Hydroxyapatite/poly-L-lactide acid screws have better biocompatibility and femoral burr hole closure than does poly-L-lactide acid alone.

Hydroxyapatite (HA)/poly-l-lactide(PLLA) composite biomaterials are available for orthopedic applications, but bioresorption and cell-mediated inflammation in bone cortex are unknown. We conducted an 84-month follow-up study with Beagle dogs that were subjected to implants with either PLLA (left femur) or HA/PLLA (right femur). Histological and radiographic analysis showed that HA/PLLA screws induced significant increases in HA content from 36 months onward and complete burr hole closure at 60 months, whereas PLLA screws did not. Moreover, PLLA screws induced more severe fibrous tissue and histiocyte infiltration. HA/PLLA screws promote earlier burr hole replacement and have superior biocompatibility compared to PLLA screws.