Zderic Ivan, Willhuber Gaston C, Ahrend Marc-Daniel, Gras Florian, Barla Jorge, Sancineto Carlos, Windolf Markus, Richards Geoff, Gueorguiev Boyko
AO Research Institute Davos, Clavadelerstrasse 8, 7270 Davos, Switzerland.
Hospital Italiano de Buenos Aires, Juan D. Perón 4190, C1199ABD Buenos Aires, Argentina.
J Orthop Translat. 2018 Nov 17;18:92-99. doi: 10.1016/j.jot.2018.10.005. eCollection 2019 Jul.
Common failure modes of dynamic hip screw are cut-out and lift-off. To minimize the latter, distal screws can be inserted in different orientations. However, the effectiveness remains controversial. The aim of this study was to biomechanically investigate the influence of distal screw orientation on construct stability.
Thirty artificial generic long bones were assigned to three groups (n = 10) and fixed with two-hole dynamic hip screw-plates, inserting distal cortical screws with neutral parallel screw orientation (A), divergent screw orientation (B) or convergent screw orientation (C). Starting at 60 N, cyclic loading was applied to the implant tip perpendicular to the lag screw axis with progressive peak load increase at a rate of 0.002 N/cycle until failure. Parameters of interest were construct stiffness and machine actuator displacement after 250, 1000 and 5000 cycles, as well as cycles to failure.
Displacement after 250, 1000 and 5000 cycles was significantly higher in Group C than in Groups A and B, < 0.01, whereas no significant differences were observed between Groups A and B, = 0.20. Specimens in Group C failed after 11,584 [standard deviation (SD), 5924] cycles, significantly earlier than those in Groups A and B [A: 27,351 (SD, 12,509); B: 28,793 (SD, 14,764)], ≤ 0.02. Cycles to failure were not significantly different between Groups A and B, > 0.99.
Parallel or divergent distal screw insertion provides similar construct stability in terms of resistance to plate lift-off. In contrast, converging screw insertion leads to inferior stability and is not advisable from a biomechanical point of view.
动力髋螺钉常见的失效模式是穿出和抬起。为了将后者降至最低，远端螺钉可以以不同方向插入。然而，其有效性仍存在争议。本研究的目的是从生物力学角度研究远端螺钉方向对结构稳定性的影响。
将30根人工模拟长骨分为三组（n = 10），并用双孔动力髋螺钉钢板固定，分别以中立平行螺钉方向（A组）、发散螺钉方向（B组）或汇聚螺钉方向（C组）插入远端皮质螺钉。从60 N开始，垂直于拉力螺钉轴线对植入物尖端施加循环载荷，峰值载荷以0.002 N/循环的速率逐渐增加，直至失效。感兴趣的参数包括250、1000和5000次循环后的结构刚度和机器致动器位移，以及失效循环次数。
C组在250、1000和500次循环后的位移显著高于A组和B组，P < 0.01，而A组和B组之间未观察到显著差异，P = 0.20。C组标本在11584 [标准差（SD），5924]次循环后失效，明显早于A组和B组 [A组：27351（SD，12509）；B组：28793（SD，14764）]，P ≤ 0.日。A组和B组之间的失效循环次数无显著差异，P > 0.99。
平行或发散方向插入远端螺钉在抵抗钢板抬起方面提供了相似得结构稳定性。相比之下，汇聚方向插入螺钉会导致稳定性较差，从生物力学角度来看并不可取。
