磷酸钙骨水泥填充椎体成形过程中椎体生物力学评价**★

背景：目前椎体成形中常用的充填剂聚甲基丙烯酸甲酯因其过高的强度会引起临近节段骨折，新型材料磷酸钙骨水泥具有骨传导性，但其在体内的生物力学情况尚不明确。 目的：模拟骨质疏松性骨折椎体的力学环境，观察磷酸钙骨水泥填充后椎体的力学变化情况，评价其在椎体成形中的适用性。 设计、时间及地点：随机对照，动物体内生物力学实验, 于2007-02/12在苏州大学实验动物中心完成。 材料：成年雌性山羊12只，双侧去卵巢法制备骨量减少动物模型。 方法：以直径4.0 mm钻头横向钻通模型山羊L2~5腰椎椎体双侧皮质，两两随机向骨缺损内注入磷酸钙骨水泥或聚甲基丙烯酸甲酯，以L1和L6椎体为对照组。 主要观察指标：生物力学测试仪测试术后2，6，12，24周各组椎体的强度和刚度。 结果：磷酸钙骨水泥组椎体强度从2周起逐渐增强，在24周时最强，各时间点与对照组相当，但均低于聚甲基丙烯酸甲酯组。磷酸钙骨水泥组椎体刚度从2周开始下降，12周达到最低，24周时上升，但各时间点间无统计学差异（P = 0.265）；聚甲基丙烯酸甲酯组刚度2~24周也无明显降低（P =0.815）；各时间点2组间比较无明显差异（P > 0.05），但都低于对照组。 结论：磷酸钙骨水泥填充后椎体具有更合适的生物力学强度，有望替代聚甲基丙烯酸甲酯在椎体成形中应用。

Biomechanics of calcium phosphate cement in vertebroplasty

BACKGROUND: Polymethyl methacrylate (PMMA), commonly used in vertebroplasty as fillings, may induce adjacent segmental fracture due to a high intensity. Calcium phosphate cement (CPC) is osteoconductive, however, its biomechanical behaviors in vivo is uncertain. OBJECTIVE: To observe the biomechanics of CPC in simulated osteoporotic vertebral fracture, so as to estimate the feasibility of CPC for vertebroplasty. DESIGN, TIME AND SETTING: A control observational animal experiment was performed at the Experimental Animal Center of Soochow University from February to December 2007. MATERIALS: Twelve adult female goats underwent bilateral ovariectomy to prepare osteopenia models. METHODS: Bilateral cortex of L2-5 vertebra in every model goat was drilled to center of the sagittal plane with ?4.0mm drill. The holes were filled with CPC and PMMA randomly. L1 and L6 vertebra bodies served as controls. MAIN OUTCOME MEASURES: The intensity and stiffness of the augmented vertebras at 2, 6, 12, and 24 weeks were determined by material testing system. RESULTS: The vertebral intensity of PMMA group was increased since the second week, and reached peak value at 24 weeks, which was similar to the control group at each time point, but lower than CPC group. The intensity of PMMA group was decreased from the second week, and reached minimal value at 12 weeks, increased from the 24th week; however there were no significant differences among all time points (P =0.265). The stiffness of PMMA was not significantly decreased from 2 weeks to 24 weeks (P=0.815), and no differences were found between any two time points (P > 0.05), but lower than control group. CONCLUSION: The biomechanical property of the vertebras filled with CPC becomes appropriate, and may replace PMMA in vertebroplasty.