Clinical and histological study of ossified ligamentum flavum in the thoracic spine

Thirty three patients with thoracic myelopathy due to ossified ligamentum flavum (OLF), which have been treated surgically in our clinic, were analyzed from the view point of both clinical and histological study in order to classify the clinical characteristic and the mechanism of formation and growth of OLF. The most frewuent initial symptom was numbness of the lower extermities, with was later gradually aggravated. Finally, gait disturbance and bladder dydfunction were the main findings at the time of admission. When spinal cord compression syndrome is evident, laminectomy with excision of OLF is needed for decompression of the cord. In this series post operative results were excellent in 15%, good in 43%, fair in 21%, unchanged in 15% and worsened in 6%, at the time of discharge. Follow up study (average 9 years after operation) indicated that the results almost maintained for long duration, however, several cases showed lower results. Average clinical points based on JOA score (11 point) were 7.3 at the time of discharge and 7.0 at the time of follow up. The cases with lowered results has spinal canal canal stenosis or other combined spinal disorder, and long duration from the onset to the first visit to our clinic. Histologically at the ligament osseous jundtion, elastic fivers decreased and appeared to be irregular. On the other hand, collagen fibers increased and was hyalinized. Histological changes were dominant at the ligament -osseous junction, where fibrocartilaginous cell were noted, comparing with at the central part of the ligament.