Digital Industrial Design and Manufacturing Research Unit, Department of Mechanical Engineering, Faculty of Engineering at Sriracha, Kasetsart University, Chonburi 20230, Thailand.
Department of Orthopaedic Surgery, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand.
Injury. 2022 Feb;53(2):323-333. doi: 10.1016/j.injury.2021.11.064. Epub 2021 Dec 8.
The aim of this study was to assess biomechanical performance of short and long Cephalomedullary nail constructs consisting of different number of distal screw for stabilizing different levels of subtrochanteric fracture.
The femur obtained from computed tomography scanner was used to create a transverse fracture at 15 mm (level A), 35 mm (level B), and 55 mm (level C) below the lesser trochanter. Short and long Cephalomedullary nails were virtually inserted to the fractured femur. Four-node tetrahedral element was used to build up finite element (FE) models for biomechanical analysis. The analysis focused on post-operative stage of partial weight-bearing.
Stress on the implant localized at the surface between lag screw/nail and distal screw/nail. Short Cephalomedullary nail exhibited higher stress than long Cephalomedullary nail. The stress in short Cephalomedullary nail could be reduced by using two distal screws fixation and the fracture at level A produced less stress than that of level B and C. Either short or long nail with two distal screws is sufficient to withstand the stress magnitude produced from the physiologic load. When single dynamic distal screw was used, stress on implant, elastic strain at fracture gap, and bone stress reached the high values. Elastic strain of the fracture gap at level C were less than that of level A and B, but no statistically significant difference. There was no proximal cancellous bone damage observed from the FE analysis.
Long Cephalomedullary nail with at least two distal locking screws remains a proper implant for subtrochanteric fracture fixation in overall locations. However, short Cephalomedullary nail with two distal screws may be a candidate for a high subtrochanteric fracture. Single dynamic screw insertion is strongly not recommended with either short or long nail regarding implant failure.
本研究旨在评估由不同数量的远端螺钉组成的短型和长型股骨近端髓内钉在稳定不同位置的转子下骨折中的生物力学性能。
使用从 CT 扫描仪获得的股骨来创建横向骨折，分别在小转子下 15mm（A 级）、35mm（B 级）和 55mm（C 级）处。将短型和长型股骨近端髓内钉虚拟插入到骨折的股骨中。使用四节点四面体单元来建立用于生物力学分析的有限元（FE）模型。分析集中在部分负重的术后阶段。
植入物上的应力集中在尾钉/钉和远端螺钉/钉之间的表面上。短型股骨近端髓内钉的应力高于长型股骨近端髓内钉。使用两个远端螺钉固定可以降低短型股骨近端髓内钉的应力，并且 A 级骨折产生的应力小于 B 级和 C 级骨折。无论是短型还是长型钉，使用两个远端螺钉都足以承受生理负荷产生的应力大小。当使用单个动态远端螺钉时，植入物上的应力、骨折间隙的弹性应变和骨应力达到高值。C 级骨折间隙的弹性应变小于 A 级和 B 级，但无统计学差异。FE 分析未观察到近端松质骨损伤。
至少有两个远端锁定螺钉的长型股骨近端髓内钉仍然是整体位置转子下骨折固定的合适植入物。然而，对于高转子下骨折，使用两个远端螺钉的短型股骨近端髓内钉可能是候选方案。对于短型或长型钉，不建议单独使用动态螺钉插入，因为这会导致植入物失效。
