1Department of Neurosurgery, Medical College of Wisconsin, Milwaukee, Wisconsin.
2School of Mechanical Engineering, Vellore Institute of Technology, Chennai, India; and.
J Neurosurg Spine. 2023 Apr 7;39(1):28-39. doi: 10.3171/2023.3.SPINE2340. Print 2023 Jul 1.
Spinal cord stress/strain during neck motion contributes to spinal cord dysfunction in degenerative cervical myelopathy (DCM), yet the effect of surgery on spinal cord biomechanics is unknown. It is expected that motion-preserving and fusion surgeries for DCM will have distinct effects on spinal cord biomechanics. The aim of this study was to compare changes in spinal cord biomechanics after laminectomy with fusion, laminectomy, and laminoplasty using a patient-specific finite element model (FEM) for DCM.
A patient-specific FEM of the cervical spine and spinal cord was created using MRI from a subject with mild DCM. Multilevel laminectomy with fusion, laminectomy, and laminoplasty were simulated for DCM using the patient-specific FEM. Spinal cord von Mises stress and maximum principal strain during neck flexion-extension, lateral bending, and axial rotation were recorded. Segmental range of motion, intradiscal pressure, and capsular ligament strain were also measured. FEM outputs were calculated as a change with respect to the preoperative values and compared between the three models.
Across the surgical levels, spinal cord stress increased after laminectomy for neck flexion (+50%), neck extension (+37.8%), and axial rotation (+23%). Similarly, spinal cord strain increased in neck extension (+118.4%) and axial rotation (+75.1%) after laminectomy. Laminoplasty was associated with greater spinal cord stress in neck flexion (+57.4%) and increased strain in lateral bending (+56.7%) and axial rotation (+20.9%). Compared with laminectomy and laminoplasty, spinal cord biomechanics for laminectomy with fusion revealed significantly reduced median extension stress (13.7 kPa vs 9.7 kPa, p = 0.03), lateral bending strain (0.01 vs 0.007, p = 0.007), axial rotation stress (3.7 kPa vs 2.1 kPa, p = 0.04), and axial rotation strain (0.017 vs 0.009, p = 0.04).
Spinal cord strain decreased in neck flexion in all three models, yet spinal cord stress increased with neck flexion for laminectomy and laminoplasty. Changes in spinal cord biomechanics for laminoplasty parallel those for laminectomy with fusion except during neck flexion, lateral bending, and axial rotation. Compared with motion-preserving approaches such as laminectomy and laminoplasty, laminectomy with fusion was associated with the lowest spinal cord stress and strain in flexion-extension, lateral bending, and axial rotation of the neck.
颈椎运动时脊髓的压力/应变会导致退行性颈椎脊髓病（DCM）中的脊髓功能障碍，但手术对脊髓生物力学的影响尚不清楚。预计 DCM 的保留运动和融合手术将对脊髓生物力学产生明显不同的影响。本研究的目的是使用 DCM 的患者特定有限元模型（FEM）比较减压融合术、单纯减压术和椎板成形术后脊髓生物力学的变化。
使用 MRI 从患有轻度 DCM 的患者中创建颈椎和脊髓的患者特定 FEM。使用患者特定的 FEM 模拟 DCM 的多节段椎板切除术加融合术、单纯椎板切除术和椎板成形术。记录颈椎屈伸、侧屈和轴向旋转时脊髓的von Mises 应力和最大主应变。还测量了节段活动范围、椎间盘内压力和囊韧带应变。FEM 输出是相对于术前值的变化，并在三种模型之间进行比较。
在手术水平上，颈椎屈伸时脊髓压力增加（+50%），颈椎伸展时脊髓压力增加（+37.8%），颈椎旋转时脊髓压力增加（+23%）。同样，颈椎伸展时脊髓应变增加（+118.4%），颈椎旋转时脊髓应变增加（+75.1%）。与单纯减压术和椎板成形术相比，颈椎屈伸时脊髓压力增加（+57.4%），侧屈和轴向旋转时脊髓应变增加（+56.7%和+20.9%）。与单纯减压术和椎板成形术相比，减压融合术的脊髓生物力学显示颈椎伸展时的中位伸展应力明显降低（13.7kPa 比 9.7kPa，p=0.03），侧屈应变（0.01 比 0.007，p=0.007），轴向旋转时的压力（3.7kPa 比 2.1kPa，p=0.04）和轴向旋转应变（0.017 比 0.009，p=0.04）。
三种模型中颈椎屈伸时脊髓应变均降低，但颈椎屈伸时脊髓压力增加。椎板成形术的脊髓生物力学变化与减压融合术相似，除了颈椎屈伸、侧屈和旋转。与保留运动的方法（如单纯减压术和椎板成形术）相比，减压融合术与屈伸、侧屈和旋转时的脊髓压力和应变最低。
