Biomechanical Study Of The Pull-out Force On The Percutaneous Pedicle Screw Of Different Tranverse Angle Were Placed

Objective: To analyze the relationships between the percutaneous pediclescrews’ angle and their lossening,through observing the pull out strength and pull outpower using different angle of the percutaneous pedicle screws both on the sagittaland coronal planes.Methods:36calves lumbar vertebral body were divided into six groupsrandomly(A1A2A3B1B2B3),using the same size pedicle screws and same implantdepth，Group A was divided into three parts by three horizontal screw implant anglesas0°,10°,15°.Group B was divided into three parts by three sagittal screwimplant angles as0°,10°,15°.all of them were inserted with coronal angle of0°.Using the universal testing machine to do the pull-out test with2mm/minspeed,record the load-displacement curve, measure the percutaneous pedicle screwpull-out force and pullout energy, and use a statistical software to analyze results.Results:（1）The results showed that as the pedicle screw angle increased,thepullout force and pullout energy increased in both of the two groups.The maximumpullout energy of group A3increased40.0%than group A1, and Pulloutthe energy increased43.9%. The maximum pullout energy of group A2increased40.0%than group A1, and Pullout the energy increased39.3%. Themaximum pullout energy of group A3increased8.9%than group A2and Pulloutthe energy increased7.7%.（P<0.05）；The maximum pullout energy of group B3increased37.3%than group B1, and Pullout the energy increased41.5%. Themaximum pullout energy of group B2increased31.0%than group B1, and Pulloutthe energy increased40.0%. The maximum pullout energy of group B3increased9.3%than group B2and Pullout the energy increased8.5%.（P<0.05）.（2）Load–displacement curveshows thatafterthe screws began to loose,the screws holdingforce decreased gradually, not immediately,which suggesting that the screw looseningis a progressive process.we can prevent the screw pullout by earlier detection. Conclusion:1, the pull-outstrength and pullout energy increased gradually as thescrews implant anglulation increased in both the coronal and sagital planes.2, Load–displacement curve shows that after the screws looseningand holding force decreased gradually, not immediately.