Biomechanical effects of posterior lumbar interbody fusion with vertical placement of pedicle screws compared to traditional placement

BACKGROUND The pedicle screw technique is widely employed for vertebral body fixation in the treatment of spinal disorders.However,traditional screw placement methods require the dissection of paraspinal muscles and the insertion of pedicle screws at specific transverse section angles(TSA).Larger TSA angles require more force to pull the muscle tissue,which can increase the risk of surgical trauma and ischemic injury to the lumbar muscles.AIM To study the feasibility of zero-degree TSA vertical pedicle screw technique in the lumbosacral segment.METHODS Finite element models of vertebral bodies and pedicle screw-rod systems were established for the L4-S1 spinal segments.A standard axial load of 500 N and a rotational torque of 10 N/m were applied.Simulated screw pull-out experiment was conducted to observe pedicle screw resistance to pull-out,maximum stress,load-displacement ratio,maximum stress in vertebral bodies,load-displacement ratio in vertebral bodies,and the stress distribution in pedicle screws and vertebral bodies.Differences between the 0-degree and 17-degree TSA were compared.RESULTS At 0-degree TSA,the screw pull-out force decreased by 11.35%compared to that at 17-degree TSA(P<0.05).At 0-degree and 17-degree TSA,the stress range in the screw-rod system was 335.1-657.5 MPa and 242.8-648.5 MPa,separately,which were below the fracture threshold for the screw-rod system(924 MPa).At 0-degree and 17-degree TSA,the stress range in the vertebral bodies was 68.45-78.91 MPa and 39.08-72.73 MPa,separately,which were below the typical bone yield stress range for vertebral bodies(110-125 MPa).At 0-degree TSA,the load-displacement ratio for the vertebral bodies and pedicle screws was slightly lower compared to that at 17-degree TSA,indicating slightly lower stability(P<0.05).CONCLUSION The safety and stability of 0-degree TSA are slightly lower,but the risks of screw-rod system fracture,vertebral body fracture,and rupture are within acceptable limits.

Position and complications of pedicle screw insertion with or without image-navigation techniques in the thoracolumbar spine:a meta-analysis of comparative studies

Computer-navigated pedicle screw insertion is applied to the thoracic and lumbar spine to attain high insertion accuracy and a low rate of screw-related complications.However,some in vivo and in vitro studies have shown that no advantages are gained with the use of navigation techniques compared to conventional techniques.Additionally,inconsistent conclusions have been drawn in various studies due to different population characteristics and methods used to assess the accuracy of screw placement.Moreover,it is not clear whether pedicle screw insertion with navigation techniques decreases the incidence of screw-related complications.Therefore,this study was sought to perform a meta-analysis of all available prospective evidence regarding pedicle screw insertion with or without navigation techniques in human thoracic and lumbar spine.We considered in vivo comparative studies that assessed the results of pedicle screw placement with or without navigation techniques.PubMed,Ovid MEDLINE and EMBASE databases were searched.Three published randomized controlled trials（RCTs） and nine retrospective comparative studies met the inclusion criteria.These studies included a total of 732 patients in whom 4,953 screws were inserted.In conclusion,accuracy of the position of grade I,II,III and IV screws and complication rate related to pedicle screw placement were significantly increased when navigation techniques were used in comparison to conventional techniques.Future research in this area should include RCTs with well-planned methodology to limit bias and report on validated,patient-based outcome measures.

Treatment of Thoracolumbar Vertebrate Fracture by Transpedicular Morselized Bone Grafting in Vertebrae for Spinal Fusion and Pedicle Screw Fixation

