Arndt Christoph, Voigt Christian, Steinke Hanno, Salis-Soglio Georg V, Scholz Roger
University of Leipzig, Department of Orthopaedic Surgery, Laboratory for Biomechanics, Liebigstr. 20, 04103 Leipzig, Germany.
J Biomech Eng. 2012 Jan;134(1):011007. doi: 10.1115/1.4005686.
After total hip arthroplasty, impingement of implant components may occur during every-day patient activities causing increased shear stresses at the acetabular implant-bone interface. In the literature, impingement related lever-out moments were noted for a number of acetabular components. But there is little information about pelvic load transfer. The aim of the current study was to measure the three-dimensional strain distribution at the macrostructured hemispherical interface and in the periphery of a standard acetabular press-fit cup in an experimental implant-bone substitute model. An experimental setup was developed to simulate impingement loading via a lever arm representing the femoral component and the lower limb. In one experimental setup 12 strain gauges were embedded at predefined positions in the periphery of the acetabular cup implant inside a tray, using polyurethane composite resin as a bone substitute material. By incremental rotation of the implant tray in steps of 10 and 30 deg, respectively, the strains were measured at evenly distributed positions. With the described method 288 genuine strain values were measured in the periphery of an embedded acetabular cup implant in one experimental setup. In two additional setups the strains were evaluated at different distances from the implant interface. Both in radial and meridional interface directions strain magnitudes reach their peak near the rim of the cup below the impingement site. Values of equatorial strains vary near zero and reach their peaks near the rim of the cup on either side and in some distance from the impingement site. Interestingly, the maximum of averaged radial strains does not occur, as expected, close to the interface but at an interface offset of 5.6 mm. With the described experimental setup it is now possible to measure and display the three-dimensional strain distribution in the interface and the periphery of an embedded acetabular cup implant. The current study provides the first experimental proof of the high local stresses gradients in the direct vicinity of the impingement site. The results of the current study help for a better understanding of the impingement mechanism and its impact on acetabular cup stability.
全髋关节置换术后，在患者日常活动过程中，植入部件可能会发生撞击，导致髋臼植入物与骨界面处的剪切应力增加。在文献中，已注意到许多髋臼部件存在与撞击相关的撬出力矩。但关于骨盆负荷转移的信息却很少。本研究的目的是在实验性植入物 - 骨替代模型中，测量标准髋臼压配杯的宏观结构半球形界面及其周边的三维应变分布。开发了一种实验装置，通过代表股骨部件和下肢的杠杆臂来模拟撞击载荷。在一个实验装置中，使用聚氨酯复合树脂作为骨替代材料，将12个应变片嵌入托盘内髋臼杯植入物周边的预定位置。通过分别以10度和30度的步长逐步旋转植入物托盘，在均匀分布的位置测量应变。用所描述的方法，在一个实验装置中，对嵌入的髋臼杯植入物周边测量了288个真实应变值。在另外两个装置中，在距植入物界面不同距离处评估应变。在径向和子午界面方向上，应变大小在撞击部位下方杯缘附近达到峰值。赤道应变值在零附近变化，并在杯缘两侧且距撞击部位一定距离处达到峰值。有趣的是，平均径向应变的最大值并非如预期那样出现在靠近界面处，而是出现在界面偏移5.6毫米处。利用所描述的实验装置，现在可以测量并显示嵌入的髋臼杯植入物界面及其周边的三维应变分布。本研究首次通过实验证明了撞击部位紧邻区域存在高局部应力梯度。本研究结果有助于更好地理解撞击机制及其对髋臼杯稳定性的影响。
