| When sacroiliac joints fracture and dislocate, the vertical and vertical directions of pelvis were not stable. Biomechanical experiments proved that sacroiliac screw internal fixation could provide pelvic enough stability, and its biomechanical effect equals or exceeds to other internal fixations. Meanwhile, clinical practice proved the sacroiliac screw is one of the most effective methods of treating the sacroiliac composite structure damage. The individual difference of sacral lateral mass is big, those anatomy is deep, and the anatomical structure around the sacroiliac joint is complex.There was not a unified standard for the exact position and best direction to insert the sacroiliac screw in the existing literatures,and anatomy information related to the operation was still lack. All of these limit the sacroiliac screw technology popularization.In recent years, percutaneous sacroiliac screw internal fixation,which based on perspective and navigation technologys, was widely popular for less invasive and fixed reliable.But percutaneous sacroiliac screw internal fixation is based on Closed reduction, preoperative measurement of the screwing trajectory's parameters on the injured side and intraoperative X-ray monitoring. While the sacroiliac joints of a part of patients,who are suitable to applicate the sacroiliac screw technology, are still restored hardly or reseted poorly on the injured side after traction in clinic. Because the injured side don't be reseted, we cannot directly measure the corresponding screwing trajectory's parameters before operation.It affects the intraoperativ selection on the inserting screw's point, the inserting screw's direction,screw's size and length. The measurement after open reduction not only delays surgical time, increasess surgical risk, but also probably causes the reseted sacroiliac joints to dislocate again by carrying patients. In order to find a more simple and accurate method, which measures the screwing trajectory's parameters of the ideal sacroiliac screw by Computed Tomography,to guide inserting screws,we applicate three-dimensional reconstruction technique of Computed Tomography to simulate sacroiliac screw internal fixation on the left and right sacroiliac joints of eleven frozen pelvic specimens of normal adults,and measure the screwing trajectory's parameters of the ideal sacroiliac screw,and verify the accuracy by inserting screws. In order to explore the feasibility of individual measuring the parameters of the screwing trajectory of the screw on the uninjured side by application of computed tomography before open reduction and internal fixation using sacroiliac screw to guide the placement of screw on the injured side on a part of patients,whose sacroiliac joints are still restored hardly or reseted poorly on the injured side after traction in clinic,we individually inserted iliosacral screws according to the measurement results the screwing trajectory's parameters of the opposite side on eleven frozen pelvic specimens of normal adults.In addition,there were few reportment about the study in biomechanical properties of the sacroiliac screws by three-dimensional finite element both at home and abroad. The aim of this study was to evaluate biomechanical properties of single Si screwing's fixation and S1, S2 double screwing's fixation when anterior ring was stable and unstable,and provide theory basis to choice the ways of sacroiliac screw internal fixation by establishing vertically unstable pelvic three-dimensional finite element model. Part one The study of measuring method in the screwing trajectory's parameters of the ideal sactciliac screw by computed tomography.Objectives In order to find a more simple and accurate method which measures the screwing trajectory's parameters of the ideal sacroiliac screw by Computed Tomographyto guide inserting screws,and verify its accuracy,and discuss ite clinical significance.Methods First, the left and right sacroiliac joints of eleven frozen pelvic specimens of normal adults were performed internal fixation using sacroiliac screw by the helical computed tomography of the three-dimensional reconstruction, and measured the screwing trajectory's parameters of the ideal sactciliac screw by digital makes(The accuracy is 0.1 mm) and angle measurement instrument(The accuracy is 0.1°).Second, eleven pelvic specimens (twenty -two sacroiliac joints) were individually validated by the iliosacral screws according to the measurement result