Insertion Torque Of Pedicle Screw In Patients With Various Syndrome Differentiations: A Clinical And Finite Element Study

ObjectiveThrough clinical observation and finite element research,the difference in pedicle screw insertional torque between patients with various syndrome differentiations was analyzed,to give the general range of pedicle screw insertional torque of patients with different bone masses,to investigate the relationship between pedicle screw insertional torque and bone density,bone metabolism index,pedicle size,etc.,to explore the influence of different bone density and different specifications of screws on the stability of pedicle screw internal fixation,and provide valuable information for the surgeon.Methods(1)A total of 32 patients undergoing posterior lumbar internal fixation in the Department of Spine Orthopedics,First Affiliated Hospital of Guangzhou University of Traditional Chinese Medicine(TCM)from October 2020 to March 2021 were retrospectively analyzed.All patients completed the operation successfully,and the screw position was good after review.Record the preoperative TCM syndrome types of all patients.(2)Collect the maximum insertional torque generated during the intraoperative nail placement of the patients.According to the preoperative TCM syndrome type,the patients were divided into 4 groups: liver and kidney deficiency type(GSKX),phlegm-dampness block(TSZZ),qi stagnation and blood stasis type(QZXY),qi deficiency and blood stasis type(QXXY),and the torque value range of each group was compared.According to the bone mineral density T value,the patients were divided into 3 groups: group A,normal bone mass group,-1.0≤T value;group B,Osteopenia Group,-2.5<T value<-1.0;group C,osteoporosis group,T value ≤-2.5;compare the torque range of each group.(3)Collect the patient’s vertebral bone mineral density,lumbar average bone mineral density,femoral neck bone mineral density,hip bone mineral density,height,weight,BMI,fixed fusion segment,age,gender,bone metabolism markers,uric acid,Alkaline phosphatase,blood calcium,blood phosphorus,blood magnesium,parathyroid hormone,hypersensitivity thyrotropin,total triiodothyronine,thyroxine,free triiodothyronine,free thyroxine,vertebral arch Root width,pedicle height,screw inclination angle,and single factor analysis were used to screen out statistically significant influencing factors,which were included in multiple linear regression for further analysis.(4)The L4 vertebrae model was established by 3D finite element software,the pedicle screw was scanned by the scanner,and a more simulated 3D screw model was constructed,and then the L4 pedicle screw internal fixation model was established.To study the magnitude of the reaction force generated when the pedicle screw is pulled out 1mm along the axis of the screw when fixing the vertebral body,and to evaluate the axial extraction strength of the pedicle screw.When the vertebral body is displaced 2mm in different directions relative to the screw,the magnitude of the reaction force generated is used to evaluate the internal fixation strength of the pedicle screw.Results(1)A total of 32 patients with posterior lumbar internal fixation,139 pedicle screws were enrolled.Group comparison according to the patient’s TCM syndrome type showed that there were statistically significant differences in torque values between TSZZ type(2.79±0.68 Nm)and QZXY type type(3.42±0.74 Nm),QXXY type(2.41±0.99 Nm)and GSKX type(1.20 ±0.46 Nm),TSZZ type and GSKX type,QZXY type and QXXY type,QZXY type and GSKX type(P=0.04、0.001、0.001、0.001、0.001).(2)Group comparison according to the bone mineral density T value of the vertebral body showed that the torque level of group A was(2.74±0.87)Nm,the torque level of group B was(1.67±0.75)Nm,the torque level of group C was(1.28±0.58)Nm,there were statistically significant differences in torque values between group B and group A and between group A and group C(F=23.686,P<0.001);group comparison according to the femoral neck bone mineral density T value showed that the torque level of group A was(3.10±0.88)Nm,the torque level of group B was(2.17±0.86)Nm,the torque level of group C was(1.48±0.87)Nm,there were statistically significant differences in torque values between group A and group B,group A and group C,group B and group C(F=33.303,P<0.001);group comparison according to the average bone mineral density T value of patients L1-4 lumbar vertebrae showed that the torque level of group A was(2.78±0.99)Nm,the torque level of group B was(1.98±0.86)Nm,the torque level of group C was(1.71±0.85)Nm,there were statistically significant differences in torque values between group A and group B,group A and group C(F=17.65,P<0.001);According to the group comparison of the patients’ hip bone mineral density T value,the group comparison showed that the torque level of group A was(2.55±0.97)Nm,the torque level of group B was(2.31±0.95)Nm,the torque level of group C was(1.14±0.58)Nm,there were statistically significant differences in torque values between group A and group C,group B and group C(F=16.855,P<0.001).(3)The analysis results of influencing factors showed that: in terms of screws,the results of single factor analysis showed that there was a significant positive correlation between the insertion torque of the pedicle screw,the width of the pedicle and the bone density of the vertebral body.However,When these two factors were included in the multiple linear regression for further analysis,only a significant positive correlation was found between the bone density of the vertebral body and the insertion torque of the pedicle screw,which indicates that compared to the width of the pedicle,the bone density of the vertebral body has a greater influence on the insertion torque of the pedicle screw;for the patient,the results of a single factor analysis show that age and various bone density parameters are closely related to the patient’s screw insertion torque.There is multiple collinearity,so the step-by-step method is used to incorporate multiple linear regression analysis.The results show that age and the bone mineral density of the L4 vertebral body are independent influencing factors of the screw placement torque.(4)The results of the axial pullout test of pedicle screws showed that the better the bone mass of the vertebral body,the larger the screw diameter and the longer the length,the higher the pullout strength.The results of the pedicle screw internal fixation strength test showed that with the continuous increase of the screw size,the damage load required for the left and right movement of the lumbar spine and the lateral turnover showed different degrees of increase,indicating that its stability was better.ConclusionsThe insertional torque of the pedicle screw was different in patients with different syndrome types.The torque value of Qi stagnation and blood stasis type was the highest,and the liver and kidney deficiency type was the lowest.The insertional torque of pedicle screws was different in patients with different degrees of osteoporosis.Bone density was highly related to the stability of pedicle screws.The maximum screw extraction force and internal fixation strength of the normal bone mass group were significantly higher than those of the osteoporosis group.The larger the diameter and the longer the length of the pedicle,the resistance to pullout The higher the output capacity,the better the stability.The bone mineral density of the vertebral body and age were independent factors affecting the insertional torque of the pedicle screw during lumbar internal fixation,and had important predictive value for evaluating the strength of lumbar pedicle screw fixation.