Al2O3), or a composite of cerium-stabilized tetragonal zirconia and aluminum oxide (Ce-TZP / Al2O3).

[0012] In an embodiment of the invention, the bottom and top surfaces of the structural ceramic body are parallel to each other.

[0013] In an embodiment of the invention, the bottom and top surfaces of the structural ceramic body are not parallel to one another.

[0014] In an embodiment of the present invention, the structural ceramic body has a thin portion and a thick portion, and the average diameter of the through holes is smaller closer to the thin portion and larger closer to the thick portion.

[0015] In an embodiment of the present invention, corners between the peripheral surface and the top and bottom surfaces are rounded at most, and corners between the inner surface of the through hole and the top and bottom surfaces are also rounded at most.

[0016] In an embodiment of the invention, the through holes of the structural ceramic body are filled with a bone graft.

[0017] In an embodiment of the present invention, an area fraction of a total opening area of ​​the through holes on the top surface to an area of ​​the top surface is equal to or greater than 10%.

[0018] In an embodiment of the present invention, the ratio of the total opening area of ​​the through holes in the upper surface to the area of ​​the upper surface is equal to or greater than 50%.

[0019] In an embodiment of the present invention, the periphery of the structural ceramic body is arcuate, wavy or sawtooth.

[0020] In an embodiment of the present invention, the at least one through hole is a plurality of through holes, the plurality of through holes being evenly distributed in the structural ceramic body. Effect of the Invention

[0021] Based on the above, the present invention uses a structural ceramic body as the basic material of the intervertebral fusion device, and provides at least one through-hole of a specific shape therein, thereby adjusting the rigidity of the intervertebral fusion device to approach the rigidity of bone. The rigidity of the intervertebral fusion device can be adjusted to meet the needs of each patient by changing the number and size of the through-holes. In addition, since the material of the intervertebral fusion device is ceramic, it is harmless to the human body, has sufficient strength to support the body weight, and does not interfere with electromagnetic waves such as X-rays, MRI, and CT, so that it is easy to follow up after surgery. In the present invention, the peripheral surface of the structural ceramic body is wavy or sawtooth, which can prevent the intervertebral fusion device from slipping after being embedded between the vertebral bodies, and can maintain high stability of the intervertebral fusion device embedded in the vertebrae.

[0022] In order to make the above features and advantages of the present invention comprehensible, the present invention will be described in detail below with reference to the accompanying drawings. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a top view of an intervertebral fusion device according to a first embodiment of the present invention. [Figure 2A] FIG. 2 is a side view of the intervertebral fusion device of FIG. [Figure 2B] FIG. 2 is a side view of the alternative intervertebral fusion device of FIG. [Figure 2C] FIG. 2 is a side view of yet another alternative intervertebral fusion device of FIG. [Figure 2D] FIG. 2 is a side view of yet another alternative intervertebral fusion device of FIG. [Diagram 3] FIG. 1 is a top view of an intervertebral fusion device according to a second embodiment of the present invention. [Figure 4] FIG. 13 is a top view of an intervertebral fusion device according to a third embodiment of the present invention. [Diagram 5] FIG. 1 is a top view showing a structure according to Comparative Example 1. [Figure 6] FIG. 11 is a top view showing a structure according to Comparative Example 2. [Figure 7] Top view showing the structure of Experimental Example 1 [Figure 8] Top view showing the structure of Experimental Example 2 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings, but the present invention can be implemented in various forms and is not limited to the embodiments described below. In the drawings, for ease of understanding, the size of each area, part, through hole, length and width of the device may not be drawn according to actual scale, and for ease of understanding, in the following description, similar components are given similar symbols.

[0025] FIG. 1 is a top view of an intervertebral fusion device according to an embodiment of the present invention, FIG. 2A is a side view of the intervertebral fusion device of FIG. 1, FIG. 2B is a side view of another intervertebral fusion device of FIG. 1, FIG. 2C is a side view of yet another intervertebral fusion device of FIG. 1, and FIG. 2D is a side view of yet another intervertebral fusion device of FIG. 1.

