Bone fixation plates and plate sets

Abstract

To improve stress distribution in bone fixation plates for maxillary osteoplasty made of bioabsorbable material. [Solution] The Step Plate SP is a bone fixation plate made of bioabsorbable material used in maxillary osteoplasty. The Step Plate SP comprises a first annular portion 11, a second annular portion 12, and a third annular portion 13, a first connecting portion 14 connecting the first annular portion 11 and the second annular portion 12, and a second connecting portion 15 connecting the second annular portion 12 and the third annular portion 13. The second connecting portion 15 comprises a step 10S bent in the thickness direction of the Step Plate SP. The width of the second annular portion 12 is greater than the width of the first annular portion 11. The width of the second connecting portion 15 is greater than the width of the first connecting portion 14.

Description

Technical Field

[0001] The present invention relates to an osteosynthesis plate and a plate set used for maxillofacial osteotomy.

Background Art

[0002] Le Fort I osteotomy (hereinafter also referred to as LI), which is an example of maxillofacial osteotomy, is widely known as a surgical procedure for treating jaw deformities by changing the position of the upper jaw. In LI, the upper jaw bone is cut horizontally, and the lower part of the cut upper jaw bone is fixed in a moved state at the target position, thereby promoting bone healing while preventing recurrence of jaw deformities. As an example of LI, a method of fixing maxillary bone fragments with plates at a total of four locations, namely the lateral margins of the piriform aperture and the subzygomatic crest on both the left and right sides of the face, is widely used as an excellent fixation method. In general, the lateral margin of the piriform aperture refers to a position adjacent to the lateral edge of the piriform aperture.

[0003] [[ID=1**]]

[0004] To solve these problems, for example, the development of bioabsorbable materials such as poly-L-lactic acid (PLLA) has been promoted. In addition, as an example of a bioabsorbable material, HA / PLLA, which is a composite material combining hydroxyapatite (HA) and poly-L-lactic acid, is known. Since HA / PLLA has useful functions as an osteosynthesis material, such as excellent shape processability, osteoconductivity, and bioactive effects, it is used for the treatment of jaw deformities.

[0005] ​ On the other hand, HA / PLLA is known to have inferior mechanical strength compared to metallic materials such as titanium. Therefore, a combination of titanium plates and bioabsorbable material plates is generally employed. For example, Non-Patent Literature 1 discloses a technique in which a titanium plate is used on the infrazygomatic ridge while a bioabsorbable PLLA plate is used next to the piriform orifice. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Masaki Nagai, et al., "On the stability of the jawbone after maxillofacial repositioning surgery in patients with mandibular prognathism," Journal of the Japanese Society for Jaw Deformities, August 2008, Vol. 18, No. 3, pp. 214-220. [Overview of the project] [Problems that the invention aims to solve]

[0007] The technology disclosed in Non-Patent Document 1 involves applying plates made of bioabsorbable materials to some of the plates used in LI (Liquid Insulation). In other words, the technology disclosed in Non-Patent Document 1 does not make all of the plates used in LI from bioabsorbable materials. Furthermore, because the face has numerous nerves and a delicate distribution of bone strength, the shape design of the plates requires precision. For this reason, it was technically difficult to make all of the plates used in LI from bioabsorbable materials. [Means for solving the problem]

[0008] The bone fixation plate for solving the above problem is a bone fixation plate used in maxillary osteoplasty, used on the side of the piriform orifice, and is L-shaped by a first long side portion extending along a first long side direction and a first short side portion extending along a first short side direction intersecting the first long side direction, the first long side portion comprising a first annular portion, a second annular portion, and a third annular portion aligned along the first long side direction, a first connecting portion connecting the first annular portion and the second annular portion, and a second connecting portion connecting the second annular portion and the third annular portion, the first short side portion comprising a fourth annular portion located in the first short side direction relative to the third annular portion, and a third connecting portion connecting the third annular portion and the fourth annular portion, the material constituting the bone fixation plate is a bioabsorbable material, and the second connecting The part comprises a step bent in the thickness direction of the bone joint plate, the thickness of the bone joint plate is 0.9 mm to 1.6 mm, the tensile yield stress of the bioabsorbable material is 60 MPa to 80 MPa, the length of the first long side is 15 mm to 25 mm, the angle between the first long side and the first short side is 90 degrees to 105 degrees, each of the first annular part, the second annular part, the third annular part, and the fourth annular part is provided with a first through hole having a diameter of 1.5 mm to 3.0 mm, the width of the first annular part is 4.6 mm ± 0.3 mm in the direction perpendicular to the first long side direction, the width of the second annular part is greater than the width of the first annular part, and the width of the first connecting part is 2.3 mm ± 0.The width of the second connecting portion is 3 mm, the width of the second connecting portion is greater than the width of the first connecting portion and less than the width of the second annular portion, the bone fixation plate is a first step plate used as a first bone fixation plate in combination with a second bone fixation plate used in the lower zygomatic ridge in maxillary osteoplasty, the second bone fixation plate is one selected from a second step plate and a non-step plate, which have the same shape and material as the first step plate, the non-step plate has a flat shape and forms an L shape with a second long side portion extending along the second long side direction and a second short side portion extending along the second short side direction intersecting the second long side direction, the second long side portion has a fifth annular portion, a sixth annular portion and a seventh annular portion aligned along the second long side direction, a fourth connecting portion connecting the fifth annular portion and the sixth annular portion, and a fifth connecting portion connecting the sixth annular portion and the seventh annular portion, The non-step plate comprises, the second short side portion having an eighth annular portion located in the second short side direction relative to the seventh annular portion, and a sixth connecting portion connecting the seventh annular portion and the eighth annular portion, the material constituting the non-step plate being the bioabsorbable material, the thickness of the non-step plate being equal to the thickness of the first bone joint plate, the length of the second long side portion being 15 mm or more and 25 mm or less, and the inferior angle between the second long side portion and the second short side portion being 90 degrees or more and 1 The angle is 0.5 degrees or less, and each of the fifth, sixth, seventh, and eighth annular portions is provided with a second through-hole having a diameter of 1.5 mm to 3.0 mm. In the direction perpendicular to the second long side direction, the width of the fourth connecting portion is 2.3 mm ± 0.3 mm, and the width of the fifth connecting portion is greater than the width of the fourth connecting portion and smaller than the width of the second connecting portion in the direction perpendicular to the first long side direction of the first bone fixation plate.

[0009] In the step plate described above, by making the width of the second annular portion larger than the width of the first annular portion, and by making the width of the second connecting portion larger than the width of the first connecting portion, the stress distribution of the second connecting portion and the second annular portion, which are subjected to relatively high stress, can be improved. Furthermore, by making the width of the fifth connecting portion of the non-step plate larger than the width of the fourth connecting portion, and smaller than the width of the second connecting portion in the step plate, the stress distribution of the fifth connecting portion of the non-step plate can be improved while ensuring workability. In addition, since the face has many nerves and a delicate bone strength distribution, it is desirable to increase the dimensions of only the areas where relatively high stress is applied, rather than simply increasing the overall dimensions of the bone joint plate. In this respect, according to this embodiment, the stress distribution can be suitably improved while suppressing excessive enlargement of the step plate and non-step plate made of bioabsorbable material.

[0010] In the above-described bone fixation plate, the width of the second annular portion may be 5.1 mm ± 0.3 mm in the direction perpendicular to the first long side direction, and the width of the second connecting portion may be 3.3 mm or more and 4.5 mm or less. With the above configuration, even when a load of 600 N, which is assumed to be a sudden occlusal force, is applied, it is possible to suppress the application of stress exceeding the tensile yield stress to the step plate made of bioabsorbable material.

[0011] In the bone joint plate described above, the height of the step may be configured to be between 1.0 mm and 5.0 mm. By setting the height of the step of the step plate to between 1.0 mm and 5.0 mm, the stress distribution of the second connection portion and the second annular portion can be suitably improved.

[0012] In the above-described bone fixation plate, the tensile yield stress of the bioabsorbable material may be 70 MPa or higher. By adopting the dimensional setting of this embodiment for a bone fixation plate made of the above-described bioabsorbable material, it is possible to suppress the application of stress to the bone fixation plate that exceeds the tensile yield stress, even when a load of 600 N, which is assumed to be a sudden occlusal force, is applied.

[0013] In the above-described bone fixation plate, the bioabsorbable material may consist of at least one selected from the group consisting of hydroxyapatite, tricalcium phosphate, apatite carbonate, and octacalcium phosphate, and polylactic acid or a lactic acid-glycolic acid copolymer. Any of the above-described bioabsorbable materials can achieve the mechanical strength required for a bone fixation plate.

[0014] In the bone joint plate described above, the width of the fifth annular portion may be 4.6 mm ± 0.3 mm in the direction perpendicular to the second long side direction, the width of the sixth annular portion may be greater than the width of the fifth annular portion and 5.1 mm ± 0.3 mm, and the width of the fifth connecting portion may be 3.0 mm ± 0.2 mm. By setting the width of the fifth connecting portion in the non-step plate within the above range, the stress distribution can be improved while ensuring more favorable workability at the fifth connecting portion of the non-step plate. Furthermore, by setting the width of the sixth annular portion in the non-step plate within the above range, the stress distribution of the sixth annular portion, which may be subjected to high stress, can be improved.

