IN VIVO EVALUATION OF A REDUCED MODULUS BONE CEMENT

骨水泥型全关节术后最常见的并发症 更换程序是松开一个或两个组件。这个 松动过程始于骨水泥处的骨吸收。 界面。局部应力过大和亚微米碎片的存在 都可以触发骨骼的吸收，开始松动的级联反应。 一种模数较低、韧性较高的骨水泥 聚甲基丙烯酸甲酯(PMMA)将降低局部接触应力和 产生的颗粒碎片更少。任何不规则的界面，例如 骨-骨水泥界面，在几何位置接触应力会有峰值 和材料的不连续性。根据数量化模型 材料接触，包括解析和数值接触，应力将是 如果水泥的弹性模数降低，则降低。一种低模数 丙烯酸骨水泥，与聚甲基丙烯酸丁酯珠粒在PMMA中配制 基质，已经开发出了它的静态和粘弹性材料 对其性质进行了表征。它在体温下的模数是 明显低于PMMA，其韧性要大得多。 正在进行的体外实验正在验证局部接触应力 假设。水泥的模数达到了预期的效果。 邻接骨的剪切应变；减小骨水泥模数会降低 因此会减少引发松动的微小损伤 卡斯卡德。初步的活体研究支持这一结论 可以通过减少界面接触来降低松动速率 压力。松动率，通过放射和机械评估， 绵羊人工全髋关节置换术中的应用 粘固剂显著低于绵羊的标准PMMA骨 使用的是水泥。 合乎逻辑的下一步是对松动率进行更大规模的活体研究 对先导研究的结果进行统计验证。松动 使用标准PMMA和折算模数植入组件的速率 丙烯酸骨水泥将在绵羊全髋关节模型中进行比较。

The most frequent postoperative complication of cemented total joint replacement procedures is loosening of one or both components. The loosening process begins with resorption of bone at the bone-cement interface. Excessive local stresses and the presence of submicron debris can each trigger the resorption of bone and start the loosening cascade. A bone cement with a lower modulus and greater toughness than polymethylmethacrylate (PMMA) will decrease local contact stresses and produce less particulate debris. Any irregular interface, such as the bone-cement interface, will have peaks in contact stress at geometrical and material discontinuities. According to quantitative models for materials contact, both analytical and numerical, the stresses will be reduced if the elastic moduli of the cement are reduced. A low-modulus acrylic bone cement, formulated with polybutylmethacrylate beads in a PMMA matrix, has been developed and its static and viscoelastic material properties have been characterized. Its modulus at body temperature is significantly lower than that of PMMA and its toughness is much greater. Ongoing in vitro experimentation is verifying the local contact stress hypothesis. The modulus of the cement has the expected effect of the shear strain of the adjacent bone; reducing the cement modulus reduces the bone strain and will thus reduce microdamage which triggers the loosening cascade. Preliminary in vivo investigations support the conclusion that loosening rates can be decreased by diminution of the interface contact stresses. The loosening rate, assessed radiographically and mechanically, in sheep total hip arthroplasties using a reduced-modulus acrylic bone cement was significantly lower than that in sheep where standard PMMA bone cement was used. The logical next step is a larger in vivo investigation of loosening rates to statistically validate the findings of the pilot study. The loosening rates of components implanted using standard PMMA and reduced-modulus acrylic bone cements will be compared in a sheep total hip model.