Biomechanical and Histologic Evaluation of the Norian Craniofacial Repair System and Norian Craniofacial Repair System Fast Set Putty in the Long-Term Reconstruction of Full-Thickness Skull Defects in a Sheep Model

Abstract

The purpose of this study was to investigate the long-term (12 months) strength and osteoconductive properties of two forms of carbonated calcium phosphate cements (i.e., the Norian Craniofacial Repair System and Norian Craniofacial Repair System Fast Set Putty) and to compare these two bone cement forms to an autogenous cranial bone graft in a full-thickness skull defect adult sheep model. Twenty-six sheep were assigned to one of eight groups (n = 3 per group). A 4.5-cm2 full-thickness defect was created in the right and left parietal bones. Reconstruction was performed with a full-thickness cranial bone autograft, the Craniofacial Repair System, or Fast Set Putty. Skull samples were harvested at day 1, 6 months, and 12 months. Biomechanical testing was performed using a vertical drop test. Although the Craniofacial Repair System and Fast Set Putty osseointegrated fully, there was little osteoconduction at 12 months. The Craniofacial Repair System was the weakest reconstruction, presenting the lowest peak force transmission and the highest displacement at 12 months. Fast Set Putty showed significantly higher values for peak force transmission and lower displacement when compared with the Craniofacial Repair System. The Craniofacial Repair System progressively lost strength over the course of this study. Fast Set Putty demonstrated greater strength and rigidity than the Craniofacial Repair System. Both implants had limited bone ingrowth from defect borders, but both cements osteointegrated completely. Bone grafts regained biostructural characteristics and strength similar to those of intact bone and clinically performed the same in this sheep model.