Background

Traditional pedicle screws are the gold standard for lumbar spine fixation; however, cortical screws along the midline cortical bone trajectory may be advantageous when lumbar decompression is required. While biomechanic investigation of both techniques exists, cortical screw performance in a multi-level lumbar laminectomy and fusion model is unknown. Furthermore, longer-term viability of cortical screws following cyclic fatigue has not been investigated.

Methods

Fourteen human specimens (L1–S1) were divided into cortical and pedicle screw treatment groups. Motion was captured for the following conditions: intact, bilateral posterior fixation (L3–L5), fixation with laminectomy at L3–L5, fixation with laminectomy and transforaminal lumbar interbody fusion at L3–L5 both prior to, and following, simulated in vivo fatigue. Following fatigue, screw pullout force was collected and “effective shear stress” [pullout force/screw surface area] (N/mm²) was calculated; comparisons and correlations were performed.

Findings

In flexion-extension and lateral bending, all operative constructs significantly reduced motion compared to intact (P < 0.05), regardless of pedicle or cortical screws; only posterior fixation with and without laminectomy significantly reduced motion in axial rotation (P < 0.05). Pedicle screws significantly increased average pullout strength (944.2 N vs. 690.2 N, P < 0.05), but not the “effective shear stress” (1.01 N/mm² vs. 1.1 N/mm², P > 0.05).

Interpretation

In a posterior laminectomy and fusion model, cortical screws provided equivalent stability to pedicle screw fixation, yet had significantly lower screw pullout force. No differences in “effective shear stress” warrant further investigation of the effect of screw length/diameter in the aforementioned screw trajectories.

中文翻译：

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从疲劳减压腰椎切除术模型中选择皮质螺钉和椎弓根螺钉的指南显示出相似的稳定性和较少的骨矿物质密度依赖性

背景

传统的椎弓根螺钉是腰椎固定的金标准。然而，当需要腰椎减压时，沿着中线皮质骨轨迹的皮质螺钉可能是有利的。虽然存在两种技术的生物力学研究，但多层腰椎椎板切除术和融合模型的皮质螺钉性能尚不清楚。此外，尚未研究过周期性疲劳后皮质螺钉的长期生存能力。

方法

将十四个人体标本（L1-S1）分为皮质和椎弓根螺钉治疗组。在以下情况下捕获了运动：完整的，双侧后路固定（L3-L5），在L3-L5的椎板切除术固定，在模拟的体内疲劳之前和之后的椎板切除术和L3-L5的椎间孔融合治疗。 。疲劳后，收集螺钉的拔出力并计算“有效剪切应力” [拔出力/螺钉表面积]（N / mm ²）。进行比较和相关。

发现

在屈伸和侧向弯曲中， 与椎弓根或皮质螺钉相比，所有手术结构均较完整状态显着降低运动（P <0.05）。仅在有或没有椎板切除术的情况下进行后路固定可显着降低轴向旋转运动（P  <0.05）。椎弓根螺钉显着提高了平均拔出强度（944.2 N vs. 690.2 N，P  <0.05），但不是“有效剪切应力”（1.01 N / mm ² vs. 1.1 N / mm ²，P  > 0.05）。

解释

在后椎板切除和融合模型中，皮质螺钉提供了与椎弓根螺钉固定相同的稳定性，但螺钉拔出力明显较低。在“有效剪切应力”方面没有差异，因此需要进一步研究上述螺杆轨迹中螺杆长度/直径的影响。