[0015] A plate set for solving the above problem is a plate set comprising: a step plate used in maxillary osteoplasty for at least one of the lateral piriform or subzygomatic ridge; and a non-step plate used in maxillary osteoplasty for the subzygomatic ridge and in combination with the step plate used in the lateral piriform or ridge, wherein the material constituting the step plate and the non-step plate is a bioabsorbable material, the step plate is formed in an L shape by a first long side portion extending along a first long side direction and a first short side portion extending along a first short side direction intersecting the first long side direction, the first long side portion comprises a first annular portion, a second annular portion, and a third annular portion aligned along the first long side direction, a first connecting portion connecting the first annular portion and the second annular portion, and a second connecting portion connecting the second annular portion and the third annular portion, and the first short side portion is the The step plate comprises a fourth annular portion located in the first short-side direction relative to the third annular portion, and a third connecting portion connecting the third annular portion and the fourth annular portion, wherein the second connecting portion comprises a step bent in the thickness direction of the step plate, the thickness of the step plate is 0.9 mm or more and 1.6 mm or less, the tensile yield stress of the bioabsorbable material is 60 MPa or more and 80 MPa or less, and the length of the first long side portion is 15 mm or more and 25 mm or less, and the The inferior angle between the first long side and the first short side is 90 degrees or more and 105 degrees or less. Each of the first, second, third, and fourth annular sections is provided with a first through-hole having a diameter of 1.5 mm or more and 3.0 mm or less. In the direction perpendicular to the first long side direction, the width of the first annular section is 4.6 mm ± 0.3 mm, the width of the second annular section is greater than the width of the first annular section, and the width of the first connecting section is 2.3 mm ± 0.The width of the second connecting portion is 3 mm, and the width of the second connecting portion is greater than the width of the first connecting portion and less than the width of the second annular portion. The non-step plate has a flat shape and is formed by a second long side portion extending along the second long side direction and a second short side portion extending along the second short side direction intersecting the second long side direction. The second long side portion includes a fifth annular portion, a sixth annular portion, and a seventh annular portion aligned along the second long side direction, a fourth connecting portion connecting the fifth annular portion and the sixth annular portion, and a fifth connecting portion connecting the sixth annular portion and the seventh annular portion. The second short side portion includes an eighth annular portion located in the second short side direction relative to the seventh annular portion, and a second connecting portion connecting the seventh annular portion and the eighth annular portion. The plate set comprises six connecting portions, the thickness of the non-step plate being equal to the thickness of the step plate, the length of the second long side being 15 mm to 25 mm, the inferior angle between the second long side and the second short side being 90 degrees to 105 degrees, each of the fifth, sixth, seventh, and eighth annular portions having a second through-hole with a diameter of 1.5 mm to 3.0 mm, the width of the fourth connecting portion being 2.3 mm ± 0.3 mm in the direction perpendicular to the second long side direction, the width of the fifth connecting portion being greater than the width of the fourth connecting portion and smaller than the width of the second connecting portion in the direction perpendicular to the first long side direction of the step plate. A plate set combining a step plate and a non-step plate allows for the selection of an optimally shaped bone fixation plate according to the patient's skeletal shape and the amount of movement of the lower bone relative to the upper bone.

[0016] In the above plate set, the width of the second annular portion is 5.1 mm ± 0.3 mm in the direction perpendicular to the first long side direction, the width of the second connecting portion is 3.3 mm or more and 4.5 mm or less, the width of the fifth annular portion is 4.6 mm ± 0.3 mm in the direction perpendicular to the second long side direction, the width of the sixth annular portion is greater than the width of the fifth annular portion and is 5.1 mm ± 0.3 mm, and the width of the fifth connecting portion is 3.0 mm ± 0.2 mm. [Effects of the Invention]

[0017] According to the present invention, it is possible to improve the stress distribution in an osteotomy plate for maxillofacial bone formation composed of a bioabsorbable material.

Brief Description of the Drawings

[0018] [Figure 1] Figure 1 is a front view of a skull showing the state of use of the osteotomy plate. [Figure 2] Figure 2 is a side view of a skull showing the state of use of the osteotomy plate. [Figure 3] Figure 3 is a perspective view of a step plate having a 2 mm step. [Figure 4] Figure 4 is a perspective view of a non-step plate. [Figure 5] Figure 5 is a front view of the step plate shown in Figure 3. [Figure 6] Figure 6 is a rear view of the step plate shown in Figure 3. [Figure 7] Figure 7 is a plan view of the step plate shown in Figure 3. [Figure 8] Figure 8 is a bottom view of the step plate shown in Figure 3. [Figure 9] Figure 9 is a right side view of the step plate shown in Figure 3. [Figure 10] Figure 10 is a left side view of the step plate shown in Figure 3. [Figure 11] Figure 11 is a cross-sectional view of the step plate taken along line A-A of Figure 5. [Figure 12] Figure 12 is a cross-sectional view of the step plate taken along line B-B of Figure 5. [Figure 13] Figure 13 is a cross-sectional view of the step plate taken along line C-C of Figure 5. [Figure 14] Figure 14 is a perspective view of a step plate having a 4 mm step. [Figure 15] Figure 15 is a bottom view of the step plate shown in Figure 14. [Figure 16] Figure 16 is a front view of the non-step plate shown in Figure 4. [Figure 17] Figure 17 is a rear view of the non-step plate shown in Figure 4. [Figure 18] Figure 18 is a plan view of the non-step plate shown in Figure 4. [Figure 19] Figure 19 is a bottom view of the non-step plate shown in Figure 4. [Figure 20] Figure 20 is a right side view of the non-step plate shown in Figure 4. [Figure 21] Figure 21 is a left side view of the non-step plate shown in Figure 4. [Figure 22] Figure 22 is a cross-sectional view of the step plate as seen from the DD line in Figure 16. [Figure 23] Figure 23 is a cross-sectional view of the step plate as seen from the EE line in Figure 16. [Figure 24] Figure 24 is a cross-sectional view of the step plate as seen from the FF line in Figure 16. [Figure 25] Figure 25 is a schematic diagram representing the analytical model used for stress analysis. [Figure 26] Figure 26 is a front view of the plate model used for stress analysis. [Figure 27] Figure 27 is a contour plot showing the Von-Mises stress applied to each plate model under a load of 600 N in the preliminary analysis. [Figure 28] Figure 28 is a graph showing the Von-Mises stresses experienced by each part of the first plate model under load in the preliminary analysis. [Figure 29] Figure 29 is a graph showing the Von-Mises stresses experienced by each part of the first plate model in response to the load during the first stress analysis. [Figure 30] Figure 30 is a graph showing the Von-Mises stresses experienced by each part of the first plate model in response to the load during the second stress analysis. [Figure 31] Figure 31 is a graph showing the Von-Mises stresses experienced by each part of the first plate model in response to the load in the third stress analysis. [Figure 32] Figure 32 is a contour plot showing the Von-Mises stresses applied to each plate model in the first and fourth stress analyses. [Figure 33] Figure 33 is a contour plot showing the Von-Mises stresses applied to each plate model in the second and fifth stress analyses. [Figure 34] Figure 34 is a contour plot showing the Von-Mises stresses applied to each plate model in the third and sixth stress analyses. [Figure 35] Figure 35 is a graph showing the Von-Mises stresses experienced by each part of the plate model placed on the infrazygomatic ridge when a load of 300 N is applied, in both the seventh stress analysis and the preliminary analysis. [Figure 36] Figure 36 is a graph showing the Von-Mises stresses experienced by each part of the plate model placed next to the pear-shaped opening when a load of 300 N is applied, in both the seventh stress analysis and the preliminary analysis. [Figure 37] Figure 37 is a graph showing the Von-Mises stresses experienced by each part of the plate model placed on the infrazygomatic ridge when a load of 600 N is applied, in both the seventh stress analysis and the preliminary analysis. [Figure 38] Figure 38 is a graph showing the Von-Mises stresses experienced by each part of the plate model placed next to the pear-shaped opening when a load of 600 N is applied, in both the seventh stress analysis and the preliminary analysis. [Figure 39] Figure 39 is a six-view drawing of a step plate (step: 2 mm) that is symmetrical to the step plate shown in Figure 3, where (a) is the front view, (b) is the rear view, (c) is the top view, (d) is the bottom view, (e) is the right side view, and (f) is the left side view. [Figure 40] Figure 40 is a six-view drawing of a non-step plate that is symmetrical to the non-step plate shown in Figure 4, where (a) is the front view, (b) is the rear view, (c) is the top view, (d) is the bottom view, (e) is the right side view, and (f) is the left side view. [Figure 41]Figure 41 is a six-view drawing of a step plate (step: 4 mm) that is symmetrical to the step plate shown in Figure 14, where (a) is the front view, (b) is the rear view, (c) is the top view, (d) is the bottom view, (e) is the right side view, and (f) is the left side view. [Modes for carrying out the invention]

[0019] An embodiment of the osteosynthesis plate and plate set will be described with reference to Figures 1 to 41. The osteosynthesis plate of this embodiment is used in maxillary osteoplasty. The plate set includes multiple osteosynthesis plates.

[0020] <Usage Status> First, the usage of the bone fixation plate will be explained with reference to Figures 1 and 2. Figures 1 and 2 illustrate a skull 100 that has undergone a Le Fort I osteotomy (hereinafter referred to as LI), which is an example of maxillary osteoplasty.

[0021] As shown in Figures 1 and 2, the bone fixation plate of this embodiment, in the LI, joins and fixes a lower bone portion 101, which includes the lower part of the maxilla cut laterally, and an upper bone portion 102, which includes the upper part of the maxilla and the adjacent zygomatic bone. In the LI, with the lower bone portion 101 moved back and forth to match the mandible 103, the lower bone portion 101 and the upper bone portion 102 are joined and fixed by the bone fixation plate.

[0022] In this embodiment, a pair of first bone fixation plates P1 and a pair of second bone fixation plates P2 are used to join and fix the lower bone portion 101 and the upper bone portion 102. The first bone fixation plates P1 are positioned adjacent to the lateral edges of the piriform aperture 104 on both the left and right sides. The second bone fixation plates P2 are positioned on the inferior ridges 105 of the zygomatic bones on both the left and right sides. The first bone fixation plates P1 are positioned closer to the piriform aperture 104 than the second bone fixation plates P2.

[0023] The pair of first bone fixation plates P1, one for the left and one for the right, have a roughly L-shape that is symmetrical to each other. Similarly, the pair of second bone fixation plates P2, one for the left and one for the right, also have a roughly L-shape that is symmetrical to each other. These bone fixation plates are fixed to the lower bone portion 101 and the upper bone portion 102, respectively, by fixing screws.

