Spinal cord shape factor as a predictor of postoperative functional outcome in thoracic ossification of the posterior longitudinal ligament.

Abstract

Retrospective Cohort Study. To investigate the utility of the spinal cord Shape Factor (SF) as a preoperative predictor of surgical outcomes in patients with thoracic ossification of the posterior longitudinal ligament (OPLL). Two institutions in Japan. We retrospectively reviewed 39 patients who underwent posterior decompression with fusion for thoracic OPLL. Preoperative SF was calculated from axial MRI at the most compressed level using the formula: SF = 4π × (cross-sectional area) / (perimeter)². Surgical outcome was evaluated by the recovery rate of the modified Japanese Orthopaedic Association (mJOA) score one year postoperatively. The relationship between preoperative factors, including SF, and the recovery rate was analyzed. ROC curve analysis was used to determine the predictive value of SF. The mean mJOA recovery rate was 48.84 ± 19.26%. SF showed a significant positive correlation with the postoperative mJOA score and the recovery rate. SF was significantly higher in the good recovery group (recovery rate ≥ 50%) compared to the poor recovery group. ROC analysis revealed SF was a significant predictor of good recovery (AUC = 0.7842), with an optimal cutoff value of 0.43. The preoperative SF is an objective morphological parameter that reflects the degree of spinal cord deformation in thoracic OPLL. While the correlations were relatively weak, a lower SF, representing greater irregularity of the spinal cord, was associated with poorer functional recovery. These findings underscore the importance of spinal cord morphology, specifically its circularity, as a factor influencing postoperative outcomes.