[0026] As shown in Figures 1, 2A, 2B, 2C, and 2D, the intervertebral fusion device 10 of this embodiment has a structural ceramic body 100. The structural ceramic body 100 is basically made of a material that is harmless to the human body and safe for use inside the body. Although bone is a hard tissue inside the body, the elastic modulus of bone is relatively low. For example, the elastic modulus of cortical bone is 7 GPa to 30 GPa. Therefore, it is desirable that the stiffness of the intervertebral fusion device 10, which is embedded between vertebrae and adheres closely to the cortical bone, is as close as possible to the stiffness of the cortical bone.

[0027] The structural ceramic body 100 of the intervertebral fusion device 10 is formed to include a bottom surface 102, a top surface 104, a peripheral surface 106 connecting the bottom surface 102 and the top surface 104, and a plurality of through holes 108, 110 penetrating the bottom surface 102 and the top surface 104. The provision of the through holes 108, 110 allows the rigidity of the intervertebral fusion device 10 to approach the rigidity of cortical bone. In order to prevent the intervertebral fusion device 10 from slipping between the vertebral bodies, it is preferable that the peripheral surface 106 is wavy or sawtooth. In order to avoid stress concentration, the corners of the structural ceramic body 100 between the bottom surface 102 and the peripheral surface 106 and the corners of the top surface 104 and the peripheral surface 106 are rounded to an R. The corners of the peripheral surface 106 are also rounded to an R. The corners of each of the through holes 108, 110 and the bottom surface 102 and the top surface 104 are also rounded to a radius of 0.02 mm. This design avoids sharp corners in the fusion device 10. The lack of sharp corners helps to avoid stress concentrations and improves the stress uniformity of the fusion device 10 under body weight.

[0028] In one embodiment, the material of the structural ceramic body 100 is a ceramic material such as zirconium oxide (ZrO2), aluminum oxide (Al2O3), cerium oxide (CeO2), yttrium oxide (Y2O3), magnesium oxide (MgO), titanium oxide (TiO2), silicon oxide (SiO2), zinc oxide (ZnO), bioactive glass (Bioglass), silicon nitride, silicon carbide, or a composite material thereof. To tailor the stiffness of structural ceramic body 100 to the needs of the individual patient and to provide sufficient strength to support body weight, for example, the material of structural ceramic body 100 may be yttrium stabilized tetragonal zirconia (Y-TZP), cerium stabilized tetragonal zirconia (Ce-TZP), a composite of yttrium stabilized tetragonal zirconia and aluminum oxide (Y-TZP / Al2O3), or a composite of cerium stabilized tetragonal zirconia and aluminum oxide (Ce-TZP / Al2O3).

[0029] Regarding the design details of the through holes 108, 110, first, the upper and lower limits of the stiffness of the structural ceramic body 100 can be estimated according to the following formulas (quoted from CL Hsieh, WH Tuan, TT Wu, Elastic behaviour of a model two-phase material, J. European Ceram. Soc., Vol. 24, page 3789-3793, 2004):

[0030] 1. Upper limit of stiffness of structural ceramic bodies Rigidity of structural ceramic body = (volume fraction of ceramic) x (rigidity of ceramic) + (volume fraction of through holes) x (rigidity of air)...Equation (1) Since the stiffness of air is zero, equation (1) above can be simplified to: Rigidity of structural ceramic body = (volume fraction of ceramic) x (rigidity of ceramic)...Equation (2)

[0031] 2. Lower limit of stiffness of structural ceramic bodies 1 / (Structural ceramic body stiffness)=(Ceramic volume fraction) / (Ceramic stiffness)+(Voltage fraction of through holes) / (Air stiffness)...Equation (3) Since the stiffness of air is zero, no value can be obtained from equation (3). A lower limit for the stiffness of structural ceramic bodies can be estimated using the extremely low stiffness of air, 0.01 GPa.