[0024] In addition, by combining LI with mandibular osteoplasty such as sagittal split ramus osteotomy, the position of not only the lower bone portion 101 of the maxilla but also the mandible 103 may be altered. In this case, the mandible 103 is divided into three sections, left and right, and then the central section is repositioned anteriorly and posteriorly before the mandible 103 is fixed using a pair of third osteosynthesis plates P3 on the left and right sides. The third osteosynthesis plates P3 may have any shape.

[0025] <Bone fixation plate> Refer to Figures 3 to 24 to explain the bone fixation plates used in LI. Note that in Figure 3 and Figures 5 to 15, the X1, Y1, and Z1 axes are three mutually orthogonal axes. Also, in Figure 4 and Figures 16 to 24, the X2, Y2, and Z2 axes are three mutually orthogonal axes.

[0026] Figures 3 to 24 illustrate the shape of the bone fixation plate used on the left side of skull 100 (right side in Figure 1) as viewed from the patient. The shape of the bone fixation plate used on the right side of skull 100 (left side in Figure 1) as viewed from the patient is symmetrical to the shape of the bone fixation plate used on the left side of skull 100.

[0027] As shown in Figure 3, the step plate SP is formed in a substantially L-shape by a first long side portion 10 extending along the first long side direction and a first short side portion 20 extending along the first short side direction intersecting the first long side direction. The first long side portion 10 of the step plate SP is provided with a step 10S, which is a step bent in the thickness direction of the step plate SP.

[0028] As shown in Figure 4, the non-step plate NP forms a substantially L-shape with a second long side portion 30 extending along the second long side direction and a second short side portion 40 extending along the second short side direction intersecting the second long side direction. The non-step plate NP has a flat shape without a stepped shape bent in the thickness direction.

[0029] The first osteosynthesis plate P1 is a step plate SP as shown in Figure 3. The second osteosynthesis plate P2 is one of either the step plate SP shown in Figure 3 or the non-step plate NP shown in Figure 4.

[0030] In other words, in LI, step plates SP may be used for both the first bone fixation plate P1 and the second bone fixation plate P2. In this case, the step plate SP used as the first bone fixation plate P1 is the first step plate, and the step plate SP used as the second bone fixation plate P2 is the second step plate. Alternatively, a step plate SP may be used for the first bone fixation plate P1, and a non-step plate NP may be used for the second bone fixation plate P2. Furthermore, a step plate SP may be used for one of the pair of second bone fixation plates P2, and a non-step plate NP may be used for the other of the pair of second bone fixation plates P2. The plate set of this embodiment also includes step plates SP and non-step plates NP.

[0031] The step plate SP shown in Figure 3 and the non-step plate NP shown in Figure 4 are both composed of bioabsorbable materials. The bioabsorbable material includes at least one selected from the group consisting of hydroxyapatite, tricalcium phosphate, carbonate apatite, and octacalcium phosphate, and polylactic acid or a lactic acid-glycolic acid copolymer. Alternatively, the bioabsorbable material may be in the form of a lactic acid-glycolic acid copolymer, polylactic acid, etc. Polylactic acid may be poly-L-lactic acid alone, or it may contain poly-L-lactic acid and poly-D-lactic acid.

[0032] One example of a bioabsorbable material is a composite material containing hydroxyapatite and polylactic acid (hereinafter referred to as HA / PLLA). Because HA / PLLA is thermoplastic, it can be softened by heating it with hot water during surgery, allowing the shape of the bone fixation plate to be adjusted to the patient's skeletal shape.

[0033] The tensile yield stress of the bioabsorbable material is 60 MPa to 80 MPa. A tensile yield stress of 70 MPa or higher is more preferable. The tensile yield stress of the bioabsorbable material refers to the yield stress observed in the stress-strain curve obtained by a tensile test in accordance with JIS K7161-1:2024. The bioabsorbable material used in this embodiment exhibits a yield point in the stress-strain curve.

[0034] <Step Plate SP> The shape of the step plate SP will be described in detail with reference to Figures 5 to 15. As shown in Figures 5 and 6, in the step plate SP, the direction in which the first long side portion 10 extends is along the X1 axis. The thickness direction of the step plate SP is along the Z1 axis.

[0035] The step plate SP comprises a first surface S1 facing the front of the page in Figure 5, and a second surface S2 facing the front of the page in Figure 6. When the step plate SP is fixed to the skull 100, the first surface S1 faces away from the skull 100, and the second surface S2 faces towards the skull 100.

[0036] As shown in Figure 5, the step plate SP has a chamfer E1 on the outer edge of its first surface S1. In contrast, as shown in Figure 6, the second surface S2 of the step plate SP does not have a chamfer E1.

[0037] As shown in Figure 5, the first long side portion 10 comprises a first annular portion 11, a second annular portion 12, and a third annular portion 13. The first annular portion 11, the second annular portion 12, and the third annular portion 13 are arranged in this order along the direction of the first long side. The third annular portion 13 is the part of the first long side portion 10 that connects to the first short side portion 20. The second annular portion 12 is located between the first annular portion 11 and the third annular portion 13.

[0038] The first long side portion 10 includes a first connecting portion 14 and a second connecting portion 15. The first connecting portion 14 connects the first annular portion 11 and the second annular portion 12. The second connecting portion 15 connects the second annular portion 12 and the third annular portion 13.

[0039] The first short side portion 20 extends from the third annular portion 13 in the direction of the first short side intersecting the X1 axis. The first short side portion 20 comprises a fourth annular portion 21 and a third connecting portion 22. The fourth annular portion 21 is located in the direction of the first short side relative to the third annular portion 13. The third connecting portion 22 connects the third annular portion 13 and the fourth annular portion 21.

[0040] When the step plate SP is viewed along the Z1 axis, the inferior angle θ1 between the first long side portion 10 and the first short side portion 20 is between 90 degrees and 105 degrees, for example, 100 degrees. The inferior angle θ1 is the right angle or obtuse angle between the center line CL1 of the first long side portion 10 and the center line CL2 of the first short side portion 20 when the step plate SP is viewed along the Z1 axis. In other words, the inferior angle θ1 is the right angle or obtuse angle between the first long side direction in which the first long side portion 10 extends and the first short side direction in which the first short side portion 20 extends.

[0041] The first annular portion 11, the second annular portion 12, the third annular portion 13, and the fourth annular portion 21 are each provided with a screw insertion hole H1. Each screw insertion hole H1 is a first through hole having the same shape as the others. Fixing screws for fixing the step plate SP to the lower bone portion 101 and the upper bone portion 102 are inserted through the screw insertion holes H1.

[0042] The step plate SP fixes the lower bone portion 101 to the upper bone portion 102 by fixing the first annular portion 11 and the second annular portion 12 to the upper bone portion 102, and by fixing the third annular portion 13 and the fourth annular portion 21 to the lower bone portion 101.

[0043] As shown in Figure 6, the length L1 along the X1 axis in the first long side portion 10 is between 15 mm and 25 mm, for example, about 20 mm. Also, the length L2 along the first short side direction from the end of the third annular portion 13 to the end of the fourth annular portion 21 is between 7 mm and 20 mm, for example, 10 mm.

[0044] The first connecting portion 14 is constricted in the Y1 axis direction perpendicular to the first long side direction, between the first annular portion 11 and the second annular portion 12. The width W1 of the first connecting portion 14 is, for example, 2.3 mm ± 0.3 mm. The width W1 of the first connecting portion 14 is, for example, the minimum width in the Y1 axis direction between the first annular portion 11 and the second annular portion 12. For example, the width W3 of the third connecting portion 22 in the direction perpendicular to the first short side direction is equal to the width W1 of the first connecting portion 14.

[0045] The width W2 of the second connecting portion 15 in the Y1 axis direction is greater than the width W1 of the first connecting portion 14. The width W2 of the second connecting portion 15 is smaller than the width W5 of the second annular portion 12 (see Figure 13), which will be described later. As an example, the width W2 of the second connecting portion 15 is 3.3 mm or more and 4.5 mm or less. It is more preferable that the lower limit of the width W2 of the second connecting portion 15 is 3.5 mm or more.

[0046] As shown in Figures 7 to 10, the plate thickness T1 of the step plate SP is between 0.9 mm and 1.6 mm, for example, between 1.4 mm and 1.6 mm. The second connecting portion 15 is provided with a step 10S, which is a step bent in the Z1 axis direction. In the step plate SP, the third annular portion 13 and the fourth annular portion 21 are offset toward the first surface S1 side along the Z1 axis direction, with respect to the first annular portion 11 and the second annular portion 12, with respect to the step 10S. The step plate SP is configured to fit the step that occurs when the lower bone portion 101 is moved forward relative to the upper bone portion 102, thereby creating a step between the lower bone portion 101 and the upper bone portion 102.

[0047] The height SH of step 10S in step plate SP corresponds to the distance at which the third annular portion 13 and the fourth annular portion 21 are offset toward the first surface S1 side relative to the first annular portion 11 and the second annular portion 12 in the Z1 axis direction. Therefore, the height SH of step 10S may be adjusted according to the amount of forward movement of the lower bone portion 101 relative to the upper bone portion 102.

[0048] The height SH of step 10S is, for example, 1.0 mm or more and 5.0 mm or less. For example, if the target value of the height SH of step 10S is 2 mm, the height SH of step 10S is, as an example, 1.0 mm or more and 3.0 mm or less, preferably 1.5 mm or more and 2.5 mm or less, and more preferably 1.7 mm or more and 2.3 mm or less. In this case, it is more preferable that the upper limit of the height SH of step 10S is 2.0 mm or less. For example, if the target value of the height SH of step 10S is 4 mm, the height SH of step 10S is, as an example, 3.0 mm or more and 5.0 mm or less, preferably 3.5 mm or more and 4.5 mm or less, and more preferably 3.7 mm or more and 4.3 mm or less.

[0049] Figures 3 and 5-13 illustrate the step plate SP1 when the height SH of step 10S is 2.0 mm. As shown in Figures 7 and 8, when the height SH of step 10S is 2.0 mm, step 10S is inclined in the Z1 axis direction at an angle less than perpendicular to the plane containing the X1 and Y1 axes.

