新型可吸收骨水泥的制备及其应用于小牛椎体标本压缩性骨折椎体成形术的生物力学研究

目的 探讨聚富马酸丙二醇酯（PPF）/β-磷酸三钙（β-TCP）制备新型可吸收骨水泥的配方及其应用于小牛椎体标本压缩性骨折椎体成形术的生物力学性能研究。方法 采用两步法制备PPF,使用凝胶渗透色谱仪测量PPF的数均分子量、重均分子量及聚合度分布指数,使用MR氢谱对PPF进行结构分析。将制备好的PPF与β-TCP按照10∶1、5∶1、3∶1、2∶1配制不同热交联反应体系,制备4种不同配方的PPF/β-TCP可吸收骨水泥,选择抗压强度和压缩模量均较高的骨水泥进行后续实验。选取2~3岁健康小牛腰椎L₁~L₄节段标本4具,分离出16个椎体,使用牙托粉填平每个椎体的椎板凹陷部位,测量每个椎体的受力面积。选择椎体受力面积相近的10个椎体,按数字表法随机分为PPF/β-TCP组和甲基丙烯酸甲酯（PMMA）组,每组5个。PMMA组和PPF/β-TCP组椎体使用MTS-858力学机器制备压缩性骨折模型,对比2组完成模型制备时的椎体高度、抗压强度和刚度。PPF/β-TCP组和PMMA组分别使用PPF/β-TCP骨水泥和标准PMMA骨水泥对压缩骨折模型行椎体成形术,对比2组骨水泥注入量,术后椎体高度、椎体恢复百分比,椎体抗压强度、刚度。结果 PPF数均分子量为1 637±55,重均分子量为1 741±68,聚合分布指数为1.06。MR氢谱结构分析提示反应产物为PPF。配方1~4 PPF/β-TCP可吸收骨水泥抗压强度分别为（53.5±1.5）、（63.2±0.4）、（97.9±5.5）、（100.8±3.2）MPa,压缩模量分别为（0.97±0.04）、（1.05±0.05）、（1.10±0.10）、（0.45±0.18）GPa。选取压缩模量与抗压强度均高的配方3 PPF/β-TCP可吸收骨水泥用于椎体成形术。PPF/β-TCP组和PMMA组小牛椎体标本的椎体体积、高度、受力面积差异均无统计学意义（P值均>0.05）。PPF/β-TCP组和PMMA组的椎体压缩性骨折后高度、椎体成形术后椎体高度以及椎体高度恢复百分比差异均无统计学意义（P值均>0.05）。组内比较：PPF/β-TCP组椎体压缩性骨折椎体成形手术前后椎体抗压强度分别为（2 282±341）N和（1 848±219）N,椎体刚度分别为（215±27）N/mm和（182±15）N/mm,差异均无统计学意义（t=2.14、2.13,P值均>0.05）;PMMA组压缩性骨折椎体成形手术前后抗压强度分别为（2 350±289）N和（3 105±452）N,椎体刚度分别为（221±26）N/mm和（296±37）N/mm,差异均有统计学意义（t=2.81、3.21,P值均<0.05）。组间比较：PPF/β-TCP组与PMMA组术中骨水泥注入量差异无统计学意义（P>0.05）;PPF/β-TCP组与PMMA组发生压缩性骨折时椎体抗压强度和刚度差异均无统计学意义（P值均>0.05）,椎体成形术后椎体抗压强度和刚度PMMA组均大于PPF/β-TCP组,差异均有统计学意义（t=4.99、5.61,P值均<0.05）。结论 PPF与β-TCP按照3∶1配制的可吸收骨水泥具有与人椎体力学性能相近、交联温度低等特点。在治疗小牛椎体压缩性骨折模型时,PPF/β-TCP可吸收骨水泥与PMMA骨水泥术中注入量相近,两者恢复椎体高度的效果相当;且PPF/β-TCP可吸收骨水泥注入后椎体力学性能优于注入PMMA骨水泥者,具有替代PMMA骨水泥治疗椎体压缩性骨折的潜力。

Preparation of novel absorbable bone cement and its biomechanical evaluation in vertebroplasty for calf vertebral compression fractures

