Tarala M, Janssen D, Telka A, Waanders D, Verdonschot N
Orthopaedic Research Laboratory, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
Proc Inst Mech Eng H. 2011 Jan;225(1):8-15. doi: 10.1243/09544119JEIM825.
In total hip arthroplasty, micromotions at the implant-bone interface influence the long-term survival of the prosthesis. These micromotions are often measured using sensors that are fixed to the implant and bone at points that are remote from the interface. Given that the implant-bone system is not rigid, errors may be introduced. It is not possible to assess the magnitude of these errors with the currently available experimental methods. However, this problem can be investigated using the finite element method (FEM). The hypothesis that the actual interface micromotions differ from those measured in the experimental manner was tested using a case-specific FE model, validated against deflection experiments. The FE model was used to simulate an 'experimental' method to measure micromotions. This 'experimental' method was performed by mimicking the distance between the measurement points; the implant point was selected at the interface while the bony point was at the outer surface of bone. No correlation was found between the micromotions computed at the interface and when using remote reference points. Moreover, the magnitudes of micromotions computed with the latter method were considerably greater. By reducing the distance between the reference points the error decreased, but the correlation stayed unchanged. Care needs to be taken when interpreting the results of micromotion measurement systems that use bony reference points at a distance from the actual interface.
在全髋关节置换术中，植入物与骨界面处的微动会影响假体的长期存活率。这些微动通常使用固定在远离界面的植入物和骨上的传感器进行测量。鉴于植入物 - 骨系统并非刚性，可能会引入误差。用目前可用的实验方法无法评估这些误差的大小。然而，这个问题可以使用有限元方法（FEM）进行研究。使用针对特定病例的有限元模型测试了实际界面微动与实验测量微动不同的假设，该模型通过挠度实验进行了验证。有限元模型用于模拟一种测量微动的“实验”方法。这种“实验”方法是通过模拟测量点之间的距离来进行的；植入点选择在界面处，而骨点位于骨的外表面。在界面处计算的微动与使用远程参考点时计算的微动之间未发现相关性。此外，用后一种方法计算的微动幅度要大得多。通过减小参考点之间的距离，误差减小，但相关性保持不变。在解释使用远离实际界面的骨参考点的微动测量系统的结果时需要谨慎。