[0032] From the above formulas (2) and (3), it can be seen that as the number of through holes increases, the rigidity of the structural ceramic body 100 decreases. Therefore, the number of through holes may be one, or as in this embodiment, the structural ceramic body 100 may have a plurality of through holes 108, 110 evenly distributed therein. For example, when the total open area ratio of the through holes 108, 110 is 10%, the rigidity of the structural ceramic body 100 decreases by 10% or more. Therefore, by changing the number and diameter of the through holes 108, 110, it is possible to adjust the rigidity of the structural ceramic body 100.

[0033] In addition to rigidity, the intervertebral fusion device 10 must be strong enough to support the body weight. In particular, the intervertebral fusion device 10 must be strong enough to withstand the impact of a person running or jumping. Since the external load is mainly applied to the intervertebral fusion device 10 along the direction of the spine, it is preferable that the central axis of each of the through holes 108, 110 is parallel to the extension direction of the spine.

[0034] As shown in FIG. 2A, the upper surface 104 is an inclined upper surface. The inner surface 112 of the through holes 108, 110 is formed into a curved surface that is convex inward. The diameter of the through hole 108 gradually increases from the center C1 of the through hole 108 toward the bottom surface 102 and the upper surface 104. The diameter of the through hole 110 similarly increases from the center C2 of the through hole 110 toward the bottom surface 102 and the upper surface 104. In order to avoid stress concentration, the corners of the inner surface 112 of the through holes 108, 110 and the upper surface 104 and the bottom surface 102 are rounded to the limit. Since the bottom surface 102 and the upper surface 104 are the portions that contact the vertebrae, the area of ​​the structural ceramic body 100 that actually contacts the vertebrae is small, and the effective rigidity of the structural ceramic body 100 is reduced. For example, the area fraction of the total opening area of ​​the through holes 108, 110 in the upper surface 104 to the area of ​​the upper surface 104 is 10% or more, for example, 10%, 20%, 30%, 40%, 50%, 60%, etc., and preferably 50% or more. As described above, the elastic modulus can be adjusted by changing the number and diameter of the through holes 108, 110, so that the rigidity of the structural ceramic body 100 can be reduced.

[0035] In addition, since the diameters of the centers C1 and C2 of the through holes 108 and 110 are small, the ability of the intervertebral fusion device 10 to withstand an external load can be improved. The intervertebral fusion device 10 has different thicknesses depending on the location in order to match the shape of the vertebrae. The thin portion 104a of the upper surface 104 is the thin portion of the structural ceramic body 100, and the thick portion 104b is the thick portion of the structural ceramic body 100. In the through holes 108 and 110, the average diameter of the through holes 108 is smaller closer to the thin portion 104a of the upper surface 104, and the average diameter of the through holes 110 is larger closer to the thick portion 104b of the upper surface 104. For example, the average diameter of the through holes 108 may be smaller than the average diameter of the through holes 110, and the number of the through holes 108 may be smaller than the number of the through holes 110. From the standpoint of structural strength, it is preferable that the distance s1 from the inner surface 112 of the center C1 of the through-hole 108 to the thinnest part of the thin portion 104a be greater than the thinnest thickness t1 of the structural ceramic body 100.

[0036] In another embodiment, as shown in FIG. 2B, the bottom surface 102 and the top surface 104 of the structural ceramic body 100 are parallel to each other, so that the structure of FIG. 2B does not have a thin portion and a thick portion. The through holes 108, 110 are formed in a funnel shape, and the hole diameters of the through holes 108, 110 are gradually enlarged from the bottom surface 102 to the top surface 104. The through holes are formed in a funnel shape, so that the contact area between the top surface 104 of the structural ceramic body 100 and the vertebrae is reduced, the effective stiffness of the structural ceramic body 100 is reduced, and the subsequent unidirectional filling of the bone prosthesis (not shown) is also facilitated. As described above, the elastic modulus can be adjusted by changing the number of the through holes 108, 110 and the size of the opening, so that the stiffness of the structural ceramic body 100 can be further reduced.

[0037] In other embodiments, as shown in FIG. 2C, the bottom surface 102 and top surface 104 of the structural ceramic body 100 are wavy or sawtooth, or the bottom surface 102 and top surface 104 are provided with pyramidal or granular protrusions to enhance fixation to the upper and lower vertebrae.

