JP3148932B2 - Biodegradable and absorbable plate for internal fixation of fracture - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molded article suitable for fixing and assisting a bone at the time of bone damage or fracture until the bone is formed. More specifically, the material strength is maintained until the damage or reconstruction of the fracture site gradually progresses, and the strength is restored to a level that hardly interferes with daily life, and then the bone is substantially reconstructed. The present invention relates to a polylactic acid surgical molded article for osteosynthesis having a controlled strength, shape, and size so that it is decomposed and absorbed into a living body when formation is completed.

[0002]

2. Description of the Related Art In orthopedic surgery and oral surgery, high-strength osteosynthesis plates and screws are used for reducing fractures. Such artificial materials for osteosynthesis function only for a period until the fracture heals, and after the healing, it is necessary to remove the bone as early as possible to prevent the weakening of the bone.

At present, most of osteosynthesis plates and the like widely used in clinical practice are made of metal, and ceramics have recently appeared. In particular, the metal plate has a problem that the elasticity of the material itself is too high, which rather lowers the strength of the surrounding bone and damages the living body due to elution of metal ions. Further, since the material used for the metal plate is much stronger than the strength of the material of the present invention, if the thickness and shape of the metal plate are used as they are, there is a problem in strength, so that they cannot be used. Therefore, it is conceivable to increase the thickness or the width, but the size is limited depending on the part to be used. Therefore, its shape must be designed to be as small and thin as possible, while retaining the minimum necessary strength to support the fracture. In addition, if a material that has the same or slightly higher elastic modulus as that of living bone and is biodegradable and absorbable is used for osteosynthesis, re-operation for removal becomes unnecessary, Should be able to rule out the various adverse effects of long-term in vivo presence.

[0004] Under such circumstances, development of osteosynthesis materials using polylactic acid or lactic acid-glycolic acid copolymer, which is a biodegradable and absorbable material, has been actively promoted.

[0005] For example, M. Vert, F.R. Chabot et al. Have synthesized polylactic acid or a lactic acid-glycolic acid copolymer for osteosynthesis plates, and have a compression bending modulus of 3.4 GPa (347 kg / m3) made of 100% polylactic acid.
m ² ) (Makromol
Chem. Suppl. , 5, 30-41, 198
1). D. C. Tunc has a compression bending elastic modulus of 520.
kg / mm ² of polylactic acid osteosynthesis plate (Report of the 9th USA Biomaterials Society Abstracts, 6, 4)
7, 1983).

Japanese Unexamined Patent Publication (Kokai) No. 59-97654 discloses a method for synthesizing polylactic acid as a material for a resorbable bone fixing device. The tensile strength of this polylactic acid is about 580 kg / cm. ^It is a low value of ^2, and there is no explanation about the method of forming and processing polylactic acid.

[0007] J. J. W. Leenslag, A .;
J. Pennings et al. Synthesized polylactic acid having a viscosity average molecular weight of about 1,000,000, and the compression bending elastic modulus of an osteosynthesis plate using the high molecular weight polylactic acid was 5 GPa (510 kg).
/ Mm ² ) (Biomater).
ials, 8, 70, 1987) is too high in molecular weight and has drawbacks in moldability.

[0008]

As described above, many studies have been reported to improve the mechanical properties of polylactic acid-based osteosynthesis materials, and various methods have been tried, but they are still used sufficiently in clinical practice. No material of satisfactory strength has been developed that can be performed.

The present inventors have proposed in Japanese Patent Application No. 62-333333 a biodegradable and absorbable surgical material having a similar or slightly higher quality as that of a living bone. However, when such materials are actually implanted, there is a problem that there is a great difference between the required strength and the duration thereof depending on the site.

That is, what are the suitable values of the compressive bending strength, the compressive bending elastic modulus, and the tensile strength of the polylactic acid according to each part of the bone of the human body, and the polylactic acid having the actual values required for each part. It has not been elucidated yet what shape is good in the molding material and how good is its size. Further, the shape and size of the molded product that can maintain the strength are not yet clear.

