Reduction of Spinal Cord Cross-Sectional Area Is Associated With Myelopathy in Severe Cervical Ossification of the Posterior Longitudinal Ligaments

BACKGROUND AND OBJECTIVES: Cervical ossification of the posterior longitudinal ligament (OPLL) is a progressive condition that leads to spinal cord compression, yet clinicians frequently encounter a significant mismatch between radiological severity and clinical symptoms. This study aimed to identify the most reliable radiological predictors of myelopathy in patients with severe cervical OPLL, with a specific focus on spinal cord-based parameters that account for individual anatomic variations. METHODS: We retrospectively reviewed 300 patients with severe cervical OPLL (occupying ratio >50%). Radiological metrics included occupying ratio, space available for the spinal cord, cord compression ratio, compressed spinal cord cross-sectional area, and %decreased spinal cord area (SCA) (percentage reduction from normal area). Myelopathy was defined as a modified Japanese Orthopaedic Association (mJOA) score ≤17. RESULTS: Among all parameters, %decreased SCA demonstrated the highest diagnostic accuracy for myelopathy [area under curve (AUC) 0.904; 95% CI: 0.863-0.941; cutoff: 15.2%; sensitivity 82.3%; specificity 91.8%], significantly outperforming the occupying ratio (AUC 0.717) and space available for the spinal cord (AUC 0.751). For moderate myelopathy (mJOA ≤14), %decreased SCA showed even higher discriminative performance (AUC 0.931, cut-off 16.3%). It also showed the strongest correlation with mJOA (ρ = -0.772, P < .001) and was the most significant independent predictor in multivariate analysis (β = -0.118 per 1% increase; P < .001). In addition, T2 signal change, OPLL morphology, male sex, and increased local range of motion were independent factors associated with myelopathy severity. CONCLUSION: %Decreased SCA is a highly reliable, cord-specific indicator for assessing myelopathy severity in patients with severe cervical OPLL. Our findings suggest that clinical impairment is determined by a combination of cord-based measurements, dynamic factors (range of motion), and intrinsic cord changes, rather than simple bony canal dimensions alone. LEVEL OF EVIDENCE: Class III.