| BackgroudIn the field of trauma surgery and spinal surgery,many diseases often require posterior spinal-pelvic fixation,such as traumatic spinal pelvic separation(H-shaped or U-shaped fractures,etc.),complicated traumatic sacral comminuted fracture,sacral fractures with nerve damage,scoliosis and Kyphosis,sacral tumors,lower lumbar sacral tuberculosis,severe lumbar spondylolisthesis,etc.require reconstruction of spine-pelvic stability.Iliolumbar fixation has become one of the reliable fixation methods.Kach et al.reported for the first time that five patients with unstable longitudinal vertical fractures of the sacrum(Denis Ⅱ or Ⅲ fractures)were treated with L5 pedicle screw combined with iliac wing screw fixation.The follow-up results were satisfactory and the internal fixation was reliable.Schildhauer et al.proposed the triangular fixation technique that combined spinal-pelvis fixation system with sacroiliac screw lateral fixation.Biomechanical studies showed that triangular fixation technique could further increase the stability of spinal pelvis and enhance the fixation strength.In spine-pelvic fixation,the nail-rod connection system is more flexible,and there are more choices of screw placement and direction on the ilium,and multiple screws can be placed to enhance the fixation effect.A review of the literature found that there are multiple anchoring channels during iliac screw fixation:from posterior superior iliac spine to iliac crest;from 24mm above superior posterior superior iliac spine to inferior margin of anterior inferior iliac spine;from posterior superior iliac spine to anterior inferior iliac spine;1cm inferior posterior superior iliac spine,1cm medial to anterior inferior iliac spine;2cm inferior posterior superior iliac spine to anterior inferior iliac spine,and from posterior inferior iliac spine to anterior inferior iliac spine.etc have been studied and reported.At present,there is no uniform standard for the placement of iliac screws,and the biomechanical effects of bilateral single iliac screws with different channels on the stability of the pelvis have not been discussed.In special cases of spine and pelvic diseases that affect different areas,bilateral double iliac screws are more advantageous than bilateral single iliac screws because they provide a stronger fixation on the basis of spine and pelvic fixation.In terms of biomechanics,bilateral double iliac screws have high structural rigidity in compression and torsion.Yu et al.conducted a biomechanical comparison between bilateral double iliac screws and bilateral single iliac screws in iliac lumbar fixation,and pointed out that the double iliac screws located in the subiliac column show stronger vertical compression stiffness and torsional stiffness than the single iliac screw and the double iliac screws are located in the upper iliac column at the same time,or located in the upper iliac column and the lower iliac column.Yilmaz et al.studied the safe placement of multiple iliac screws through anatomy,radiology,and cadaveric morphometry and concluded that the first iliac screw channel is from the posterior superior iliac spine to the anterior inferior iliac spine,and the second iliac screw which is the best channel should be placed between the posterior superior iliac spine and the posterior inferior iliac spine.The specific channel position of the second iliac screw needs further biomechanical research.None of the above studies pointed out the specific placement of the second iliac screw,nor did it compare the biomechanical properties of the dual iliac screws with different channels of the inferior iliac column.The research content of this subject was divided into three parts:The first part studies the CT imaging data of different iliac screw channels in iliac lumbar fixation,compares different channel morphometry,and provides imaging basis for better selection of iliac screw channels;the second part studies The biomechanical effects of iliac screws with different channels in iliac lumbar fixation on the stability of the pelvis,provide a basis for determining the best single iliac screw channel,and in-depth exploration of the best combination of double iliac screw fixation positions;the third part had finite element analysis on the effects of different channels of iliac scerws(bilateral unilateral iliac scerw fixation and bilateral bilateral iliac scerw fixation)on the biomechanical stability of the pelvis in iliac lumbar fixation,and compares the stress distribution of different fixation methods.This study aims to analyze the biomechanical mechanism of iliac lumbar fixation,determine the best iliac nail placement plan,and provide a scientific basis for a more reasonable and