Prevalence and Radiological Features of Thoracic Ossification of the Ligamentum Flavum in Korea—A Retrospective Comparative Cohort Study Using MRI ^†

(1) Purpose: Thoracic ossification of the ligamentum flavum (OLF) is increasingly recognized in East Asian populations, but reliable estimates in clinical settings remain limited. This study aimed to determine the clinic-based, lower thoracic (T8–T12) MRI prevalence of OLF among patients undergoing lumbar spine MRI for low-back pain and to identify radiological features associated with OLF. (2) Materials and Method: A cohort of patients with lower back pain who underwent L-Spine MRI studies in a tertiary medical center from January 2008 to December 2009 was created. Patients with thoracic OLF were identified, and a twice-fold sex-and-age-matched control group of patients without OLF, was randomly extracted. Radiological features in two groups were compared. (3) Results: The lower thoracic prevalence of OLF was 2.7%, significantly increasing in patients aged ≥60 years. OLF was most frequently involved in level T10-T11 (43%), and 23 cases (36%) showed multiple-level involvement. OLF was strongly associated with localized degenerative changes at the affected level, including higher degree of degenerative disc change, disc height loss, and more osteophyte formations. (4) Conclusions: Thoracic OLF is not a rare condition in patients with lower back pain. Patients with thoracic OLF were more likely to show features of focal degenerative changes, such as disc degeneration, osteophyte formation, and disc height loss on the level of OLF. Therefore, if initial plain radiographs of patients with neurologic deficits show evidence of degenerative change in the lower thoracic spine, a higher index of suspicion for thoracic OLF should prompt further evaluation.