骨水泥的单体-粉配置及强化老年人骨质疏松椎体的生物力学效果

Monomer-to-powder ratio of polymethylmethacrylate and its biomechanical evalu ation for the application in vertebroplasty

目的 了解聚甲基丙烯酸甲酯 (PMMA)不同单体 粉配比 (1∶2、2∶3、1∶1)的配置对聚合过程和机械力学性质的影响 ;评价 2∶3配置的PMMA对强化老年人骨质疏松椎体的生物力学效果 ,为临床应用提供指导。 方法 将PMMA液 (ml)、粉 (g)比例按 1∶2、2∶3、1∶1配比 ,观察其聚合过程及测试屈服压缩强度。各取 13个正常和骨质疏松腰椎椎体 ,进行前屈压缩试验 ,测试初始抗压强度和刚度 ,给骨质疏松椎体经椎弓根注入单体 粉配比为 2∶3的骨水泥强化修复 ,测试强化后的抗压强度和刚度。 结果 3种单体 粉配比的PMMA ,随着单体液相增多 ,混合至出丝时间、混合至面团时间、混合至硬化时间延长 (P <0 0 1) ,而屈服压缩强度下降 (P <0 0 5或P <0 0 1)。骨质疏松组椎体强度和刚度〔分别为 (1598± 53 1)N、(650± 13 5)N/mm〕明显低于正常对照组〔分别为 (73 4 0± 671)N、(2 2 75± 2 58)N/mm〕 ,强化修复组椎体强度和刚度〔分别为 (53 4 0± 542 )N、(112 0± 162 )N/mm〕均高于其初始强度 (P <0 0 1)。 结论 骨水泥的单体 粉配比影响体外聚合过程 ,因此进行不同配比的PMMA强化时要掌握不同的注射时机。椎体骨密度与椎体生物力学性质密切相关 ,虽然 2∶3配比的骨水泥机械力学性质较 1∶2下降 。

Objective To understand the effect of changing monomer to powder ratio(1∶2, 2∶3, 1∶1 ) of polymethylmethacrylate(PMMA) on the compressive material properties, and to evaluate the strength and stiffness of osteoporotic vertebral bodies subjecte d to compression fractures and subsequently treated with bipedicular injections of 2:3 PMMA cements ( TJ-Ⅱ bone cement). Methods PMMA were classified into three groups according the ratio of monomer-to-pow der as 2∶3,1∶2,1∶1. Polymerizing process in vitro was measured respectively in each group. Cylindrical specimens were prepared in each group and compressed . BMD of seven cadaveric lumbar bodies were evaluated with QCT, and twenty-six vertebral bodies(VBS) were divided into two groups: normal group(n=13) and osteo porotic group(n=13). Each VBS compressed in a material testing machine to determ ine initial strength and stiffness. The osteoporotic fractures then were repaire d using a transpedicular injection of TJ-Ⅱ and recrushed. Results The period of the polymerizing process during the polymerizing and compressiv e strength among 3 groups with different ratio of monomer to powder were signifi cantly different. The strength and stiffness in normal group 〔(7340±671) N, (2275±258) N/mm〕 and vertebroplastic group 〔(5340±542) N, (1120±162) N/mm〕 were significant higher than those in osteoporotic group 〔(1598±531) N, (650±135) N/mm)〕(P<0 01). ConclusionsAltering the monomer-to-powder ratio affects the cement’s polymerizing proces s and its properties. Altered cements provide sufficient mechanical augmentation and may be candidates for clinical use in vertebroplasty, these biomechanical r esults have yet to be substantiated in clinical study.