effective clinical application.Part one Comparative study on radiographic of different iliac screw channels in Jumbo-iliac fixation.Objective:To study and analyze the CT radiographic data of different iliac screw channels in lumbo-iliac fixation,and to analyze and compare the morphology of the channels,so as to provide a basis for better selection of iliac screw channels.Methods:In this study,40 normal domestic adults were randomly selected from the CT imaging database of Shandong Provincial Hospital and our hospital,including 28 males and 12 females.The age ranged from 29 to 50,with an average age of 41.2.Three commonly used iliac screw channels were selected in lower column of iliac bone:channel A from the posterior superior iliac spine to the anterior inferior iliac spine,channel B from 1cm below the posterior superior iliac spine,1cm from the medial side to the anterior inferior iliac spine,and channel C from 2cm below the posterior superior iliac spine to the anterior inferior iliac spine.The total length of each channel,the width of the bone plate at the second stenosis of channel,the length from the entry point to the second stenosis were measured and compared.Results:The total length of iliac screw channel:the total length of channel A was(130.1±7.5 mm),the total length of channel B was(114.8±10.3 mm),and the total length of channel C was(110.7±8.1 mm)and the differences were statistically significant(P<0.0001).Studies showed that channel A was the longest among the three channels.There was no statistically significant difference in the total length between channel B and channel C(P>0.05).the width of the bone plate at the second stenosis of channel:A channel width is(11.2+1.4 mm)and B channel width(12.2+1.7 mm),C channel width(13.6+1.7 mm)and difference had statistical significance(P<0.05).And B channel narrow width and C channel narrow width were statistically significant differences(P<0.05)that the C channel the narrow width was the widest in the three channels.And the length from the entry point to the second stenosis:there were statistically significant differences between(79.3±6.3 mm)in channel A and(70.5±7.5 mm)in channel B and(63.8±4.7 mm)in channel C(P<0.05),and there were statistically significant differences between the length from the entry point to the second stenosis in channel B and the length from the entry point to the second stenosis in channel C(P<0.0001).Conclusions:Among three iliac screw passages in Chinese,those are all suitable for the common type of iliac screw placement in clinic.The channel from the posterior superior iliac spine to the anterior inferior iliac spine is long and the iliac plate is narrow,which can accommodate the slender iliac screw.The iliac screw channels from 1cm below the posterior superior iliac spine,1cm medial to the anterior inferior iliac spine,and 2cm below the posterior superior iliac spine to the anterior inferior iliac spine are short,and the iliac plate is thick,which could accommodate the stubby screw.Part two Biomechanical study of the stability of pelvic with lumbo-iliac fixation using iliac screw with different channelsObjective:Lumbo-iliac fixation for injury of unstable posterior pelvic ring:(1)Biomechanical tests were conducted to explore the effect of bilateral single iliac screw with different channels on the stability of pelvic and provide the basis for the best single iliac screw channel(2)Biomechanical tests were conducted to investigate the effect of bilateral double iliac screws on the stability of the pelvic,and to explore the placement position of the double iliac screws.Methods:The pelvis specimens of 10 adult cadavers treated with formaldehyde solution were selected,and the lumbar 3 vertebral body was reserved to 10cm of the upper end of the bilateral femur.The muscle,fat and other tissues were removed.The osseous and ligament structures of the anterior and posterior rings of the pelvis were kept intact,as well as the structures of the bilateral hip joints and accessory ligaments.Pelvis specimens were fixed on a biomechanical test machine to eliminate the creep effect,and biomechanical tests of normal pelvis specimens were carried out,and they were used as the control group.Unstable type Tile C1 pelvic injury model(pubic symphysis separation and left Denis II sacrum fracture)was made.The pubic symphysis was fixed with a five-hole reconstruction plate.The posterior pelvic ring was treated with iliolumbar fixation:(1)randomly selected 5 pelvic specimens for three channels single ilium screw fixed on both sides as follows:channel A from the posterior superior iliac spine to the anterior inferior iliac spine,channel B from 1cm below the posterior superior iliac spine,1cm from the medial side to the anterior inferior iliac spine,and channel C from 2cm below the posterior superior iliac spine to the anterior inferior iliac spine.The biomechanical test results(including axial vertical compression test and axial rotation test)of the stability of the pelvic were compared with those of the iliac screw with three channels.(2)The remaining 5 pelvic specimens were fixed with bilateral double iliac screw in three different combinations:channel A+channel B;channel A+channel C;channel B+channel C.To compare the biomechanical test results of the stability of the pelvic with bilateral double iliac screws.Results:(1)The biomechanical test results of bilateral single iliac screw with three channels.① Results of axial vertical compression test:under 500N axial vertical compression,the vertical displacement of the whole pelvic fixed by iliac screw in the three channels was greater than that of the complete pelvic(1.852±0.104mm),and the difference was statistically significant(P<0.05).the displacement of the whole pelvic in channel B(2.054±0.248mm)was smaller than that in channel A and C(2.153±0.175mm,2.370⒈0.167mm,respectively),and there is no significantly different between the vertical displacement of channel B and channel A(P>0.05).While the displacement of the whole pelvic in channel B was not significantly different from that of the complete pelvic(P>0.05),the displacement of the whole pelvic in channel A was significantly different from that of the complete pelvic(P>0.05).The axial stiffness of the whole pelvic fixed by iliac screw with three kinds of channels was significantly lower than that of the complete pelvis,and the difference was statistically significant(P<0.05).the axial stiffness of channel B(246.15±27.85N/mm)is greater than that of channel A and channel C(233.43±18.5N/mm、211.79±14.58N/mm,respectively),while the axial stiffness of channel B was not statistically significant different from that of the complete pelvis(P>0.05).② Axial rotatio’n test results:Under the axial rotation of 6N·m,the torsion angles of the whole pelvic fixed by the iliac screw with the three channels were significantly greater than that of the complete pelvic,and the difference was statistically significant(P<0.01).The pelvic torsion angle of channel B(2.708±0.280°)is smaller than that of channel A and channel C(2.973±0.274° and 3.411±0.197°,respectively),and there is no significantly different between the pelvic torsion angle of channel B and channel A(P>0.05).The overall pelvic torsion stiffness of the three channels was significantly lower than that of the complete pelvic,and the difference was statistically significant(P<0.05).The torsional stiffness of channel C(1.764±0.101N·m/°)was lower than that of channel A and channel B,and the difference was statistically significant(P<0.05).The torsional stiffness of channel A(2.032±0.187N·m/°)and channel B(2.234±0.223N·m/°)showed no significant difference(P>0.05).(2)Biomechanical test results of three different combinations of bilateral double iliac screws:① Results of Axial vertical compression test:under 500N vertical load,the vertical displacement of the whole pelvic under the three combinations of bilateral double iliac screws fixation was all lower than that of the complete pelvic,and the difference was statistically significant(P<0.05).the whole pelvic vertical displacement(1.648±0.05 mm)fixed by channel A+channel C is less than that fixed by channel A+channel B and by channel B+channel C(1.721±0.045 mm,1.741±0.044 mm respectively),the difference had statistical significance(P<0.05),while the latter two has no statistical significance(P>0.05)The axial stiffness of the whole in the three combinations pelvic fixed with bilateral double-iliac screw was significantly stronger than that of the complete pelvis,and the difference was statistically significant(P<0.05).The axial stiffness(303.55±9.2N/mm)fixed by channel A+channel C was higher than that fixed by channel A+channel B and by channel B+channel C,and the differences were statistically significant(P<0.05).There was no significant difference in the axial stiffness between fixed by channel A+channel B(290.73±7.76N/mm)and fixed by channel B+channel C(287.34±7.17N/mm)(P>0.05).② Results of Axial rotation test:the overall pelvic torsion Angle of the three combinations of bilateral double iliac screws fixation under 6N·m torsion load was lower than that of the complete pelvic,and the difference was statistically significant(P<0.05).There was no significant difference in the overall pelvic torsion Angle at three different combinations.The axial stiffness of the whole pelvic in the three combinations of bilateral double iliac screws was significantly stronger than the torsion stiffness of the complete pelvic,and the difference was no statistically significant(P>0.05).the overall pelvic ring torsional stiffness at fixed by channel A+channel B(2.866±0.139N·m/°),fixed by channel A+channel C(2.834±0.152N-m/°),fixed by channel B+channel C(2.732±0.235N·m/°)had no significant difference(P>0.05).Conclusions:the biomechanical test of lumbo-iliac fixation for unstable pelvic ring injuries,(1)three channels of bilateral single iliac screw(channel A from the posterior superior iliac spine to the anterior inferior iliac spine,channel B from 1cm below the posterior superior iliac spine,1cm from the medial side to the anterior inferior iliac spine,and channel C from 2cm below the posterior superior iliac spine to the anterior inferior iliac spine)fixation can effectively restore the stability of the reconstruction of the pelvis.The overall rigidity difference between channel B and channel A is not statistically significant,but the overall displacement and torsion angle of the channel B are smaller than that of the channel A,indicating that the B channel is more in line with biomechanical conduction,and the channel C is the worst stability.when to use iliolumbar fixation in clinical practice,it is suggested to choose 1cm below the posterior superior iliac spine and 1cm medial to the anterior inferior iliac spine.(2)The overall structural rigidity of the three combinations of bilateral double iliac nail fixation is stronger than the overall structural rigidity of the complete pelvis.The overall vertical displacement and axial rigidity of the channel A+channel C fixation is better than that of the channel A+channel B fixation and channel B+channel C fixed.The torsional angle and torsional stiffness of the three combinations of bilateral double iliac screws were similar.Therefore,the position of the double iliac screws:the first screw is from the posterior superior iliac spine to the anterior inferior iliac spine,and the second screw is from 2cm below the posterior superior iliac spine to the anterior inferior iliac spine.Part three Finite element analysis of the influence of different channels of iliac screws in lumbo-iliac fixation on the biomechanical stability of the pelvicObjective:Establish a finite element model of lumbo-iliac fixation:(1)use three-dimensional finite element analysis to explore the effect of different channels of bilateral single iliac screws on the biomechanical stability of the pelvic.(2)Using three-dimensional finite element analysis to explore the effect of bilateral double iliac screws on the biomechanical stability of the pelvic.Methods:Recruit one domestic healthy adult male volunteer.Through the CT scan,the image of the lumbar spine,pelvis and femur is obtained,and the 3D model of the pelvis is made and meshed by importing the Mimics 21.0 software and Geomgic studio.Use Pro/Engineer 5.0 and Hypermesh12.0 software to draw iliac screws,pedicle screws,connecting rods,transverse connecting rods,reconstruction plates,screws,etc,set the properties of various materials,Young’s modulus,etc.Import the L4-pelvic-proximal femoral three-dimensional finite element model,pedicle screw,iliac nail,etc.into Ansys 13.0 software for finite element experimental research.The pelvic Tile C1 Type injury model(separation of pubic symphysis,left sacrum Denis type II fracture)was made.Simulate 5-hole reconstruction plate fixation of the pubic symphysis and lumbo-iliac fixation for the treatment of posterior pelvic ring surgery.(1)The first part of the finite element analysis is bilateral single iliac screws fixation,divided into ABC three ways of fixation:A channel posterior superior iliac spine to the anterior inferior iliac spine,the B channel from 1cm below the posterior superior iliac spine,1cm from the medial side to the anterior inferior iliac spine,and the C channel from 2cm below the posterior superior iliac spine to the anterior inferior iliac spine.(2)The second part of the finite element analysis of bilateral double iliac screws fixation:A channel+B channel,A channel+C channel,B channel+C channel.Simulate the standing position of the human body,set boundary conditions on femur ends and apply 500N vertical downward force and 10N·m torque in different directions on the upper surface of L4.Simulate flexion,extension,lateral bending,rotation and other working conditions,obtain the internal fixation nail and rod system,vertebral body iliac stress cloud diagram,displacement cloud diagram,and deformation cloud diagram through finite element,and compare the overall displacement of the model with different fixation methods,The overall stress distribution,the stress distribution,maximum value and deformation of