OBJECTIVEThe histological changes of rhBMP-2/calcium phosphate cement (CPC) were evaluated in vertebroplasty on nonhuman primate models in order to determine the feasibility of this carrier formulation instead of PMMA.

METHODSPercutaneous vertebroplasty (PVP) was performed in 4 adult rhesus monkeys which were evenly distributed in two groups. Ten vertebral bodies(VBs) from T10 to L7, of each rhesus were selected, and the 20 VBs in each group were randomly divided into 3 sub-groups. Group A:8 VBs, filled with rhBMP-2/CPC; Group B:6 VBs, filled with injectable PMMA; Group C:6 VBs, as control, filled with normal saline. The 2 rhesus monkeys in each group were killed at 2 and 6 months after operation, respectively, and the specimens of all the 40 VBs were collected for histological examination.

RESULTSIn group A,radiographic and histologic studies confirmed that part of the rhBMP-2/CPC cement degraded with new bone and new vessels ingrowth into the material after 2 months. No gap, fibrous hyperplasia or sclerotic callus was found in the interface. After six months, the cement was almost completely replaced by mature bone tissue. In group B, no new bone formation and material degradation but inflammatory cell infiltration and fibrous membrane gap were found 2 months after operation. After 6 months, the inflammatory cell infiltration subsided, the fibrous membrane gap became narrower, but there were still no new bone formation and material degradation. In group C, the tunnels were filled with irregular new trabeculae after 2 months and unrecognizable from the surrounding mature bone after 6 months, indicating the completion of bone healing.

CONCLUSIONSWith the characteristic of osteo-induction, the rhBMP-2/CPC can accelerate the healing of vertebral bone in nonhuman primates. Bone substitution is synchronous with material degradation, and the complete degradation of this material in late stage can avoid the potential adverse effects of PMMA on contiguous vertebral fracture and annulus degeneration. It might be a perfect bone substitute material for vertebroplasty instead of PMMA in the future.