3 Discussion

3.1 The choices of material for duraplasty in CMI associated with SM: The mechanism about the formation of syringomyelia in CMI is still not clarified ^[4]. Most authors believed that the formation of SM is related to the obstruction of CSF circulation around the foramen magnum in CMI ^{[1, 5, 6]}. The surgical treatment of CMI with SM includes decompression of the posterior fossa, let the dura open or repair with some materials (duraplasty)^[7], but up to now it is still argued about the option of operation ^{[1, 5, 8, 9]}, Milhorat ^[1] suggested duraplasty should be done in most patient. Now some dural substitutes including autologous periosteum ^[10] or fascia and synthetic dural substitute were used. In our hospital the following materials have been used for this purpose: the fascia superficialis around the incision which can be obtained easily and needs not a new incision but it is usually thicker than the dura matter and often forms to a defect around the incision, causing infection of the inc