The definition and measurement of spinal cord compression. The compressing rate (CR) was defined as the thickness of the condensed spinal cord (N) divided by the anteroposterior diameter of the spinal cord (M) on the sagittal image on magnetic resonance imaging T2-weighted scanning preoperatively. CR = N/M × 100%. The CR and anteroposterior sagittal diameter of the spinal canal was measured at the most stenotic part of the spinal cord (S) on magnetic resonance imaging T2-weighted scanning.