Histological Changes of an Injectable rhBMP-2/Calcium Phosphate Cement in Vertebroplasty of Rhesus Monkey

Study Design. A histologic study of recombinant human bone morphogenetic protein-2/calcium phosphate cement (rhBMP-2/CPC) using adult rhesus monkeys in vivo. Objective. To evaluate the histologic changes of rhBMP-2/CPC in vertebroplasty and determine the feasibility of this bone substitution instead of polymethylmethacrylate ( PMMA). Summary of Background Data. Previous studies have shown that the new rhBMP-2/nanoscale CPC has a suitable strength and injection for vertebroplasty. However, the osteoinductive properties and biodegradable characteristics are still unclear. Methods. Percutaneous vertebroplasty (PVP) was performed in 4 adult rhesus monkeys of 2 groups. Ten vertebral bodies (VBs) from T10-L7 of each rhesus were selected, and the 20 VBs in each group were randomly divided into 3 subgroups. Subgroup A (rhBMP-2/CPC): 8 VBs, filled with rhBMP-2/CPC; Subgroup B (PMMA): 6 VBs, filled with injectable PMMA; Subgroup C (control): 6 VBs, filled with normal saline. The 2 rhesus monkeys from each of the groups were killed at 2 and 6 months after operation, respectively. Individual specimens from the 40 VBs were collected for histologic observation. Results. In subgroup A, radiographic and histologic observations showed that the part of the rhBMP-2/CPC cement degraded with new bone and new vessel ingrowths, into the material, after 2 months. In addition, gaps, fibrous hyperplasia, or sclerotic callus were not found in the interface. After 6 months, the cement was nearly all replaced by mature bone tissue. In subgroup B, the inflammatory cell infiltration and fibrous membrane gapping were found after 2 months, and subsided partly at 6 months. But no new bone formation and material degradation were discovered. In subgroup C, the tunnels were filled with irregular new trabeculae after 2 months and unrecognizable from the surrounding mature bone after 6 months. Conclusion. It is confirmed that the rhBMP-2/CPC is an osteoinductive and biodegradable material (in animal trials). It may also be an alternative to PMMA in order to achieve biostabilization in a vertebroplasty.