However, even if a polylactic acid molded product is decomposed and absorbed in the human body, it is not preferable for the human body if it exists in the human body for a long period of time. It is desirable to be done. Therefore, it would be more desirable if the shape was as small and thin as possible and had the minimum necessary strength to support the fracture.

The present invention has been made in view of the above circumstances. Its purpose is to have a mechanical strength equivalent to or slightly higher than that of the living bone of each part as a molded product, and to maintain that strength for a necessary time until the bone is regenerated after implantation in the living body. For internal fixation of fractures with three elements: shape, size, and size that is unnecessarily too large and does not require extra time for disassembly, deterioration, or absorption and fits well in the surgical site An object of the present invention is to provide a biodegradable and absorbable plate.

[0013]

The biodegradable and absorbable plate for an internal fixation material of a fracture according to the present invention is obtained by stretching a melt molded product of polylactic acid, and has a viscosity average molecular weight (MW) of the product.
Is 200,000 or more, and the compressive bending strength according to JIS-K7203 is 25.0 × 10 ^{2 to} 55.0 × 10 ² kg /
cm ² , compression flexural modulus of 15.0 × 10 ^{2 to} 35.0
× 10 ² kg / mm ² , and the degree of crystallinity determined by density measurement is 10 to 60%.
18mm, length 35-200mm, thickness 1.0-4.5
mm, the cut surface of which is perpendicular to the longitudinal direction, is a molded product having a substantially semicircular or semicircular outer shape and a wide inverted U-shaped inner shape.

The plate of the present invention having such a shape has a structure reinforced with respect to bending force, and has improved physical properties. In addition, the said intensity | strength was calculated | required by the conversion formula of JIS-K7203 from the maximum load and the cross-sectional area of a plate.

By the way, the polylactic acid-based material can be improved in crystallinity by heat treatment. Crystalline materials have higher bending strength and elastic modulus than amorphous materials. The amorphous phase is more likely to penetrate body fluids (moisture), so the apparent hydrolysis is faster and the crystalline phase is slower. The higher the molecular weight of the polymer used, the better the mechanical properties of the crystalline material. However, when the degree of crystallinity is increased by the heat treatment, the initial strength is improved, but the polylactic acid is unstable due to heat and is deteriorated to lower the molecular weight. Then, the hydrolysis rate is increased, and the strength is rapidly deteriorated. In other words, by retaining an appropriate molecular weight and crystallinity, a biodegradable and absorbable surgical material having mechanical properties and hydrolysis resistance that can be used as a material for osteosynthesis and bone fixation can be obtained.

The polylactic acid used in the present invention will be described in more detail. The polylactic acid is prepared from an optically active L-form or D-form lactic acid by a conventional method (CE Love, US Pat. No. 2,6).
68, 182), a lactide that is a cyclic dimer of lactic acid is synthesized, and then the lactide is subjected to ring-opening polymerization. This polylactic acid is inferior in heat stability, so that considering the molecular weight reduction during melt molding, it is necessary that the viscosity average molecular weight is at least 300,000 or more, and the higher the molecular weight, the higher the strength of the surgical material. Suitable to get. However, if the molecular weight is too high, a high temperature and high pressure are required during melt molding, causing a significant decrease in molecular weight, and as a result, the molecular weight after melt molding will be less than 200,000. It is difficult to obtain a high-strength surgical material. Therefore, it is appropriate to use those having a viscosity average molecular weight of about 300,000 to 600,000, and preferably those having a molecular weight of about 350,000 to 550,000, especially about 400,000 to 500,000. You.

Further, the biodegradable and absorbable plate for an internal fixation material of the present invention is made from the above-mentioned polylactic acid as a raw material, and is formed into a predetermined shape by melt molding using a deformed mold or the like, for example, extrusion molding or press molding. A method obtained by further uniaxially stretching in the major axis direction, and a melt molded into a flat plate shape, and then uniaxially stretching in the major axis direction to obtain a molded product, which is then substantially half-axially oriented in the major axis direction. There is a method of bending into a circular shape or a substantially flat U shape.