[0038] In another embodiment, as shown in FIG. 2D, the perimeter 106 of the structural ceramic body 100 may be arcuate to help distribute stress within the structural ceramic body 100.

[0039] In another embodiment, the bottom surface 102 and the top surface 104 of the structural ceramic body 100 are inclined surfaces and are not parallel to each other. For example, the intervertebral fusion device 10 has a structure similar to that of FIG. 2A, but the bottom surface 102 of the structural ceramic body 100 is inclined from the thick portion 104b to the thin portion 104a, so that the thickness of the thinnest portion is smaller than t1 in FIG. 2A. The average diameter of the through holes 108 is smaller closer to the thin portion 104a, and the average diameter of the through holes 110 is larger closer to the thick portion 104b. Meanwhile, the bottom surface 102 of the structural ceramic body 100 may be inclined from the thin portion 104a to the thick portion 104b in accordance with the curvature of the vertebrae, so that the intervertebral fusion device 10 of the present invention is not limited to the contents shown in the drawings, and the structure can be changed as necessary.

[0040] In the first embodiment of the present invention, the bone filler (not shown) filled in the through holes 108, 110 of the structural ceramic body 100 is, for example, autogenous bone or a synthetic bone filler. The synthetic bone filler may be, but is not limited to, hydroxyapatite, tricalcium phosphate, calcium sulfate, or a solid solution or composite material thereof. By filling the through holes 108, 110 with the bone filler before surgery, the bone filler adheres to the vertebrae after surgery, and ions and substances that help bone healing are slowly released, thereby achieving bone fusion. For example, the bone filler contains ions and growth factors that promote bone healing and bone fusion, such as strontium ions that promote bone formation and suppress bone resorption. The transport of strontium ions in the vertebral region can be achieved by a solid solution of calcium salts and strontium solute. Since the decomposition of the strontium calcium solid solution takes several months to several years, the hardness of the vertebral bone can be maintained for a long period of time by using such a bone filler. The strontium calcium solid solution is filled into the through holes 108, 110 in the form of a bone filler before surgery.

[0041] The intervertebral fusion device 10 may be manufactured by, but is not limited to, the following methods.

[0042] First, in one embodiment, zirconia is used as the main raw material of the structural ceramic body 100, and yttrium oxide or cerium oxide is added to stabilize the crystal phase. In order to avoid deterioration over time in a humid environment (inside the human body), the content of the yttrium oxide is preferably 3 mol% or more. For example, the content of yttrium oxide in zirconia is in the range of 3 mol% to 8 mol%. The content of cerium oxide is preferably 5 mol% or more. Since the rigidity of aluminum oxide is about twice that of zirconia, the addition of aluminum oxide particles suppresses the volume expansion of zirconia and also suppresses the volume expansion of zirconia due to aging, thereby improving the aging resistance of zirconia. Therefore, based on the total weight of the structural ceramic body 100, the content of aluminum oxide is preferably 30 wt% or less, and less than 0.1 wt% of the aluminum oxide dissolves in zirconia.

[0043] In another embodiment, the material of the structural ceramic body 100 can be Ce-TZP / Al2O3, which is resistant to aging at room temperature, and the raw materials include 70 vol% (ZrO2-10 mol% CeO2) and 30 vol% Al2O3.

[0044] In another embodiment, the structural ceramic body 100 is made of a composite material consisting of 67.9 wt% ZrO2, 10.6 wt% CeO2, 21.5 wt% Al2O3, and less than 0.1 wt% other oxides (MgO and / or TiO2).

[0045] The raw materials are then made into a green body, which may be formed by a molding technique such as, but not limited to, die-pressing, isostatic pressing, slip casting, or injection molding, and then subjected to a debinding treatment at a temperature of 600° C. or less to remove all the binder contained in the green body, thereby extending the shelf life of the green body.

