Biomechanical Study Of The Pedicle Screw On Sacrum 2 (1)

Pedicle screw fixation system, as is currently the most common spinal surgical technique of posterior spinal fixation methods, its history can be traced back to the 19th century, 50's, With medical workers' better understanding of spinal pedicle anatomy, continuous updating and improvement of the pedicle screw fixation system , presenting of spine-three-column-theory and its theoretical biomechanical verifying ,pedicle screw fixation systems have been widely used in cervical thoracic lumbar sacral vertebral as treatment of trauma, infection, tuberculosis, tumor, congenital and degenerative diseases.And its application in the sacrum are confined to the sacral pedicleThe study1.The study abroad about sacral-2- pedicle began in 1991 , Mirkovic did the anatomical study of sacral-2- vertebrae and prompt the method of implanting screws . Research in Our country about sacral-2- pedicle began in 2002, Sun He and Xu Chuanda studied the anatomy of sacral-2- pedicle-screw -implanting-method , and both inside and outside of the sacral-2- pedicle-screw -implanting-method is presented.In the year 2008, in view of previous methods are given a regional and not a fixed anatomical point, Li Ye, Li Gang, etc, started a new anatomic study of sacral-2-pedicle-screw -implanting-method and both inside and outside screw -implanting-method were presented,so the operability is improved..However, because of sacral vertebral are fusioned together, there is no sacral-2-vertebral body on the definition of the pedicle anatomy, the so-called sacral -2 -"pedicle" is not on the true meaning of the pedicle.How about the pullout strength of its pedicle screw. There is no reported study about maximal axial pull-out strength of sacral-2- "pedicle" screw fixation or its sacral strain distribution in different parts .So, as Li Ye sacral-2- pedicle screw studies' continue, we will design experiments in accordance with their method, hereinafter referred to as "sacral-2- pedicle-screw -forward-inside-implanting-method " .We designed experiments about pull-out force of "sacral-2- pedicle-screw -forward-inside-implanting-method " and its sacral strain distribution, compared with those of pedicle1screw sacral , in order to provide biomechanical data of "sacral-2- pedicle-screw -forward-inside- implanting-method " before the clinical application.Objective: To measure and compare the maximum axial pull-out strength and its sacral strain distribution of sacral-2-"pedicle" screw ("sacral-2- pedicle-screw -forward-inside-implanting-method " ) and sacral-1-"pedicle" screws ("sacral-1- pedicle-screw -forward-inside-implanting-method "),in order to provide biomechanical data of "sacral-2- pedicle-screw -forward- inside- implanting-method " before the clinical application.Method:Before the experiment,remove the 6 specimens (frozen adult sacral with lumbar and sacroiliac joint ) after thawing at room temperature, remove the lumbar, iliac bone and soft tissue .Then implant S1 S2 pedicle screws in accordance with the methods above.Paste the resistance strain gauges to sacrum in accordance with the placement process of "8 measuring points pasting method of resistance strain gauges on sacrum ".24 hours later,the sacral specimens are natural dried, placed respectively the six dry sacral specimens on the working table of Shimadzu AG-10TA universal testing machine ,and then connect the the resistance strain gauges and the bridge arms of static and dynamic analysis system of strain with wires, wiring for the half-bridge, temperature compensation for outside compensation.Driven universal testing machine and the machine carried out experiments on the axial pedicle screw pull-out strength test at speed of 5mm/min ,measuring the maximum pull-out strength ,at the same time through the static and dynamic analysis system of strain to measure the measuring points the value of the strain.Measurement indicators (1) the maximal axial pull-out strength of sacral-2-"pedicle" screw ("sacral-2- pedicle-screw -forward-inside-implanting-method " ) and sacral-1- "pedicle" screws ("sacral-1- pedicle-screw -forward-inside- implanting- method ") (2) the resistance strain gauge measurement of "8 measuring points pasting method of resistance strain gauges on sacrum " corresponds to the pull-out strength . Statistical analysis was performed using SPSS statistical software.Results: The results show that the pull-out force on the 1st screw (left sacral 1 ), is 497.5±8.6N, and pull-out strength on 2nd screw (right sacral 2 )for 514.5±9.4N, 3rd screw (left sacral 2)for 218±9.3N, 4th screw (rightsacral 2) for 250.5±5.5N. With maximal axial pull-out strength on 3rd screw , the maximum strain occurred at point3,and point 3 is on the edge of 3rd screw .,where is left sacral vertebral lamina. It's near the screw, so the strain is maximum . the Minimum strain occurred at point3, the point is the farthest one from the screw, so the strain is minimum. With maximal axial pull-out strength on 4th screw , the maximum strain occurred at point 4,and point4 is on the edge of 4th screw .,where is right sacral vertebral lamina, the site is near the site of stress and affected by stress concentration,so strain there is maximum.Conclusion:The maximal axial pull-out strength on sacral-2-"pedicle" screw ("sacral-2- pedicle-screw -forward-inside-implanting-method " ) :the left side for 218±9.3N, the right to 250.5±5.5N. Compared to its left and right side there was no significant difference; and compared to s2 and s1 the difference is significant. With maximal axial pull-out strength on sacral-2-"pedicle" screw , the maximum strain occurred on at the measuring point 4( right sacral vertebral lamina), 131.1με, which is not sufficient to do harm to sacrum.So the "sacral-2- pedicle-screw -forward-inside-implanting-method " is in line with the principles of biomechanics.If it was performed in clinical practice ,we would have to take its enhancing problem into consideration.