Thirty cases showing hard discs were collected fro m 206 consecutive cases of posteri or disk herniation during th e past one and a half years period. According to th e shape of hard disc and th e presence of margi nal bone defect (MBD) of vertebral end plate, 30 cases could be categori zed into 4 distinct groups. They were small hard disc with focal MBD (group 1), lage hard disc with broad based MBD (group 2) , hard disc seperated from vertebral body without MBD (group 3) and hard disc fused

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... th vertebral body wi th out MBD (group 4). The re were 14 patients in group 1. In all but one case , th e hard dis cs and MBDs were located at the paramedial as pect of th e posteri or margin of the end plate. Te n (76 .9 %) of these had Schmorl 's nodes and these