[0046] Once the size and shape of the patient-specific intervertebral fusion device 10 is known, a milling machine (e.g., a 5-axis milling machine) is used to machine the green body into the shape of the intervertebral fusion device 10. The size and shape of the patient-specific intervertebral fusion device 10 can be obtained, for example, from an x-ray, MRI, or CT scan, and the scan file can be converted into a digital data file and sent to the milling machine for machining.

[0047] Next, a sintering process is performed. During the sintering process, the green body is expected to experience linear shrinkage of approximately 10% to 20%, so the size of the green body is larger than the size of the sintered intervertebral fusion device 10. Since the shrinkage of the green body is relatively uniform in each direction, it is possible to estimate the dimensions of the green body once the size and shape of the sintered intervertebral fusion device 10 is determined.

[0048] 3 is a top view showing an intervertebral fusion device according to a second embodiment of the present invention. The technical terms of the first embodiment are used for the same components as those of the first embodiment. The description of the same components can be found in the description of the first embodiment, so the description will be omitted.

[0049] 3, the peripheral surface 302 of the structural ceramic body 300 of the intervertebral fusion device 30 is wavy or sawtooth-like, which increases the contact area with the human tissue and prevents the intervertebral fusion device 30 from slipping after implantation between the vertebral bodies. The top surface 300a and bottom surface (not shown) of the structural ceramic body 300 may also be wavy or sawtooth-like, or may have pyramidal or granular protrusions, to enhance fixation to the upper and lower vertebrae. The thin portion 304a is the thin portion of the structural ceramic body 300, and the thick portion 304b is the thick portion of the structural ceramic body 300. Therefore, the through-hole 306 closest to the thin portion 304a is the smallest, the central through-hole 308 is the largest, the through-hole 310 between the through-holes 306 and 308 is intermediate, and the through-holes 312 on either side of the through-hole 308 close to the thick portion 304b are slightly smaller than the central through-hole 308 but larger than the through-hole 310. Note that the intervertebral fusion device 30 is rounded all around (periphery 302) to avoid stress concentration at any one point, and the openings on the top surface 300a and bottom surface (not shown) are also rounded.

[0050] 4 is a top view showing an intervertebral fusion device according to a third embodiment of the present invention. The technical terms of the first embodiment are used for the same components as those of the first embodiment. The description of the same components can be found in the description of the first embodiment, so the description will be omitted.

[0051] As shown in Fig. 4, the distance s2 between the peripheral surface 402 of the structural ceramic body 400 of the intervertebral fusion device 40 and the nearest through-holes 108, 110 is the same. The peripheral surface 402 is rounded, that is, the corners 402a of the peripheral surface 402 are rounded. In order to prevent slippage of the intervertebral fusion device 40 after it is embedded between the vertebral bodies and to maintain high stability of the intervertebral fusion device 40 embedded in the vertebrae, the peripheral surface 402 of the intervertebral fusion device 40 is wavy (or sawtooth) as shown in Fig. 4. In addition, the top surface 400a and the bottom surface (not shown) of the intervertebral fusion device 40 may also be wavy (or sawtooth) (or may have cone-shaped or granular protrusions) to strengthen the fixation to the upper and lower vertebrae.

[0052] Below, several simulation experiments for verifying the effects of the present invention will be shown, but the present invention is not limited to the following contents.

[0053] <Comparative Example 1>

[0054] Structure: As shown in the top view of Figure 5, the square structure has a square hole in the center. The top and bottom surfaces of the square structure are both 12 mm x 12 mm, and the thickness of the structure is 9 mm. The size of the square hole is 8 mm x 8 mm (the inner surface is flat). The top surface area of ​​the square structure is 80 mm 2 The through holes occupy 44% of the top surface area.

[0055] Simulation method: Apply a normal force of 30,000N to the top surface, calculate the maximum equivalent stress (von Mises stress) and average stress generated during the compression process, and analyze the above structure through simulation structural calculation.

[0056] Simulation results: The maximum stress was 805 MPa, and the average stress was 361 MPa. It can be seen that the maximum stress occurs at the four outer corners of the base of the square structure, and that the stress is concentrated at the right angles.

