JP2864113B2 - Biodegradable absorbable rib fixation pin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rib fixing pin for fixing a rib until a bone is formed when the rib is damaged, fractured or cut off.

[0002]

2. Description of the Related Art In orthopedic surgery and the like, a high-strength osteosynthesis plate or a screw is used for reducing a fractured portion.
Such artificial materials for osteosynthesis function only until the fracture heals, and after the healing, it is necessary to remove the bone as early as possible to prevent 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. However, these materials have problems that the elasticity of the material itself is too high, which lowers the strength of the surrounding bone, that the material has a high elasticity and is brittle, and that the living body is damaged by elution of metal ions. Therefore, if a material having the same or slightly higher elastic modulus as that of living bone and being 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 and lactic acid-glycolic acid copolymer for osteosynthesis plates, and have a 100% polylactic acid with a compression flexural modulus of 3.4 GPa (340 kg / mm ² ). (Makromol Chem. Suppl., 5, 30-
41, 1981). D. C. Tunc reports a polylactic acid osteosynthesis plate with a compressive bending modulus of 520 kg / mm ² (Abstracts of the 9th USA Biomaterials Society,
6, 47, 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
And others synthesize polylactic acid with a viscosity average molecular weight of about 1,000,000,
It has been reported that the osteosynthesis plate using the high molecular weight polylactic acid had a compression bending elastic modulus of 5 GPa (500 kg / mm ² ) (Biomaterials, 8, 70, 1987).
However, it is too high in molecular weight and there is a problem in moldability.

As described above, many studies for improving the mechanical properties of the polylactic acid-based osteosynthesis material have been reported, and various methods have been tried, but they are still satisfactory enough to be used in clinical practice. No strength material has been developed. The present inventors have proposed in Japanese Patent Application No. 62-333333 a biodegradable and absorbable surgical material having a strength about the same as or slightly higher than that of a living bone, and obtained a clinically usable material. This material is used after being cut into various sizes and shapes of osteosynthesis plates, pins, screws, screws and the like.

[0009]

As described above, various polylactic acid-based osteosynthesis materials have been developed. However, the shape of the osteosynthesis material is limited to a straight plate, a pin, or the like. Was difficult to insert into the costal cavity. There was also anxiety about the fixation in the intrathecal space.

The present invention has been made in view of the above circumstances, and has as its object to provide a rod-shaped pin having an optimum shape as a rib fixing pin.

[0011]

The polylactic acid used in the present invention is as follows. That is, high molecular weight polylactic acid is
Melt molding, for example, extrusion molding or press molding under the temperature condition of the melting point or 220 ° C.
The film was stretched under a temperature condition of 0 to 160 ° C. or in a nitrogen atmosphere or oil in order to suppress a decrease in molecular weight due to oxidative decomposition. It has a compressive bending strength of 16.0 × 10 ^{2.
~25.0 × 10 2 kg / cm 2} , compression flexural modulus of 5.5 × 10 ² ~24.0 × 10 ² molded of tough polylactic acid kg / mm ^2. In the present invention, a molded article of polylactic acid having the above physical properties is formed into an arcuate rod according to the shape of a rib.

That is, the biodegradable and absorbable rib fixation pin according to claim 1 of the present invention is for joining a rod-shaped rib in which a polylactic acid molded product formed by melt molding and stretched has an arcuate shape. No. 2 has a compression bending strength of 1 of the above polylactic acid molded product.
6.0 × 10 ^{2 to} 25.0 × 10 ² kg / cm ² , and compression bending elastic modulus of 5.5 × 10 ^{2 to} 24.0 × 10 ² kg / cm ² .
It has a strength of mm ² .

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The polylactic acid used in the present invention will be described in detail. Polylactic acid is prepared from optically active L-form or D-form lactic acid by a conventional method (CE Love, US Pat.
No. 68,182), a lactide, which is a cyclic dimer of lactic acid, is synthesized, and then the lactide is subjected to ring-opening polymerization. Since this polylactic acid is inferior in thermal stability, considering the molecular weight reduction at the time of melt molding, it is preferable 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 rib fixing pin. Suitable for. However, if the molecular weight is too high, a high temperature and high pressure are required during melt molding, resulting in a significant decrease in the molecular weight, and as a result, the molecular weight after melt molding will be less than 200,000, resulting in high strength. It is difficult to obtain a rib fixation pin. Therefore, it is appropriate to use those having a viscosity average molecular weight of about 300,000 to 600,000.
Those having a molecular weight of preferably 350,000 to 550,000, especially about 400,000 to 500,000 are particularly preferably used.

The molded product of polylactic acid is prepared by using polylactic acid as a raw material as described above, melt-molding it into a rod shape or a plate shape, for example, extrusion molding, press molding, and then uniaxially stretching in the major axis direction. Obtained by:

The temperature conditions for the melt extrusion molding must be in the 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 the melt extrusion molding is preferably 200,000 or more, and more 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 a stretching operation. 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 conditions of the melt extrusion molding are desirably set to the minimum extrusion pressure at which extrusion is possible in accordance with the viscosity (molecular weight) of the molten raw material polymer in order to minimize the decrease in molecular weight. Therefore, when the molecular weight of the raw material polymer is up to 600,000, 260 kg / cm ² or less, and when the molecular weight is 400,000 to 500,000, 170 to 210 kg / cm ^2.
An extrusion pressure of about ² is appropriate.

