Table_2_More Anterior in vivo Contact Position in Patients With Fixed-Bearing Unicompartmental Knee Arthroplasty During Daily Activities Than in vitro Wear Simulator.docx

BackgroundWhile in vitro wear simulation of unicompartmental knee arthroplasty (UKA) showed outstanding long-term wear performance, studies reported that polyethylene (PE) wear was responsible for 12% fixed-bearing (FB) UKA failure. This paper aimed to quantify the in vivo 6-degrees-of-freedom (6-DOF) knee kinematics and contact positions of FB UKA during daily activities and compare with the previous results of in vitro wear simulator.
MethodsFourteen patients following unilateral medial FB UKA received a CT scan and dual fluoroscopic imaging during level walking, single-leg deep lunge, and sit-to-stand motion for evaluating in vivo 6-DOF FB UKA kinematics. The closest point between surface models of the femoral condyle and PE insert was determined to locate the medial compartmental articular contact positions, which were normalized relative to the PE insert length. The in vivo contact area was compared with the in vitro wear region in previous simulator studies.
ResultsThe in vivo contact positions during daily activities were more anterior than those in the previous in vitro wear simulator studies (p < 0.001). Significant differences in the femoral anteroposterior translation and tibial internal rotation during the stance phase were observed and compared with those in lunge and sit-to-stand motions (p < 0.05). The in vivo contact position located anteriorly and medially by 5.2 ± 2.7 and 1.8 ± 1.6 mm on average for the stance phase, 1.0 ± 2.4 and 0.9 ± 1.5 mm for the lunge, and 2.1 ± 3.3 and 1.4 ± 1.4 mm for sit-to-stand motion. The in vivo contact position was in the more anterior part during the stance phase (p < 0.05).
ConclusionThe current study revealed that the contact position of FB UKA was located anteriorly and medially on the PE insert during in vivo weight-bearing activities and different from previous findings of the in vitro wear simulator. We should take in vivo 6-DOF knee kinematics and contact patterns of FB UKA into account to reproduce realistic wear performance for in vitro wear simulator and to improve implant design.

【研究背景】尽管单髁膝关节置换术（unicompartmental knee arthroplasty, UKA）的体外磨损模拟实验展现出优异的长期耐磨性能，但已有研究表明，聚乙烯（polyethylene, PE）磨损是导致12%固定衬垫型（fixed-bearing, FB）UKA失败的原因。本研究旨在量化日常活动中固定衬垫型UKA的体内六自由度（6-degrees-of-freedom, 6-DOF）膝关节运动学参数与接触位置，并与既往体外磨损模拟实验的结果进行对比。【研究方法】本研究纳入14例行单侧内侧固定衬垫型UKA的患者，在平地行走、单腿深度弓步及坐站运动期间对其进行CT扫描与双透视成像，以评估体内固定衬垫型UKA的六自由度运动学参数。通过确定股骨髁表面模型与聚乙烯衬垫表面模型之间的最近点，来定位内侧间室的关节接触位置，并以聚乙烯衬垫的长度为基准对接触位置进行归一化处理。将本研究获得的体内接触面积与既往体外磨损模拟实验中的磨损区域进行对比。【研究结果】日常活动中的体内接触位置较既往体外磨损模拟实验的结果更偏前方（p < 0.001）。与单腿弓步及坐站运动相比，站立相期间股骨前后平移与胫骨内旋存在显著差异（p < 0.05）。站立相时体内接触位置平均前移5.2±2.7mm、内移1.8±1.6mm；单腿弓步时分别为1.0±2.4mm与0.9±1.5mm；坐站运动时分别为2.1±3.3mm与1.4±1.4mm。站立相时体内接触位置更偏前方（p < 0.05）。【研究结论】本研究表明，在体内负重活动期间，固定衬垫型UKA的接触位置位于聚乙烯衬垫的前内侧区域，与既往体外磨损模拟实验的结果存在差异。为了在体外磨损模拟实验中复现真实的磨损性能，并优化假体设计，我们需要考虑固定衬垫型UKA的体内六自由度膝关节运动学特征与接触模式。