[0050] As shown in Figures 11 to 13, the screw insertion hole H1 is provided with a counterbore HE1. The counterbore HE1 is located on the first surface S1 side of the screw insertion hole H1. The counterbore HE1 is formed, for example, at a 45-degree angle with respect to the plane including the first surface S1.

[0051] As shown in Figures 12 and 13, the diameter φD1 of the screw insertion hole H1 is, for example, 1.5 mm to 3 mm, or 1.5 mm to 2.2 mm. As shown in Figure 12, the width W4 of the first annular portion 11 in the Y1 axis direction is, for example, 4.6 mm ± 0.3 mm. It is more preferable that the lower limit of the width W4 of the first annular portion 11 is 4.6 mm or more. Also, for example, the outer diameter of the circular portion of the third annular portion 13 is equal to the width W4 of the first annular portion 11. For example, the width of the fourth annular portion 21 in the direction perpendicular to the first short side direction is equal to the width W4 of the first annular portion 11.

[0052] As shown in Figure 13, the width W5 of the second annular portion 12 in the Y1 axis direction is greater than the width W4 of the first annular portion 11. For example, the width W5 of the second annular portion 12 is 5.1 mm ± 0.3 mm. It is more preferable that the lower limit of the width W5 of the second annular portion 12 is 5.1 mm or greater. Furthermore, the structure is designed to satisfy both the requirement that the width W5 of the second annular portion 12 is greater than the width W4 of the first annular portion 11 and that it satisfies the above numerical range.

[0053] Figures 14 and 15 show step plate SP2 as an example of step plate SP, where the height SH of step 10S is 4.0 mm. As shown in Figures 14 and 15, step plate SP2 with a height SH of 4.0 mm has the same shape as step plate SP1 with a height SH of 2.0 mm, except for step 10S. As shown in Figure 15, when the height SH of step 10S is 4.0 mm, step 10S is bent approximately perpendicular to the plane containing the X1 axis and the Y1 axis.

[0054] <Non-Step Plate NP> The shape of the non-step plate NP will be described in detail with reference to Figures 16 to 24. As shown in Figures 16 and 17, in the non-step plate NP, the direction in which the second long side portion 30 extends is along the X2 axis. The thickness direction of the non-step plate NP is along the Z2 axis.

[0055] The non-step plate NP comprises a third surface S3 facing the front of the paper in Figure 16 and a fourth surface S4 facing the front of the paper in Figure 17. When the non-step plate NP is fixed to the skull 100, the third surface S3 faces away from the skull 100, and the fourth surface S4 faces towards the skull 100.

[0056] As shown in Figure 16, the non-step plate NP has a chamfer E2 on the outer edge of its third surface S3. In contrast, as shown in Figure 17, the fourth surface S4 of the non-step plate NP does not have a chamfer E2.

[0057] As shown in Figure 16, the second long side portion 30 comprises a fifth annular portion 31, a sixth annular portion 32, and a seventh annular portion 33. The fifth annular portion 31, the sixth annular portion 32, and the seventh annular portion 33 are arranged in a straight line in this order along the direction of the second long side. The seventh annular portion 33 is the part of the second long side portion 30 that connects to the second short side portion 40. The sixth annular portion 32 is located between the fifth annular portion 31 and the seventh annular portion 33.

[0058] The second long side portion 30 includes a fourth connecting portion 34 and a fifth connecting portion 35. The fourth connecting portion 34 connects the fifth annular portion 31 and the sixth annular portion 32. The fifth connecting portion 35 connects the sixth annular portion 32 and the seventh annular portion 33.

[0059] The second short side portion 40 extends from the seventh annular portion 33 in the direction of the second short side, intersecting the X2 axis. The second short side portion 40 comprises the eighth annular portion 41 and the sixth connecting portion 42. The eighth annular portion 41 is located in the direction of the second short side relative to the seventh annular portion 33. The sixth connecting portion 42 connects the seventh annular portion 33 and the eighth annular portion 41.

[0060] When the non-step plate NP is viewed along the Z2 axis, the inferior angle θ2 between the second long side portion 30 and the second short side portion 40 is between 90 degrees and 105 degrees, for example, 100 degrees. The inferior angle θ2 is the right angle or obtuse angle between the center line CL3 of the second long side portion 30 and the center line CL4 of the second short side portion 40 when the non-step plate NP is viewed along the Z2 axis. In other words, the inferior angle θ2 is the right angle or obtuse angle between the direction of the second long side in which the second long side portion 30 extends and the direction of the second short side in which the second short side portion 40 extends.

[0061] The fifth annular portion 31, the sixth annular portion 32, the seventh annular portion 33, and the eighth annular portion 41 are each provided with screw insertion holes H2. Each screw insertion hole H2 is a second through hole having the same shape as the others. Fixing screws for fixing the non-step plate NP to the lower bone portion 101 and the upper bone portion 102 are inserted through the screw insertion holes H2.

[0062] The non-step plate NP fixes the lower bone portion 101 to the upper bone portion 102 by fixing the fifth annular portion 31 and the sixth annular portion 32 to the upper bone portion 102, and fixing the seventh annular portion 33 and the eighth annular portion 41 to the lower bone portion 101.

[0063] The non-step plate NP has a substantially flat plate shape that does not have a stepped shape corresponding to step 10S of the step plate SP. The non-step plate NP is used in places where the step difference between the lower bone portion 101 and the upper bone portion 102 is small, for example, when the movement of the lower bone portion 101 relative to the upper bone portion 102 is biased to either the left or right side in addition to parallel movement in the front and back. Alternatively, the non-step plate NP is used when moving the lower bone portion 101 backward relative to the upper bone portion 102. In addition, if the step difference between the lower bone portion 101 and the upper bone portion 102 is small, the non-step plate NP may also be used for the first bone fixation plate P1 positioned next to the piriform foramen.

[0064] As shown in Figure 17, the length L3 along the X2 axis in the second long side portion 30 is between 15 mm and 25 mm, for example, about 20 mm. Also, the length L4 along the second short side direction from the end of the seventh annular portion 33 to the end of the eighth annular portion 41 is between 7 mm and 20 mm, for example, about 10 mm.

[0065] The fourth connecting portion 34 is constricted in the Y2 axis direction perpendicular to the second long side direction, between the fifth annular portion 31 and the sixth annular portion 32. The width W6 of the fourth connecting portion 34 is, for example, 2.3 mm ± 0.3 mm. The width W6 of the fourth connecting portion 34 is, for example, the minimum width in the Y2 axis direction between the fifth annular portion 31 and the sixth annular portion 32. For example, the width W8 of the sixth connecting portion 42 in the direction perpendicular to the second short side direction is equal to the width W6 of the fourth connecting portion 34.

[0066] The width W7 of the fifth connection portion 35 in the Y2 axis direction is greater than the width W6 of the fourth connection portion 34. Also, the width W7 of the fifth connection portion 35 is smaller than the width W2 of the second connection portion 15 in the step plate SP. The width W7 of the fifth connection portion 35 is preferably, for example, 3.0 mm ± 0.2 mm.

[0067] As shown in Figures 18 to 21, the plate thickness T2 of the non-step plate NP is equal to the plate thickness T1 of the step plate SP. That is, the plate thickness T2 of the non-step plate NP is between 0.9 mm and 1.6 mm, for example, between 1.4 mm and 1.6 mm.

[0068] As shown in Figures 22 to 24, as an example, the screw insertion hole H2 of the non-step plate NP has the same shape as the screw insertion hole H1 of the step plate SP. That is, the screw insertion hole H2 is provided with a counterbore HE2. The counterbore HE2 is provided on the third surface S3 side of the screw insertion hole H2. The counterbore HE2 is formed at a 45-degree angle with respect to the plane including the third surface S3. As shown in Figures 23 and 24, the diameter φD2 of the screw insertion hole H2 is, for example, 1.5 mm to 3 mm, and as an example, 1.5 mm to 2.2 mm.

[0069] As shown in Figure 23, the width W9 of the fifth annular portion 31 in the Y2 axis direction is, for example, 4.6 mm ± 0.3 mm. It is more preferable that the lower limit of the width W9 of the fifth annular portion 31 be 4.6 mm or greater. Also, for example, the outer diameter of the circular portion of the seventh annular portion 33 is equal to the width W9 of the fifth annular portion 31. For example, the width of the eighth annular portion 41 in the direction perpendicular to the second short side direction is equal to the width W9 of the fifth annular portion 31.

[0070] As shown in Figure 24, the width W10 of the sixth annular portion 32 in the Y2 axis direction is greater than the width W9 of the fifth annular portion 31. For example, the width W10 of the sixth annular portion 32 is 5.1 mm ± 0.3 mm. It is more preferable that the lower limit of the width W10 of the sixth annular portion 32 be 5.1 mm or greater. Furthermore, the structure is designed to satisfy both the requirement that the width W10 of the sixth annular portion 32 is greater than the width W9 of the fifth annular portion 31 and that it satisfies the above numerical range.

[0071] <Stress analysis of bone fixation plates> Next, with reference to Figures 25 to 37, a stress analysis simulation performed to determine the dimensions of the bone fixation plate in this embodiment will be described. In this simulation, the stress applied to the bone fixation plate during occlusion was estimated by finite element analysis.

[0072] Figure 25 shows the analysis model 200 used in this simulation. The analysis model 200 is a three-dimensional mesh model for performing finite element analysis. The analysis model 200 comprises a lower bone model 201, an upper bone model 202, a pressure piece model 203, and a plate model.

[0073] The lower bone model 201 is a three-dimensional model that reproduces the lower bone 101 of the patient. The upper bone model 202 is a three-dimensional model that reproduces the upper bone 102 of the patient. The lower bone model 201 and the upper bone model 202 can be created using postoperative CT (Computed Tomography) images of the skull 100 of a patient who actually underwent LI.

