Zubair Adnan, Samuelson Eric M, Morris Randal P, Foreman Mark, Gagnon-Bartsch Johann A, Rosenfeld Scott B
Department of Orthopaedic Surgery and Rehabilitation.
The University of Texas Medical Branch, School of Medicine.
J Pediatr Orthop. 2020 Oct;40(9):487-491. doi: 10.1097/BPO.0000000000001604.
The vast majority of pediatric distal-third tibial shaft fractures can be treated with closed reduction and casting. If conservative measures fail, then these fractures are usually treated with 2 antegrade flexible intramedullary nails. A postoperative cast is usually applied because of the tenuous fixation of the 2 nails. Recent studies have described the use of 4 nails to increase the stability of the fixation, a technique that may preclude the need for postoperative casting. The purpose of this biomechanical study is to quantify the relative increase in stiffness and load to failure when using 4 versus 2 nails to surgically stabilize these fractures.
Short, oblique osteotomies were created in the distal third of small fourth-generation tibial sawbones and stabilized with 2 (double) or 4 (quadruple) flexible intramedullary nails. After pilot testing, 5 models per fixation method were tested cyclically in axial compression, torsion, and 4-point bending in valgus and recurvatum. At the end of the study, each model was loaded to failure in valgus. Stiffness values were calculated, and yield points were recorded. The data were compared using Student's t tests. Results are presented as mean±SD. The level of significance was set at P≤0.05.
Stiffness in valgus 4-point bending was 624±231 and 336±162 N/mm in the quadruple-nail and double-nail groups, respectively (P=0.04). There were no statistically significant differences in any other mode of testing.
The quadruple-nail construct was almost 2 times as stiff as the double-nail construct in resisting valgus deformation. This provides biomechanical support for a previously published study describing the clinical success of this fixation construct.
绝大多数小儿胫骨远端三分之一骨干骨折可通过闭合复位和石膏固定进行治疗。如果保守治疗失败，这些骨折通常采用两根顺行弹性髓内钉治疗。由于两根钉子的固定不牢固，术后通常会应用石膏。最近的研究描述了使用四根钉子来增加固定的稳定性，这种技术可能无需术后石膏固定。这项生物力学研究的目的是量化使用四根钉子与两根钉子手术稳定这些骨折时，刚度和破坏载荷的相对增加量。
在小型第四代胫骨锯骨模型的远端三分之一处制作短斜形截骨，并使用两根（双钉）或四根（四钉）弹性髓内钉进行固定。经过预试验后，每种固定方法的5个模型在轴向压缩、扭转以及外翻和后凸的四点弯曲试验中进行循环测试。在研究结束时，每个模型在外翻方向加载至破坏。计算刚度值并记录屈服点。使用学生t检验比较数据。结果以平均值±标准差表示。显著性水平设定为P≤0.05。
四钉组和双钉组在外翻四点弯曲试验中的刚度分别为624±231和336±162N/mm（P = 0.04）。在任何其他测试模式中均无统计学显著差异。
在抵抗外翻变形方面，四钉结构的刚度几乎是双钉结构的两倍。这为先前发表的描述这种固定结构临床成功的研究提供了生物力学支持。
