Thoracic myelopathy caused by ossification of the ligamentum flavum: a report of 18 cases

Object. Thoracic myelopathy caused by ossification of the ligamentum flavum (OLF) is a rare entity, most evident in Japan. The authors studied the clinical manifestations, radiological aspects, surgical treatment, and pathogenesis of this disease. Methods. Eighteen patients with OLF-induced thoracic myelopathy underwent laminectomy. The severity of myelopathy varied. Complete paraplegia was seen in three cases. Compression of the upper and middle third of the thoracic spine was evident in six cases and of the lower third in 12 cases. Multilevel OLF was demonstrated in 13 cases. In most cases, the ossified ligamentum flavum appears as a V-shaped lesion on computerized tomography and magnetic resonance images. In all patients the diameter of the posterior spinal canal, already narrowed, was further exacerbated by the OLF. Laminectomy was limited to the levels of compression, and the ligamentum flavum was resected in all cases. The symptoms and signs improved in 13 cases and stabilized in four cases. In one case symptoms recurred as a result of ossified lesions forming at other sites. Histological examination showed that the mode of development of the ossified ligaments was endochondral ossification. Conclusions. Reports of OLF-induced myelopathy are rare and mainly described in Japan. The incidence also seems high in North Africa. An early laminectomy limited to the level of compression is recommended. Ossified ligamentum flavum is different from the calcification of the ligamentum flavum, which is due to crystal deposits.