[0074] The plate model is positioned across the lower bone model 201 and the upper bone model 202. The analysis model 200 includes the first plate model 211, the second plate model 212, the third plate model 213, and the fourth plate model 214 as plate models. Each plate model is fixed to the lower bone model 201 and the upper bone model 202 together with the screw-shaped model 220.

[0075] The first plate model 211 and the second plate model 212 are three-dimensional models that reproduce the first osteosynthesis plate P1, which is positioned next to the piriform aperture in the skull 100. The third plate model 213 and the fourth plate model 214 are three-dimensional models that reproduce the second osteosynthesis plate P2, which is positioned on the inferior zygomatic crest 105 in the skull 100. The first plate model 211 and the third plate model 213 are located to the left of the piriform aperture 104 as viewed from the patient. The second plate model 212 and the fourth plate model 214 are located to the right of the piriform aperture 104 as viewed from the patient.

[0076] The pressure piece model 203 is a plate-shaped model used to apply a load F1, which replicates the occlusal force from the mandible 103, to the maxillary dentition of the lower bone model 201. In this simulation, the load F1 is applied to the lower bone model 201 by vertically displacing the pressure piece model 203 from bottom to top.

[0077] Generally, occlusal force is considered to be around 75N to 300N. For example, there have been reports of patients who underwent LI in combination with sagittal split ramus osteotomy having an occlusal force of approximately 316N preoperatively, approximately 159N one month postoperatively, and approximately 254N one year postoperatively. On the other hand, LI is sometimes performed alone without surgery on the mandible. Also, since there are individual differences in occlusal force, when considering the shape of the bone fixation plate in stress analysis simulation, it is necessary to consider occlusal forces above the average. For example, there have been reports of cases where an occlusal force of around 500N to 600N was observed one year postoperatively, although it was sudden. Therefore, the load F1 in this embodiment was set to at least 600N or more.

[0078] In the lower bone model 201, a mouthpiece-like model shape is added to the lower part of the maxillary dentition, creating a nearly flat surface that faces the pressure piece model 203. That is, the load F1 from the pressure piece model 203 is applied vertically to the lower bone model 201.

[0079] The lower bone model 201 and the upper bone model 202 are positioned to match the relative position of the lower bone 101 to the upper bone 102 in the actual LI. Therefore, each plate model is positioned to match the actual usage of the LI. In this simulation, the lower bone model 201 was moved 2 mm forward relative to the upper bone model 202.

[0080] Furthermore, a 1 mm gap is provided between the lower bone model 201 and the upper bone model 202. If the postoperative CT image of the patient's skull 100 were simply modeled in three dimensions as the analysis model 200, unintended interference between bones may occur depending on the patient's skeletal shape. In this regard, providing a gap between the lower bone model 201 and the upper bone model 202 avoids unintended interference between the two bone models.

[0081] Furthermore, in this simulation, the bone surrounding the lower bone model 201 and upper bone model 202, including the portion corresponding to the mandible 103, is omitted, and a load F1, which reproduces the occlusal force from the mandible 103, is applied perpendicularly to the lower bone model 201. By simplifying the model shapes around the lower bone model 201 and upper bone model 202 in this way, bone interference with other bones can be avoided. Therefore, this simulation can simulate a worst-case scenario in which all of the load F1 from the pressing piece model 203 is applied to each plate model via the lower bone model 201.

[0082] Furthermore, the actual movement of transmitting occlusal force from the mandible 103 is complex, making accurate reproduction difficult. In this respect, this simulation simplifies the process by assuming that the load F1 from the pressure piece model 203 is applied vertically, allowing for comparison and examination of multiple cases with different conditions.

[0083] <Preliminary Analysis> As shown in Figure 26, in this simulation, stress analysis was first performed using a plate model that reproduced the step plate SP. Specifically, a preliminary analysis was first performed using a plate model having a first reference shape. The first reference shape corresponds to the shape of the conventional step plate SP.

[0084] In the first standard shape, the width W1 of the first connecting part 14 and the width W2 of the second connecting part 15 were set to 2.3 mm, the width W4 of the first annular part 11 and the width W5 of the second annular part 12 were set to 4.6 mm. In the first standard shape, the length L1 of the first long side part 10 was set to 20 mm, the length L2 from the end of the third annular part 13 to the end of the fourth annular part 21 was set to 10 mm, and the inferior angle θ1 between the first long side part 10 and the first short side part 20 was set to 100 degrees. In the first standard shape, the plate thickness T1 was set to 1.4 mm, the height SH of the step 10S was set to 2 mm, the diameter φD1 of the screw insertion hole H1 was set to 2.2 mm, the width of the fourth annular part 21 was set to 4.6 mm, and the width W3 of the third connecting part 22 was set to 2.3 mm. In the first standard shape, the outer diameter of the circular portion of the third annular part 13 was set to 4.6 mm. In the first standard plate model, a chamfer E1 is provided on the outer edge of the first surface S1, forming a 45-degree angle with respect to the plane containing the first surface S1. In the first standard plate model, a counterbore HE1 is provided in each screw insertion hole H1, forming a 45-degree angle with respect to the plane containing the first surface S1. Although Figure 26 shows the first plate model 211 located to the left of the piriform opening 104 as viewed from the patient, the above dimensions were also applied to the other plate models.

[0085] In the plate model of the first reference shape, HA / PLLA with a tensile yield stress of 72 MPa was set as the material. In the stress analysis simulation, the value of the Von-Mises stress (hereinafter referred to as von Mises stress) for each point PA to PI shown in Figure 26 was measured for load F1. In the stress analysis using the plate model that reproduces the step plate SP, point PD was set as the position of step 10S of the second connection part 15.

[0086] In the preliminary analysis, the first reference shape was applied to all of the first plate models 211 through 4th plate models 214, and stress analysis was performed. Figure 27 shows contour plots representing the magnitude of the von Mises stress applied to each plate model when a load F1 of 600 N was applied in the preliminary analysis. In the contour plots shown in Figure 27, etc., darker colors indicate larger von Mises stresses.

[0087] As shown in Figure 27, in the preliminary analysis, when a load F1 of 600N was applied, the stresses applied to the first annular section 11, the first connecting section 14, the fourth annular section 21, and the third connecting section 22 were relatively low in all plate models. On the other hand, in the preliminary analysis, when a load F1 of 600N was applied, relatively high stresses were observed in the second annular section 12 and the second connecting section 15 in all plate models.

[0088] Furthermore, preliminary analysis revealed that the first plate model 211 and the second plate model 212, positioned lateral to the piriform aperture, experienced higher stress than the third plate model 213 and the fourth plate model 214, positioned at the inferior ridge 105 of the zygomatic bone.

[0089] Figure 28 shows the values ​​of the von Mises stress for each point PA to PI shown in Figure 26 in the first plate model 211, in relation to the load F1 in the preliminary analysis. In Figure 28 and the graphs in Figures 29 to 31 described later, the straight dashed lines extending from left to right represent the tensile yield stress of the material (72 MPa). In Figure 28 and the graphs in Figures 29 to 31 described later, the range of occlusal forces from 500 N to 600 N, which are above average among the values ​​reported as occlusal forces one year post-surgery, is indicated by dots. In the legend of Figure 28 and Figures 29 to 31 described later, the points marked with a circle among points PA to PI indicate the point where the von Mises stress reached 72 MPa before the load F1 reached 600 N.

[0090] As shown in Figure 28, preliminary analysis revealed that at points PC, PD, and PE corresponding to the second connection portion 15 of the first plate model 211, and at points PH and PI corresponding to the second annular portion 12, the von Mises stress reached 72 MPa when the load F1 reached 600 N. In other words, assuming an occlusal force of 600 N, applying the first reference shape to the first osteosynthesis plate P1 positioned next to the piriform orifice suggests that a stress exceeding the tensile yield stress will be applied to the first osteosynthesis plate P1.

[0091] Furthermore, in the preliminary analysis, stress analysis was performed under similar conditions using an analytical model 200 created from four other postoperative CT images in which the displacement of the lower bone portion 101 relative to the upper bone portion 102 in the LI was similar. As a result, it was confirmed that, in all patient models, the plate model placed next to the piriform orifice experienced higher stress than the plate model placed at the inferior zygomatic ridge 105. In addition, in all patient models, it was confirmed that the von Mises stress reached 72 MPa at the second annular portion 12 and the second connecting portion 15 of the plate model placed next to the piriform orifice when the load F1 reached 600 N.

[0092] <Stress Analysis of the First to Sixth Processes> Next, as plate models that reproduce the step plate SP, stress analyses 1 to 6 were performed using plate models having the first shape, second shape, and third shape in addition to the first reference shape described above. In the plate models of the first to third shapes, the width W2 of the second connection part 15 and the width W5 of the second annular part 12 were made larger than in the plate model of the first reference shape, based on the results of the preliminary analysis. Note that in the plate models of the first to third shapes, the dimensions other than the width W2 of the second connection part 15 and the width W5 of the second annular part 12, as well as the material settings, are the same as in the plate model of the first reference shape.

[0093] In the first shape, the width W2 of the second connecting part 15 was set to 2.7 mm. In the second shape, the width W2 of the second connecting part 15 was set to 3.0 mm. In the third shape, the width W2 of the second connecting part 15 was set to 3.5 mm. In the first to third shapes, the width W5 of the second annular part 12 was set to 5.1 mm.

[0094] First, the analysis conditions for the first to third stress analyses will be explained. In the first to third stress analyses, one of the first, second, or third shapes was applied to the first plate model 211 and the second plate model 212, which are placed next to the piriform orifice and subjected to higher stress. Then, the first reference shape (W2=2.3mm, W5=4.6mm) was applied to the third plate model 213 and the fourth plate model 214, which are placed at the inferior zygomatic ridge 105.

[0095] In the first stress analysis, the first shape (W2=2.7mm, W5=5.1mm) was applied to the first plate model 211 and the second plate model 212. In the second stress analysis, the second shape (W2=3.0mm, W5=5.1mm) was applied to the first plate model 211 and the second plate model 212. In the third stress analysis, the third shape (W2=3.5mm, W5=5.1mm) was applied to the first plate model 211 and the second plate model 212.

