Dynamic Intramedullary Stress and Strain Correlates with Neurological Dysfunction in Degenerative Cervical Myelopathy

Introduction: Degenerative cervical myelopathy (DCM) is the leading cause of non-traumatic spinal cord injury. Intramedullary stress and strain contribute to axonal and myelin injury in DCM. Finite element models (FEM) quantify intramedullary stress and strain non-invasively, but their relationship to neurological function has not been investigated. This study examines whether pre-surgical intramedullary stress and strain correlate with neurological function in DCM patients.

Methods: Patient-specific FEMs of the cervical spine were created using pre-surgical MRI data of 20 DCM patients (13 females, 7 males, mean age 62.7±11.6 years). Intramedullary stress and strain during flexion and extension were quantified using FEMs. Pre-surgical neurological function of DCM patients was assessed for sensorimotor hand function and balance. Correlations between FEM-derived intramedullary biomechanics and neurological function were calculated while controlling for age.

Results: Mean intramedullary stress and strain at the level of maximum cord compression during neck flexion was 7.6±3.7 and 4.3±2.0 kPa respectively. Elevated intramedullary strain in flexion at the level of maximum compression was correlated with decreased right-hand sensation (r= -0.58, p=0.014) and decreased right hand dexterity (r=0.5, p=0.039). Elevated intramedullary stress at the level of maximum cord compression during flexion was associated with decreased right-hand sensation (r= -0.55, p=0.02) and decreased hand dexterity (r= 0.55, p=0.026).

Conclusion : Elevated intramedullary stress and strain, particularly during neck flexion, correlates with baseline neurological function in DCM. The results demonstrate that neck movement, in addition to cord compression, contributes to neurological dysfunction in DCM and this should be taken into consideration when planning motion preserving surgeries for DCM.