Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria St, Toronto, ON M5B-2K3, Canada.
J Mech Behav Biomed Mater. 2012 Dec;16:121-35. doi: 10.1016/j.jmbbm.2012.09.005. Epub 2012 Sep 20.
There is no "gold standard" treatment for femoral mid-shaft fractures near the tip of a hip implant. Moreover, no study has quantified the changes in a femur's mechanical properties from injury through to healing. The present aim was to predict overall stiffness and peak bone stress in the same femur after injury, repair, and healing with respect to its intact condition. Stage 1 was an intact femur. Stage 2 mimicked a femur with a hip stem. Stage 3 had a 5-mm fracture gap repaired with a plate and screws. Stage 4 represented complete fracture union. Experiments were done on a synthetic femur with strain gages and subjected to 1500 N of axial force. Finite element (FE) models were validated against experiments and then re-analyzed using a clinical-level force of 3000 N. At 1500 N, FE vs. experimental strains had excellent linear agreement (R=0.94; slope=0.97). At 3000 N, FE stiffnesses were 2167 N/mm (Stage 1), 2359 N/mm (Stage 2), 973 N/mm (Stage 3), and 3348 N/mm (Stage 4), showing that Stage 3 was the least stable compared to Stage 1. At 3000 N, FE bone stresses yielded peaks of 75.7 MPa at the load application point (Stage 1), 29.0 MPa near the hip implant tip (Stage 2), 126.3 MPa at the distal portion of the plate (Stage 3), and 69.3 MPa at the proximal portion of the plate (Stage 4), showing that Stage 3 was most vulnerable to re-injury compared to Stage 1. Stress shielding and high stresses were present not only after hip implantation and plating, but also after healing.
对于靠近髋关节植入物尖端的股骨中段骨折，目前没有“金标准”的治疗方法。此外，没有研究量化过从受伤到愈合过程中股骨机械性能的变化。本研究旨在预测同一股骨在受伤、修复和愈合后的整体刚度和峰值骨应力，与完整状态相比。第 1 阶段为完整股骨。第 2 阶段模拟带有髋关节柄的股骨。第 3 阶段，用钢板和螺钉修复 5mm 骨折间隙。第 4 阶段代表完全骨折愈合。实验在带有应变片的合成股骨上进行，并施加 1500N 的轴向力。有限元（FE）模型通过实验进行了验证，然后使用临床水平的 3000N 力重新进行了分析。在 1500N 时，FE 与实验应变具有极好的线性一致性（R=0.94；斜率=0.97）。在 3000N 时，FE 刚度分别为 2167N/mm（第 1 阶段）、2359N/mm（第 2 阶段）、973N/mm（第 3 阶段）和 3348N/mm（第 4 阶段），表明与第 1 阶段相比，第 3 阶段最不稳定。在 3000N 时，FE 骨应力在加载点处产生 75.7MPa 的峰值（第 1 阶段）、髋关节植入物尖端附近产生 29.0MPa 的峰值（第 2 阶段）、钢板远端产生 126.3MPa 的峰值（第 3 阶段）和钢板近端产生 69.3MPa 的峰值（第 4 阶段），表明与第 1 阶段相比，第 3 阶段最容易再次受伤。在髋关节植入和钢板固定后，不仅在愈合后，还存在应力屏蔽和高应力。