In the case of melt molding with good productivity, it is carried out using a usual extruder under the following temperature and pressure conditions. That is, the temperature condition of the melt extrusion molding needs to be in a temperature range from the melting point of the polylactic acid to 220 ° C. or less. At a temperature lower than the melting point, melt extrusion becomes difficult. On the other hand, at a temperature higher than 220 ° C., the molecular weight is significantly reduced due to the thermal instability of polylactic acid, and the viscosity average molecular weight after melt extrusion molding is lower than 200,000. Because it becomes.

The molecular weight of the molded product after melt extrusion molding is preferably 200,000 or more, particularly preferably in the range of 250,000 to 400,000, and if it is less than 200,000, improvement in mechanical properties cannot be expected even by stretching. In order to minimize the decrease in molecular weight, it is important to carry out melt extrusion at a temperature slightly higher than the melting point of the raw material polymer. Therefore, the raw material polymer having a molecular weight of about 400,000 to 500,000 as described above When using, it is desirable to perform melt extrusion molding under a temperature condition of 200 ° C. or less. It is preferable that the molecular weight after molding is higher from the viewpoint of mechanical strength.

Similarly, the pressure condition of the melt extrusion molding is desirably set to a minimum extrusion pressure at which extrusion can be performed in accordance with the viscosity (molecular weight) of the molten raw material polymer in order to minimize the molecular weight reduction. Accordingly, the molecular weight of the starting polymer in the case of up to 600,000 260 kg / cm ² or less, if molecular weight of 400,000 to 500,000 is appropriate to the 170~210kg / cm ² approximately extrusion pressure.

Before the melt extrusion molding, it is desirable that the raw material polymer pellets are dried by heating under reduced pressure in advance to sufficiently remove water.

The molded product obtained by melt extrusion molding is
Since the viscosity average molecular weight is maintained at 200,000 or more, it has considerable strength, but does not reach the intended strength yet. Therefore, as described above, the molded product is further uniaxially stretched in a long axis direction (extrusion direction) in a flow of liquid paraffin, silicone oil, or heated nitrogen to thereby orient the polymer molecules and improve the strength.

The crystallinity of the material can be increased by heating during stretching. However, if the crystallinity of the material is increased by heat treatment, the initial strength will be improved, but the molecular weight will be reduced, so the hydrolysis rate will be faster and the strength retention period will be shorter than that of amorphous materials. is necessary. Therefore, the temperature condition during stretching is 60 to 1 as described above.
A range of 60 ° C. is preferable, and a temperature lower than 60 ° C. is not preferable because it is too close to the glass transition temperature. Conversely 160 ° C
As described above, particularly when the temperature exceeds 180 ° C., the molecular weight is reduced, and sliding deformation between molecules takes precedence, so that molecular orientation does not occur and improvement in strength cannot be expected. The heating time is desirably within 10 minutes.

Next, the stretching ratio is desirably 2 to 6 times. If the draw ratio is less than 2 times, the molecular orientation becomes insufficient and it is difficult to satisfactorily improve the strength. On the other hand, if it is 6 times or more, fibrillation occurs and the hydrolysis resistance is reduced. It is.

The material obtained by the above-mentioned production method has a biodegradable and absorbable property, and is unlikely to have an adverse effect in a living body unlike conventional metal surgical materials. Moreover,
The molecular weight reduction during melt molding is kept to a minimum, the viscosity average molecular weight after melt molding is kept at 200,000 or more, and the molecular orientation and crystallinity are given by stretching. That is, this surgical material has a compressive bending strength of 25.0 × 10
^{2 to} 55.0 × 10 ² kg / cm ² , compression bending elastic modulus of 15.0 × 10 ^{2 to} 35.0 × 10 ² kg / mm ² , crystallinity of 10 to 60%, and high strength Have And in this invention, as a plate for an internal fixation material of a fracture part, width is 10-18 mm, length is 35-2.
00 mm, thickness of 1.0 to 4.5 mm, and a cut surface orthogonal to the length direction is formed into a shape in which a substantially semicircular or semicylindrical outer shape and a wide inverted U-shaped inner shape are overlapped. It has a unique shape.

