Diffo Kaze Arnaud, Maas Stefan, Kedziora Slawomir, Belsey James, Haupert Alexander, Wolf Claude, Hoffmann Alexander, Pape Dietrich
Faculty of Science, Technology and Communication, University of Luxembourg, 6, rue R. Coudenhove-Kalergi, L-1359, Luxembourg, Luxembourg.
Department of Orthopedic Surgery, Centre Hospitalier de Luxembourg, L-1460, Luxembourg, Luxembourg.
J Exp Orthop. 2018 Aug 8;5(1):28. doi: 10.1186/s40634-018-0144-6.
Many different fixation devices are used to maintain the correction angle after medial open wedge high tibial osteotomy (MOWHTO). Each device must provide at least sufficient mechanical stability to avoid loss of correction and unwanted fracture of the contralateral cortex until the bone heals. In the present study, the mechanical stability of following different implants was compared: the TomoFix small stature (sm), the TomoFix standard (std), the Contour Lock, the iBalance and the second generation PEEKPower. Simplified loading, usually consisting of a vertical load applied to the tibia plateau, is used for experimental testing of fixation devices and also in numerical studies. Therefore, this study additionally compared this simplified experimental loading with a more realistic loading that includes the muscle forces.
Two types of finite element models, according to the considered loading, were created. The first type numerically simulated the static tests of MOWHTO implants performed in a previous experimental biomechanical study, by applying a vertical compressive load perpendicularly to the plateau of the osteotomized tibia. The second type included muscle forces in finite element models of the lower limb with osteotomized tibiae and simulated the stance phase of normal gait. Section forces in the models were determined and compared. Stresses in the implants and contralateral cortex, and micromovements of the osteotomy wedge, were calculated.
For both loading types, the stresses in the implants were lower than the threshold values defined by the material strength. The stresses in the lateral cortex were smaller than the ultimate tensile strength of the cortical bone. The implants iBalance and Contour Lock allowed the smallest micromovements of the wedge, while the PEEKPower allowed the highest. There was a correlation between the micromovements of the wedge, obtained for the simplified loading of the tibia, and the more realistic loading of the lower limb at 15% of the gait cycle (Pearson's value r = 0.982).
An axial compressive load applied perpendicularly to the tibia plateau, with a magnitude equal to the first peak value of the knee joint contact forces, corresponds quite well to a realistic loading of the tibia during the stance phase of normal gait (at 15% of the gait cycle and a knee flexion of about 22 degrees). However, this magnitude of the knee joint contact forces overloads the tibia compared to more realistic calculations, where the muscle forces are considered. The iBalance and Contour Lock implants provide higher rigidity to the bone-implant constructs compared to the TomoFix and the PEEKPower plates.
在胫骨高位内侧开放楔形截骨术（MOWHTO）后，使用了许多不同的固定装置来维持矫正角度。每种装置必须提供至少足够的机械稳定性，以避免矫正丢失和对侧皮质骨意外骨折，直到骨愈合。在本研究中，比较了以下不同植入物的机械稳定性：TomoFix小身材（sm）型、TomoFix标准（std）型、Contour Lock、iBalance和第二代PEEKPower。简化加载通常包括施加于胫骨平台的垂直载荷，用于固定装置的实验测试以及数值研究。因此，本研究还将这种简化的实验加载与包括肌肉力在内的更实际的加载进行了比较。
根据所考虑的加载情况创建了两种类型的有限元模型。第一种类型通过在截骨胫骨的平台上垂直施加垂直压缩载荷，对先前实验生物力学研究中进行的MOWHTO植入物的静态测试进行数值模拟。第二种类型在胫骨截骨的下肢有限元模型中纳入肌肉力，并模拟正常步态的站立期。确定并比较模型中的截面力。计算植入物和对侧皮质骨中的应力以及截骨楔形块的微动。
对于两种加载类型，植入物中的应力均低于材料强度定义的阈值。外侧皮质骨中的应力小于皮质骨的极限抗拉强度。iBalance和Contour Lock植入物使楔形块的微动最小，而PEEKPower允许的微动最大。在步态周期的15%时，胫骨简化加载获得的楔形块微动与下肢更实际加载之间存在相关性（皮尔逊值r = 0.982）。
垂直于胫骨平台施加的轴向压缩载荷，其大小等于膝关节接触力的第一个峰值，与正常步态站立期（步态周期的15%，膝关节屈曲约22度）时胫骨的实际加载情况相当吻合。然而，与考虑肌肉力的更实际计算相比，这种膝关节接触力的大小使胫骨过载。与TomoFix和PEEKPower钢板相比，iBalance和Contour Lock植入物为骨 - 植入物结构提供了更高的刚性。
