Mair S, Weninger P, Högel F, Panzer S, Augat P
Institut für Biomechanik, Berufsgenossenschaftliche Unfallklinik Murnau, Prof.-Küntscher-Straße 8, 82418 Murnau am Staffelsee.
Unfallchirurg. 2013 Apr;116(4):338-44. doi: 10.1007/s00113-011-2099-2.
Distal radius fractures continue to show significant complication rates after operative treatment with locked plating. Failure occurs by screw loosening or screw penetration in the distal fragment. Placement of additional screws may enhance the stiffness of fracture fixation. The aim of this study was to determine the fatigue properties of different screw configurations in distal radius plate osteosynthesis with biomechanical tests and finite element analysis (FEA).
Unstable distal radius fractures were created in 12 human cadaveric bone specimens and were fixed with volar locking plates. Group 4SC was fixed with four screws in the distal row and group 6SC with two additional screws the row below. Dynamic loading was applied physiologically. The radial shortening, the angulation of the distal fragment and the failure mechanism were determined by experimental tests and were further elucidated by FEA.
Group 6SC showed a significantly lower radial shortening and inclination. Breakage of the screws within the plate was noted in group 4SC, while moderate screw penetration was observed in group 6SC. FEA confirmed the biomechanical tests. In group 4SC elevated von Mises strain in the locking mechanism explained the inclination of the screws and the distal fragment. The elastic strain in group 6SC was increased at the screw-bone interface which explained the resulting screw penetration.
The failure mechanism in volar plating of distal radius fractures depended on the number of screws and their configuration. Using two more screws increases construct stiffness and angular stability under dynamic loading. However, increased stiffness also promoted screw penetration mainly in osteoporotic bone. Compared to screw penetration, loss of reposition and inclination of the distal fragment observed in the 4SC configuration is more likely to result in clinical complications.
桡骨远端骨折采用锁定钢板手术治疗后，并发症发生率仍较高。失败原因包括螺钉松动或远端骨折块内螺钉穿出。增加螺钉数量可能会提高骨折固定的刚度。本研究旨在通过生物力学测试和有限元分析（FEA）确定桡骨远端钢板内固定中不同螺钉配置的疲劳特性。
在12具人体尸体骨标本上制造不稳定的桡骨远端骨折，并用掌侧锁定钢板固定。4SC组在远端排用4枚螺钉固定，6SC组在其下一排额外增加2枚螺钉。以生理方式施加动态载荷。通过实验测试确定桡骨缩短、远端骨折块的成角情况及失败机制，并通过FEA进一步阐明。
6SC组的桡骨缩短和成角明显更低。4SC组观察到钢板内的螺钉断裂，而6SC组观察到螺钉有中度穿出。FEA证实了生物力学测试结果。在4SC组，锁定机制中升高的冯·米塞斯应变解释了螺钉和远端骨折块的倾斜。6SC组在螺钉 - 骨界面的弹性应变增加，这解释了由此导致的螺钉穿出。
桡骨远端骨折掌侧钢板固定的失败机制取决于螺钉数量及其配置。多使用2枚螺钉可增加结构刚度和动态载荷下的角稳定性。然而，刚度增加也主要在骨质疏松骨中促进了螺钉穿出。与螺钉穿出相比，4SC配置中观察到的远端骨折块复位丢失和倾斜更有可能导致临床并发症。
