Ossification of thoracic ligamenta flava.

Although ligamentum flavum ossification (LFO) often occurs in normal persons, there are no reports of its detection on lateral chest radiographs made during screening examinations. Review of 1,744 consecutive lateral chest radiographs identified LFO in 6.2% of males and 4.8% of females. LFO occurred mainly at the intervertebral segments from T9-T10 through T12-L1. Most prevalent was the hook-shaped LFO, protruding inferiorly from the inferior facets into the projections of the intervertebral foramina. Though LFO can cause severe neurologic symptoms, none of the affected persons in this study reported such symptoms. LFO was first visualized radiographically when the subjects were 20-40 years old, and it may be a physiologic condition. The LFO in these cases existed independent of thoracic posterior longitudinal ligament ossification, diffuse idiopathic skeletal hyperostosis, and degenerative osteoarthritis.