Here, the shape of the plate of the present invention will be described more specifically. 1 to 4 show the shape of the plate in the present invention.

FIG. 1A is a perspective view of the plate, which has a shape like a bamboo divided into half.
Is a transverse sectional view, and (c) is a longitudinal sectional view.

FIG. 2A is a perspective view of a plate slightly thicker than that of FIG. (B) is a transverse sectional view, and (c) is a longitudinal sectional view.

FIGS. 1 and 2 show a shape in which the substantially semicircular outer shape and the wide inverted U-shaped inner shape according to the present invention are overlapped.

FIG. 3 (a) is a perspective view of a molded portion having an outer shape of a semicylindrical shape and a shape formed by combining a wide inverted U-shaped inner shape. (B) and (c) in FIG.
Is a cross-sectional view and a vertical cross-sectional view thereof.

FIG. 4 shows a shape of the plate of FIG. 1 in which only holes are provided for screwing.
(A) is a perspective view, (B) is a cross-sectional view in which a hole is cut, and (C) is a longitudinal sectional view.

The shapes shown in FIGS. 2 and 3 can also have a recess at the hole, and it goes without saying that such a shape does not depart from the technical idea of the present invention.

The shape of the plate in the present invention is such that the surface along the bone has a concave groove, that is, an inverted U-shape, and the surface on the opposite side has a substantially semicircular or semi-cylindrical shape (including a substantially trapezoidal shape). Can be said to be something.

According to the knowledge of clinical orthopedic surgery, it is necessary to restore the strength and function of the human body to a point where the prosthetic material can be removed after the bone is damaged or broken at each part of the human body. The duration is from 4 weeks to 16 weeks. In addition, when a molded article of polylactic acid to be implanted in a living body is used in a certain site, the period during which the strength must be maintained in the living body differs depending on each site. But,
Maintaining strength in a living body does not have to be maintained at 100% during that period. In vivo, the biodegradable polylactic acid has a lower molecular weight due to hydrolysis of ester bonds. In fact, the surface of the molded article of polylactic acid comes into contact with body fluids and hydrolysis occurs, gradually progressing to the inside, causing cracks,
As a result, the strength of the molded product is reduced. Therefore, there is a period in which the intensity hardly changes,
Then, after a short period in which the strength gradually decreases, a sharp decrease occurs.

During the period of the decrease in strength, the recovery of the joint of the living bone is progressing, and the reduction of polylactic acid and the recovery of the living bone are added. The molded article does not necessarily have to maintain 100% strength. Rather, most of the strength is lost shortly after the recovery period, and it is desirable that the bone is not strained. The meaning of the above-mentioned strength deterioration rate of 4 to 16 weeks in this sense is as follows. In other words, considering the individual differences of the living body, the strength of the molded product at the end of recovery is about 30% or more, preferably 50% or more, of the initial strength of the molded product. It is necessary to select the stretching ratio), the size of the molded product of polylactic acid, and its thickness.

[0036]

In general, when a polymer is used as a structural material in consideration of its own strength, deterioration of the strength is not so much a problem. This is because the deterioration rate is extremely slow, and there is little need to consider deterioration.

However, when the biodegradability is used as one function as in the case of the polylactic acid of the present invention,
The decomposition rate and the time when the strength of the structural material is lost are extremely important in practical use. In particular, in the case of use in a living body, it can be said that there is no practical use if the strength deterioration considerably progresses at a stage where the strength is lost too quickly and the bone at the fracture site is insufficiently regenerated.

The hydrolysis of a polyester-type biodegradable polymer such as polylactic acid is based on the decomposition of ester bonds in its primary structure. This is the decomposition rate of the substance at the molecular level, but the actual decomposition is slightly alkaline (pH =
7.4) originate from the part in contact with bodily fluids. Therefore, hydrolysis is performed from the surface of the screw, plate or the like actually used, and the size of the surface (ratio to the volume) is a determinant of the strength deterioration of the object.
In other words, a molded product having a small surface area (a shape with a large number of surface irregularities) deteriorates relatively quickly as an object, whereas a molded product having a large surface area with a small surface area (a shape with a small number of surface irregularities) is a material. Is relatively slow.

