Degradation-resistant character of synthetic hydroxyapatite blocks filled in bone defects

The long-term changes of both the implanted hydroxyapatite (HA) blocks and the bone around them were observed radiologically to investigate the clinical usefulness of HA. HA blocks were used as a space filler in surgically created bone defects of seven cases due to curettage of bone tumours or removal for bone grafts, and they were followed up for 78 to 109 months. Bone formation around HA blocks peaked within 1 year after implantation, and then it faded gradually. However, shapes of HA blocks were rarely changed in all the cases. A clear zone around HA blocks was never observed. HA blocks were biocompatible and demonstrated a character resistant to degradation.