Aim. To investigate the bioactivity of the self- designed biodegradable osteosynthetic devices made of resorbable hydroxyapatite microparticles/ poly- DL- lactide （HA/PDLLA） composites. Method. Forty- three rabbits with a transverse transcondylar osteotomy of the distal femur were fixed intramedullary by a HA/PDLLA rod

the duration of follow- up were 3， 6， 12

24 and 36 weeks. Histological

scanning electron microscopic （SEM）

energy dispersive X- ray （EDX） and biomechanical analyses were done. Results. Active new bone formation and direct bone- bonding were seen at the bone- implant interface. Generous apatite crystals deposited and grew on the surface of the composites at 3～ 6 weeks postoperation. The interfacial shear strength increased significantly. Conclusion. Through the incorporating of resorbable HA microparticles

specific bone- bonding and active osteogenic capacity is introduced. This kind of bioactivity

together with other properties such as sufficient mechanical strength

enhanced biocompatibility and radiopacity

which are intrinsically unobtainable in totally resorbable polymer/polymer systems

make the HA/PDLLA composites become a desirable material for the internal fixation of cancellous bone.