Background: Diffuse idiopathic skeletal hyperostosis (DISH) is a degenerative condition characterized by progressive ossification of anterior longitudinal ligaments, creating rigid spinal segments that act as lever arms susceptible to traumatic forces. The resulting fused segments restrict spinal flexibility and increase fracture instability compared to normal spine. While cervical DISH (c DISH) is known to be associated with increased paralysis severity and high mortality rates, the impact of DISH not extending to the cervical region (non-c DISH) on cervical spinal cord injury (SCI) severity remains unexplored. We investigated the relationship between non-c DISH and paralysis severity in cervical SCI patients.

Methods: Among 516 cervical SCI patients (2011- 2023), 403 who underwent whole-spine CT and had classifiable ASIA impairment scales were included. DISH prevalence in thoracic, cervicothoracic, thoracolumbar, and whole-spine regions was examined. Relationships between DISH presence, age

>65 years, high-energy trauma, sex, cervical OPLL, and severe paralysis (ASIA grades A-B) were analyzed using ANOVA. Multivariate logistic regression explored associations between severe paralysis and c DISH/non-c DISH after Bonferroni correction.

Results: DISH prevalence was 21.1% (thoracic), 5.7% (cervicothoracic), 7.9% (thoracolumbar), and 2.2% (whole spine). Significant differences in ASIA impairment scale distribution were observed between DISH and non-DISH groups (P<0.05). Multivariate analysis revealed significant associations between severe paralysis and DISH presence (OR 2.03, 95% CI 1.20-3.42) and male sex (OR 2.00, 95% CI 1.00-

4.02). Both c DISH and non-c DISH were associated with severe paralysis compared to no DISH (c DISH: OR 4.56, 95% CI 2.09-9.96, P<0.001; non-c DISH: OR

1.76, 95% CI 1.01-3.06, P<0.05).

Conclusions: This study demonstrates that non-c DISH significantly increases the risk of severe cervical SCI, suggesting that thoracolumbar rigidity may biomechanically compromise cervical spine vulnerability during trauma. These findings have important clinical implications for risk assessment and management strategies in DISH patients sustaining cervical injuries.