Objective To compare the stability of the lumbar intervertebral segmental stiffness after three types of interbody fusion(ALIF,PLIF and TLIF)with or without lateral transpedicular screws fixation.Methods Fifteen bovine lumbers were divided into 7 groups,with each performed nondestructive tests.Results(1)Comparing with the intact group,the mean axis compression stiffness decreased by 28.3%,18.4%,11.5% (P<0.05),respectively;the mean anteroposterior shear stiffness decreased by 21.6%,17.5%,5.9% (P<0.05),respectively in ALIF(1) 2PLIF(1)and TLIF(1)group;the axial rotational stiffness decreased by 38.6%,49.1%,27.2%,respectively(2)By applying internal fixation,comparing with the non-internal fixation interbody fusion group,their mean axis compression stiffness and anteroposterior were separately increased by 87.8%,77.9%,75.9%(P<0.05)and 60.6%,68.1%,63.1%(P<0.05), respectively;Their axial rotational stiffness increased by 95.1%,110.9%,87.6% (P<0.05),respectively.Conclusion (1)Three types of Lumbar interbody fusion without additional internal fixation showed less stable than the normal intact lumbar.Only when transpedicular screws fixation applied,their stability could increased greatly and become much more stable than normal intact lumbar.(2)TLIF is the most stable one in the three types.