The ultrastructure and resorptive pattern of cancellous onlay bone grafts in the craniofacial skeleton.

The authors' laboratory has shown cancellous onlay bone grafts to resorb faster than cortical grafts. To understand the nature of cancellous bone grafts beyond volumetric measurements, a temporal analysis of the internal microarchitecture of these grafts was performed. Their hypothesis is that the forces of remodeling and resorption cause cancellous onlay bone grafts to develop a denser, more interconnected, and a more mechanically stable microarchitecture. Twenty-five adult New Zealand White rabbits were used in this study and were divided into three groups. Microcomputed tomography (MCT) was performed on all cancellous bone grafts to obtain detailed information regarding the microarchitecture of the cancellous bone. Bone graft specimens were examined histologically, and histomorphometric analysis was also performed. Their results show that cancellous onlay bone grafts develop a higher bone volume fraction, mean trabecular thickness, connectivity, and degree of anisotropy. Furthermore, cancellous onlay bone grafts developed a lower bone surface area-to-volume ratio and mean trabecular separation. The unique combination of MCT technology and histomorphometric techniques proved to be effective in providing a qualitative and quantitative ultrastructural analysis of cancellous onlay bone grafts over time. The authors were able to show changes in the internal microarchitecture of cancellous onlay bone grafts as they were remodeled and resorbed. Specifically, they found the cancellous onlay bone grafts to develop a more dense, less trabecular, more organized, and more interconnected internal ultrastructure over time. Their findings have helped to provide a reproducible description of the temporal sequence of changes in bone microarchitecture, revascularization, and internal remodeling.