Finite element analysis of the effects of different ossification types and spinal canal occupancy rates on dynamic spinal cord stress in cervical ossification of the posterior longitudinal ligament.

OBJECTIVE

To investigate the effects of ossification type and spinal canal occupancy rate on dynamic spinal cord stress in cervical ossification of the posterior longitudinal ligament (C-OPLL) using finite element analysis.

METHODS

A validated C2-C7 finite element model was constructed from CT and MRI data of a healthy volunteer. Three C-OPLL types (focal, segmental, continuous) were simulated at 20%, 40%, and 60% occupancy rates. Spinal cord stress was analyzed under nine flexion-extension angles (+20° to -20°).

RESULTS

Spinal cord stress increased exponentially at 60% occupancy across all types. Focal ossification produced the highest stress (0.1196 MPa at 60% occupancy/maximum flexion), 30.4% higher than continuous type. At 60% occupancy, the stress sensitivity threshold decreased to ±5° motion. Dural stress consistently exceeded spinal cord parenchyma stress (1.6-2.1 times).

CONCLUSION

In this single-subject finite element model at C4-C5, focal C-OPLL produced the highest peak spinal cord stress at this level. The 60% occupancy rate was identified as a critical biomechanical threshold above which stress increased exponentially and became highly sensitive to minor motion (±5°). These findings are hypothesis-generating and suggest that patients with ≥60% occupancy at C4-C5 may warrant close follow-up. However, because this study is based on a single healthy volunteer, the proposed thresholds require validation through patient-specific models and prospective studies before clinical application.