Thoracic posterior longitudinal ligament ossification in a fixed population; longitudinal radiological observations

All lateral chest radiographs of 34 persons with posterior longitudinal ligament ossification (PLLO) in the thoracic spine were reviewed for date of its onset and its progress. These observations spanned as long as 18 years. Upper mid-thoracic PLLO first appeared under the age of 40, then increased in extent in the vertical axis until the age of 50. Lower thoracic PLLO occurred later than upper mid-thoracic PLLO. In the lower thoracic and lumbar regions, degeneration of the vertebrae and discs apparently were focal factors which triggered the development of thoracic PLLO. PLLO apparently developed in a different way in the upper and mid-thoracic regions, where the vertebrae and discs were unremarkable at the time of its initial appearance, and degenerative abnormalities did not predispose to it. (author)