the internal fixation.Results:(1)The first part is the result of the three-channel bilateral single iliac screw fixation:the displacement degree of the three-channel iliac screw under the upright working condition decreases from the L4,the L5,and the sacrum.The overall model displacement(2.02mm)of the A channel fixation is smaller than the fixed overall displacement of the B channel and the C channel(2.4mm and 2.78mm respectively),and the overall displacement of the C channel is the largest.In rotation conditions,the displacement range of the right rotation is larger than that of the left rotation,and the overall displacement of the right rotation is greater than that of the left rotation.In terms of displacement,the left rotation displacement of the fixed model of A channel(2.11mm)is smaller than that of the B channel And C channel fixed model(2.49mm,2.97mm respectively).In terms of the overall stress of the model,the maximum stress of the model is all expressed on the surface of the fixture.The bilateral iliac screws,connectors,and longitudinal rods of the three channel models all have large stress concentrations,and the iliac screws and connectors are more obvious around.The maximum stress value of the internal fixation of the B channel fixed under the conditions of upright,forward flexion,left bending and left rotation(213.98MPa,338.96MPa,297.06MPa,200.95MPa respectively)is significantly less than the maximum stress value of the other two channels.In the upright working condition,the maximum fixed stress value in channel B is 71.4%of the maximum fixed stress value in channel A.In the left rotation condition,the maximum stress value of the B channel is only 65.9%of the maximum stress value of the A channel.It shows that the fixed stress distribution of the B channel is scattered,and the maximum stress value is small,it is the less likely to break the nail.In terms of vertebral body and iliac stress,the maximum stress of vertebral body in various working conditions except for extension:A channel fixation<B channel fixation<C channel;under upright,forward flexion,left bending,and right rotation conditions:A channel fixation iliac bone stress maximum>B channel fixation>C channel,it can be seen that the overall stress distribution of the B channel fixation model is more reasonable.(2)The second part compares the results of three combinations of bilateral double iliac screws:the overall displacement and movement of the A channel+B channel fixation model under various working conditions is similar to that of the A channel+C channel fixation.In terms of the overall stress of the model,the maximum stress of the model is also shown on the surface of the fixture.There are stress concentrations in the bilateral double iliac screws,connectors,and longitudinal rods of the three combined models.The stress distribution of the upper and lower two iliac screws is relatively scattered.The maximum stress value of the internal fixation of the A-channel+C-channel fixed model under the conditions of upright,rear extension,and right-side bending(190.52MPa,76.29MPa,288.55MPa respectively)is significantly smaller than the maximum stress value of the other two fixed combinations.In terms of vertebral body and ilium stress,the maximum stress of the vertebral body and ilium under various conditions of the A channel+B channel fixation model is similar to the results of the A channel+C channel fixation.Conclusions:Establish a finite element model of iliac lumbar fixation for the treatment of pelvic instability injury(1)Three channels of bilateral single iliac screw fixation:channel 1cm below the posterior superior iliac spine,1cm to the medial side to the anterior inferior iliac spine has mechanical stability,and the overall stress distribution is more reasonable,the maximum stress value of the internal fixation is small,the fatigue resistance is strong,and the nail breakage is not easy to occu r.Under various working conditions,the stresses of the three channel models are mainly concentrated at the junction of the iliac screw body and the screw tail,which is the position where the internal fixation of the spine-pelvic internal fixation is more likely to occur.(2)Three combined channels for bilateral double iliac nail fixation:channel the posterior superior iliac spine to the anterior inferior iliac spine combined with channel 2cm below the posterior superior iliac spine to the anterior inferior iliac spine.The fixation has good biomechanical stability and internal fixation.The stress distribution of the internal is small,and the stress distribution of the upper and lower iliac screws on the same side is relatively scattered. |
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