[0057] <Comparative Example 2>

[0058] Structure: As shown in the top view of Figure 6, the square structure has three circular through holes. The top and bottom surfaces of the square structure are both 12 mm × 12 mm, and the thickness of the structure is 9 mm. The diameter of each circular through hole is 3 mm (the inner surface is flat). The top surface area of ​​the square structure is 123 mm. 2 The through holes occupy 15% of the top surface area.

[0059] Simulation method: Apply a normal force of 30,000N to the top surface, calculate the maximum equivalent stress and average stress generated during the compression process, and analyze the above structure through simulation structural calculation.

[0060] Simulation results: The maximum equivalent stress is 552 MPa, and the average stress is 233 MPa. This comparison shows that as the area of ​​the structure increases, both the maximum equivalent stress and the average stress decrease. The maximum stress occurs at the four outer corners of the base of the square structure, which shows that the stress is concentrated at the right angles.

[0061] <Example 1>

[0062] Structure: As shown in the top view of Figure 7, in the wavy structure, the three circular through holes have inwardly convex curved surfaces, the two larger through holes have an outer diameter of 4 mm and a central diameter of 2 mm, the smaller through hole has an outer diameter of 3 mm and a central diameter of 1.5 mm, and the thickness of the structure is 9 mm. The top surface area of ​​the structure is 73 mm 2 The through holes occupy 42% of the top surface area. In this structure, all corners are rounded.

[0063] Simulation method: Apply a normal force of 30,000N to the top surface, calculate the maximum equivalent stress and average stress generated during the compression process, and analyze the above structure through simulation structural calculation.

[0064] Simulation results: The maximum equivalent stress is 568 MPa, and the average stress is 255 MPa. Compared with Comparative Example 2, the upper surface area is 123 mm 2 From 73 mm 2 Even if the stress is reduced to , the maximum equivalent stress and the average stress are hardly increased. According to the simulation results, it is better that no right angle is formed anywhere in the structure to suppress stress concentration. In addition, since the through hole is convex inward, the stress inside the through hole is significantly reduced. Therefore, it is possible to effectively reduce the rigidity of the structure by increasing the opening area and reducing the contact area with the vertebrae. In addition, since the through hole is convex inward, the possibility of internal stress concentration can be reduced. In addition, since the formation of right angles on the surface of the through hole is suppressed, the possibility of stress concentration can be further reduced.

[0065] <Example 2>

[0066] Structure: As shown in the top view of Figure 8, the structure has a wavy shape, the three circular through holes have inwardly convex curved surfaces, the two larger through holes have an outer diameter of 4 mm and a central diameter of 2 mm, the smaller through hole has an outer diameter of 3 mm and a central diameter of 1.5 mm, and the thickness of the structure is 9 mm. The top surface area of ​​the structure is 56 mm 2 The through holes occupy 54% of the top surface area. In this structure, all corners are rounded.

[0067] Simulation method: Apply a normal force of 30,000N to the top surface, calculate the maximum equivalent stress and average stress generated during the compression process, and analyze the above structure through simulation structural calculation.

[0068] Simulation results: The maximum equivalent stress is 738 MPa, and the average stress is 303 MPa. Compared with Comparative Example 2, the upper surface area is 123 mm 2 From 56 mm 2 Even if the thickness of the through hole is significantly reduced to 10 mm, the increase in the average stress is limited. The simulation results show that it is better to prevent right angles from being formed anywhere in the structure to prevent stress concentration. In addition, the through hole is convex inward, so the stress inside the through hole is significantly reduced. In addition, the corrugated design can reduce the area of ​​the top and bottom surfaces, and reduce the contact area with the vertebrae, which can effectively reduce the rigidity of the structure. In addition, the through hole is convex inward, so the possibility of internal stress concentration can be reduced. In addition, the formation of right angles on the surface of the through hole can be prevented, so the possibility of stress concentration can be further reduced.

[0069] Analyzing these four examples, we can see that:

[0070] A. In order to reduce stress concentration, it is better to avoid forming right angles anywhere in the structure.

