后踝骨折复位程度对胫距关节接触情况的影响

Effect of various reduction degrees of posterior malleolus fracture on tibiotalar joint contact

目的通过生物力学及有限元分析法了解大块后踝骨折不同复位程度对胫距关节接触情况的影响。方法选取6具成人新鲜小腿一足标本。用DDL实验机按照中立位、背屈10°和跖屈15°的不同加载力度，并通过Tek-Scan关节压敏片相关法分析正常状态、后踝骨折、1mm台阶、2mm台阶、1mm间隙、2mm间隙时，胫距关节的接触面积、接触压强和峰值压强。构建踝关节三维有限元模型，并模拟相关生物力学工况。结果正常胫距关节中立位500N时接触面积为（4.94±0.67）cm2，胫距关节的接触力度为加载力度的（83.4±2.7）％。后踝骨折固定1mm间隙时，预设加载差异均无统计学意义；1mm台阶时，仅跖屈15。加载时差异有统计学意义（P〈0.05）；2mm台阶和2mm间隙时，在多种预设加载下差异均有统计学意义（P〈0.05）。有限元分析的趋势结果与相关生物力学研究一致。结论对于大块后踝骨折应尽量解剖复位。如存在复位困难，也应该将骨折块移位控制在1mm台阶和2mm间隙以内，如此可基本恢复踝关节的接触协调性。

Objective To evaluate the effect of various reduction degrees of large posterior malleolus fracture on contact condition of the tibiotalar joint using biomeehanieal and finite element methods. Methods Six fresh adult cadaveric calf -foot were tested with different loadings in neutral position, 10 degree of dorsiflexion, and 15 degree of plantar flexion. Models included the intact ankle and posterior malleolus fracture （ not fixed, fixed with 1 mm step-off, fixed with 2 mm step-off, fixed with 1 mm gap, or fixed with 2 mm gap）. Tibiotalar joint contact area, contact pressure, and peak pressure were measured using the Tek-Scan pressure sensor. In addition, a three-dimensional finite element model of the an-kle joint was established and tested under the simulated biomechanieal conditions. Results After a 500 N axial loading in the intact ankle, contact area of the tibiotalar joint was （ 4.94±0.67 ） cm2 and loading strength of the tibiotalar joint was （ 83.4±2.7） % of total loading strength. Contact area of the tibiotalar joint in the fracture model fixed with 1 mm gap demonstrated no significant difference in all loading conditions compared with the intact model. In 15 degree of plantar flexion, contact area of the tibiotalar joint differed between the fracture model fixed with 1 mm step-off and the intact model （ P 〈 0.05 ）. In multiple loading conditions, contact area of the tibiotalar joint differed between the fracture models fixed with 2 mm step-off or 2 mm gap and the intact model （ P 〈 0.05 ）. Results of finite element analysis were conformed to the related biomechanical study. Conclusions Anatomic reduction should be pursued for large posterior malleolus fracture. If difficulty exists, fracture displacement should be within 1 mm step-off and 2 mm gap so as to restore the inter-joint congruity.