| Surgical fixation is used to treat patients with certain lumbar spinal conditions such as fractures, degenerative spondylolisthesis, tumors, degenerative scoliosis, and sever disc disease. Several devices have been used for this purpose. The pedicle screw fixation device had been applied to clinic in 1960s. Because of its hard fixtation , little operational trauma and easy operational way ,the method has been used widely now; now, the method has be looked as the standard way to treat low back spine disorders; at the same time ,more and more people suffered for some disapprociate operation treatment; some of them have to accept another operation to dissolve the pain; and some medical dispute had resulted from them; and now how and what should we do to solve the question has become an important topic.The most important factors which affect the revision operations are the breakage of the pedicle screw, lossening of pedicle fixation, dislocation of lumbar internal device (7 cases) and lumbar adjacent instability after fixation, and so on. Among them, the breakage of the pedicle screw could often result in medical tackle. It's reported by Yahiro that 7.1% of all patients had broken pedicle screws, and Yuan et al reported that the internal fixation system failure could be seen in 6.7% bone-fracture patients, and such phenomena could also be seen in about 2.6%retrogression disease patients ; in our 592 patients ,the data is about 4.9%.AF and RF fixation system failure is 49 patients ,which is 56.92% of all revision operations, so it is necessary to know the stress distribute characteristic of the 2 fixation system. The finite element method is an ideal tool to study the stress distribution in all parts of the fixation device and hence design a better fixation device in the study. The models of AF and RF fixation system have been set up.We could check different stress distribute on them under different conditions,which is important for doctors and the apparatus designers.Chapter One Clinical Research of Revision of Pedicle ScrewsObjective1 .In order to increases the success rates of the operation and satisfactory clinical outcomes .factors which result in the breakage of short segment pedicle screw instrumentation after spinal internal fixation were taken into account.2. To discuss such factors's role on the reason of revision operation and their effect on the outcome of follow-up visit after revision operation .for example age,sex,operation way .profession and so on.3. To evaluate the therapeutic effect of revision operation and their follow-up visit outcome.4. To find out the ways to decrease complications of short segment pedicle screw after spinal internal fixation.Methods1. To find the situation of implant fixation fixation, all patients who need accept revision operation should be examined by X-ray examination, some of them should be examined by CT or MRI. go over their firstly operation reason and operation way .treatment post-operation. Analyses the reason of the revision ;decide the revision fashion; evaluate the outcome of revision operation and its follow-up visitoutcome.the outcome data would be evaluated by Prolo function and economical standard.2. Stastical analyses:the qualitation data would be described by percent;and the quantitation data would be described by mean±standard deviation;before been analysised;all should be tested by Kolmogorov-Smimov Z test;between different groups; consistent with mormal distribution datas would be tested by independence sample T test;other datas would be tested by Mann-Whitney test; Logistic regression way would be used to analyse the dangerous factor.all these test would be finished by SPSS 11.0 stastical soft.Rusultsl.the stastical analysis of population:among all revision operation cases;the data were analyzed .significant difference between age (F=6.205> P < 0.001) % occupation (F=14.28> P=0.048) ;but no significant difference between sex.2.Compared the first time operation with the revision operation cases; significant difference could be found between the operational time the flood in the operation;at the same time,the operation way were more difficult.The P value of them were 0.485, 0.42 and < 0.001 by turns.3.The cause to the revision operation cases;the brake of implanted fixation system,the loosen of crews,the stimulation to nerve roots and the formation of false articular joint occupy 93% of all cases.Among them,the technical cause occupy 76%,the other is non- technical causes.3.1 The technical cause to the revision operation: (Dthe uncorrectly indication of operation;especially is too loosen;more care should be payed to the old bone rarefaction and the post-operation of young lumbar disc protrusion(the average age of false articular joint formation and screws loosen were 52.5 years old and 50.91 years old ). ?The unsuitable operation way and implant fixation system. ?Thetechnical of operation, especially the location of screws; among the group; 22 cases of screws loosen and nerve's stimulation were caused by the unsuitable screws location ;the major cause is unfamiliar with anatomy structure, especially on fracture and Degeneration cases; incorrect use of spinal technique(the wrong angel and depth 10cases);and one revision operation was caused by the laceration of putamen and uncorrectly repaired. (4) Uncompletely depression of canalis spinalis,conclude the uncompletely depression of nerve roots;the uncompletely depression of disci intervertebrales;and unsatisfied replacement of bone fracture and slippage of vertebral body. ?The incorrectness way of bone graft;among the revision operation group,all cases accepted lateral vertebral plate bone graft;and the ratio of this bone graft confluence was very low. ?The incorrectional treatment post-operation loading too early;and the shorter protection of orthosis;and the fatigue failure(the average time is 18.85ms) or loosen (the average time is 19ms) of implant fixation system for later dislodgment.3.2 The untechnical causes of complication: (J)The quality of implanted fixation system,among the revision group;the stainless steel material account for 91.67%.? The insufficient design of implanted fixation system;the uneven stress distribution of implanted systems;the lower screws and the conjunction location between the screws and roles were the main stress centrostigma,and at the same time they were the major location where the breakage often happen(18 cases ,account 75% of all ).