To enhance the fusion of graft bone in thoracolumbar vertebrae and minimize the postoperative loss of correction, short-segment pedicle screw fixation was reinforced with posterior moselizee bone grafting in vertebrae for spinal fusion in patients with thoracrolumbar vertebrate fractures. Seventy patients with thoracrolumbar vertebrate fractures were treated by short-segment pedicle screw fixation and were randomly divided into two groups. Fractures in group A （n=20） were rein-forced with posterior morselized bone grafting in vertebrae for spinal fusion, while patients group B （n=50） did not receive the morselized bone grafting for bone fusion. The two groups were compared in terms of kyphotic deformity, anterior vertebral height, instrument failure and neurological functions after the treatment. Frankel grading system was used for the evaluation of neurological evaluation and Denis scoring scale was employed for pain assessment. The results showed that the kyphosis correction was achieved in both group A and group B （group A： 6.4 degree; group B： 5.4 degree）/At the end of follow-up, kyphosis correction was maintained in group A but lost in group B （P=0.0001）. Postoperatively, greater anterior height was achieved in group A than in group B （P〈0.01）. During follow-up study, anterior vertebral height was maintained only in Group A （P〈0.001）. Both group A and group B showed good Denis pain scores （P1 and P2） but group A outdid group B in terms of control of severe and constant pain （P4 and P5）. By Frankel criteria, the changes in neurological functions in group A was better than those of group B （P〈0.001）. It is concluded that reinforcement of short-segment pedicle fixation with morselized bone grafting for the treatment of patients with thoracolumbar vertebrae fracture could achieve and maintain kyphosis correction, and it may also increase and maintain anterior vertebral height. Morselized bone grafting in vertebrae offers immediate spinal stability in patients with thoracolumbar vertebrate fractures, decreases the instrument failure and provides better postoperative pain control than without the morselized bone grafting.

A new free-hand pedicle screw placement technique with reference to the supraspinal ligament

We sought to compare the safety and accuracy of a new free-hand pedicle screw placement technique to that of the conventional technique. One hundred fifty-three consecutive adult patients with simple fracture in the tho- racic or/and lumbar spine were alternately assigned to either the new free-hand or the conventional group. In the new free-hand technique group, preoperative computerized tomography （CT） images were used to calculate the targeted medial-lateral angle of each pedicle trajectory and the pedicle screw was inserted perpendicular to the corresponding supraspinal ligament. In the conventional technique group, the medial-lateral and cranial-caudal angle of each pedicle trajectory was determined by intraoperatively under fluoroscopic guidance. The accuracy rate of pedicle screw placement, the time of intraoperative fluoroscopy, the operating time and the amount of blood loss during operation were respectively compared. All screws were analyzed by using intraoperative ra- diographs, intraoperative triggered electromyography （EMG） monitoring data, postoperative CT data and clinical outcomes. The accuracy rate of pedicle screw placement in the new free-hand technique group and the conven- tional technique group was 96.3% and 94.2% （P 〈 0.05）, respectively. The intraoperative fluoroscopy time of the new technique group was less than that of the conventional technique group （5.37 seconds vs. 8.79 seconds, P 〈 0.05）. However, there was no statistical difference in the operating time and the amount of blood loss during op- eration （P 〉 0.05）. Pedicle screw placement with the free-hand technique which keeps the screw perpendicular to the supraspinal ligament is an accurate, reliable and safe technique to treat simple fracture in the thoracic or lum- bar spine.

Techniques and accuracy of thoracolumbar pedicle screw placement

Pedicle screw instrumentation has been used to stabilize the thoracolumbar spine for several decades. Although pedicle screws were originally placed via a freehand technique, there has been a movement in favor of pedicle screw placement with the aid of imaging. Such assistive techniques include fluoroscopy guidance and stereotactic navigation. Imaging has the benefit of increased visualization of a pedicle's trajectory, but can result in increased morbidity associated with radiation exposure, increased time expenditure, and possible workflow interruption. Many institutions have reported high accuracies with each of these three core techniques. However, due to differing definitions of accuracy and varying radiographic analyses, it is extremely difficult to compare studies side-by-side to determine which techniques are superior. From the literature, it can be concluded that pedicles of vertebrae within the mid-thoracic spine and vertebrae that have altered morphology due to scoliosis or other deformities are the most difficult to cannulate. Thus, spine surgeons would benefit the most from using assistive technologies in these circumstances. All other pedicles in thethoracolumbar spine should theoretically be cannulated with ease via a free-hand technique, given appropriate training and experience. Despite these global recommendations, appropriate techniques must be chosen at the surgeon's discretion. Such determinations should be based on the surgeon's experience and the specific pathology that will be treated.

