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

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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.


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.


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.

Abbreviations used in this paper:CT = computed tomography; JOA = Japanese Orthopaedic Association; OLF = ossification of the ligamentum flavum; OPLL = ossification of the posterior longitudinal ligament.

Article Information

Address reprint requests to: Toshimi Aizawa, M.D., Ph.D., 1-1, Seiryo-machi, Aoba-ku, Sendai 980-8574, Japan. email:

© AANS, except where prohibited by US copyright law.



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    Bar graph showing the distribution of OLF in relation to the intervertebral disc level considered responsible for the myelopathy. More than half of the ossified ligamenta flava are at the T10–11 and T11–12 levels. In the upper thoracic region, the lesions were most frequently located at the T2–3 segment.

  • View in gallery

    The CT classification of OLF, with scans obtained at the middle of the facet joint. A: Lateral type. The ossified ligamentum flavum is located only in the capsular portion of the ligamentum flavum, which can be detected at the lateral edge of the spinal canal. B: Extended type. The ossified ligamentum flavum is located at the surface of the ligamentum flavum but extends to the interlaminar portion of the ligament. C: Enlarged type. The ossified ligamentum flavum protrudes into the spinal canal, but both sides of ossified ligamenta flava are not fused at the middle. D: Fused type. Bilateral ossified ligamenta flava fuse at the middle of the spinal canal, but an incision can be found at the middle of the ossified ligamentum flavum. E: Tuberous type. Fused ossified ligamenta flava make a tuberous mass at the middle of the spinal canal.

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    Preoperative CT myelogram obtained in a patient with OLF and ossified dura mater at the T10–11 level. The ossified ligamentum flavum adheres to the ossified dura on the right side of the spinal cord, and little contrast medium between the cord and ossified ligamentum flavum is detected.

  • View in gallery

    Line graph showing the pre- and postoperative JOA scores obtained in 72 patients. The score improved in 66 patients during a mean follow-up period of 46 months.



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