<正>Objective:To observe the changing of biomechanical features during the degradation course of poly-D

L-lactic acid （PDLLA） rods in vivo and in vitro and to evaluate its value as an internal fixation material. Methods:PDLLA rods were emerged into PBS simultaneous body fluid with constant temperature of 37 C and the rods were embedded into muscle tissue of 20 rabbits for degradation in vitro and in vivo . The rods were taken out in 2

4

6. 8 and 12 weeks. Biomechanical features of bending

shearing and axial compression strength

rigidity and elastic modulus were observed during the degradation course. Statistical method was used to test the changes of biomechanical parameters. Results: （1） There was similar changes of bending

compressive

shearing strength and bending

compressive and shearing rigidity of the PDLLA rods between in vivo and in vitro. （2）Bending

compressive

shearing strength decreased 33%

18% and 43% respectively within the first stage of the degradation

and after 6 weeks of degradation

they decreased slowly. （3）Elastic modulus

bending

compressive and shearing rigidity.decreased sharply during the 6 weeks of degradation

with a drop of 22%

39% and 30% respectively

and after 8 weeks

they decreased slowly. Even after 12 weeks of degradation

the strength of the rods was still higher than that of sponge bone. Conclusion: During the degradation of the material

the strength and rigidity of PDLLA rods can meet the need of fracture fixation of cancellous bones.