Posterior Selective Thoracic Fusion in Adolescent Idiopathic Scoliosis Patients:a Comparison of All Pedicle Screws versus Hybrid Instrumentation

Objective To analyze the influence of segmental pedicle screws versus hybrid instrumentation on the correction results in adolescent idiopathic scoliosis patients undergoing posterior selective thoracic fusion. Methods By reviewing the medical records and roentgenograms of adolescent idiopathic scoliosis patients who underwent selective thoracic fusion from February 2000 to January 2007 in our hospital, the patients were divided into 2 groups according to different instrumentation fashions： Group A was hook-screw-rod （hybrid） internal fixation type, Group B was screw-rod （all pedicle screws） internal fixation type, and the screws were used in every segment on the concave side of the thoracic curve. The parameters of the scoliosis were measured and the correction results were analyzed. Results Totally, 48 patients （7 males, 41 females） were included, with an average age of 14.4 years old and a mean follow-up time of 12.3 months. Thirty and 18 patients were assigned to group A and group B, respectively. The mean preoperative coronal Cobb angles of the thoracic curve were 48.8° and 47.4°, respectively. After surgery, they were corrected to 13.7° and 6.8°, respectively. At final follow-up, they were 17.0° and 9.5°, with an average correction rate of 64.6% and 79.0%, respectively, and the correction rate of group B was significantly higher than that of group A （P=0.003）. The mean preoperative coronal Cobb angles of the lumbar curve were 32.6° and 35.2°, respectively. After surgery, they were corrected to 8.6° and 8.3°, respectively. At final follow-up, they were 10.3° and 11.1°, with an average correction rate of 66.8% and 69.9%, respectively, and the correction rate of group B was significantly higher than that of group A （P=0.003）. The correction loss of the thoracic curve and lumbar curve in the 2 groups were 3.1° and 1.8°, 2.4° and 2.4°, respectively. No significant difference was noted （both P〉0.05）. The decompensation rate at final follow-up in these 2 groups were 4% （1/25） and 7.1% （1/14） respectively, with no significant difference （P〉0.05）.

Pedicle Screw Fixation with Kyphoplasty Decreases the Fracture Risk of the Treated and Adjacent Non-treated Vertebral Bodies:a Finite Element Analysis

Adjacent vertebral fractures are common in patients with osteoporotic vertebral compression fractures（OVCFs） after kyphoplasty.This finite element study was to examine whether short segment pedicle screw fixation（PSF） with kyphoplasty may decrease the fracture risk of the treated and adjacent non-treated vertebrae after kyphoplasty for OVCFs.By simulating cement augmentation with or without short segment pedicle screw fixation（PSF）,two tridimensional,anatomically detailed finite element models of the T10–L2 functional spinal junction were developed.The insertion of pedicle screws into the intact vertebra apparently decreased the stress distribution of the treated vertebra in vertical compression and other load situations.The stress distribution in the bone structures of the intact vertebra adjacent to the intact-screwed vertebra was much less than that in the one adjacent to the treated vertebra.The insertion of pedicle screws into the intact vertebra greatly decreased the maximum displacement of the cortical bones and cancellous bones of the vertebrae.Our results indicated that short segment PSF with kyphoplasty may decrease the fracture risk of the treated and adjacent non-treated vertebrae in the management of OVCFs.

Comparison of Clinical Outcomes of Cortical Bone Trajectory and Traditional Pedicle Screw Fixation in Posterior Lumbar Interbody Fusion

Posterior lumbar interbody fusion (PLIF) is a common surgical procedure and widely used in the treatment of lumbar degenerative disc disorders. Traditionally, posterior lumbar interbody fusion is done by using the traditional pedicle screw (PS) which offers great advantages, but at the same time it has some disadvantages which include the risk of superior facet joint violation and muscle damage. Recently, an alternative method of screw insertion via cortical bone trajectory (CBT) has been invented which has less invasive process and can be placed without the drawbacks associated with the traditional pedicle screw. However, it has to remain an interest whether CBT will provide similar or greater clinical outcomes compared to PS in PLIF. So the main aim of this review is to compare the clinical outcomes of cortical bone trajectory and traditional pedicle screw fixation in posterior lumbar interbody fusion based on the articles published on this topic. Compared to the traditional pedicle screw fixation, PLIF with CBT has similar clinical outcome based on pain intensity, ODI status and JOA score, as well as similar fusion rate and radiological evaluated complication such as loosening of screw. In addition PLIF with CBT has advantages of less facet joint violation, less blood loss, less intraoperative muscle damage and perioperative pain. On the basis of this study, we can suggest that PLIF with CBT can be considered as a reasonable alternative to PS in PLIF.