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

The extruded product obtained by melt extrusion has a viscosity average molecular weight of 200,000 or more.
It has considerable strength, but still does not reach the desired strength. Therefore, as described above, the extruded 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 to improve the strength.

Further, the crystallinity of the material can be increased by heating at the time of 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 at the time of stretching is preferably in the range of 60 to 160 ° C., and the temperature lower than 60 ° C. is not preferable because it is too close to the glass transition temperature. Conversely, 160 ° C or higher, especially 18
If the temperature exceeds 0 ° 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 molded product of polylactic acid obtained by the above-mentioned production method has biodegradability and absorbability, and is unlikely to have an adverse effect in a living body unlike conventional metal materials. In addition, the viscosity average molecular weight after melt molding is kept at 200,000 or more by minimizing the decrease in molecular weight during melt molding, and further, molecular orientation and crystallization are given by stretching.
This polylactic acid molded product has a compression bending strength of 16.0 × 10 ^2.
２５25.0 × 10 ² kg / cm ² , compression bending elastic modulus 5.5 × 10 ² 〜24.0 × 10 ² kg / mm ² , crystallinity 10-60%, high strength It will be.

The polylactic acid molded product thus obtained is formed into a curved, arc-shaped molded product by secondary molding, cutting, or the like, thereby forming a fixing pin for joining ribs. With the arcuate fixing pin, it can be easily inserted into the curved medullary cavity of the ribs, and because of the arcuate shape, elasticity can be applied so that it can be pressed in and the fixing force increases.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The rib fixing pin of the present invention will be described below with reference to examples.

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. As the temperature condition, the cylinder part was 19
8 ° C, Adapter part 200 ° C, Dice part 200
C., and was melt-extruded into square or round bars. When the viscosity average molecular weight of the obtained molded product was measured, it was found to be 22.
It was ten thousand. In addition, the following [Equation 1] was used for the viscosity formula in this case.

(Equation 1)

Next, this molded product was uniaxially stretched twice in the major axis direction in liquid paraffin at 105 ° C. to obtain a polylactic acid molded product.

Next, the stretched polylactic acid molded product was cut to obtain a polylactic acid molded product pin shown in FIGS. FIG. 1 is a front view, and FIG. 2 is a plan view. As for the size of the pin, the length L is 37.5 mm, and the length of one side is 3 mm to 4 m.
m having a substantially square cross section, and as is apparent from FIG.
It is an arcuate rod having 50 curved surfaces. This is used as a rib fixing pin.

[0028] The physical properties and in vitro
In order to examine the strength deterioration at o, a test piece (dimensions: φ5.0 mm × length 80 m) was obtained from a uniaxially stretched polylactic acid molded product.
m) was prepared. The compression bending strength of the obtained test piece was 17
20 kg / cm ² , compression flexural modulus is 610 kg / mm
² , and the crystallinity was 28%.

Further, the test piece was immersed in a physiological saline solution at 37 ° C. for 3 months, and thereafter, the compressive bending strength of the test piece was measured to be 1700 kg / cm ² , and the compressive bending elastic modulus was 600 kg / mm. ^2, it was found that does not occur the most strength deterioration.

The compressive bending strength and the compressive bending elastic modulus are measured based on JIS K-7203, and the crystallinity is calculated from the density measured by the following method.

The measurement was carried out at 30 ° C. using a density gradient tube of n-hexane / carbon tetrachloride system. Prior to the measurement, the sample was placed in n-hexane to remove bubbles, and degassed for 30 minutes.

The degree of crystallinity was calculated from the measured density according to the following equation (Equation 2).

(Equation 2)

[0033]

As can be understood from the above description, the biodegradable and absorbable rib fixation pin for connecting a rib of the present invention has an arcuate rod shape, so that the rib is inserted into the medullary cavity. It is easy to remove, and the bow shape gives elasticity to make it easy to press-fit and increase the fixing force. Furthermore, since it has a certain strength, the fixing pin of the present invention does not break during joining.

[Brief description of the drawings]

FIG. 1 is a front view of a rib fixing pin according to an embodiment of the present invention.

FIG. 2 is a plan view of the rib fixing pin of the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-259674 (JP, A) JP-A-61-213047 (JP, A) JP-A-3-149059 (JP, A) JP-A-1- 198553 (JP, A) Japanese Utility Model Laid-Open 4-103146 (JP, U) Japanese Patent Publication No. 45-31696 (JP, B1) Japanese Patent Publication No. 2-501122 (JP, A) Japanese Patent Publication No. 1-1501289 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) A61L 27/00 A61F 2/28

Claims (2)

(57) [Claims] 1. A biodegradable and absorbable rib fixing pin for joining a rib in the form of a rod formed from a melt-formed and stretched polylactic acid molded product having an arcuate shape. 2. The polylactic acid molded product has a compressive bending strength of 16.0.
× 10 ^{2 to} 25.0 × 10 ² kg / cm ² , and a compressive flexural modulus of 5.5 × 10 ^{2 to} 24.0 × 10 ² kg / mm ²
The biodegradable and absorbable rib fixation pin according to claim 1, which is: