Thoracic Stenosis Secondary to Ossification of the Ligamentum Flavum

ABSTRACT

The thoracic portion of the spinal cord is susceptible to compression by hypertrophic ossification of the spinal ligament in the thoracic spinal canal. Unlike ossification of the posterior longitudinal ligament(OPLL) in the cervical spine, however, thoracic myelopathy due to ossification of the ligamentum flavum(OLF) may be overlooked, misdiagnosed, or treated inappropriately. This is mainly because of lack of knowledge of this condition. We therefore describe our experience with 22 cases of thoracic myelopathy secondary to ossification of the ligamentum flavum among 45 cases of thoracic stenosis. The clinical manifestations of this condition and the results of its surgical treatment are described. The most common cause of thoracic stenosis was OLF(48.9%) and the most common symptoms were numbness or tingling in the legs(81.8%) and motor weakness of the lower extremities(72.7%). Radiologically, OLF occurred mainly at intervertebral segments T9-T10 through T12-L1(86.2%), the most prevalent site was T11-T12(31.0%). Most OLF involved multiple intervertebral segments(81.8%) particularly two or three segments (59.1%). Eleven of the 22 patients were also suffering from other ossified conditions such as OPLL(45.5%) at other spinal sites, suggesting that ossification has a common underlying etiology. According to the authors' experience, surgical treatment, particularly laminectomy, was usually successful and outcomes were very promising(excellent, 27.3% ; good, 45.5%). OLF of the thoracic spine is no longer an uncommon condition and the authors believe that early diagnosis and appropriate surgical treatment, before irreversible damage to the spinal cord has occurred, may be the key to better results.