[0096] Figure 29 shows the values ​​of the von Mises stress for each point PA to PI in the first plate model 211 with respect to the load F1 in the first stress analysis. As shown in Figure 29, in the first stress analysis, at point PC corresponding to the second connection part 15 and point PI corresponding to the second annular part 12 of the first plate model 211, the von Mises stress reached 72 MPa when the load F1 reached 600 N.

[0097] In other words, assuming an occlusal force of 600N, applying the first shape to the first osteosynthesis plate P1 positioned next to the piriform orifice suggested that the first osteosynthesis plate P1 would be subjected to a stress exceeding its tensile yield stress. However, compared to the results of the preliminary analysis, the number of points where the von Mises stress reached 72MPa was reduced, indicating that increasing the width W2 of the second connection portion 15 and the width W5 of the second annular portion 12 tended to improve the stress distribution.

[0098] Figure 30 shows the values ​​of the von Mises stress for each point PA to PI in the first plate model 211 with respect to the load F1 in the second stress analysis. As shown in Figure 30, in the second stress analysis, at point PE corresponding to the second connection 15 of the first plate model 211, the von Mises stress reached 72 MPa when the load F1 reached 600 N.

[0099] In other words, assuming an occlusal force of 600N, applying the second shape to the first osteosynthesis plate P1 positioned next to the piriform orifice suggested that the first osteosynthesis plate P1 would be subjected to a stress exceeding its tensile yield stress. However, compared to the results of the preliminary analysis and the first stress analysis, the number of points where the von Mises stress reached 72MPa decreased, indicating that increasing the width W2 of the second connection portion 15 tended to improve the stress distribution.

[0100] Figure 31 shows the values ​​of the von Mises stress for each point from PA to PI in the first plate model 211 in the third stress analysis, with respect to the load F1. As shown in Figure 31, in the third stress analysis, even when a load F1 of 600 N was applied, the von Mises stress was less than 72 MPa at all points from PA to PI.

[0101] In other words, by applying the third shape to the first osteosynthesis plate P1 positioned next to the piriform orifice, it was shown that even when assuming an occlusal force of 600N, it is possible to suppress the application of stress exceeding the tensile yield stress to the first osteosynthesis plate P1.

[0102] Next, the analysis conditions for the 4th to 6th stress analyses will be explained. In the 4th stress analysis, the first shape (W2=2.7mm, W5=5.1mm) was applied to all of the 1st plate model 211 to the 4th plate model 214. In the 5th stress analysis, the second shape (W2=3.0mm, W5=5.1mm) was applied to all of the 1st plate model 211 to the 4th plate model 214. In the 6th stress analysis, the third shape (W2=3.5mm, W5=5.1mm) was applied to all of the 1st plate model 211 to the 4th plate model 214.

[0103] Figure 32 shows the first analysis image 301 and the second analysis image 302 together. The first analysis image 301 is a contour plot showing the magnitude of the von Mises stress applied to each plate model when a load F1 of 600N is applied in the first stress analysis. The second analysis image 302 is a contour plot showing the magnitude of the von Mises stress applied to each plate model when a load F1 of 600N is applied in the fourth stress analysis. In Figure 32, the first reference shape is applied to the third plate model 213 and the fourth plate model 214, which are enclosed by dashed lines in the first analysis image 301, while the first shape is applied to the other plate models.

[0104] Figure 33 shows the third analysis image 303 and the fourth analysis image 304 together. The third analysis image 303 is a contour plot showing the magnitude of the von Mises stress applied to each plate model when a load F1 of 600N is applied in the second stress analysis. The fourth analysis image 304 is a contour plot showing the magnitude of the von Mises stress applied to each plate model when a load F1 of 600N is applied in the fifth stress analysis. In Figure 33, the first reference shape is applied to the third plate model 213 and the fourth plate model 214, which are enclosed by dashed lines in the third analysis image 303, while the second shape is applied to the other plate models.

[0105] Figure 34 shows the fifth analysis image 305 and the sixth analysis image 306 together. The fifth analysis image 305 is a contour plot showing the magnitude of the von Mises stress applied to each plate model when a load F1 of 600N is applied in the third stress analysis. The sixth analysis image 306 is a contour plot showing the magnitude of the von Mises stress applied to each plate model when a load F1 of 600N is applied in the sixth stress analysis. In Figure 34, the first reference shape is applied to the third plate model 213 and the fourth plate model 214, which are enclosed by dashed lines in the fifth analysis image 305, while the third shape is applied to the other plate models.

[0106] As shown in Figure 32, a comparison of the first analysis image 301 and the second analysis image 302 confirmed that changing the plate model placed on the inferior zygomatic ridge 105 from the first reference shape to the first shape improved the stress distribution of the modified plate model itself. On the other hand, changing the plate model placed on the inferior zygomatic ridge 105 from the first reference shape to the first shape did not result in a significant change in the stress experienced by the plate model placed next to the piriform aperture.

[0107] Furthermore, the results in Figures 33 and 34 show that a similar trend was observed when the plate model placed on the infrazygomatic ridge 105 was changed from the first reference shape to the second shape, and also when the plate model placed on the infrazygomatic ridge 105 was changed from the first reference shape to the third shape.

[0108] From the above results, it was confirmed that by making the width W2 of the second connecting portion 15 and the width W5 of the second annular portion 12 larger than the first reference shape, the stress distribution of the second connecting portion 15 and the second annular portion 12, which are subjected to relatively high stress, can be improved.

[0109] In particular, in the third shape, where the width W2 of the second connecting portion 15 is 3.5 mm and the width W5 of the second annular portion 12 is 5.1 mm, it was confirmed that even when a large occlusal force of about 500 N to 600 N is applied, it is possible to suppress the application of stress exceeding the tensile yield stress to the bone joint plate. In this embodiment, the width W2 of the second connecting portion 15 is set to 3.3 mm or more and 4.5 mm or less, taking tolerances into account, and the width W5 of the second annular portion 12 is set to 5.1 mm ± 0.3 mm. In this embodiment, for each dimension of the step plate SP other than the width W2 of the second connecting portion 15 and the width W5 of the second annular portion 12, numerical ranges that take tolerances into account the dimensions used in the stress analysis were adopted.

[0110] Furthermore, in LI, the only intraoperative processing performed on the step plate SP is fine-tuning of the shape of the first connection portion 14 and the third connection portion 22. Therefore, even if the width W2 of the second connection portion 15 and the width W5 of the second annular portion 12 are made larger than the first standard shape, it does not affect the machinability during surgery.

[0111] <Stress analysis of non-step plate NP> In this simulation, a seventh stress analysis was performed using a plate model that reproduced the non-step plate NP. In the seventh stress analysis, the stress analysis was performed using a plate model having a second reference shape. The second reference shape corresponds to the shape of the conventional non-step plate NP.

[0112] In the second standard shape, the width W6 of the fourth connecting portion 34 and the width W7 of the fifth connecting portion 35 were set to 2.3 mm, the width W9 of the fifth annular portion 31 and the width W10 of the sixth annular portion 32 were set to 4.6 mm. In the second standard shape, the length L3 of the second long side portion 30 was set to 20 mm, the length L4 from the end of the seventh annular portion 33 to the end of the eighth annular portion 41 was set to 10 mm, and the inferior angle θ2 between the second long side portion 30 and the second short side portion 40 was set to 100 degrees. In the second standard shape, the plate thickness T2 was set to 1.4 mm, the diameter φD2 of the screw insertion hole H2 was set to 2.2 mm, the width of the eighth annular portion 41 was set to 4.6 mm, and the width W8 of the sixth connecting portion 42 was set to 2.3 mm. In the second standard shape, the outer diameter of the circular portion of the seventh annular portion 33 was set to 4.6 mm. In the plate model of the second standard shape, a chamfer E2 is provided on the outer edge of the third surface S3, forming a 45-degree angle with respect to the plane containing the third surface S3. In the plate model of the second standard shape, a counterbore HE2 is provided in each screw insertion hole H2, forming a 45-degree angle with respect to the plane containing the third surface S3.

[0113] In the plate model of the second reference shape, HA / PLLA with a tensile yield stress of 72 MPa was set as the material. In the seventh stress analysis, the second reference shape was applied to all of the plate models from the first plate model 211 to the fourth plate model 214, and the stress analysis was performed.

[0114] Furthermore, in the seventh stress analysis, the values ​​of the von Mises stress under load F1 were measured for each point at the same location as points PA to PI shown in Figure 26. In the seventh stress analysis, point PD was positioned midway between points PC and PE in the fifth connection section 35.

[0115] Figures 35 to 38 show the results of a preliminary analysis using the first standard shape step plate SP, and the results of the seventh stress analysis using the second standard shape non-step plate NP. Figures 35 to 38 use the average value of the stress analysis results from five patient models. In Figures 35 to 38, the results of the seventh stress analysis are indicated with dots, while the preliminary analysis results are shown in white. Furthermore, in Figures 35 to 38, the straight dashed lines extending horizontally represent the tensile yield stress (72 MPa) of the material.

[0116] Figure 35 shows the von Mises stress applied to each point PA to PI in the plate model placed on the inferior zygomatic ridge 105, under the condition of applying a load F1 of 300 N in each of the seventh stress analysis and preliminary analysis. Figure 36 shows the von Mises stress applied to each point PA to PI in the plate model placed next to the piriform aperture, under the condition of applying a load F1 of 300 N in each of the seventh stress analysis and preliminary analysis.

[0117] From the results in Figures 35 and 36, it was confirmed that when a load F1 of 300 N, equivalent to a typical occlusal force, was applied, the stress did not exceed the tensile yield stress in either the first standard shape step plate SP or the second standard shape non-step plate NP. Furthermore, it was confirmed that the stress applied to each point of the second standard shape non-step plate NP was equal to or less than the stress applied to each point of the first standard shape step plate SP.

