Biomechanical Study Of The Influence For The Pedicle Screws Fixation When The Pedicle Cortex Perforation

Thoracic and lumbar pedicle width are different. The T5's pedicle width could be only 3.0mm. In some researches the scale of L1's pedicle width below 5.0mm is 20%,now the widely used pedicle screws' diameter are from 4.5mm to 6.0mm,so the pedicles will be perforated when the screws are planted. In some reports,the cortex thickness around the pedicle underside > upside > inside > outside,even the wrong operation can penetrate the outer cortex during the surgery. The pedicle provides 60% of the total hold force to hold the screw,which is the main part for the fixation. So when the pedicles are penetrated,it's sure to affect the stability of the screws system.Therefore,we have constructed a model of the outer cortical perforation after the screw placement,and studied the pull-out force and energy of pedicle screws with different plant depth(75ï¼… & 100%).Our results suggest: the outer cortical perforation pedicle marckedly affects the hold force to the screws. The hold force can not be increased greatly by inserting the scews more deeply. The hold power of the pedicle is stronger than that of the vertebral body. Increasing the screw insertion depth can refoem the degree of the pull-out process.