Porous Surface Modified Bioactive Bone Cement For Vertebroplasty: An In Vivo Evaluation

Background: Osteoporosis (OP) is one of the three major diseases in elderly populationin China. By the age of50years,the prevalence of OP in women is nearly20.7%; in men,the corresponding figure is14.4%. The incidence of OP increases markedly with age,evenas high as66%in women after the age of80years. Vertebral compression fracture is themost common complication of osteoporosis. Spine is the most serious part for OPinvolvement. The prevalence of OP at spine is28%in women aged50years or older,which is much higher than the15%at femur. Therefore, vertebral fractures are the mostcommon of all osteoporotic fractures. In china, it is estimated that there are around1.81million osteoporotic fractures each year,and the number is predicted to36.75million by2020. Patients with vertebral compression fracture can present with severe back pain orneurological dysfunction, and kyphotic deformities that cause biomechanical changes inthe spinal segment and increase the incidence of adjacent vertebral fractures, forming avicious cycle of "fracture-deformity-re-fracture". Thus, it is important and significant to augment impaired bony structures in order to maintain or improve strength and stability ofthe spinal column, to reduce the prevalence of osteoporotic vertebral compressionfracture,and to correct the kyphotic deformities caused by OP.Vertebroplasty and kyphoplasty are two percutaneous minimally invasive techniques intreating symptomatic VCFs patients who do not have neurological impairment. The mostcommonly used cement in vertebroplasty is polymethyl methacrylate (PMMA). However,the limitations of PMMA could not be ignored, including un-absorbable, poorbiocompatibility, missing osteoconductivity and excessive stiffness.In the previous study, we have showed the development and characteristic of a novelinjectable Porous Surface Modified Bioactive Bone Cement (PSMBBC), which had goodbioactivity in vitro, appropriate biomechanical strength, partial degradability, and wascomposed of bioglass, chitosan and PMMA. However, whether it can be use as a fillingmaterial for vertebroplasty or its effects on strengthening osteoporotic vertebrae stillremain unknown. Thus, the aim of this study is to determine the feasibility andeffectiveness of the PSMBBC for vertebroplasty of aiding osteoporotic vertebrae in anosteoporosis model.Materials and Methods: The novel Porous Surface Modified Bioactive Bone Cementwas composed of bioglass,chitosan and PMMA as weight ratio4:5:1, and a solid: liquidmass ratio of1.5:1was used. Samples of cured cement were immersed in15ml phosphatebuffered saline (PBS) at37°C and kept for4weeks. In order to measure the mechanicalproperties of the novel bone cement in vitro, the compressive strength values wereexamined.by biomechanical tests. Meanwhile, the samples were soaked in SBF and the invitro bioactivity of the novel bine cement was assess by X-ray diffraction (XRD).80adultfemale New Zealand white rabbits were randomly divided into two groups. Theovariectomy group (n=72) received bilateral ovariectomy (OVX), and the sham group(n=8) only received the sham operation. Then, the rabbits of the OVX group wererandomly divided into three groups: PMMA group, Bioactive Bone Cement group (BBC)and control group (CON). PMMA and BBC were administrated to osteoporotic vertebraein Vertebroplasty, respectively. The animals were sacrificed at1w,4w,12w after the procedure. Micro-CT analysis, biomechanical tests and histological analysis wereperformed at each time point.Results: The glass and CS particles were uniformly distributed in the polymeric matrix fordry cement samples by SEM analysis. A significantly lower compressive strength (P<0.05)was observed for the BBC compared to the PMMA bone cement at each degradation time.Newly formed apatites were confirmed by XRD at7day. From4to12weeks after bonecements implantation, the bone volume fraction (BV/TV,%) of the BBC group increasedfrom28.27±1.69%to38.43±1.34%. However, the BV/TV of the PMMA group showedno significant differences. At4weeks, direct contact between bone and bone cement wasobserved in the BBC group. At12weeks, it showed neo intact bone trabecular formed inPSMBBC group. Furthermore, the maximum compressive strength values of the BBCgroup were significantly higher than that of the control group at each time point afterimplantation. At1,4weeks, the maximum compressive strength values of the BBC groupwere lower than that of the PMMA group. At12weeks, it showed no difference betweenthe two groups.Conclusion：This study suggests that the novel Porous Surface Modified Bioactive BoneCement has a certain osteogenicability, appropriate biomechanical strength, partialdegradability, making it an excellent material for vertebroplasty.