Particularly, in a material in which the strength of polylactic acid is increased to the same level as that of bone by stretching polylactic acid, a slight deterioration causes the strength as an object to rapidly decrease to a value considerably lower than a practical level. Therefore, the surface area, that is, shape and size of the molded article must be carefully determined. If only strength is important, the molded product is large,
What is necessary is just to use a thing with a smooth surface and a simple shape. However, there is a limit to the size of the molding required at the treatment site.
In addition, if the decomposition product is too large, the decomposition proceeds, and when the decomposition product is subsequently absorbed into the living body, the amount is too large, and there is a concern about unnecessary reaction with the living body.

The degradation of strength due to hydrolysis starts with the formation of cracks on the surface. Since the crack serves as a notch, the measured strength is reduced. Experience has shown that this surface cracking is a leading factor in the actual onset of strength degradation rather than a reduction in molecular weight. In other words, although the molecular weight of the polymer on the surface in contact with the body fluid has been reduced by hydrolysis, a large crack that can be visually observed does not occur unless this progresses to some extent inside the molded product. If the surface layer alone deteriorates, the strength deterioration of the entire molded product is not so large.
It is most desirable that the time required for the bone to regenerate is approximately equal to the time required for the deterioration to progress to the inner layer of the molded article and cause cracks, and for the strength to be regenerated.

In fact, it is the wall thickness of the molded article that determines the timing of this desirable strength reduction. Therefore, the thickness of the plate needs to be at least 1 mm or more. However,
If the thickness is too large as described above, the strength will increase, but this is not preferable for bone regeneration. That is, although the time required for the regeneration of human bones varies depending on the site, surgical experience has shown that the time required for the implanted polymer to maintain its strength is as long as about 16 weeks. I have. In such a period, the thickest part of the molded product is required to be about 4.5 mm in order to maintain the initial strength or the strength which is not deteriorated to a hindrance. However, the thickness of the molded product should be thicker at the parts that are easily decomposed by body fluids and at the parts where mechanical strength is required.
0 to 18 mm, the length direction is 35 to 200 mm,
A cross section in the longitudinal direction having a substantially semicircular or flat U-shape is excellent as an inner fixing material for supporting a fractured portion.

The shape of the plate is such that its cross section in the longitudinal direction is substantially semicircular or semicylindrical in shape and the wide inverted U-shaped inner shape is overlapped with that of fixing the bone at the time of fracture. The strength required in the longitudinal direction is particularly important, and if the rigidity in the longitudinal direction is insufficient, the fractured portion may be bent. Therefore, without increasing the thickness of the plate too much,
Moreover, the rigidity in the length direction is particularly increased. In addition, since the plate has a wide inverted U-shaped inner shape, the plate easily conforms to the bone of the fractured portion, and has an extremely preferable shape for fixing the bone. Further, a shape such that the head of the screw does not protrude from the upper surface of the plate as in the shape of FIG. 4 is desirable for maintaining the screw strength. Also, with regard to the screw for fixing the plate to the bone, sufficient consideration must be given to the shape of the screw thread and the size of the screw core. Further, since the plate in the present invention is stretched in the length direction, the internal strain due to molding is small, and since it is physically uniform throughout, the variation in partial strength is very small, and the reliability is low. It can be used as

[0043]

Next, an embodiment of the plate for a polylactic acid-based fixing material of the present invention will be described.

Example 1 A polylactic acid pellet having a viscosity average molecular weight of 420,000 was dried under reduced pressure at 80 to 120 ° C. for 24 hours, and the dried pellet was put in an extruder and left under reduced pressure for about 40 minutes. Thereafter, the temperature of the extruder was set at 198 ° C. for the cylinder portion, 200 ° C. for the adapter portion, and 200 ° C. for the die portion, and melt extrusion molding was performed so as to have a substantially semicircular cross-sectional shape with a radius of 5 mm. It was 200,000 when the viscosity average molecular weight of the obtained molded product was measured.