Successful outcomes of unilateral vs bilateral pedicle screw fixation for lumbar interbody fusion:A meta-analysis with evidence grading

BACKGROUND Whether it’s better to adopt unilateral pedicle screw(UPS)fixation or to use bilateral pedicle screw(BPS)one for lumbar degenerative diseases is still controversially undetermined.AIM To make a comparison between UPS and BPS fixation as to how they work efficaciously and safely in patients suffering from lumbar degenerative diseases.METHODS We have searched a lot in the databases through 2020 with index terms such as“unilateral pedicle screw fixation”and“bilateral pedicle screw fixation.”Only randomized controlled trials and some prospective cohort studies could be found,yielding 15 studies.The intervention was unilateral pedicle screw fixation;Primarily We’ve got outcomes of complications and fusion rates.Secondarily,we’ve achieved outcomes regarding total blood loss,operative time,as well as length of stay.Softwares were installed and utilized for subgroup analysis,analyzing forest plots,sensitivity,heterogeneity,forest plots,publication bias,and risk of bias.RESULTS Fifteen previous cases of study including 992 participants have been involved in our meta-analysis.UPS had slightly lower effects on fusion rate[relative risk(RR)=0.949,95%CI:0.910 to 0.990,P=0.015],which contributed mostly to this metaanalysis,and similar complication rates(RR=1.140,95%CI:0.792 to 1.640,P=0.481),Δvisual analog scale[standard mean difference(SMD)=0.178,95%CI:-0.021 to 0.378,P=0.080],andΔOswestry disability index(SMD=-0.254,95%CI:-0.820 to 0.329,P=0.402).In contrast,an obvious difference has been observed inΔJapanese Orthopedic Association(JOA)score(SMD=0.305,95%CI:0.046 to 0.563,P=0.021),total blood loss(SMD=-1.586,95%CI:-2.182 to-0.990,P=0.000),operation time(SMD=-2.831,95%CI:-3.753 to-1.909,P=0.000),and length of hospital stay(SMD=-0.614,95%CI:-1.050 to-0.179,P=0.006).CONCLUSION Bilateral fixation is more effective than unilateral fixation regarding fusion rate after lumbar interbody fusion.However,JOA,operation time,total blood loss,as well as length of stay were improved for unilateral fixation.

Investigation of optical reflectance from different animal vertebra along the fixation trajectory of pedicle screw in frequency domain

Accurate placement of pedicle screw(PS)is crucial in spinal surgery.Developing new real-time intra-operative monitoring and navigation methods is an important direction of clinical appli-cation research.In this paper,we studied the spectrum along the fixation trajectory of PS in frequency domain to tackle the accuracy problem.Fresh porcine vertebrae,bovine vertebrae and ovine vertebrae were measured with the near-infrared spectrum(NIR)device to obtain the reflected spectrum from the vertebrae.Along the fixation trajectory of PS,average energy from different groups was calculated and used for identifying different tissues and compared to achieve the optimal recognition factor.Compared with the time domain approach,the frequency domain method could divide the spectra measured at different tissue points into different groups more stably and accurately,which could serve as a new method to assist the PS insertion.The results gained from this study are significant to the development of hi-tech medical instruments with independent intellectual property rights.

Treatment of Anderson Type II Odontoid Fracture in Elderly Patients by Posterior Pedicle Screw Fixation Combined with Iliac Bone Grafting

Objectives: To explore the treatment and related prognosis of elderly patients with Anderson II odontoid fracture with posterior pedicle screw fixation combined with iliac bone grafting. Methods: Retrospective analysis of 17 cases of elderly patients with Anderson II odontoid fracture who underwent posterior pedicle screw fixation combined with iliac bone grafting from January 2013 to December 2016. 17 patients had a history of trauma before surgery, and they all have varying degrees of atlantoaxial instability or subluxation and varying degrees of neck occipital pain and limited mobility. Result: No spinal cord or vertebral artery injury occurred during surgery. Follow-up information is complete. The follow-up period was 6 to 48 months (mean 27.4 ± 12.4 months). Postoperative imaging review prompted a good reduction of cervical spine, stable sequence;no pedicle screw loosening, fracture, iliac bone graft at the location of the situation, odontoid fracture and bone healing at the good, the patient after cervical rotation are limited to varying degrees. Conclusion: Posterior pedicle screw fixation combined with iliac bone grafting in elderly patients with Anderson II odontoid fracture can achieve good stability, and the prognosis is good, but long-term cervical rotation function may be affected to varying degrees.