[0118] Figure 37 shows the von Mises stress applied to each point PA to PI in the plate model placed on the infrazygomatic ridge 105 when a load F1 of 600 N is applied in both the seventh stress analysis and the preliminary analysis. From the results in Figure 37, it was confirmed that when a load F1 of 600 N is applied, the stress does not exceed the tensile yield stress, regardless of whether the plate model placed on the infrazygomatic ridge 105 is a step plate SP of the first reference shape or a non-step plate NP of the second reference shape.

[0119] Figure 38 shows the von Mises stresses applied to each point PA to PI in the plate model placed next to the pear-shaped opening, under the condition of applying a load F1 of 600 N in both the seventh stress analysis and the preliminary analysis. From the results in Figure 38, it was confirmed that when the plate model placed next to the pear-shaped opening is a step plate SP of the first reference shape, stresses exceeding the tensile yield stress are applied, as stated in the preliminary analysis results. On the other hand, it was confirmed that when the plate model placed next to the pear-shaped opening is a non-step plate NP of the second reference shape, stresses exceeding the tensile yield stress are not applied.

[0120] Furthermore, at point PD located at the fifth connection point 35, a stress close to the tensile yield stress was observed. Therefore, it is desirable to improve the stress distribution of the fifth connection point 35 by making the width W7 of the fifth connection point 35 larger than that of the second reference shape. However, during LI surgery, the fifth connection point 35 of the non-step plate NP may be bent or twisted to deform the non-step plate NP to conform to the patient's bone surface. Therefore, when setting the dimensions of the fifth connection point 35, it is necessary to ensure workability during surgery.

[0121] Therefore, prototypes of the non-step plate NP were fabricated in three levels, with the width W7 of the fifth connection part 35 set to 2.3 mm (second standard shape), 3.0 mm, and 3.5 mm. In addition, the stress applied to points PH and PI located in the sixth annular part 32 was less than 50% of the tensile yield stress, but depending on the patient's skeletal structure, higher stress may be applied. For this reason, in the prototype, the width W10 of the sixth annular part 32 was set to 5.1 mm, the same as the width W5 of the second annular part 12 of the step plate SP.

[0122] A physician with experience in LI evaluated the intraoperative machinability of three prototype levels that were fabricated. As a result, intraoperative machinability was possible for all three levels of prototypes. In particular, among the three prototype levels, two prototypes with a width W7 of the fifth connection part 35 of 2.3 mm or 3.0 mm were confirmed to have excellent machinability.

[0123] Therefore, it was confirmed that by setting the width W7 of the fifth connection part 35 to 3.0 mm, the stress distribution of the fifth connection part 35 can be improved without worsening intraoperative machinability. In other words, it was confirmed that by making the width W7 of the fifth connection part 35 larger than the width W6 of the fourth connection part 34, and smaller than the width W2 of the second connection part 15 in the step plate SP, the stress distribution of the fifth connection part 35 can be improved without worsening intraoperative machinability.

[0124] In this embodiment, the width W7 of the fifth connecting portion 35 was set to 3.0 mm ± 0.2 mm, taking tolerances into account, and the width W10 of the sixth annular portion 32 was set to 5.1 mm ± 0.3 mm. In this embodiment, for each dimension of the non-step plate NP other than the width W7 of the fifth connecting portion 35 and the width W10 of the sixth annular portion 32, the numerical ranges obtained by taking tolerances into account the dimensions used in the stress analysis were adopted.

[0125] <External shape of bone fixation plate> Figures 39 to 41 show six-view drawings illustrating the appearance of the bone fixation plate used on the right side of the skull 100 (left side of the page in Figure 1) as seen from the patient. Figure 39 shows the appearance of step plate SP1, where the height SH of step 10S is 2.0 mm. Figure 40 shows the appearance of non-step plate NP. Figure 41 shows the appearance of step plate SP2, where the height SH of step 10S is 4.0 mm. In Figures 39 to 41, characteristic parts of each bone fixation plate in this embodiment are shown with solid lines, and other parts are shown with dashed lines. The boundary between the solid and dashed parts is shown with a dotted line.

[0126] <Effects of the Embodiment> (1) In the step plate SP, the width W5 of the second annular portion 12 is made larger than the width W4 of the first annular portion 11, and the width W2 of the second connecting portion 15 is made larger than the width W1 of the first connecting portion 14. This improves the stress distribution of the second connecting portion 15 and the second annular portion 12, which are subjected to relatively high stress.

[0127] (2) In this embodiment, the width W7 of the fifth connection portion 35 of the non-step plate NP is made larger than the width W6 of the fourth connection portion 34, and smaller than the width W2 of the second connection portion 15 of the step plate SP. This makes it possible to improve the stress distribution in the fifth connection portion 35 of the non-step plate NP while ensuring workability.

[0128] (3) Because the face has numerous nerves and a delicate bone strength distribution, it is desirable to increase the dimensions of only the areas where relatively high stress is applied, rather than simply increasing the overall dimensions of the bone fixation plate. In this regard, according to this embodiment, the stress distribution can be suitably improved while suppressing excessive enlargement of the step plate SP and non-step plate NP made of bioabsorbable material.

[0129] (4) In the step plate SP, the width W2 of the second connecting portion 15 is set to 3.3 mm or more and 4.5 mm or less, and the width W5 of the second annular portion 12 is set to 5.1 mm ± 0.3 mm. This makes it possible to suppress the application of stress exceeding the tensile yield stress to the step plate SP made of bioabsorbable material, even when a load of 600 N, which is assumed to be a sudden occlusal force, is applied.

[0130] (5) In the step plate SP, the height SH of the step 10S is set to 1.0 mm or more and 5.0 mm or less. With a step plate SP having such a step 10S, the stress distribution of the second connecting portion 15 and the second annular portion 12 can be suitably improved.

[0131] (6) In this embodiment, a bioabsorbable material with a tensile yield stress of 60 MPa to 80 MPa, preferably 70 MPa or more, is used as the material for the bone fixation plate. By adopting the dimensional setting of this embodiment for a bone fixation plate made of such a bioabsorbable material, it is possible to suppress the application of stress to the bone fixation plate that exceeds the tensile yield stress, even when a load of 600 N, which is assumed to be a sudden occlusal force, is applied.

[0132] (7) The bioabsorbable material of this embodiment comprises at least one selected from the group consisting of hydroxyapatite, tricalcium phosphate, apatite carbonate, and octacalcium phosphate, and polylactic acid or a lactic acid-glycolic acid copolymer. Such a bioabsorbable material can achieve the mechanical strength required for a bone fixation plate.

[0133] (8) By setting the width W7 of the fifth connection portion 35 in the non-step plate NP to 3.0 mm ± 0.2 mm, the stress distribution can be improved in the fifth connection portion 35 of the non-step plate NP while ensuring more favorable machinability. In addition, by setting the width W10 of the sixth annular portion 32 in the non-step plate NP to 5.1 mm ± 0.3 mm, the stress distribution in the sixth annular portion 32, which may be subjected to high stress, can be improved.

[0134] (9) With a plate set that combines a step plate SP and a non-step plate NP, it is possible to select an optimal bone fixation plate shape according to the patient's skeletal shape and the amount of movement of the lower bone portion 101 relative to the upper bone portion 102.

[0135] <Example of changes> This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0136] The quantities of step plates SP and non-step plates NP in a plate set are not limited. Furthermore, a plate set may include multiple step plates SP with different step heights SH. For example, a plate set may include a step plate SP1 with a height SH of 2.0 mm, a step plate SP2 with a height SH of 4.0 mm, and a non-step plate NP. Alternatively, a plate set may include either a step plate SP1 with a height SH of 2.0 mm or a step plate SP2 with a height SH of 4.0 mm, and a non-step plate NP.

[0137] If no excessive stress is applied to the sixth annular portion 32, the width W10 of the sixth annular portion 32 in the non-step plate NP is not limited to 5.1 mm ± 0.3 mm. The width W7 of the fifth connection portion 35 is not limited to 3.0 mm ± 0.2 mm, provided that the intraoperative machinability of the non-step plate NP is not impaired and excessive stress is not applied to the fifth connection portion 35. In the non-step plate NP, the width W7 of the fifth connection portion 35 may be greater than the width W6 of the fourth connection portion 34 and smaller than the width W2 of the second connection portion 15 in the step plate SP.

[0138] The bioabsorbable material constituting the bone fixation plate is not limited in type, as long as it possesses the necessary physical properties (e.g., mechanical strength) for a bone fixation plate. Furthermore, the bioabsorbable material constituting the bone fixation plate only needs to have a tensile yield strength of at least 60 MPa.

[0139] If no excessive stress is applied to the second connecting portion 15 and the second annular portion 12, the height SH of the step 10S in the step plate SP may be less than 1.0 mm or greater than 5.0 mm.

[0140] In the step plate SP, the width W2 of the second connecting portion 15 is at least greater than the width W1 of the first connecting portion 14, and its dimensions are not limited to 3.3 mm or more and 4.5 mm or less. Also, in the step plate SP, the width W5 of the second annular portion 12 is at least greater than the width W4 of the first annular portion 11, and its dimensions are not limited to 5.1 mm ± 0.3 mm.

[0141] The second osteosynthesis plate P2, positioned at the subzygomatic ridge 105, can be a step plate SP with a first standard shape or a non-step plate NP with a second standard shape, depending on the patient's skeletal shape and treatment plan, which are equivalent to conventional osteosynthesis plates. In other words, the first osteosynthesis plate P1, positioned next to the piriform orifice, can be a step plate SP with the dimensions of this embodiment, while the second osteosynthesis plate P2, positioned at the subzygomatic ridge 105, can be a conventional osteosynthesis plate.

[0142] For example, when using a lactic acid-glycolic acid copolymer or polylactic acid as the bioabsorbable material, the step plate SP may take the following form: The width W4 of the first annular portion 11, the outer diameter of the circular portion of the third annular portion 13, and the width of the fourth annular portion 21 may each be 4.8 mm ± 0.6 mm. The width W5 of the second annular portion 12 may be 5.4 mm ± 0.6 mm. The width W1 of the first connecting portion 14 and the width W3 of the third connecting portion 22 may each be 2.5 mm ± 0.5 mm. The width W2 of the second connecting portion 15 may be 3.3 mm or more and 4.8 mm or less. In this case, the width W2 of the second connecting portion 15 is configured to be smaller than the width W5 of the second annular portion 12 and to satisfy the above numerical range. Furthermore, the width W5 of the second annular portion 12 is configured to be larger than the width W4 of the first annular portion 11, while also satisfying the above-mentioned numerical range.