(3)The spinal vitodynamics character on the bio-radian location often result in so greater stress distribution on the implanted systems(Tnand Li segment 12 cases accounting for 50%, L5 and Si7 cases accounting for 29.17%). ?.The change of vitodynamics post-implanted fixation often result in the close together segment's retrogression;which would accelerate the formation of false articular joint,among the group ,such cases were 8 cases.4.The revision ratio of different systems is by turns : Dick 17.78% ,Opusl7.65%,Gssl4.29%,Steffel3.25%,AF9.15%,RF8.14%,Diapason5.56% ,CD4.88%.The cause of major revision systems are as follow:among 25 AF revision cases,the breakage's cases are 11 cases,accounting 44%;and among 24 RF revision cases and 19 steffe revision cases,the nerve roots'stimulation cases are 7 cases and 8 cases;accounting the different style cases 29.2% and 42.1%;but no significant can be found among Dick systems.5. The result of revision operations:the data of the first time operation ,the time before or late of revision operations and 6 months follow-up were analysied by analysis of variance .Significant difference can be found among different time group.Tthe result proves that revision operation has good result,but no significant difference could be found among different diagnosis;such result stands that no technical difference among different doctors.The nerve roots' stimulation among the single segment fixation systems are 14 cases ( 38.9% ) ;and such data of multi-segments fixation systems are 15case (32.0%) significant difference could be found between different segments( F=5. 465, P=0. 001) or different operational times (F=314.23, P<0.001) ,and single segment fixation has better result; the result of nerve roots' stimulation case has worse result than other 4 causes;but no significant difference could be found among other 4 kinds causes.The major way of revision operation in our hospital is the dislodgment of implanted fixation systems,accountiong 62.79% of all cases.The analysis of different revision ways stands depression of vertebral canal,loosen of nerve roots, the repair of hard mask and die shorten of screws' tail have better result, ignificant difference could be found among different revision ways(P<0.001). Conclusion1. The breakage of pedicle screw is an complex problem. Many reasons cancause this complication,including material ,device ,and type of the instrumentation , surgical operation and postoperative treatment.Proper preoperative planning, careful selection of the pedicle screw instrumentation,surgical procedures and suitable postoperative treatment are imperative to prevent this kind of breakage. X-rays should be carefully examined before operation,the indication of operation should be controlled cruelty, and it is essential for spinal surgeons to choose correct surgical approaches,spinal instrumentation techniques and proper post-op treatment in order to minimize this complication; synthetic way should by done to reduce the ratio of revision operations.2. The result of revision operation were relation with the first time operation's way, the fixation segments and the way of bone graft or the revision ways.Good result could be got through revision ways,in order to raise the life quality of patients,control the patients'stiuation,reduce the genesis of medical dispute; revision operationg should be acted as soon as possible ,when the man did need revision way.Chapter two The Setup Finite Element Model of AF and RF ImplantedFixation System and Biomechanics Analysis Objective1. Set up the AF and RF implanted fixation systems' finite element model to mater the stress distribution under loaded.2. Study the the different stress distribution of AF and RF implanted fixation systems under different angel; to find the best angel to reduce the breakage of AF and RF implanted fixation systems. And raise the ratio of operation success and offer thebiomechanics proof for clinical works.3. Study the feature of AF and RF implanted fixation systems' stress distribution ,to master the difference of single segment or multi-segments implanted fixation systems.Methodsl.In clinical works ,RF systems is one single segment fixation systems;and the AF systems were multi-segments fixation system; all material were made of stainless steel;the elastic modulus of them were 1.13X10uN/ m2and the Poisson's ratio were O.3;the adopted Gaussian points of AF's screw and conjunction role were 4362 and 1075;the calculation unit were 116510 and 3608;and ;the adopted Gaussian points of RF's screw and conjunction role were 3350 and 980;the calculation unit were 95630 and 2536;all the measure data were input into the computer ,with the help of Auto CAD and the support of Super-SAP finite element analysis system;the CAD model were translated into finite element model; the different finite element model under Y axes angel 0°,the X axes 0°,5o,10o,15°;and the X axes 0°,the Y axes angel 0°,7°,15° were setup.The normal body load 500N and the ante-drag load 500N were loaded;the stress distribution and straining were measured; measure the Von Misses stress on different points;all the screws were divided into 20 segments,and the conjunction roles were divided into 12 segments from front to fro.All the implanted systems were provided by chande medical apparatus factory.result:1. AF implanted fixation systems:the greatest stress point were the lower foreside conjunction point of screw and roles ,and its rearward stress was relatively lower. The stress loading on inferiority screw roots were higher than the upper sides; no significant difference could be found between the up or lower roots,or the rightand left sides;but the stress loading on right and left sides were higher than it on up or lower roots. With the increase of X axes angel,the stress on the conjunction point between screw and roles increases; with the increase of Y axes angel;the load on the inferiority screw and roles increases,but the stress on the upper screws decreases.2.The greatest stress point on RF implanted fixation systems were roots of screws;among all sides of screws;the upper side of upper screws and the inferiority side of inferiority screw bore the greatest stress;and the inferiority screw bore higher stress than the upper screws; the stress of the lower foreside conjunction point of screw and roles were higher than others sides; With the increase of X axes angel,the stress on the conjunction point between screw and roles increases; with the increase of Y axes angel;the load on the inferiority screw and roles increases,but the stress on the upper screws decreases.3. Compared with the stress distribution between AF and RF: the stress centered point of screws on RF were higher than them on AF;but the the stress centered point of roles on AF were higher than them on RF. Conclusionl.With analysised by finite element way;the stress on different parts of implanted fixations were different;the inferiority screws and the inferiority side of conjunction role were the main stress centered point; and the stress on implanted fixations changed with the change of Y and X axes angel.In order to decrease the stress on implanted fixations and the breakage ratio of implanted systems,the angel which could result in the lower stress loading should be elected;between the single segment and multi-segments implanted systems;the stress on screws and roles were different.2.The study offer the proof of anti-fatigue intensity on stress center point for the design of medical apparatus; all the stress center point were the most often pointwhere the breakage happen.and the result of finite element measurement were the same as clinical result;the result test: the result of finite element measurement were reliable.
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