Potential contribution of pedicle screw design to loosening rate in patients with degenerative diseases of the lumbar spine:An observational study

BACKGROUND The majority of published data report the results of biomechanical tests of various design pedicle screw performance.The clinical relevance and relative contribution of screw design to instrumentation stability have been insufficiently studied.AIM To estimate the contribution of screw design to rate of pedicle screw loosening in patients with degenerative diseases of the lumbar spine.METHODS This study is a prospective evaluation of 175 patients with degenerative diseases and instability of the lumbar spine segments.Participants underwent spinal instrumentation employing pedicle screws with posterior only or transforaminal interbody fusion.Follow-up was for 18 mo.Patients with signs of pedicle screw loosening on computed tomography were registered;logistic regression analysis was used to identify the factors that influenced the rate of loosening.RESULTS Parameters included in the analysis were screw geometry,type of thread,external and internal screw diameter and helical pitch,bone density in Hounsfield units,number of levels fused,instrumentation without anterior support,laminectomy,and unilateral and bilateral total facet joint resection.The rate of screw loosening decreased with the increment in outer diameter,decrease in core diameter and helical pitch.The rate of screw loosening correlated positively with the number of fused levels and decreasing bone density.Bilateral facet joint removal significantly favored pedicle screw loosening.The influence of other factors was insignificant.CONCLUSION Screw parameters had a significant impact on the loosening rate along with bone quality characteristics,the number of levels fused and the extensiveness of decompression.The significance of the influence of screw parameters was comparable to those of patient-and surgery-related factors.Pedicle screw loosening was influenced by helical pitch,inner and outer diameter,but screw geometry and thread type were insignificant factors.

Learning curves of robot-assisted pedicle screw fixations based on the cumulative sum test

BACKGROUND In robot-assisted(RA)spine surgery,the relationship between the surgical outcome and the learning curve remains to be evaluated.AIM To analyze the learning curve of RA pedicle screw fixation(PSF)through fitting the operation time curve based on the cumulative summation method.METHODS RA PSFs that were initially completed by two surgeons at the Beijing Jishuitan Hospital from July 2016 to March 2019 were analyzed retrospectively.Based on the cumulative sum of the operation time,the learning curves of the two surgeons were drawn and fit to polynomial curves.The learning curve was divided into the early and late stages according to the shape of the fitted curve.The operation time and screw accuracy were compared between the stages.RESULTS The turning point of the learning curves from Surgeons A and B appeared in the 18th and 17th cases,respectively.The operation time[150(128,188)min vs 120(105,150)min,P=0.002]and the screw accuracy(87.50%vs 96.30%,P=0.026)of RA surgeries performed by Surgeon A were significantly improved after he completed 18 cases.In the case of Surgeon B,the operation time(177.35±28.18 min vs 150.00±34.64 min,P=0.024)was significantly reduced,and the screw accuracy(91.18%vs 96.15%,P=0.475)was slightly improved after the surgeon completed 17 RA surgeries.CONCLUSION After completing 17 to 18 cases of RA PSFs,surgeons can pass the learning phase of RA technology.The operation time is reduced afterward,and the screw accuracy shows a trend of improvement.

Evaluation of Percutaneous Pedicle Screw Fixation in Patients with Pyogenic Spondylitis of the Thoracolumbar Spine

Background: Basic principle for the treatment of pyogenic spondylitis (PS) is conservative care, but surgical intervention is often required when conservative treatment may fail. We have experienced many conservative cases of various complications due to long-term bed rest and poor pain control. Recently we have adopted percutaneous pedicle screw (PPS) fixation for the treatment of PS as a minimally invasive spine stabilization (MISt) fusion to reduce such morbidity of the conservative care. Objective: To evaluate the impact of PPS fixation in patients with PS. Study Design: A retrospective analysis of the medical records. Subjects, Methods: We reviewed 54 consecutive patients who underwent treatment in our hospital for PS during 2005-2018 and observed for more than 12 months. Of those we excluded cases showing effectiveness to initial treatment (it was defined fever relief or C-reactive protein (CRP) inversion in 3 weeks of antibiotics) so that this study is a retrospective study in cases showing initial treatment resistance. Finally, this study included 29 cases. Medical records of these 29 cases were reviewed for baseline, organism isolated and its detection rate, the clinical outcome in 12 months (Discharge, Transfer, Death), the period from the first visit to our hospital to fever relief, CRP inversion, ambulation, and Discharge or Transfer. Results: These cases were divided into two groups, the conservative group (C-group): 17 cases, and the PPS group (P-group): 12 cases. There is no statistically significant difference in fever relief (p = 0.051) and CRP inversion (p = 0.208). The period to ambulation and discharge or transfer was significantly shorter in group P (p = 0.020, p = 0.031). 1-Year survival rate was 92% in the P-group, and 71% in the C-group. There is no statistically significant difference (p = 0.354) between the two groups. The rate of Discharge to home and care facility is 58% in P-group, and 47% in C-group. And the rate of Transfer is 34% in P-group, and 35% in C-group. Conclusion: PPS fixation was effective to achieve shortening the period to ambulation and discharge or transfer. But it was not effective in infection control. This suggests that PPS fixation should be aggressively administered to patients who can expect pain relief and early ambulation by PPS fixation in the patient of PS showing resistance to initial treatment.

