To measure the angle which composed of terminal plates of C2/ 3 to C7/ T1, added the angle of procurvation and retroflexion each segment to get the extension of the intervertebral space and compare the change with them. 角度测量是自C2/3至C7/T1逐个节段测量其终板所成夹角,前曲与后伸位测得的夹角相加得出单个节段椎间隙活动范围,比较手术前、后角度变化。