Biomedical Engineering Graduate Program, The University of Western Ontario, London, ON - Canada.
J Appl Biomater Funct Mater. 2013 Dec 16;11(3):e167-71. doi: 10.5301/JABFM.2012.9266.
Implant loosening is a common complication that compromises the stability of joint replacement systems. Stem geometry is particularly influential in the stability of cemented implants, both before and after debonding occurs at the stem-cement interface. There are few studies assessing the effect of stem longitudinal curvature as a geometric factor in cemented implant stability. The purpose of this study was to compare the torsional stability of four generalized cemented implant stems (i.e., non-specific to joint), with varying degrees of longitudinal curvatures--zero, two, four, and six degrees.
Twelve specimens of each curvature angle were potted to a depth of 20 mm using bone cement, given 24 hours to cure, and then tested in a materials testing machine. Torque was applied to the stems under monotonic loading at a rate of 2.5 degrees/min, until five degrees of rotation had occurred.
There were no differences in torsional stability among the four stem curvature angles, when the magnitudes of peak torque (P=.72; 1-β = 0.13), rotation of the stem at peak torque (P=0.23; 1-β = 0.38) and work required for five degrees of stem rotation (P=.58; 1-β = 0.07) were compared.
The findings from this study demonstrate that for short stems, stem curvature angles up to six degrees does not improve torsional stability when compared to the straight stem design.
松动是一种常见的并发症，会影响关节置换系统的稳定性。在骨水泥-假体界面脱粘之前和之后，假体的柄部几何形状对水泥固定假体的稳定性都有很大的影响。目前，评估柄部纵向曲率作为影响水泥固定假体稳定性的几何因素的研究很少。本研究的目的是比较四种通用的水泥固定假体柄（即与关节无关）在不同纵向曲率（零、两、四和六度）下的扭转稳定性。
使用骨水泥将每个曲率角的 12 个样本盆栽到 20mm 的深度，固化 24 小时，然后在材料试验机上进行测试。在 2.5 度/分钟的单调加载下向柄施加扭矩，直到发生 5 度的旋转。
当比较峰值扭矩的大小（P=.72；1-β = 0.13）、峰值扭矩时的柄旋转（P=0.23；1-β = 0.38）和 5 度柄旋转所需的功（P=.58；1-β = 0.07）时，四个柄曲率角之间的扭转稳定性没有差异。
本研究的结果表明，对于短柄，与直柄设计相比，在六度以内的柄部曲率角度不会提高扭转稳定性。
