Application of High Strength Polylactide Implants for Osteosynthesis

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To overcome the drawback of the metallic device for fracture repair, ultra-high-strength poly(L-lactide)(PLLA) rods were fabricated using a drawing technique. Rods with a diameter of 3.2 mm and a draw ratio of 2.5 : 1 showed initial bending strength and modulus values of 240 MPa and 13 GPa, respectively, which is the highest reported for nonreinforced poly(L-lactide) rods used in detailed investigations of degradation. The greater the rod diameter, the longer the bending strength was maintained in phosphate buffered saline at 37ﾟC. The bending strength retention of rods implanted in the subcutis of rabbits was almost equal to that of rods in the in vitro study, while those rods implanted in the medullary cavity of rabbit femora showed a slightly lower bending strength retention. The weight of PLLA rods in the medullary cavity was reduced by 22% at 52 weeks and by 70% at 78 weeks after implantation. Histologically, no foreign body or inflammatory reaction was observed in the medullary cavity for 52 weeks. Phagocytosis by histiocyte was observed after 52 weeks and reached to the maximum level at 2 to 2.5 years after implantation. The another study on the PLLA screw in the repair of fractured rabbit bone showed that there was no significant difference of the fragments in the PLLA and stainless steel group and new bone was more abundantly detected in the PLLA group. These results suggest that the drawn PLLA screws and rods may be useful in the repair of fractured human bones.