Hayatbakhsh Zahra, Farahmand Farzam, Karimpour Morad
Department of Biomedical Engineering, Science and Research branch, Islamic Azad University, Tehran, Iran.
Mechanical Engineering Department, Sharif University of Technology, Tehran, Iran.
Arch Bone Jt Surg. 2022 Aug;10(8):712-720. doi: 10.22038/ABJS.2022.60928.3003.
The opening wedge high tibial osteotomy (HTO) fixation using the Tomofix system is at the risk of mechanical failure due to unstable fixation, lateral hinge fracture, and hardware breakage. This study aimed to investigate the effect of the level of anatomical fit (LOF) of the plate on the failure mechanisms of fixation.
A finite element model of the HTO with a correction angle of 12 degrees was developed. The LOF of the TomoFix plate was changed parametrically by altering the curvature of the plate in the sagittal plane. The effect of the LOF on the fixation performance was studied in terms of the factor of safety (FOS) against failure mechanisms. The FOSs were found by 1) dividing the actual stiffness of the plate-bone construct by the minimum allowable one for unstable fixation, 2) dividing the compressive strength of the cortical bone by the actual maximum pressure at the lateral hinge for the lateral hinge fracture, and 3) the Soderberg criterion for fatigue fracture of the plate and screws.
The increase of the LOF by applying a larger bent to the plate changed the fixation stiffness slightly. However, it reduced the lateral hinge pressure substantially (from 182 MPa to 71 MPa) and increased the maximum equivalent stresses in screws considerably (from 187 MPa to 258 MPa). Based on the FOS-LOF diagram, a gap smaller than 2.3 mm was safe, with the highest biomechanical performance associated with a 0.5 mm gap size.
Although a high LOF is necessary for the Tomofix plate fixation to avoid mechanical failure, a gap size of 0.5mm is favored biomechanically over complete anatomical fit.
使用Tomofix系统进行的开放性楔形高位胫骨截骨术（HTO）固定存在因固定不稳定、外侧铰链骨折和硬件断裂而导致机械故障的风险。本研究旨在探讨钢板的解剖贴合度水平（LOF）对固定失败机制的影响。
建立了一个矫正角度为12度的HTO有限元模型。通过改变钢板在矢状面的曲率，对TomoFix钢板的LOF进行参数化改变。从针对失败机制的安全系数（FOS）方面研究了LOF对固定性能的影响。通过以下方式找到FOS：1）将钢板-骨结构的实际刚度除以不稳定固定的最小允许刚度；2）将皮质骨的抗压强度除以外侧铰链处外侧铰链骨折的实际最大压力；3）采用钢板和螺钉疲劳断裂的Soderberg准则。
通过对钢板施加更大的弯曲来增加LOF，略微改变了固定刚度。然而，它显著降低了外侧铰链压力（从182MPa降至71MPa），并大幅增加了螺钉中的最大等效应力（从187MPa增至258MPa）。根据FOS-LOF图，小于2.3mm的间隙是安全的，间隙尺寸为0.5mm时生物力学性能最佳。
尽管对于Tomofix钢板固定来说，高LOF对于避免机械故障是必要的，但从生物力学角度来看，0.5mm的间隙尺寸优于完全解剖贴合。
