Objective The aim of this study was to evaluate the effect of reducing the bone to cast distance on the resistance of the pin to cyclic loading in equine transfixation pin casts.

Study Design Eleven pairs of cadaveric equine third metacarpal bones were prepared and one 6.3/8.0 mm transfixation pin was placed in standard fashion 10 mm proximal to the distal physeal scar into each bone. One metacarpus of each pair was tested with a distance of 10 mm (10 mm group) and the contralateral metacarpus with a distance of 20 mm (20 mm group) between the outer cortex of the bone and the fixation of the pin. Eight pairs were tested using a simplified test set-up in which the pins were fastened at both ends to polyoxymethylene-copolymer sleeves. The pins of the remaining three pairs of bones were incorporated into a fibreglass cast. All specimens were tested under cyclic loading until failure of the pin in axial compression.

Results All pins failed uni- or bilaterally at clinically relevant load levels. Pins of the 10 mm group endured significantly (p < 0.05) higher load levels and total number of cycles until failure compared with the pins of the 20 mm group.

Conclusion The distance between the bone surface and the cast at the location of pin insertion has a significant effect on resistance of the pins to cyclic loading. Therefore, the amount of padding applied underneath an equine transfixation pin cast can have an influence on the overall stability and durability of the construct.

目的 本研究的目的是评估减少骨到铸件距离对马固定销铸件中销对循环载荷的抵抗力的影响。

研究设计 准备了 11 对尸体马的第三掌骨，并将一根 6.3/8.0 毫米的穿刺针以标准方式放置在每根骨头的远端骺痕近端 10 毫米处。每对中的一个掌骨在骨外皮质与销钉固定之间的距离为10 mm（10 mm组）和对侧掌骨的距离为20 mm（20 mm组）。使用简化的测试装置测试了八对，其中销钉两端固定在聚甲醛共聚物套管上。其余三对骨头的销钉被合并到玻璃纤维铸件中。所有试样都在循环载荷下进行测试，直到销在轴向压缩中失效。

结果 所有针在临床相关负荷水平下均单侧或双侧失效。 与 20 毫米组的销钉相比，10 毫米组的销钉承受显着 ( p < 0.05) 更高的负载水平和直至失效的总循环次数。

结论 销钉插入位置处骨表面与铸件之间的距离对销钉对循环载荷的抵抗力有显着影响。因此，在马固定销铸件下方应用的填充量可能会影响结构的整体稳定性和耐用性。