Porous beta-calcium pyrophosphate as a bone graft substitute in an canine bone defect model

Hydroxyapatite(HA) has been used in various situations in which bone augmentation and restoration are required. Porous HA has been used either alone or in conjugation with freeze dried or autogenous bone, with variable clinical success. However, it has a defect that it is relatively bio-inert and remains in the host body for a long time. In this study, porous β-calcium pyrophosphate(β-CPP) has been compared with porous HA in an canine bone defect model to discover the possibility as a bone graft substitute replacing porous HA. Porous HA and porous β-CPP were implanted in the proximal tibia of 5 dogs. 2 animals were sacrificed at 8 weeks and 3 animals were sacrificed at 20 weeks after surgery. Radiographs were obtained every 4 weeks and histologie sections of the implant site were obtained at the time of sacrifice. By serial radiography, both implants showed contraction of radio-opaque area, blurring of graft margin, and piecemeal patterned incorporation of surrounding new bone. But these changes were more prominent in porous β-CPP compared with porous HA and showed more rapid resorbing features. Porous HA and porous β-CPP were completely integrated into newly formed bone after partial degradation and bony tissue ingrowth was progressing during the study period. In the case of porous β-CPP, the new bone growth was as vigorous as in HA, but the pore is larger and the wall of the scaffold is thinner and bone ingrowth in gaps between the implants was more evident than in HA, which suggest more rapid degradation of β-CPP in vivo. Preliminary report of our experiment suggests that porous β-CPP appears to provide an alternative graft material that is bioactive, more completely incorporated and more rapidly resorbable than porous HA.