of the ideal screws scanned by helical computed tomography.Finally,all measurement data were statistically processed with SPSS 13.0 software and were expressed as Mean±SD.Paired-samples t test were proceeded between left and right side of pelvic specimens.The significant standard of the statistical test was at a=0.05.Results The length of the deal screw was (87.62±1.68)mm,and the diameter was (20.26±1.20)mm. The direction of the ideal screw was (25.85±1.06)°to the coronal plane, and (19.79±1.60)°to the horizontal plane. The safe angle of the screw trajectory was (19.84±1.15)°to the coronal plane, and (23.64±1.35)°to the axial plane.The distance from the entry point was (37.02±1.67)mm to posterior superior iliac spine,and (38.30±1.14)mm to posterior inferior iliac spine. All of the twenty-two inserted iliosacral screws were entirely within the pedicle. There was no significant statistics difference between left and right side in the same individual.Conclusions The screwing trajectory's parameters of the ideal sactciliac screw are simplely and accurately measured and evaluated by the computed tomography of the three-dimensional reconstruction using the simulation of the operation of internal fixation using sacroiliac screw, having a large significance in selection of the entry point,the angle and the shape of the screw of the sacroiliac joint.After part sacroiliac screws technology eligible patients were carried out traction postoperative,sacroiliac joint is still hard restoration or reset bad. This kind of patients could be inserted iliosacral screws according to the screwing trajectory's parameters of the uninjured side.Part two The feasibility study on measuring the screwing trajectory's parameters of the ideal sactciliac screw of the health side by preoperatively application of helical computed tomography to guide the placement of screw.Objectives To explore the feasibility of individual measuring the parameters of the screwing trajectory of the screw on the uninjured side by application of helical computed tomography before open reduction and internal fixation using sacroiliac screw to guide the placement of screw on the injured side.Methods After part one, left and right sacroiliac joints of eleven cases of pelvic specimens(twenty -two sacroiliac joints) were made into vertically unstable mode by MiniBionix MTS type biomechanical test-858(MTS company, USA, Biological mechanics laboratory, southern medical university),and were individually inserted iliosacral screws according to the measurement results the screwing trajectory's parameters of the opposite side.Results All of the eleven inserted iliosacral screws of the left sacroiliac joints were entirely within the pedicle; in the right side, except one deviate out of the bone, and other ten cases were entirely within the pedicle.Conclusions The method through individual measuring the parameters of the screwing trajectory of the screw on the uninjured side by application of helical computed tomography before open reduction and internal fixation using sacroiliac screw to guide the placement of screw on the injured side has been proved a reliable method.Fart three The study in establishing normal pelvic three-dimensional finite element model.Objectives To establish reliable pelvic three-dimensional finite element model for providing a reliable digital simulation pelvic model to further research pelvic fractures damage mechanism and evaluate internal fixation.Methods First,a representative healthy adult male volunteer was choosen, who was eliminated pelvic injury, tumor, deformity and so on by Imaging examination. Second, applicating spiral CT (Toshiba Aguilion 16, Toshiba, Japan) to scan the male from article 4 lumbar sebocytes to femoral big subtrochanteric 5cm by 0.5 cm thick layer,and placing scan dates with Dicom format in a computer.Third, rebuilding pelvic osseous structure by MINICS 10.0 software (Materialise company, Belgium),and importing it into FREEFORM PLUS software(SensAbole company, United States) for burnishing, filling in holes, denoising and forming close to normal geometric entities model.Fourth, geometric entities model was imported into ANSYS 10.0 software(ANSYS company, United States),and was gridsed,and was loaded ligaments,and was inputed material mechanics properties,for establishing pelvic three-dimensional finite element model. Finally,evaluating stress transmission rule of pelcic ring and stress distribution rule of sacroiliac joints,and comparing