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.