Biomechanical Study On The Effect Of Lumbosacral Segment Degeneration In Lumbar Different Length Fixtion

Single segment, short, long segment in three different lengths of sheep lumbar posterior fixation model were established in this experiment. Through detecting, the changes of lumbosacral segment activity and lumbosacral intervertebral disc pressure change of three kinds of internal fixation model, This thesis intend to study the effect of internal fixation of lumbosacral segment degeneration after lumbar different length.The fresh whole sheep spine specimens were selected to do the biomechanical experiment. There were20spinal specimens, including7lumbar and5sacral vertebra section. Both flexion and extension were loaded on specimens in the experiment, the load torque was set to6N·m. After the loading was finished, activity and intradiscal pressure of lumbosacral segment were measured, and the data was involved in the control group. Each specimen was made to three different lengths of sheep lumbar posterior fixation model, such as a single, short, long segment, and were sequentially fixed lumbar6-7segment,5-7segment and lumbar segment3-7. All the three kinds of specimens were loaded in the way of flexion and extension, and the motion and intradiscal pressure of lumbosacral segment were measured. The obtained data were included in the single segment fixation group, short-segment fixation group and long segment fixation group respectively. Measurement method of activity was plane measuring technology, and of intervertebral disc pressure was the pressure sensitive film method. The differences of segmental motion and intradiscal pressure in the control group, single segment fixation group, short-segment fixation group and long segment fixation group, and each of the4groups were compared between themselves. The results showed that compared with control group, lumbosacral segment mobility and intradiscal pressure were increased in flexion, extension movement mode after single segment fixation, but the difference was insignificant (P>0.05), lumbosacral segment mobility and intradiscal pressure were increased in flexion, extension movement mode after short-segment fixation, and the difference was significant (P<0.05); lumbosacral segment mobility and intradiscal pressure were increased in flexion, extension movement mode after long-segment fixation, and the difference was significant (P<0.05). Compared to the short-segment fixation group, lumbosacral segment mobility and intradiscal pressure of long-segment fixation group were significantly increased in flexion, extension movement mode, and the difference was significant (P<0.05) Besides, we found that the pressure distribution of intervertebral disc was not uniform in the extension movement mode, and compared with the disc center, the lateral lumbar intervertebral disc pressure was greater.The effect of single segment fixation of the lumbosacral segment degeneration was not significant; the effects of short, long segment fixation on the degeneration of lumbosacral segment was significant; Long segmental fixation on the degeneration of lumbosacral segment has more significant effects.