Objective To explore poly propylene fumarate (PPF) /β-tricalcium phosphate (β‍-TCP) absorbable bone cement and study biomechanical properties in vertebroplasty for calf vertebral compression fractures. Methods PPF was prepared by a two-step method, and its number and weight average molecular weight were measured by gel permeation chromatography. Structural analysis of PPF was performed using MR hydrogen spectroscopy. Four kinds of PPF/β-TCP absorbable bone cement formulas formulated based on the mass ratios of 10∶1, 5∶1, 3∶1, and 2∶1 were prepared by thermal crosslinking. Bone cement with high compressive strength and compression modulus was selected for subsequent experiments. Four healthy 2-3-year-old calves were selected, and from their lumbar vertebrae L₁ to L₄, 16 vertebral bodies were isolated. In addition, the lamina depressions of each vertebral body were filled with dentate powder, and then measured the stress area of each vertebral body. Ten vertebrae with similar forced areas were randomly divided into PPF/β-TCP and PMMA groups according to the number table method with five vertebrae in each group. The vertebral bodies of the PMMA group and PPF/β‍-TCP group were used to prepare compression fracture models using the MTS-858 mechanical machine. The vertebral height, compressive strength, and stiffness of the two groups were compared when the models were prepared. The PPF/β-TCP group and PMMA group were treated with PPF/β-TCP bone cement and standard PMMA bone cement, respectively, for vertebroplasty of the compression fracture model. The amount of bone cement injection, postoperative vertebral height, vertebral recovery percentage, vertebral compressive strength, and stiffness were compared between the two groups. Results The average molecular weight of PPF was 1 637±55, meanwhile, the average molecular weight of PMMA was 1 741±68, and the polymerization distribution index was 1.06. MR structure analysis indicated that the reaction product was PPF. The compressive strength of formula 1-4 PPF/β-TCP absorbable bone cement was (53.5±1.5), (63.12±0.4), (97.9±5.5), and (100.8±3.2) MPa, respectively, and the compression modulus was (0.97±0.04), (1.05±0.05), (1.10±0.10) and (0.45±0.18) GPa, respectively. Formula 3 with high compressive modulus and compressive strength was selected for vertebroplasty. There were no significant differences found in the vertebral body volume, height, and stressed area between the PPF/β-TCP group and PMMA group (all P values >0.05). There were also no significant differences found in the vertebral height after compression, after vertebroplasty, or recovery percentage between the PPF/β‍-TCP group and PMMA group (all P values >0.05). Intra-group comparison: In the PPF/β‍-TCP group, the vertebral compressive strength was (2 282±341) N and (1 848±219) N before and after vertebroplasty, respectively. In addition, the vertebral stiffness was (215±27) N/mm and (182±15) N/mm before and after vertebroplasty, respectively, with no statistical significance (t=2.14, 2.13, all P values >0.05). The compressive strength of the PMMA group was (2 350±289) N and (3 105±452) N before and after vertebroplasty, respectively. Moreover, the vertebral stiffness was (221±26) N/mm and (296±37) N/mm before and after vertebroplasty, respectively, with statistically significant differences (t=2.81, 3.21, all P values <0.05). Comparison between groups: there was no significant difference found in intraoperative bone cement injection between the PPF/β‍-TCP group and PMMA group (P>0.05). There were no statistically significant differences in preoperative compressive strength and stiffness between the PPF/β-TCP group and the PMMA group (all P values >0.05). However, the postoperative compressive strength and stiffness of the PMMA group were greater than those of the PPF/β‍-TCP group (t=4.99, 5.61, all P values <0.05). Conclusion The absorbable bone cement prepared by PPF and β-TCP based on the ratio of 3∶1 has the characteristics of mechanical properties similar to the physical properties of human vertebrae and low cross-linking temperature. In the treatment of vertebral compression fractures, PPF/β‍-TCP absorbable bone cement, and PMMA bone cement have similar intraoperative injection volumes and can achieve the same effect of restoring vertebral height. In addition, the physical properties of vertebrae are better than PMMA cement, which can potentially replace PMMA bone cement in the treatment of vertebral compression fractures.