P5. Effect of cervical kyphosis on spinal cord biomechanics after cervical laminoplasty

Abstract

Background Context

Cervical laminoplasty is an effective motion-preserving intervention for degenerative cervical myelopathy. However, patients with preexisting cervical kyphosis often show inferior outcomes after cervical laminoplasty as compared to those with straight or lordotic spines. Kyphotic cervical spines may show limited dorsal spinal cord shift after decompression, which can explain impaired neurological recovery. Persistent adverse spinal cord tension may also contribute to poor neurological recovery for the kyphotic patient, yet this has not been studied.

Purpose

To quantify the effect of cervical sagittal alignment on spinal cord stress and strain after open door laminoplasty.

Study Design/Setting

Finite element analysis.

Patient Sample

N/A.

Outcome Measures

Spinal cord stress and strain.

Methods

We used a validated 3D finite element model of the C2-T1 spine, inclusive of the spinal cord, to investigate biomechanical changes in the spinal cord after laminoplasty. We created 3 models based on the C2-C7 Cobb angle: lordosis (20°), straight (0°) and kyphosis (-9°). For each of these models, we simulated an open door laminoplasty for the C4, C5 and C6 levels with identical dorsal spinal cord shift. A full-thickness trough was created on one side of these laminae, and a partial-thickness trough on the contralateral side to form a hinge. Additionally, the interspinous ligaments and ligamentum flavum were resected at C3–4 and C6–7. The modified laminae were then repositioned using a 1-mm-thick, double-bend titanium plate, ensuring anatomical alignment and tight screw contact. We, then simulated, physiological neck flexion and extension by applying a 2Nm moment and 75N force. Spinal cord von Mises stress and maximum principal strain, and segmental range of motion were quantitatively analyzed and compared.

Results

Spinal cord stress and strain was highest for kyphotic curvature compared to the straight and lordotic curvature across all cervical segments despite similar segmental range of motion. At the decompressed levels, average spinal cord stress in the kyphotic spine (8.73 kPa) was 2.8 times higher than the lordotic spine (3.15 kPa) and 1.3 times higher than the straight spine (6.8 kPa). At the decompressed levels, spinal cord strain in the kyphotic spine was (5.2%) was 3.6 times higher than the lordotic spine (1.4%) and 1.4 times higher than the straight spine (3.7%). Similarly, higher spinal cord stress and strain was noted for the kyphotic spine at the superior and inferior adjacent segments.

Conclusions

Cervical kyphosis was associated with high spinal cord stress and strain after laminoplasty even in the presence of adequate dorsal spinal cord shift. The results also highlight the negative consequences of progressive postsurgical kyphosis which can contribute to poor functional recovery after laminoplasty.

FDA Device/Drug Status

This abstract does not discuss or include any applicable devices or drugs.