Surgery – Instruments – Orthopedic instrumentation
Patent
1988-04-29
1990-02-06
Cannon, Alan W.
Surgery
Instruments
Orthopedic instrumentation
623 16, 264164, 606 77, A61F 504, A61F 228
Patent
active
048981869
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to bone fixing pins for use in surgery, especially for use with cut ribs, fractured bones or the like for fixing and remedying the bones.
BACKGROUND ART
Metal or alumina ceramic osteosynthetic pins have heretofore been used clinically for remedying cut or fractured bones by inserting the pin into the marrow cavity of the cut or fractured bone and fixing the bone.
However, these osteosynthetic pins have the disadvantages of being low in elasticity, exerting no shock-absorbing action relative to the movement of the fixed bone portion and stimulating the bone to cause an inflammation or retard osteogenesis. Moreover, they have poor affinity for the living body, are not absorbable by the living body and therefore have the problem of permanently remaining in the living body after the fracture has been remedied, possibly causing contamination with bacteria or an inflammation.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide an osteosynthetic pin having suitable elasticity and high affinity for the living body, absorbable by the living body after surgery and advantageously usable in regenerating and remedying the bone without causing an inflammation to the fixed portion and further without entailing the objection that could result if the pin remains permanently in the living body.
Another object of the invention is to provide an osteosynthetic pin capable of exhibiting an osteogenesis promoting effect on fixed bones.
The osteosynthetic pin of the present invention is characterized in that the pin is formed substantially of a poly-L-lactic acid having a molecular weight of at least about 70,000.
We have conducted research on various high-molecular-weight substances having affinity for living body and absorbable by the living body to explore whether these substances are usable for osteosynthetic pins. Many of the high-molecular-weight substances investigated did not have suitable elasticity required of osteosynthetic pins, were low in initial strength or failed to retain the required strength during the bone regeneration period (usually about 2 months), and were therefore unsuited to use for osteosynthetic pins. Nevertheless, we have found that of the homopolymers of L-lactic acid, only poly-L-lactic acid having a molecular weight of at least 70,000 is excellent in initial strength, retains the required strength during the bone regeneration period, permits effective regeneration and remedy of bones and is therefore very suitable for osteosynthetic pins. Moreover, the poly-L-lactic acid posseses suitable elasticity, accordingly exhibits a shock-absorbing action relative to the movement of the fixed bone portion and is unlikely to cause an inflammation or retard regeneration of bones by stimulating bones. The poly-L-lactic acid further has excellent affinity for the intramedullary tissue when placed into the marrow cavity and is gradually absorbed by the living body through hydrolysis therein, so that the acid is usable free of the objection that would result if the acid remains permanently in the living body like metal or alumina ceramics.
Although the poly-L-lactic acid to be used in the present invention is itself known, no report has been made on the acid as used for osteosynthetic pins. Homopolymers of L-lactic acid which are less than about 70,000 in molecular weight are not satisfactory in the properties required of osteosynthetic pins, i.e. in initial strength and strength retentivity during the bone regeneration period, and are not usable for the pin. The poly-L-lactic acid suited to the present invention is at least about 70,000, more preferably at least about 100,000 and most preferably at least 150,000, in molecular weight. The upper limit of the molecular weight, although not limited specifically, is generally about 150,000 in view of shapability, etc.
The molecular weight of the poly-L-lactic acid mentioned herein is determined by dissolving the acid in chloroform to a concentration of 0.2 g/d1, further diluting the solutio
REFERENCES:
patent: 4506681 (1985-03-01), Mundell
patent: 4550449 (1985-11-01), Tunc
patent: 4650488 (1987-03-01), Bays et al.
patent: 4781183 (1988-11-01), Casey et al.
Ikada Yoshito
Nakamura Tatsuo
Shimamoto Takeshi
Shimizu Yoshihiko
Suong Hyu H.
Cannon Alan W.
Gunze Limited
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