Comparison of the Pull-out Strength Between a Novel Micro-dynamic Pedicle Screw and a Traditional Pedicle Screw by Using Pull Out Test and Micro-CT

Objective To investigate the effectiveness of the micro-dynamic pedicle screw for the prevention of loosening between the screw and bone surface in lumbar spinal fusion.For this evaluation,the peek pull-out force(PPF)after fatigue resistance testing at different cycles and semidiameter of screw insertion area of micro-CT image was compared between the micro-dynamic and traditional pedicle screws.Methods Forty lumbar vertebrae received a traditional pedicle screw on one side and a micro-dynamic pedicle screw on the other side as follows:15 vertebrae underwent instant pull-out testing(group A,traditional vs.group B,micro-dynamic);15 vertebrae underwent pull-out test after 5000-cyclic fatigue loading(group C,traditional vs.group D,micro-dynamic);and 10 vertebrae underwent pull-out test after 10000-cyclic fatigue loading(group E,traditional vs.group F,micro-dynamic).All vertebrae that after fatigue loading were scanned by using micro-ct to check the semidiameter of screw insertion area.The PPF,normalized PPF(PPFn),bone mineral density(BMD)and diameter of screw insertion area were compared between all groups.Results The BMD showed a weak significant correlation with PPF(r=0.252,P=0.024).The PPF in groups A and B(P=0.485),and groups C and D(P=0.184)did not show significant difference.However,the PPF in group F was significantly greater than that measured in group E(P=0.005).The PPFn of groups A,C,and E significantly decreased as the number of cycles increased(P=0.015).Meanwhile,the PPFn of groups B,D,and F remained consistent regardless of the number of cycles(P=0.367). The semidiameter of traditional pedicle screw insertion area was significantly larger than that of micro-dynamic pedicle screw insertion area(P<0.001).Conclusions This study compared the performance of a micro-dynamic pedicle screw versus that of a traditional pedicle screw using pull-out testing and micro-CT.The results showed that the micro-dynamic pedicle screw provides similar resistance in lowcycle fatigue testing and favorable resistance in high-cycle fatigue testing versus the traditional pedicle screw.The micro-dynamic pedicle screw provides stronger fixation stability versus the traditional pedicle screw,especially in high-cyclic fatigue loading condition versus the traditional pedicle screws.

Elective thoracotomy for pedicle screw removal to prevent severe aortic bleeding

We present a case of a 33-year-old female who sustained multiple injuries of her spine, including spinous process fractures of C5 to C7 and a lamina fracture of C6 and C7. Her thoracic spine showed transverse process fractures of T4 to T10, a compression fracture and lamina fracture of T3, spinous process and transverse process fractures of T4 and T5, a rotation injury of T6, as well as a compression fracture of L1. Thirteen months after posterior thoracic spinal instrumentation, a pedicle screw was suspected to be in contact with the aorta, which was proved by computed tomography angiograms. Consequently, implant removal was planned with direct exposure of the aorta in order to allow for immediate repair if needed. So far, studies that compare different techniques to remove pedicle screws that are suspected to penetrate the aorta are missing. However, different techniques have been described in case reports, mainly minimally invasive endovascular techniques vs open techniques such as thoracotomy.

Threatened Aortic Injury by Thoracic Pedicle Screw: A Case Report

Iatrogenic vascular injury during posterior spinal surgery is a rare but potentially serious complication with treatment challenges. We report the case of threatened aortic injury by pedicle screw impingement during posterior fixation of thoracic spine T7 - T8 fracture dislocation. The removal of the conflicting screws was done posteriorly after a visual control of the absence of adventitious break-in by a thoracotomy.

