Research On Idiopathic Scoliosis Flexibility Affecting Factors And Finite Element Analysis Of Flexibility Evaluation Methods Biomechanics

[Backgrounds]Preoperative assessment of flexibility in Adolescent Idiopathic Scoliosis (AIS) isimportant for determining structural curves, selecting the segment length for fusion,defining the safe range of correction, determining the most appropriate surgicalprocedure, and estimating the results of correction. However, it is not clear whatfactors affect flexibility, and few studies have addressed this subject. Informationregarding the factors affecting flexibility would assist in advanced planning ofsurgical management and in counseling patients regarding outcomes. With theintroduction of a series of new internal fixation devices, especially the segmentalall-screw system, the correction rate (CR) has been improved, but some of theflexibility evaluation methods have been proven unable to predict surgical outcomesaccurately. The ability of all the method available changes greatly with the curvetype,thus affecting the stability and compliance of evaluation.[Objectives]The aim of this study was to determine which factors have significant andindependent effects on flexibility, and how their influence differs between adolescentand adult. The measurement of these values will aid in preoperative planning and maybe useful for providing helpful information to patients for making decisions regardingnon-operative and operative treatment options. The purpose of the second part of thisresearch was to analyze, in the condition of using precisely controlled bidirectionalorthopedic forces (push-traction film, PTF), whether this new method could minimizethe influence of radiographic technique or patient-related factors and help to showbetter curve flexibility. With the finite element simulation research, we want to makeit clear of the biomechanical changes in flexibility assessment process, and alsoto provide scientific and theoretical basis for the optimization of flexibility evaluationmethods.[Methods]1. Affecting factors of curve flexibility in skeletally immature and mature idiopathicscoliosis were analysed. The records of patients with idiopathic scoliosis whoreceived surgical treatment at our hospital were screened. The Risser sign was used toseparate the patients into a skeletally mature group (Risser grade=5) and skeletallyimmature group (Risser grade<5). Data recorded and compared were flexibility, bending angle, apical vertebral rotation, Cobb angle, curve location, prior use of bracetreatment, and number of vertebrae in the curve. Mann-Whitney U test, independenttwo-sample t test and chi-square test was used to compare the data of the two groups.Relationships between basic characteristics and flexibility were assessed usingSperman correlation coefficient and linear regression analysis.2. Precisely controlled bidirectional orthopedic forces were used to assess theflexibility in adolescent idiopathic scoliosis. The push-traction film was comparedwith supine bending (SB), suspension traction (ST) and fulcrum bending (FB) film.An electric PTF bed was designed and evaluated. Results of all the studied methodswere compared. Comparison between the Post-op angles and predicted angles wasperformed by Pearson correlation and linear regression analyses.3. Three-dimensional finite element model was used to study the scoliosis flexibilityevaluation method. Traction load was used to confirm the validation of themodel. Multiple loading conditions were set to simulate the commonly usedflexibility evaluation methods. The Cobb angle, apical vertebral shift, degree of apicalvertebral rotation, upper end vertebra tilt and lower end vertebra tilt were compared toexplore the best force load.[Results]1. The study cohort of the flexibility affecting factor analysis consisted of217patientswith Risser grade<5and131patients with Risser grade=5. There were no significantdifferences between the two groups in Cobb angle, gender, apical vertebral rotation,number of vertebrae in the curve and brace treatment. The patients in the Rissergrade=5group was older and had greater bending angle and more flexible. Thepatients in the Risser grade<5group had a higher proportion of thoracic curves. Thecorrelation analysis showed that, in the Risser grade<5group, apical vertebral rotation,Cobb angle, the number of vertebrae in the curve and thoracic curve location wasnegatively correlated with flexibility. In the Risser grade=5group, age, apicalvertebral rotation and Cobb angle were negatively correlated with flexibility. Theresults of the multiple linear regression analysis showed that in the Risser grade<5group, Cobb angle and curve location significantly affected flexibility. When curvelocation was controlled, mean flexibility decreased by a factor of0.837%for eachadditional Cobb angle degree. When Cobb angle was controlled, thoracic scoliosisshowed on average9.623%less flexibility than thoracolumbar/lumbar scoliosis. In theRisser grade=5group, Cobb angle and age significantly affected flexibility. When age was controlled, mean flexibility decreased by a factor of0.498for each additionalCobb angle degree. When Cobb angle was controlled, the mean flexibility decreasedby a factor of0.731%for each additional year of age. Apical vertebral rotation,number of vertebrae in the curve, gender and brace treatment did not statisticallysignificantly affect flexibility in either group.2. Thirty-four consecutive patients were included in the present study for PTF. In MTgroup, Cobb angle in PTF was not significantly different with SB, but significantlysmaller than ST and bigger than FB. In TL/L group, PTF was significantly smallerthan ST, but not significantly different from SB and FB. There was no significantdifference between the results of PTF and Post-op both in MT and TL/L groups. Theresults of correlation and linear regression analyses showed that in terms of MTcurves, angles shown in all methods were linearly correlated with the postoperativeangle, where the PTF had the highest correlation coefficient. In terms of TL/L curves,PTF and ST were correlated with the postoperative angle, but FB and SB were notsignificantly correlated with postoperative angle.3. The results from the traction X-rays and the finite element simulation werecompared. The X-axis coordinate value (Wilcoxon test) and the Z-axis coordinatevalues (paired t test) were not significantly different. The curve from vertebral bodycenter showed good agreement with the finite element simulation. Data came fromvariety loading mode was analyzed with Sperman related analysis. The main thoracicCobb angle, the upper thoracic Cobb angle, the apicalvertebra (T8) deviation from the sacral midline, the upper endvertebra (T5) tilt angle and the lower end vertebra (T11) tilt angle showed a negativecorrelation with the pushing pressure. The apical vertebra (T8) rotation showeda positive correlation with the pushing pressure. T3rotation wasnot significantly related with the pushing pressure. There was no significant linearrelationship between the traction force and above all measurement values. The modelwith full body weight push and without traction load showed the best correction formain thoracic curve, followed by the model with1/2body weight loading in bothtraction and push.[Conclusions]In summary, this research demonstrated that Cobb angle and curve location havesignificant influences on main curve flexibility in skeletally immature idiopathicscoliosis. We also confirmed the significant influence of Cobb angle and age on curve flexibility in skeletally mature idiopathic scoliosis. The measurement of these valueswill aid in preoperative planning and may be useful for providing helpful informationto patients for making decisions regarding non-operative and operative treatmentoptions. The second section of this research was the first study reporting the use ofbidirectional orhtopedic forces in curve flexibility evaluation. The method using aPTF force about half of the body weight showed a accurate prediction of thepost-operation angle both in MT and TL/L curves. Correlation and linear regressionanalyses also confirmed that the method was a stable and accurate method. In thisstudy, a virtual platform was build for flexibility evaluation research and the finitemodel was confirmed effective. Different traction and push pressure loading modelswere studied and we found that the model with full body weight push and withouttraction load showed the best correction for main thoracic curve, followed by themodel with1/2body weight loading in both traction and push. Results of this researchprovided scientific and theoretical basis for the optimization of flexibility evaluationmethods.