The viscosity equation in this case is [η] = 5.
45 × 10 ⁻⁴ M ^0.73 (chloroform at 25 ° C.) was used.

Next, this molded product was uniaxially stretched twice in the longitudinal direction in liquid paraffin at 105 ° C.
A test piece was prepared by cutting the test piece into cm. The compressive flexural strength, compressive flexural modulus and crystallinity of the test piece at the initial stage and after immersion in physiological saline at 37 ° C. for 3 months were measured. Table 1 shows the results.

The above compressive bending strength and compressive bending elastic modulus are calculated from the maximum strength and the cross-sectional area of the test piece according to JIS K-7.
203. The crystallinity is calculated from the density measured by the following method. (Density measurement) The density was measured at 30 ° C. using an n-hexane-carbon tetrachloride-based density gradient tube. Prior to measurement, the sample was placed in n-hexane and degassed for 30 minutes to remove air bubbles. The crystallinity was calculated from the measured density according to the following equation. 1 / ρ = X / ρc− (1-X) / ρa X: Crystallinity ρ: Actual measured density of sample ρc: Crystal density (= 1.290 g / cm ³ ) ρa: Amorphous density (= 1) .248 g / cm ³ )

Example 2 A pellet of polylactic acid having a viscosity average molecular weight of 440,000 was molded under the same conditions as in Example 1, and the viscosity average molecular weight of the molded product was measured to be 220,000.

Next, a test piece was prepared in the same manner as in Example 1, and a strength test was performed. Table 1 shows the results.

Example 3 A polylactic acid pellet having a viscosity-average molecular weight of 400,000 was melt-extruded into a flat plate under the same conditions as in Example 1. Next, this molded product is uniaxially stretched twice in the long axis direction in 105 ° C. liquid paraffin,
Bending into a semicircle with a radius of 5 mm
m to prepare a test piece. The compressive flexural strength, compressive flexural modulus, and crystallinity of the test piece at the initial stage and after immersion in physiological saline at 37 ° C. for 3 months were measured. Table 1 shows the results.

Example 4 The initial viscosity average molecular weight was 42.
Ten thousand polylactic acid pellets were melt-extruded under the same conditions as in Example 1 so as to have a substantially semicircular (crescent) cross-section with a radius of 5 mm, and the molded product was subjected to long axis in 105 ° C. liquid paraffin. Uniaxially stretched twice in the direction
A test piece was prepared by cutting the test piece into cm. The compressive flexural strength, compressive flexural modulus, and crystallinity of the test piece at the initial stage and after immersion in physiological saline at 37 ° C. for 3 months were measured. Table 1 shows the results.
Shown in

Example 5 A test piece was prepared and subjected to a strength test in the same manner as in Example 4 except that a polylactic acid pellet having a viscosity average molecular weight of 440,000 was used. Table 1 shows the results.

Example 6 Pellets of polylactic acid having a viscosity average molecular weight of 420,000 were melt-molded under the same conditions as in Example 1. Next, this molded product is uniaxially stretched twice in the major axis direction in 105 ° C. liquid paraffin, processed into a substantially semicircle (crescent) having a radius of 5 mm, cut into a length of 5 cm, and a test piece is cut. Produced. Initial temperature of this test piece and 37 ° C
The compression bending strength, compression bending elastic modulus, and crystallinity after immersion in physiological saline for 3 months were measured. Table 1 shows the results.

Example 7 A polylactic acid pellet having a viscosity-average molecular weight of 400,000 was prepared in the same conditions as in Example 1 by molding into a mold having a cross section of a semicircular shape and an inner shape of a wide U-shape. This was used for melt extrusion molding, and this molded product was uniaxially stretched twice in the longitudinal direction in liquid paraffin at 105 ° C., and cut into a length of 5 cm to prepare a test piece. Compressive flexural strength of the test specimen at the initial stage and after immersion in 37 ° C physiological saline for 3 months,
The compression bending modulus and crystallinity were measured. Table 1 shows the results.