Intracardiac,pulmonary cement embolism in a 67-year-old female after cement-augmented pedicle screw instrumentation:A case report and review of literature

BACKGROUND We report a case of Intracardiac,pulmonary,and intravenous cement embolism after cement-augmented pedicle screw instrumentation in treating spondylolisthesis underlying osteoporotic bone,which was successfully managed by conservative treatment.We describe the treatment and outcome of the patient,hoping to shed light on the management of bone cement embolism.CASE SUMMARY A 67-year-old female suffered from progressive low back pain and numbness in lower extremities for 30 years.She was diagnosed with L4 and L5 spondylolisthesis,spinal stenosis,and osteoporosis.The patient underwent spinal canal decompression,an interbody fusion of L4/5 and L5/S1,cement-augmented pedicle screw instrumentation in L4-L5 segments,and regular pedicle screw in S1 segments.Three days postoperatively,a sudden drop in oxygen saturation occurred.Computerized tomography scan confirmed Intracardiac,pulmonary,and intravenous embolism.The patient was treated conservatively by continuous low-flow oxygen inhalation,anti-coagulation,and antibiotic therapy for 1 mo and continued anticoagulation treatment for 6 mo.The patient showed no further symptoms in a 30-mo follow-up.CONCLUSION Intracardiac,pulmonary cement embolism after cement-augmented pedicle screw instrumentation is extremely rare.Careful clinical and radiographic evaluation is required in multiple sites of bone cement embolism.Conservative treatment may be a primary consideration in scattered emboli without life-threatening conditions,but a clinical decision should be made on an individualized basis.

Fatigue Life Analysis of Fixed Structure of Posterior Thoracolumbar Pedicle Screw

In order to analyze the fatigue life of the posterior thoracolumbar fixed structure, a loading model was established in accordance with the anti-fatigue test requirements specified by ASTM Standard F1717-04. Two three-dimensional Models of the fixed structure with two bars and four bars were built by 3D software (UG), and imported into ANSYS software for static analysis. The maximum and minimum stresses of risk nodes under different loads and moments were obtained. The fatigue life was then calculated using relevant mathematical formula of S-N curve and Goodman curve. It was found that the stress at the middle of the crossbeam between the two bars is larger than the surroundings and is liable to suffer from fatigue.

Accuracy of pedicle screw placement in Lenke 1 adolescent idiopathic scoliosis surgery using intraoperative navigation with a simple calibration technique

Objective:To compare the position and the grade of screw perforation in Lenke 1 adolescent idiopathic scoliosis(AIS)surgery using intraoperative navigation system with and without calibration technique,and to explore the related factors of navigation deviation and the clinical significance of calibration technique.Methods:From 2014 to 2017,a total of 45 Lenke 1 AIS surgical cases were enrolled in this study.The 23 surgical cases were assisted with intraoperative navigation system(Navigation group)and another 22 cases received surgery using intraoperative navigation system with calibration technique(Calibration group).In two groups,the basic information and radiological data were all recorded.Postoperative CT scan with 3D reconstruction was used to analyze the accuracy of pedicle screw placement,as well as the length and position of cortical perforation.Results:There was no statistical difference between two groups in gender,age,Risser sign,both preoperative Cobb angles and flexibility of the major curve,as well as numbers of pedicle screws.477 and 469 pedicle screws were implanted in the navigation group and the calibration group respectively.The rate for major pedicle perforations 2 mm(grades 2,3)was 7.8%in navigation group.It was statistically significant difference from the 4.3%screw misplacement in calibration group(P=0.014).In navigation group,the rates of major pedicle perforations 2 mm were medial:3.4%,lateral:3.6%and anterior:0.6%respectively.The corresponding rates were 1.1%,2.6%and 0.4%in calibration group respectively.The rates of the medial cortical perforation 2 mm showed statistical difference between two groups(P=0.016).No serious complications,such as nerve or vascular injury,were found in all patients.Conclusion:Intraoperative navigation system with calibration technique provides the real-time monitoring of navigation deviation,the higher accuracy of pedicle screw insertion,the lower medial cortical perforation rate and the less complication rate,as well as a simple calibration technique with higher accuracy of screw placement in comparison to intraoperative navigation system for Lenke 1AIS surgery.