Short- and long-term effects of vertebroplastic bone cement on cancellous bone

Vertebroplasty using poly(methyl methacrylate) (PMMA) bone cement is the most common method to treat osteoporotic vertebral fractures. However, several questions of interest remain to be clarified, including how does PMMA affect the cement-bone interface area and surrounding bone tissue, can damaged bone tissues be repaired, how will PMMA change the bone interface over the long-term, and what happens to PMMA itself? The purpose of this study is to investigate these concerns and provide a basis for clinical evaluation. We made bone defects in the lumbar vertebrae of New Zealand rabbits as a model of osteoporosis and injected them with bone cement. A mechanical testing machine was used to perform axial compression, three-point bending, and twisting resistance tests to observe and investigate the short- and long-term biomechanical properties of PMMA after implantation. Optical, fluorescence, scanning electron microscopy, and nanoindentation were used to observe the changes in the interface microstructure. PMMA can rapidly establish the strong support with stable function in the near future. Biomechanical experiments showed that biomechanical property of bone cement group was significantly higher than those in the other two groups (P<0.05) biomechanical property of bone cement group may decline with the time, but it's still better than that of OP in the control group (P<0.05). Histomorphological observation result shows that under osteoporosis state the bone grows slower, also bone's rebuilding time extended. And in the later period, main bone's continuous osteoporosis has some impact on the interface. Nano-indentation testing shows that the young modulus and stiffness of the interface among bone, material and interface were significantly differences (P<0.05). Bone cement had gave the best nano indentation hardness, then was interface and bone tissue. PMMA bone cement was able to quickly support and stabilize the defect in the short term, and bone growth restarted at the bone interface and was tightly integrated. However, over the long-term, fluorescent signal was weakened, osteoclasts appeared, the mechanical indicators for both the interface and the whole vertebra decreased, and bone resorption was eventually greater than bone formation, resulting in bone loss. Therefore, vertebroplasty is not the end of treatment, and we need to further study ways to improve the bone cement material, which is crucial for long-term vertebroplasty efficacy, to better treat osteoporosis.