Experimental Study Of The Effect Of Laminectomy On The Screw Extraction Force Of Cortical Bone Trajectory

Objective:To compare the effect of Conventional pedicle screw(CPS),enhanced bone cement screw Fenestrated pedicle screw(FPS)and cortical bone locus screw Cortical bone trajectory(CBT)in the intact vertebrae and laminectomy vertebrae,and to investigate the effect of laminectomy on the stability of the screws.It provides a reference value for selecting the best screws for surgical treatment of lumbar diseases.Method:Collect 8 specimens of lumbar vertebrae from Faure Marin's adult cadavers,collect lumbar vertebrae 1 to 5 as cadaver segments.The free40 vertebrae were randomly divided into two groups,each with 20 vertebrae,the whole vertebra and the vertebral lamina were removed,and the same screws were placed on both sides of the vertebrae.After the specimen was successfully embedded,the embedded vertebrae were placed on the fixed frame of an electronic universal testing machine.During the test,the longitudinal axis of the screw was pulled out on the same axis as the test,and axial traction was carried out at a uniform speed at 10mm/min speed,when the screw pulled out the distance over 2mm or the screw loosened.When the screw pulls out more than 2mm or loosens the screw(mainly manifested as the destruction of the cortical bone of the pedicle),it is regarded as screw pull-out.When it was found that the axial pulling force of the screw was reduced by the computer data acquisition system,the test was stopped and the maximum axial pulling force(F-max)of the screws was recorded at the vertebral body.The load displacement curve was recorded by the computer data acquisition system and the load displacement curve was automatically generated.Result:(1)The maximum pull-out force of CPS screws in complete vertebrae and laminectomy vertebrae were:(657.48 + 72.06)N,(630.07 +73.16)N.The two groups were compared with independent sample t test.It was found that the maximum pulling force of the CPS screw in the complete vertebra was larger than that of laminectomy,and there was no significant difference between the two(P>0.05).It showed that the pulling force of the CPS screw in the complete vertebra and laminectomy vertebra had no significant difference.(2)The CBT screw was in the complete vertebra and the laminectomy.The maximum pull-out force of the vertebral body was(752.35 + 68.93)N and(593.21 + 65.88)N respectively.The two groups were compared with independent sample t test.It was found that the maximum pulling force of the CBT screw in complete vertebra was significantly greater than that of laminectomy,with statistical significance(P<0.05).(3)The maximum pulling force of the FPS screw in complete vertebra and laminectomy were(1186.35 + 74.71)N and(964.71+ 62.53)N respectively.The two groups were compared with independent sample t test.It was found that the maximum pulling force of FPS screws was larger than that of laminectomy,and there was no statistical significance(P>0.05).There was no significant difference in the maximum pulling force of FPS screws in the different vertebrae.Conclusion:Laminectomy has a certain effect on the stability of CBT screws.In laminectomy,CBT screws the pulling force is less than that of CPS screws.It is suggested that CBT screws should be used carefully in laminectomy or spondylolisthesis patients.CBT screws or FPS screws can be used in complete vertebrae in order to improve the effect of pullout force.