results with human experiments by simulating bipedal stand and loading 500N on the sacral vertebral surface.Results The pelvic three-dimensional finite element model possesses 221139 nodes and 143115 elements Among of them,the cortex bone, cancellous bone,pubic. symphysis and articular cartilage were all the solid32-elements,and the ligaments were all the link-elements. The stress evenly symmrtry distributed on both half pelvis,and the the maximum stress Located in nearby sciatic big cut trace after pelvic loaded. When simulating bipedal stand,the sacral vertical displacement was 0.698 mm in sagittal plane,and the average angular displacement was 1.69°, basically consistenting with relevant reports of cadaeric biomechanical experiment.Conclusions Building the three-dimensional finite element model in this study objectively reflected the pelvis real anatomical configuration and biomechanics behaviour,which was effective and reliable.Part four Establishing screw internal fixation models of sacroiliac joint dislocation and analysising mechanical properties of the screw by three-dimensional finite elementObjective To evaluate biomechanical properties of single Si screwing's fixation and S1, S2 double screwing's fixation when anterior ring was stable and unstable,for providing theory basis to choice the internal fixation ways of pelvic fracture by establishing vertically unstable pelvic three-dimensional finite element model.Method Establishing three-dimensional finite element models of simple sacroiliac joint dislocation (A model),and the sacroiliac joint dislocation and pubic symphysis separation (B model) on the base of the thirdexperiment.They were fixed using both single S1 screws (Ⅰclass fixed) and S1, S2 double screws (Ⅱclass fixed).Thus,we obtained four screw internal fixation models of sacroiliac joint dislocation(AⅠmodel, AⅡmodel,BⅠmodel, and BⅡmodel). Through nonlinear analysis of finite element on the four kinds of model,we calculated the displacement and the stress distribution of the Si screw,and compared those with normal pelvis.Results The results of displacement curve of very points in the taking path on the surface of the S1 screw of four screw internal fixation models of sacroiliac joint dislocation show:the displacement of the S1 screw increased gradually from the screw head to nail.The comparative results of the maximal displacement:All model<BⅡmodel<AⅠmodel< normal pelvic<BⅠmodel, AⅡmodel, BⅡmodel, and A I model respectively is normal pelvic 55%,82%,96%,and BⅠmodel was the normal pelvic 1.93 times (AⅠmodel:1.6x 3010-3m; AⅡmodel:9.324 x 10-4m; BⅠmodel:3.271x10-3m; BⅡmodel:1.400x 10-3m; normal pelvic:1.698x 10-3m). The results of stress curve of very points in the taking path on the surface of the S1 screw of four screw internal fixation models of sacroiliac joint dislocation and stress convective of the S1 screw:the stress of the Si screw concentrately distributes,and the peak appears in the places passing the sacroiliac joints. The comparative results of the greatest stress:BⅠmodel>AⅠmodel> BⅡmode 1> AⅡmodel> normal pelvic. BⅠmodel, AⅠmodel, BⅡmodel, and AⅡmodel respectively was normal pelvis 736 times,348 times,162 times,75 times (AⅠmodel:3.285x108 N; AⅡmodel:7.093 x 107 N; BⅠmodel:6.941 x 108 N; BⅡmodel:1.532 x 108 N; normal pelvic:9.433 x105N).Conclusions After anatomical reattachment of the pure fracture dislocation of sacroiliac joints, pelvic ring fixed by S1 screw the can obtain reliablestability.Thus,no significance to take a risk to insert the S2 screw.When the sacroiliac joint fracture dislocate and the pubic symphysis separate, the posterior ring fixed purely by S1 screw can't restore the stability. Comparing with single S1 screwing's fixation, S1, S2 double screwing's fixation can gain better stability.The biomechanical properties of the anterior ring are equal to the S2 screw.The S2 pedicle is lesser.There are high risks and operational difficulties to insert the S2 screw because of the S2 screw easily injuring Surrounding nerves and accessing sacral tube.Moreover,the risk of the anterior ring fixed by steel plates is lowl,and the pelvic is stable.Thus, when the sacroiliac joint fracture dislocate and the pubic symphysis separate,the best fixation is the anterior ring fixed by steel plates and the posterior ring fixed by the S1 screw.The S1 screw easily produces fixed fatigue and breakages in the places passing the sacroiliac joints. |
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