Objective:To explore the early development of adjacent segment after posterior fusion of lumbar. Methods:From 2004 to 2007, 21 pateints with thoracolumbar fractures were treated by pedicle fixation combined with lumbar posterior fusion as experimental group. The patients from the out-patient department without any vertebral diseases were as control group. We measured the width of ligamentum flava, small joint, and intervertebral foramen, the facet tropism and the facet angle. Results:The width of ligamnetum flavum of experiment group were increased compared with the control group. The facet tropism were bigger in experimental group than the control group. There were not statistical significance in the width of small joint and facet angle between the experimental group and the control group. Conclusion:The adjacent segment were changed after lumbar posterior fusion due to the change of biomechanical force. It is very important for clinical guide to understand the changes of adjacent segment.