The biomechanical effect of different types of ossification of the ligamentum flavum on the spinal cord during cervical dynamic activities.

Ossification of the ligamentum flavum (OLF) is thought to be an influential etiology of myelopathy, as thickened ligamentum flavum causes the stenosis of the vertebral canal, which could subsequently compress the spinal cord. Unfortunately, there was little information available on the effects of cervical OLF on spinal cord compression, such as the relationship between the progression of cervical OLF and nervous system symptoms during dynamic cervical spine activities. In this research, a finite element model of C1-C7 including the spinal cord featured by dynamic fluid-structure interaction was reconstructed and utilized to analyze how different types of cervical OLF affect principal strain and stress distribution in spinal cord during spinal activities towards six directions. For patients with cervical OLF, cervical extension induces higher stress within the spinal cord among all directions. From the perspective of biomechanics, extension leads to stress concentration in the lateral corticospinal tracts or the posterior of gray matter. Low energy damage to the spinal cord would be caused by the high and fluctuating stresses during cervical movements to the affected side for patients with unilateral OLF at lower grades.