Potential Influence of Sagittal Parameters in the Pathogenesis of Patients With the Thoracic Ossification of the Ligamentum Flavum.

Purpose: There are many causes of thoracic ossification of the ligamentum flavum (TOLF), of which mechanical stress factors have gained increasing attention. This study aimed to explore the potential pathogenesis of TOLF by comparing spinal sagittal alignment parameters between patients with TOLF and an asymptomatic population.

Methods: We retrospectively included patients who underwent surgical treatment for thoracic myelopathy caused by OLF at Peking University Third Hospital from 2012 to 2022. Sagittal alignment parameters measured by picture archiving and communication system were compared between the TOLF group and a control group with independent t-test, Wilcoxon rank-sum test, and Chi-Squared test. Patients with caudal insertion of OLF above the T10 level were categorized into Group 1, while those with caudal insertion below the T10 level were categorized into Group 2. Sagittal alignment parameters were then compared among these two groups and the control group.

Results: Compared with the control group, the OLF group exhibited less lumbar lordosis (44.46° ± 11.41° vs. 52.55° ± 9.70°, p < 0.001), greater thoracolumbar curvature, greater PI-LL mismatch, and greater SVA imbalance. In patients with caudal insertion of the OLF above the T10 level, PI, PT, and LL were smaller compared to the control group. Patients with caudal insertion below the T10 level had smaller LL, greater thoracolumbar kyphosis, more severe SVA imbalance, and more severe PI-LL mismatch.

Conclusion: Patients with TOLF have a straighter spine. Mechanical stress plays a more significant role in the development of TOLF in patients with caudal lesions below the T10 level. In patients with TOLF not involving the thoracolumbar segment, factors other than mechanical stress, such as endocrine factors, may play a more crucial role in the development of TOLF.