| Objective:1.To provide reliable biomechanical theoretical support for the clinical application of single anterior approach to the fixation of acetabular posterior column fractures with iliac-ischium plate,and to supplement the solid model experiments lacking in finite element mechanical analysis.To improve the operation mode of complex acetabular fracture,to reduce surgical trauma and complications,and to promote the recovery of joint function.2.To understand the main displacement fracture module and displacement direction after internal fixation of acetabular posterior column fracture in standing position and sitting position,to guide the clinical renewal of internal fixation method and to provide biomechanical reliability basis.Method:1.Approved by the Ethics Committee of Southwest Medical University.2.36 intact fresh cadavers were obtained,including intact pelvis and proximal 1/3 femurs.Soft tissue attached to the specimens was removed,and the glenoid and part of the articular capsule were preserved.X-ray fluoroscopy and naked eye observation ruled out malformation,pathological changes and severe osteoporosis,according to the fixed position of reconstruction plate?short iliac-ischium plate,traditional posterior column plate,long iliac-ischium plate?.Specimens was randomly divided into 1-A / 1-B / 1-C and 2-A /2-B / 2-C6 groups,The bone mineral density?BMD?of 6 groups of specimens was measured and the difference was analyzed statistically.3.Establishment of steel plate shape and fracture model: point H at the top of the great notch of the posterior column of acetabulum,point O at the center of the acetabulum,point P at the junction of the ischial branch and the inferior pubic branch,and point of three points.Group 3.5mm pelvic reconstruction plate was preformed before modeling to ensure that the plate attached well to the bone surface,then the pendulum saw was sawed along the marked wire to form the acetabular posterior column fracture model.The specimens of group A C were located along the medial side of the pelvis.Along the iliac bone,the posterior edge of arcuate line,the medial side of the posterior column of acetabulum and the direction of ischial tubercle,6 holes and 3.5 mm pelvic reconstruction plates were placed across the fracture line,respectively.The iliac plate;Group B specimen in hip The posterior column of the acetabulum was 1.5 cm from the edge of the acetabulum,and the reconstruction plate of pelvis with 10 holes 3.5 mm was placed along the direction of the back of ilium,the posterior column and the tubercle of ischium.Two screw holes at the tail end of the plate and four screw holes near the fracture line were placed at the distal end of the plate to the tubercle of the ischium.4.Load loading:group 1 and group 2 were subjected to continuous loading of 0-1800 N and 0-600 N respectively in one-foot standing position and one-sidesitting position by mechanical testing machine.5.data recording and conversion: before loading will sign with a steel ball drill into the medial acetabular bone needle broken distal,through a set of mutually perpendicular HD cameras were collected under dynamic load displacement image,every 100 N record of a mold marking needle position image,and then through the three-dimensional displacement coordinate conversion target,biomechanical analysis stability.6.Statistical analysis: the data were analyzed using SPSS 22 software,6samples of bone mineral density T value with single factor variance analysis,displacement statistical description of median and four percentile,different fixation methods,point displacement,displacement between the groups were compared using the Wilcoxon rank sum test.At P? 0.05,there was statistically significant difference.Result:1.Under the load of one foot standing position,the fracture end displacement was positively correlated with the load size in the anterior short plate,the front long plate and the rear long plate.There was no significant difference in relative displacement among the groups?P > 0.05?.The relative displacement of all groups was not more than 3 mm under the load with the limit of 1800 N.Failure criteria of intra-articular fracture.2.unilateral seated loading,anterior short plate,anterior long plate.When the relative displacement between fracture ends was lower than 3mm.100N-600 N under all loads,the anterior long plate group was in phase.Thedisplacements were lower than those in the anterior short plate group.At100N-400 N,the relative displacement of the front long plate group was lower than that of the rear long plate group?500N and 600N?,and there was no significant difference between the two groups?P > 0.05?.Except for 200 N load,the relative displacement of the front short steel plate group was lower than that of the rear long steel plate group,and the difference was statistically significant?P ? 0.05?.3.When the standing position was loaded on one foot,the relative displacement of the front short plate group was lower than that of the rear long steel plate group.The vertical displacement > the transverse displacement > the front displacement of the anterior short plate and the rear long steel plate were significantly different between the two groups?P ? 0.05?.Forward long plate The difference between vertical displacement,transverse displacement and front displacement was statistically significant?P ?0.05?,but there was no significant difference between transverse displacement and front displacement?P > 0.05?.4.The vertical displacement of all models was higher than that of transverse displacement and anteroposterior displacement under unilateral seat loading,and the difference was statistically significant?P ? 0.05?.The transverse displacement of the rear long steel plate group was greater than that of the front and the front long steel plate group was smaller than the front and back displacement,the difference was statistically significant?P? 0.05?.There was no significant difference between lateral displacement and anteroposterior displacement in front short steel plate group?P >0.05?.The lateral displacement and proximal displacement of the fracture were transversely and anteroposterior under different loads in the experimental group with single foot standing.There was no significant difference in vertical displacement between the two groups?P > 0.05?.The anteroposterior and vertical displacement of each load was lower than that of distal fracture,and the difference was statistically significant?P ? 0.05?,but there was no significant difference in transverse displacement?P > 0.05?.Conclusion:1.The iliac-ischium plate can provide the same biomechanical stability as the traditional posterior column plate fixation,and the stiffness of the fixation structure is high,which can meet the need of postoperative rehabilitation of acetabular posterior column fracture.2.After internal fixation of acetabular posterior column fracture,vertical displacement > transverse displacement and anteroposterior displacement.3.After the internal fixation of acetabular posterior column fracture,the stress was distributed and the load was transferred evenly.The main pelvic bone and the posterior column of acetabular fracture were all displaced by stress shock.In sitting position,the ischium nodule was the stress point.The stress was concentrated on the separation of the posterior column of the acetabulum and the displacement of the posterior column fracture. |
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