[0071] B. The smaller the area of ​​the top and bottom surfaces of the structure, the lower the rigidity of the structure. The inward convex design of the through holes can reduce the possibility of internal stress concentration.

[0072] As described above, the present invention provides an intervertebral fusion device that can be used to replace damaged cervical or lumbar discs and has adjustable stiffness to meet the needs of each patient. The material of the intervertebral fusion device is ceramic, which is harmless to the human body, has sufficient strength to support the body weight, and does not interfere with electromagnetic waves such as X-rays, MRI, and CT, making it easy to follow up after surgery.

[0073] The present invention has been disclosed as an embodiment, but is not intended to be limited thereto. Those skilled in the art may make some variations and modifications without departing from the scope of the present invention, which is defined in the appended claims. [Explanation of symbols]

[0074] 10, 30, 40 intervertebral fusion devices 100, 300, 400 Structural ceramic body 102 Bottom 104, 300a, 400a top 104a, 304a Thin section 104b, 304b thick part 106, 302, 402 circumferential surface 108, 110, 306, 308, 310, 312 Through holes 112 Inside 402a Corner C1, C2 center RR stop s1, s2 distance t1 thickness

Claims

1. 1. An intervertebral fusion device having a structural ceramic body having a bottom surface, a top surface, a peripheral surface connecting the bottom surface and the top surface, and up to three through holes extending through the bottom surface and the top surface, an area ratio of a total opening area of ​​the through holes in the upper surface to an area of ​​the upper surface is 20% or more; The inner surface of the through hole is formed into an inwardly convex curved surface, The diameter of the through hole is gradually enlarged from the center of the through hole toward the bottom surface and the top surface, corners between the peripheral surface and the top surface and the bottom surface are rounded to an extreme extent, and corners between the inner surface of the through hole and the top surface and the bottom surface are also rounded to an extreme extent, An intervertebral fusion device, wherein the peripheral surface is wavy or sawtooth.

2. The material of the structural ceramic body is zirconium oxide (ZrO ２ ), aluminum oxide (Al ２ O ３ ), cerium oxide (CeO ２ ), yttrium oxide (Y ２ O ３ ), magnesium oxide (MgO), titanium oxide (TiO ２ ), silicon oxide (SiO ２ 10. The intervertebral fusion device of claim 1, comprising: zinc oxide (ZnO), bioactive glass (Bioglass), silicon nitride, silicon carbide, or composites thereof.

3. The materials for the structural ceramic body include yttrium-stabilized tetragonal zirconia (Y-TZP), cerium-stabilized tetragonal zirconia (Ce-TZP), and a composite material of yttrium-stabilized tetragonal zirconia and aluminum oxide (Y-TZP / Al ２ O ３ ), or a composite of cerium-stabilized tetragonal zirconia and aluminum oxide (Ce-TZP / Al ２ O ３ 10. The intervertebral fusion device of claim 1, comprising:

4. 2. The intervertebral fusion device of claim 1, wherein said bottom surface and said top surface of said structural ceramic body are parallel to one another.

5. 2. The intervertebral fusion device of claim 1, wherein said bottom surface and said top surface are non-parallel to one another.

6. 6. The intervertebral fusion device of claim 5, wherein the structural ceramic body has a thin portion and a thick portion, the average diameter of the through holes being smaller closer to the thin portion and larger closer to the thick portion.

7. 2. The intervertebral fusion device of claim 1, wherein said circumferential surface is arcuate.

8. 10. The intervertebral fusion device of claim 1, wherein said through holes of said structural ceramic body are filled with a bone filler material.

9. 2. The intervertebral fusion device according to claim 1, wherein a ratio of a total opening area of ​​said through holes on said upper surface to an area of ​​said upper surface is 50% or more.

10. 2. The intervertebral fusion device of claim 1, wherein the bottom and top surfaces of the structural ceramic body are both wavy or sawtooth, or the bottom and top surfaces are provided with conical or granular protrusions.

11. 2. The intervertebral fusion device of claim 1, wherein said through holes are multiple in number and distributed throughout said structural ceramic body.

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