| 1.BackgroundOssification of thoracic ligamentum flavum (OTLF) is not rare in clinical experiences. It has been widely recognized as a main cause of myelopathy of thoracic in Asia, particularly in Japan, Recently, more and more cases of OTLF have been reported in our country, indicating it is not infrequent in Chinese. However, the pathogenesis of OTLF is poorly understood, it might be associated with degeneration, trauma, inflammation, metabolic disorder, or genetic factors, Also, there are no characteristic features of clinical appearance, and are often confused with other spinal disorder. Moreover, although laminectomy has been commonly used for treating the condition since Yamaguchi et al. reported a case in 1960, the postsurgical prognosis of OTLF is not always excellent2.3.2. ObjectiveTo investigate the pathogenesis of ossification of thoracic ligamentum flavum, and study the characteristics of its diagnosis and treatment.3.MateriaIs and methods 3.1 Clinical materials20 patients due to OTLF were operated between 1994 and April. 2002. There were 16 males and 4 females, aged from 48 to 76 years (average, 57.8years), and the course of disease ranged from 3 months to 5 years (average, 15.4years). All the patients were performed with posterior decompression, 9 cases by the technique of en bloc laminectomy, and the others decompressed by dissolved laminectomy. The follow-up period was between 8 months to 70 months, averaged 20 months.3.2 Imaging studyAll patients underwent imaging studies of plain radiograph, computed tomographic scan (CT) and magnetic resonance image (MRI), and were differentiated from other spinal disorders. We observed the involved segments of ossifications, distribution patterns, the configuration of ossifications, and the extent of spinal canal stenosis and spinal cord compression.3.3 Pathological studyEvery surgical specimen was stained with HE, and was diagnosed definitely. Scanning electron microscopy was conducted as a part of examination in 10 cases. Due to the fact that the ossification initiated from the dural face of ligamentum flavum usually3, we performed the scanning electron microscopy on the dural face of ossifications.3.4 Two surgical techniques of posterior decompression(1) en bloc laminectomy Located the segments that should be decompressed, made a furrow on the middle line of the facet joint by power drill, be careful don't pass through the inner lamina. Then made a furrow on the other side, and penetrating the ossifications. The lamina and the ossifications were lifted by the forceps clip, separated them from dural by nerve elevator or lance and removed them ( fig. 1A ) . (2)dissolved laminectomy Bited the spinous process and slimmed the laminae, thenmade a furrow on the middle line of the bilateral facet joints respectively (don't entrance the spinal canal) , and the spinal canal was opened on the middle of the lamina. Separated the ossifications from middle to lateral , then removed them (fig. IB) .3.5 Surgical outcome assessingThe surgical outcome was assessed according to a recovery scale2 by the following equation:Recovery scale =(postop score-preop score)/(11-preop score)+100%.The outcomes were ranked as good (more than 50%), fair (10%-49%), no change (0-9%), and worse (less than 0%).4. Results4.1 Results of imaging studyThere were a total of 84 ossified segments in these series, 65 (77.4%) located in lower thoracic spine, 12 (14.3%) in upper, and 7 (8.3%) in middle (figure 2). Bone bridge formation was found in 18 of 20 patients; and it was found in the adjacent intervertebral space higher or lower than the ossified segment in 16 patients, only 2 patients found in the ossified segment (figure3).The ossified lesions were classified into three types according to thedistribution patterns of ossifications on MRI, isolate type (within two laminae) in 25%, continuous type (continuously between more than two laminae) in 60% and skip type (isolate or continuous ossifications at intervals)...
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