The Natural History of Ossification of Yellow Ligament of the Thoracic Spine on MRI: A Population-Based Cohort Study

PURPOSE: To assess the natural history of ossification of yellow ligament (OYL) in the thoracic spine and determine risk factors for progression based on a longitudinal population-based cohort. METHODS: A prospective, longitudinal cohort study was performed on a population-based cohort of Southern Chinese volunteers. T2-weighted magnetic resonance imaging (MRI) was used at baseline to identify any OYL and was verified with computed tomography. Follow-up MRI was performed 5 years later. Parameters under study included the size of OYL, levels of involvement, morphology (round, triangular, beak), whether it crossed the midline and any disc degeneration. RESULTS: A total of 114 (6.1%) individuals were identified to have OYL at baseline out of the 1864 individuals. Size progression occurred predominantly at the lower thoracic region. Majority of the new OYL were also in the lower thoracic spine and was associated with higher body mass index (BMI). Smokers were associated with OYL size progression while patients with higher BMI tended to develop new OYL at follow-up. Progression commonly occurred at the lower thoracic levels and regression occurred mostly at the upper thoracic levels. CONCLUSIONS: This is the first population-based series addressing the natural history of OYL. Better understanding of the natural history of OYL may provide incentive to introduce preventive measures such as weight reduction and close monitoring for myelopathy development in those at-risk groups for progression. This is especially important for patients with lower thoracic OYL and who are smokers with higher BMI. LEVEL OF EVIDENCE: 1 (prognostic study).