骨水泥厚度影响股骨假体周围应力分布的理论研究

The changes in cement stresses are affected by cement-mantle thickness in total hip arthroplasty: a theoretical analysis

目的研究髋关节置换后股骨假体周围骨水泥层的应力分布状况,分析不同厚度的骨水泥层应力分布变化。方法采用复合梁基本理论来构建骨水泥型全髋关节置换前后假体周围骨水泥应力分布的解析理论模型,将假体周围股骨分成等距的11个断层,每个断层分成前、后、内、外四个象限,分别计算每个象限的解析解,并将骨水泥厚度的变化范围设置为0～4mm,厚度每变化0.1mm就进行取值计算,最终绘图。同样选择假体近半段和远半段的中央层面(即离开股骨头中心55mm的层面和105mm的层面)作为代表层面进行分析,以反映应力的分布情况。结果除了远半段圆形截面骨水泥厚度>1.5mm时后侧区骨水泥应力出现轻度下降外,其余各区域水泥应力均随骨水泥厚度的增加而非线性增加,但增加的速率不断下降。结论股骨内径确定时,厚层骨水泥较薄层骨水泥产生的应力更高,骨水泥裂隙的数量、增长速度和应力的大小呈正相关。厚层骨水泥假体出现相对高的裂隙增长速度主要原因系厚层骨水泥本身应力水平较高,而薄层骨水泥本身由于厚度基数不足造成全层骨水泥裂隙的出现更早,可能和假体的无菌性松动有一定关系。

Objective To investigate cement stress after total hip arthroplasty （THA） using a validated mathemalieal analytical models. Methods Changes in cement stress in the proximal femur following implantation can he estimated by composite beam theory. In the validated mathematical models, the proximal femur was divided into eleven equidistant cross sections; each section was further divided into tour qnadrants corresponding to the anterior, posterior, medial and lateral aspects of the femur. Two sections （55ram and 105mm from femoral head center） were used to calculate. Cement stress levels were evaluated when cement-mantle thickness changed from 0 to 4.0mm. And cement stress values were calculated when cement thickness changed by 0.1mm. Results In posterior quadrant of 105mm section, periprosthetic bone stress decreased with the mantle thickness from 1.5mm to 4.0mm. And cement stress decreased with the mantle thickness from 3.0mm to 4.0mm. In other quadrants and all 55mm section quadrants, cement stress were increased with cement-mantle thickness added. Conclusion Cement crack numhers and crack growth rate might not depend on cement-mantle thickness directly, but on cement stress. Cracks in thin mantles reached the full thickness of mantle soon not by the higher cement slress hut the poor thickness. These cracks may be related to the stem aseptic loosening.