Determinants of spinal cord stress and strain in degenerative cervical myelopathy: a patient-specific finite element study.

Degenerative cervical myelopathy (DCM) is the commonest cause of spinal cord dysfunction in older adults and is characterized by chronic cervical spinal cord compression. Spinal cord stress and strain during neck motion are also known contributors to the pathophysiology of DCM, yet these factors are not routinely assessed for surgical planning. The aim of this study was to measure spinal cord stress/strain in DCM using patient-specific 3D finite element models (FEMs) and determine whether spinal cord compression is the primary determinant of spinal cord stress/strain. Three-dimensional patient-specific FEMs were created for six DCM patients (mild [n = 2], moderate [n = 2] and severe [n = 2]). Flexion and extension of the cervical spine were simulated with a pure moment load of 2 Nm. Segmental spinal cord von Mises stress and maximum principal strain were measured. Measures of spinal cord compression and segmental range of motion (ROM) were included in a regression analysis to determine associations with spinal cord stress and strain. Segmental ROM in flexion-extension and axial rotation was independently associated with spinal cord stress (p < 0.001) and strain (p < 0.001), respectively. This relationship was not seen for lateral bending. Segmental ROM had a stronger association with spinal stress and strain as compared to spinal cord compression. Compared to the severity of spinal cord compression, segmental ROM is a stronger determinant spinal cord stress and strain. Surgical procedures that address segmental ROM in addition to cord compression may best optimize spinal cord biomechanics in DCM.

Spinal Cord Stress After Anterior Cervical Diskectomy and Fusion: Results from a Patient-Specific Finite Element Model.

Degenerative cervical myelopathy (DCM) is the commonest cause of cervical spinal cord dysfunction in older adults and is characterized by spinal cord compression and stress during neck motion. Although surgical decompression eliminates static spinal cord compression, cord stress resulting from flexion-extension motion of the spinal column has not been determined for single and multi-level surgical interventions. The effect of surgery on spinal cord stress is expected to change with the number of surgical levels as well as patient-specific anatomy. Using a MRI-derived patient-specific finite element model, we simulated 1-, 2- and 3-level anterior cervical diskectomy and fusion (ACDF) surgery for DCM. A substantial decrease in spinal cord stress at the level of spinal cord decompression was noted in all simulations. This was associated with a considerable increase in spinal cord stress rostral to the surgical level, and the magnitude of stress was higher in multi-level surgery. Increased spinal cord stress at the rostral adjacent segment correlated with increased segmental range of motion (r = 0.69, p = 0.002) and disk pressure (r = 0.57, p = 0.05). Together, these results indicate that ACDF for DCM is associated with adverse spinal cord stress patterns adjacent to the fusion construct, and further research is needed to determine if the altered stress is associated with clinical outcomes after surgery for DCM.