Radke Heidi, Aron Dennis N, Applewhite Aric, Zhang Guigen
Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA, USA.
Vet Surg. 2006 Jan;35(1):15-23. doi: 10.1111/j.1532-950X.2005.00106.x.
To determine if a unilateral external skeletal fixator (ESF) with a carbon fiber connecting rod (IMEX SK) without an intramedullary (IM)-pin is mechanically comparable with a unilateral ESF with a stainless-steel connecting rod (IMEX KE) with an IM-pin.
Finite-element method (FEM)-computer simulation.
FEM models were validated by comparison against data from mechanical testing. Three-dimensional FEM models of a femur with a mid-diaphyseal fracture with a 20 mm gap were developed with 4 unilateral external skeletal fixator devices (6-pin KE, 6-pin KE IM-pin, 6-pin SK, and 6-pin SK IM-pin). A 300 N load was applied to the femur at the proximal end in a direction of theta = 10 degrees distally and phi = 10 degrees laterally cranially. Relative displacements in x-, y- and z-directions at the gap were obtained and the overall stiffness was calculated as 300 N/total displacement. Load transfer at the pin-bone interface (PBI) was assessed by determining the von Mises stress maxima at the PBI-related nodes.
The 6-pin SK had superior mechanical performance compared with the 6-pin KE by exhibiting smaller displacements in all directions and higher stiffness. Compared with the 6-pin KE IM-pin, the 6-pin SK (without IM-pin) was superior in craniocaudal and lateromedial displacements, but inferior in axial displacements, overall stiffness and von Mises stress maxima. The 6-pin SK IM-pin was superior to the 6-pin KE IM-pin based on smaller displacements and higher stiffness.
Although the SK device had superior mechanical performance compared with a KE device in a unilateral configuration, the addition of an IM-pin continues to be a powerful method of enhancing mechanical performance of either IMEX SK or IMEX KE unilateral constructs in clinical cases.
Based on the results of this FEM study we recommend the use of the "tied-in" IM-pin with the ESF clinically when striving for high rigidity. In less challenging situations, a unilateral SK ESF without IM-pin might provide sufficient rigidity for a successful fracture repair.
确定不带髓内钉的碳纤维连杆单侧外固定架（IMEX SK）与带髓内钉的不锈钢连杆单侧外固定架（IMEX KE）在力学性能上是否相当。
有限元法（FEM）计算机模拟。
通过与力学测试数据对比验证有限元模型。建立了4种单侧外固定装置（6针KE、6针KE髓内钉、6针SK和6针SK髓内钉）的股骨干中1/3骨折且骨折间隙为20mm的三维有限元模型。在股骨近端沿远端θ = 10度、颅侧横向φ = 10度的方向施加300N的载荷。获取骨折间隙处x、y和z方向的相对位移，并将整体刚度计算为300N/总位移。通过确定与针-骨界面（PBI）相关节点处的von Mises应力最大值来评估针-骨界面的载荷传递。
6针SK在所有方向上的位移较小且刚度较高，与6针KE相比具有更好的力学性能。与6针KE髓内钉相比，6针SK（无髓内钉）在颅尾向和内外侧位移方面更优，但在轴向位移、整体刚度和von Mises应力最大值方面较差。6针SK髓内钉基于较小的位移和较高的刚度优于六针KE髓内钉。
尽管在单侧配置中SK装置与KE装置相比具有更好力学性能，但在临床病例中，添加髓内钉仍然是增强IMEX SK或IMEX KE单侧结构力学性能的有效方法。
基于本有限元研究结果，我们建议在临床上追求高刚度时使用与外固定架“捆绑”的髓内钉。在挑战性较小的情况下，不带髓内钉的单侧SK外固定架可能为成功的骨折修复提供足够的刚度。
