Thoracic myelopathy caused by ossification of the ligamentum flavum: clinical features and surgical results in the Japanese population

Object. Data obtained in patients with thoracic myelopathy caused by ossification of the ligamentum flavum (OLF) were retrospectively reviewed to clarify clinical features and surgical outcomes in the Japanese population. Methods. Seventy-two patients who underwent surgery for OLF-induced myelopathy in the Miyagi Prefecture, 'Japan, between 1988 and 2002 were observed for at least 2 years. Clinical data were collected from medical and operative records. The patients were evaluated pre- and postoperatively using the modified Japanese Orthopaedic Association (JOA) scale (maximum score 11). The relationships among various factors (age, sex, and preoperative duration of symptoms) affecting the preoperative severity of myelopathy and postoperative improvement were also examined. Conclusions. In this series the surgical outcome was relatively good and depended on the severity of myelopathy; thus early and correct diagnosis is required to avoid poorer results. The male/female ratio was 3.2 and the mean patient age at surgery was 61 years for men and 68 for women. The patients commonly noticed numbness or pain in their lower legs or gait disturbances. In a total of 104 decompressed intervertebral disc levels, more than 80% of the ossified ligaments were at the T9-10 level or lower. The mean preoperative JOA score of 5.1 improved to 7.9 after an average of 46 months. The postoperative results statistically depended on the preoperative severity of myelopathy. Among studies of patients with OLF-related myelopathy, the present study had the largest sample size, which should help clarify the clinical features of OLF myelopathy.