Example 8 A pellet of polylactic acid having a viscosity average molecular weight of 420,000 was melt-molded under the same conditions as in Example 1. Next, this molded product is uniaxially stretched twice in the major axis direction in a liquid paraffin at 105 ° C., and is processed so that its cross-sectional outer shape becomes a semicylindrical shape and its inner shape becomes a wide U-shape. A test piece was prepared by cutting to a length of 5 cm. The compressive flexural strength, compressive flexural modulus, and crystallinity of the test piece at the initial stage and after immersion in physiological saline at 37 ° C. for 3 months were measured. Table 1 shows the results.

(Comparative Example) A pellet of polylactic acid having a viscosity average molecular weight of 400,000 was melt-molded into a flat plate under the same conditions as in Example 1, and this molded product was then placed in a liquid paraffin at 105 ° C. in the longitudinal direction. The film was uniaxially stretched twice. The compressive flexural strength, compressive flexural modulus, and crystallinity of the test piece at the initial stage and after immersion in physiological saline at 37 ° C. for 3 months were measured. The results are shown in Table 1.

The width of the molded article in the above embodiment is about 1
The shape of FIG. 1 has a thickness of about 1 mm, and those of FIGS. 2 and 3 have a maximum thickness of 2.5 mm. The width of the molded article of the comparative example is about 19 mm and the thickness is 1.0 mm.

[0058]

[Table 1]

[0059]

As is apparent from the above results, the plate for the inner fixation material of the present invention used for a fractured part has a substantially semicircular cross section in both initial strength and strength after immersion for three months. A molded product in which the outer shape of the shape or the shape of a semicylindrical shape and the inner shape of the wide U-shape are superimposed, shows extremely excellent strength against bending, and this shows that the fracture part is sufficiently fixed, It can be said that it is effective in maintaining a stable state. In addition, since the shape in the present invention has a wide U-shaped inner shape that is easy to follow the bone, the fixation of the fracture portion has an effect that a more stable state can be maintained.

[Brief description of the drawings]

FIG. 1 shows a plate for an inner fixing material according to an embodiment of the present invention, wherein (a) is a perspective view, (b) is a cross-sectional view, and (c) is a longitudinal cross-sectional view. .

FIG. 2 shows a plate for an inner fixing material according to another embodiment of the present invention, wherein (a) is a perspective view, (b) is a transverse sectional view, and (c) is a longitudinal sectional view. is there.

FIG. 3 shows a plate for an inner fixing material according to another embodiment of the present invention, wherein (a) is a perspective view, (b) is a transverse sectional view, and (c) is a longitudinal sectional view. It is.

4A and 4B show a plate for an inner fixing material according to still another embodiment of the present invention, in which FIG. 4A is a perspective view, FIG. 4B is a transverse sectional view, and FIG. It is.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-29663 (JP, A) JP-A-60-88543 (JP, A) JP-T-3-505537 (JP, A) JP-T-3-1 501847 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 17/56-17/92 A61F 2/28-2/48 A61L 27/00-31/18

Claims (1)

(57) [Claims] A viscosity average molecular weight (M) after melt molding and stretching.
W) is 200,000 or more, and its compressive bending strength is 25.
0 × 10 ^{2 to} 55.0 × 10 ² kg / cm ² , compressive flexural modulus of 15.0 × 10 ^{2 to} 35.0 × 10 ² kg / m
m ² , crystallinity determined from density measurement is 10 to 60%
Consisting of polylactic acid, the size is 10 to 18 mm in width,
35-200 mm in length, 1.0-4.5 mm in thickness, and the cross section orthogonal to the length direction is a shape in which a substantially semicircular or semicircular outer shape and a wide inverted U-shaped inner shape overlap. A biodegradable and absorbable plate for an internal fixation material for a fractured part, which is a molded product of the above.