[0143] Furthermore, for example, when using a lactic acid-glycolic acid copolymer or polylactic acid as a bioabsorbable material, the non-step plate NP may take the following form: The width W9 of the fifth annular portion 31, the outer diameter of the circular portion of the seventh annular portion 33, and the width of the eighth annular portion 41 may each be 4.8 mm ± 0.6 mm. The width W10 of the sixth annular portion 32 may be 5.4 mm ± 0.6 mm. The width W6 of the fourth connecting portion 34 and the width W8 of the sixth connecting portion 42 may each be 2.5 mm ± 0.5 mm. The width W7 of the fifth connecting portion 35 may be 3.4 mm ± 0.6 mm. In this case, the width W7 of the fifth connecting portion 35 is configured to be smaller than the width W2 of the second connecting portion 15 of the step plate SP (where the width W2 is 3.3 mm or more and 4.8 mm or less) and to satisfy the above numerical range. Furthermore, the width W10 of the sixth annular portion 32 is configured to be greater than the width W9 of the fifth annular portion 31, while also satisfying the above-mentioned numerical range. [Explanation of Symbols]

[0144] θ1, θ2…Inferior angle H1, H2... Screw insertion holes NP...Non-step plate SP, SP1, SP2... Step Plate SH... Height T1, T2…plate thickness W1~W10...Width φD1, φD2…Diameter 10...First long side 10S…Step 11...First annular section 12...Second ring section 13...Third annular section 14…First connection section 15…Second connection section 20...First short side 21...Fourth annular section 22...Third connection section 30...Second long side 31...Fifth ring section 32...Sixth annular section 33... The 7th ring section 34…Fourth connection section 35…Fifth connection section 40...Second short side 41...8th annular section 42...Sixth connection section 100... Skull 101…Lower bone part 102...Upper bone part 103... Mandible 104... Piriforme 105...Infrazygomatic ridge

Claims

1. In maxillary osteoplasty, a bone fixation plate used lateral to the piriform orifice, An L-shape is formed by a first long side portion extending along the first long side direction and a first short side portion extending along the first short side direction intersecting the first long side direction. The first long side portion comprises a first annular portion, a second annular portion, and a third annular portion arranged along the direction of the first long side, a first connecting portion connecting the first annular portion and the second annular portion, and a second connecting portion connecting the second annular portion and the third annular portion. The first short side portion comprises a fourth annular portion located in the first short side direction relative to the third annular portion, and a third connecting portion connecting the third annular portion and the fourth annular portion. The material constituting the bone fixation plate is a bioabsorbable material. The second connecting portion includes a step bent in the thickness direction of the bone joint plate, The thickness of the bone fixation plate is 0.9 mm or more and 1.6 mm or less. The tensile yield stress of the bioabsorbable material is 60 MPa or more and 80 MPa or less. The length of the first long side is 15 mm or more and 25 mm or less. The inferior angle formed by the first long side and the first short side is 90 degrees or more and 105 degrees or less. Each of the first, second, third, and fourth annular portions is provided with a first through-hole having a diameter of 1.5 mm or more and 3.0 mm or less. In a direction perpendicular to the first long side direction, the width of the first annular portion is 4.6 mm ± 0.3 mm, the width of the second annular portion is greater than the width of the first annular portion, the width of the first connecting portion is 2.3 mm ± 0.3 mm, the width of the second connecting portion is greater than the width of the first connecting portion and less than the width of the second annular portion, The bone fixation plate is a first step plate used as a first bone fixation plate in combination with a second bone fixation plate used in the lower zygomatic ridge in the maxillary osteoplasty. The second bone fixation plate is selected from either a second step plate having the same shape and material as the first step plate, or a non-step plate. The non-step plate has a flat shape, An L-shape is formed by a second long side portion extending along the second long side direction and a second short side portion extending along the second short side direction intersecting the second long side direction. The second long side portion comprises a fifth annular portion, a sixth annular portion, and a seventh annular portion arranged along the direction of the second long side, a fourth connecting portion connecting the fifth annular portion and the sixth annular portion, and a fifth connecting portion connecting the sixth annular portion and the seventh annular portion. The second short side portion comprises an eighth annular portion located in the direction of the second short side relative to the seventh annular portion, and a sixth connecting portion connecting the seventh annular portion and the eighth annular portion. The material constituting the non-step plate is the bioabsorbable material, The thickness of the non-step plate is equal to the thickness of the first bone joint plate. The length of the second long side is 15 mm or more and 25 mm or less. The inferior angle between the second long side and the second short side is 90 degrees or more and 105 degrees or less. Each of the fifth, sixth, seventh, and eighth annular portions is provided with a second through-hole having a diameter of 1.5 mm or more and 3.0 mm or less. In the direction perpendicular to the second long side direction, the width of the fourth connection portion is 2.3 mm ± 0.3 mm, and the width of the fifth connection portion is greater than the width of the fourth connection portion and smaller than the width of the second connection portion in the direction perpendicular to the first long side direction of the first bone fixation plate. Bone fixation plate.

2. In a direction perpendicular to the first long side direction, the width of the second annular portion is 5.1 mm ± 0.3 mm, and the width of the second connecting portion is 3.3 mm or more and 4.5 mm or less. The bone fixation plate according to claim 1.

3. The height of the aforementioned step is 1.0 mm or more and 5.0 mm or less. The bone fixation plate according to claim 1 or 2.

4. The tensile yield stress of the bioabsorbable material is 70 MPa or higher. The bone fixation plate according to claim 1 or 2.

5. The bioabsorbable material comprises at least one selected from the group consisting of hydroxyapatite, tricalcium phosphate, apatite carbonate, and octacalcium phosphate, and polylactic acid or a lactic acid-glycolic acid copolymer. The bone fixation plate according to claim 1 or 2.

6. In a direction perpendicular to the second long side direction, the width of the fifth annular portion is 4.6 mm ± 0.3 mm, the width of the sixth annular portion is greater than the width of the fifth annular portion and is 5.1 mm ± 0.3 mm, and the width of the fifth connecting portion is 3.0 mm ± 0.2 mm. The bone fixation plate according to claim 1 or 2.

7. A plate set comprising: a step plate used in maxillary osteoplasty for use in at least one of the lateral aspect of the piriform or the subzygomatic ridge; and a non-step plate used in the subzygomatic ridge and in combination with the step plate used in the lateral aspect of the piriform or in the maxillary osteoplasty, The materials constituting the step plate and the non-step plate are bioabsorbable materials. The aforementioned step plate is An L-shape is formed by a first long side portion extending along the first long side direction and a first short side portion extending along the first short side direction intersecting the first long side direction. The first long side portion comprises a first annular portion, a second annular portion, and a third annular portion arranged along the direction of the first long side, a first connecting portion connecting the first annular portion and the second annular portion, and a second connecting portion connecting the second annular portion and the third annular portion. The first short side portion comprises a fourth annular portion located in the first short side direction relative to the third annular portion, and a third connecting portion connecting the third annular portion and the fourth annular portion. The second connecting portion includes a step bent in the thickness direction of the step plate, The thickness of the step plate is 0.9 mm or more and 1.6 mm or less. The tensile yield stress of the bioabsorbable material is 60 MPa or more and 80 MPa or less. The length of the first long side is 15 mm or more and 25 mm or less. The inferior angle formed by the first long side and the first short side is 90 degrees or more and 105 degrees or less. Each of the first, second, third, and fourth annular portions is provided with a first through-hole having a diameter of 1.5 mm or more and 3.0 mm or less. In a direction perpendicular to the first long side direction, the width of the first annular portion is 4.6 mm ± 0.3 mm, the width of the second annular portion is greater than the width of the first annular portion, the width of the first connecting portion is 2.3 mm ± 0.3 mm, the width of the second connecting portion is greater than the width of the first connecting portion and less than the width of the second annular portion, The non-step plate has a flat shape, An L-shape is formed by a second long side portion extending along the second long side direction and a second short side portion extending along the second short side direction intersecting the second long side direction. The second long side portion comprises a fifth annular portion, a sixth annular portion, and a seventh annular portion arranged along the direction of the second long side, a fourth connecting portion connecting the fifth annular portion and the sixth annular portion, and a fifth connecting portion connecting the sixth annular portion and the seventh annular portion. The second short side portion comprises an eighth annular portion located in the direction of the second short side relative to the seventh annular portion, and a sixth connecting portion connecting the seventh annular portion and the eighth annular portion. The thickness of the non-step plate is equal to the thickness of the step plate. The length of the second long side is 15 mm or more and 25 mm or less. The inferior angle between the second long side and the second short side is 90 degrees or more and 105 degrees or less. Each of the fifth, sixth, seventh, and eighth annular portions is provided with a second through-hole having a diameter of 1.5 mm or more and 3.0 mm or less. In the direction perpendicular to the second long side direction, the width of the fourth connecting portion is 2.3 mm ± 0.3 mm, and the width of the fifth connecting portion is greater than the width of the fourth connecting portion and smaller than the width of the second connecting portion in the direction perpendicular to the first long side direction of the step plate. Plate set.

8. In the direction perpendicular to the first long side direction, the width of the second annular portion is 5.1 mm ± 0.3 mm, and the width of the second connecting portion is 3.3 mm or more and 4.5 mm or less. In a direction perpendicular to the second long side direction, the width of the fifth annular portion is 4.6 mm ± 0.3 mm, the width of the sixth annular portion is greater than the width of the fifth annular portion and is 5.1 mm ± 0.3 mm, and the width of the fifth connecting portion is 3.0 mm ± 0.2 mm. The plate set according to claim 7.

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