Biomechanics and Imaging Group, Department of Orthopaedics, Leiden University Medical Center, The Netherlands.
Biomechanics and Imaging Group, Department of Orthopaedics, Leiden University Medical Center, The Netherlands.
J Biomech. 2014 May 7;47(7):1682-8. doi: 10.1016/j.jbiomech.2014.02.031. Epub 2014 Mar 3.
Knee contact mechanics play an important role in knee implant failure and wear mechanics. Femoral condylar contact loss in total knee arthroplasty has been reported in some studies and it is considered to potentially induce excessive wear of the polyethylene insert.Measuring in vivo forces applied to the tibial plateau with an instrumented prosthesis is a possible approach to assess contact loss in vivo, but this approach is not very practical. Alternatively, single-plane fluoroscopy and pose estimation can be used to derive the relative pose of the femoral component with respect to the tibial plateau and estimate the distance from the medial and lateral parts of the femoral component towards the insert. Two measures are reported in the literature: lift-off is commonly defined as the difference in distance between the medial and lateral condyles of the femoral component with respect to the tibial plateau; separation is determined by the closest distance of each condyle towards the polyethylene insert instead of the tibia plateau.In this validation study, lift-off and separation as measured with single-plane fluoroscopy are compared to in vivo contact forces measured with an instrumented knee implant. In a phantom study, lift-off and separation were compared to measurements with a high quality bi-plane measurement.The results of the in vivo contact-force experiment demonstrate a large discrepancy between single-plane fluoroscopy and the in vivo force data: single-plane fluoroscopy measured up to 5.1mm of lift-off or separation, whereas the force data never showed actual loss of contact. The phantom study demonstrated that the single-plane setup could introduce an overestimation of 0.22mm±±0.36mm. Correcting the out-of-plane position resulted in an underestimation of medial separation by -0.20mm±±0.29mm.In conclusion, there is a discrepancy between the in vivo force data and single-plane fluoroscopic measurements. Therefore contact loss may not always be determined reliably by single plane fluoroscopy analysis.
膝关节接触力学在膝关节假体失效和磨损力学中起着重要作用。在一些研究中报道了全膝关节置换术中股骨髁接触丢失的情况，并且认为这可能导致聚乙烯衬垫的过度磨损。使用带有仪器化假体的方法测量胫骨平台上的体内力是评估体内接触丢失的一种可能方法，但这种方法不是很实用。或者，可以使用单平面荧光透视术和姿势估计来得出股骨部件相对于胫骨平台的相对姿势，并估计股骨部件的内侧和外侧部分相对于插入物的距离。文献中报道了两种测量方法：通常将抬起定义为股骨部件的内侧和外侧髁相对于胫骨平台的距离差异；分离是通过每个髁向聚乙烯插入物的最近距离确定的，而不是胫骨平台。在这项验证研究中，使用单平面荧光透视术测量的抬起和分离与使用仪器化膝关节植入物测量的体内接触力进行了比较。在一项体模研究中，将抬起和分离与双平面测量的测量值进行了比较。体内接触力实验的结果表明，单平面荧光透视术和体内力数据之间存在很大差异：单平面荧光透视术测量的抬起或分离高达 5.1mm，而力数据从未显示出实际接触丢失。体模研究表明，单平面设置可能会导致 0.22mm±±0.36mm 的高估。校正离轴位置会导致内侧分离的低估-0.20mm±±0.29mm。总之，体内力数据和单平面荧光透视测量之间存在差异。因此，接触丢失可能并不总是可以通过单平面荧光透视分析可靠地确定。
