Department of Orthopedic Surgery and Neurological Surgery, Thomas Jefferson University, 130 S. 9th Street, Philadelphia, PA 19107, United States of America.
Musculoskeletal Education and Research Center (MERC), A Division of Globus Medical, Inc., 2560 General Armistead Avenue, Audubon, PA 19403, USA.
Clin Biomech (Bristol). 2020 Dec;80:105195. doi: 10.1016/j.clinbiomech.2020.105195. Epub 2020 Oct 10.
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.
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/mm) was calculated; comparisons and correlations were performed.
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/mm vs. 1.1 N/mm, P > 0.05).
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.
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，沿中线皮质骨轨迹的皮质螺钉可能是有利的。虽然这两种技术的生物力学研究已经存在，但皮质螺钉在多节段腰椎椎板切除术和融合模型中的性能尚不清楚。此外，尚未研究皮质螺钉在循环疲劳后的长期生存能力。
将 14 个人体标本（L1-S1）分为皮质螺钉和椎弓根螺钉治疗组。以下条件下捕获运动：完整、双侧后路固定（L3-L5）、L3-L5 椎板切除术固定、L3-L5 经皮椎间融合术后固定，以及模拟体内疲劳前后。疲劳后，收集螺钉拔出力，并计算“有效剪切应力”[拔出力/螺钉表面积]（N/mm）；进行比较和相关性分析。
在屈伸和侧屈运动中，所有手术固定物与完整结构相比（P<0.05）均显著减少了运动，无论使用椎弓根螺钉还是皮质螺钉；只有后路固定并进行椎板切除术或不进行椎板切除术时，旋转运动显著减少（P<0.05）。椎弓根螺钉显著增加了平均拔出强度（944.2N 比 690.2N，P<0.05），但“有效剪切应力”没有增加（1.01N/mm 比 1.1N/mm，P>0.05）。
在后路椎板切除术和融合模型中，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。“有效剪切应力”没有差异，需要进一步研究上述螺钉轨迹中螺钉长度/直径的影响。
