Biomechanical And Clinical Research Of A New Pedicle Screw Track Expander

BackgroundsOsteoporosis can seriously affect the fixation strength of pedicle screws.The existing nail channel expanding instruments include tapping,drill,straight clamps and so on.In the auxiliary technology of drill,the nail track can be formed by slowly advancing the low-speed rotating drill.This method can open the nail canal slowly and smoothly,but it may lead to the decrease of bone mass around the nail canal during drilling,and the sharp tip of the drill may lead to the destruction of the cortical bone of the pedicle wall or the anterior edge of the vertebral body,which has been rarely used at present.Tapping has the advantages of being simple and easy to use,labor-saving,and quickly forming screw channels,but it still cannot change the shortcomings of destroying cancellous bone.Clinicians sometimes use straight clamps to enlarge the nail canal,which can push the cancellous bone around the pedicle around and increase the local bone density of the nail canal.However,because the straight clamp is not a centrally symmetrical instrument,it may cause uneven stress in all directions of the nail channel and affect the stability of the pedicle screw.Therefore,we designed a novel pedicle screw path expansion device.ObjectiveIn order to explore its fixation strength in the vertebral body and its clinical application effect,this paper preliminatively explored the biomechanical stability and safety and reliability of the new pedicle screw track expander(PSTE)by comparing the extraction force of the implanted screw after the PSTE and the thread tap expansion,as well as the efficacy of the two devices in clinical application.Materials and methodsA new type of pedicle screw channel expander was designed by Professor Gong Mingzhi from the Second Hospital of Shandong University.The total length of the instrument is 220mm;The handle is square or cylindrical,with a length of 90mm;The drill length is 130mm,in which the tail end is 90mm cylindrical and the head end is 40mm approximately conical.The drill diameter at 40mm from the tip is 5.5mm,the drill diameter at 10mm from the tip is 2.5mm,and the tip is a hemispherical blunt head with a diameter of 2mm;The drill bit has a scale,which can directly observe the depth of the instrument.Because it is impossible to pull out screws in human body,we use isolated pig bones in this experiment.The spinal samples of two domestic pigs were randomly divided into two groups with 8 spines in each group.Group A was treated with decalcification,and group B was not treated.Different instruments were used to enlarge the pedicle canal on both sides of the spine of the two groups,the experimental group used the pedicle screw to screw the canal expander,and the control group used the thread tap.Then,all specimens were fixed under a high and low temperature universal testing machine,and the screw was pulled out of the vertebra at a constant speed.The maximum pulling force was measured and the load-displacement curve was drawn,so as to calculate the stiffness and pulling out energy.The clinical trial was a retrospective study.A total of 76 cases of spinal diseases admitted to the Second Hospital of Shandong University from January 2022 to December 2022 were included,and divided into experimental group and control group according to the way of nailway enlargement.In the experimental group,41 patients were treated with pedicle screw canal expander.In control group,35 patients were treated with thread tapping.Data on age,sex,clinical diagnosis,number of screws inserted,screw placement efficacy(good,poor),and incidence of medium-and long-term complications(screw loosening,screw ejection,etc.)were collected and compared between the two groups.ResultsIn the biomechanical experiment,the bone mineral density of group an after decalcification was 68.8%of that before decalcification,indicating that the spinal osteoporosis model had been successfully established.In group A,the maximum pullout force of the experimental group was 18.1%higher than that of the control group,and the difference was statistically significant;the stiffness increased by 19.4%,and the difference was statistically significant;there was no significant difference in pullout energy between the two groups.There was no statistical significance in the maximum pullout force,stiffness and pullout energy between the experimental group and the control group in group B.In clinical research,there was no statistical difference in the effect of screw implantation between the two groups.In terms of the incidence of mid-and long-term complications(screw loosening and prolapse),the screw loosening rate in the experimental group decreased by 52.1%compared with the control group.Although the difference between the two groups was not statistically significant(P=0.238),it still reflected the role of the new pedicle screw channel expander in reducing the screw loosening rate to some extent.This situation may be caused by the small sample size.There were no intraoperative and postoperative complications in both groups.In clinical application,the PSTE shows better convenience,higher safety and accuracy than screw tapping and straight clamps.Conclusion1.Osteoporosis can significantly reduce the stability of pedicle screw fixation.2.For patients with osteoporosis,the PSTE can achieve better biomechanical stability than tapping.3.There is no significant difference in the accuracy of screw placement and the rate of screw loosening between the patients who use the new pedicle screw expander and PSTE,indicating that they can achieve similar stability.4.In clinical application,the PSTE shows better convenience,higher safety and accuracy than tap and straight clamp,and it is a safe and reliable instrument.