Objective To ensure the equality of median sagittal diameter(MSD)at the intervertebral space (DIV) and the pedicel level(DV),and calculate the normal amount and the normal lower limit.

• 目的确定正中矢状径(median sagittal diameter,MSD)在椎间隙层面(DIV)与椎体层面(DV)是否相等,并计算出正常值和正常下限。