| BackgroundAcetabular double-column fractures is one of the most common but difficult to handle in complex acetabular fractures.The author’s clinical practice has found that whether it is a high or low acetabular double-column fracture,may involve an important anatomical structure,that is,a namely quadrilateral area.The quadrilateral area is located on the inner surface of the acetabulum,deep in position,thin in bone,and adjacent to a large number of peripheral nerves and blood vessels.It is very difficult to reduce intraoperatively.In recent years,many scholars at home and abroad have tried to use a series of new fixation strategies to fix the fractures in this area,but most fixation methods are difficult to directly fix the fractures in the quadrilateral area.Even if they are directly fixed,there is a high risk of screws entering the joint cavity of the hip by mistake.Since 2005,our department has innovatively proposed the method of non-anatomic dynamic anterior plate screw system for quadrilateral area(DAPSQ)(Patent No:ZL201320106378.0)to treat complex acetabular fractures.According to the criterion of modified Merle d’Aubigne-Postel,the excellent and good rate could reach 81.8%in follow-up of hundreds of patients with complex acetabular fractures.The first generation DAPSQ uses the reconstruction plate for temporary shaping during operation.The proportion and torsion angle of each part depends on the experience of surgeons,and it is difficult to form a unified standard.It may also increase surgical time and intraoperative bleeding.In order to solve the above problems,our team has performed many technical innovations based on the first generation DAPSQ.Compared with the first generation DAPSQ,the second generation DAPSQ is standardized titanium plate,and the length and partition ratio are more rational and standardized.The second generation DAPSQ(Patent No:ZL201621494131.0)has been put into clinical use after being approved by ethics committee in 2016.But it needs to be further clarified:Is there a difference in clinical efficacy between the two generations DAPSQ?What is the optimal number and distribution of quadrilateral screws in the second generation DAPSQ?What about the stability after fixition?Is it safe for patients to turn over the bodies,stand,sit or rotate after fixition?Based on the above background,this study will retrospectively analyze and compare the preliminary clinical efficacy of two generations DAPSQ in the treatment of acetabular double-column fracture and will evaluate the biomechanical stability of the second generation DAPSQ by the finite element analysis and cadaver model simulation to provide more biomechanical evidence for the application and promotion of this internal fixation system.Part oneComparison of the efficacy of the second and first generation DAPSQ in the treatment of acetabular double-column fracturesObjectiveTo compare the short and medium-term clinical efficacy of the second and first generation DAPSQ in the treatment of acetabular double-column fractures through a single ilioinguinal approach.MethodsA retrospective study was conducted to analyze the clinical data of 35 patients with acetabular double-column fractures admitted to the General Hospital of Central Theater Command from January 2012 to October 2018.According to the fixation method,patients were divided into two groups.The second generation DAPSQ group(SD group)consisted of 15 cases,including 12 males and 3 females with an age of 23-59 years[(49.3±8.8)years].The first generation DAPSQ group(FD group)consisted of 20 cases,including 14 males and 6 females with an age of 32-64 years[(50.4±9.1)years].The operation time,intraoperative blood loss,hospitalization time,fracture healing time,fracture reduction quality and hip function scores were recorded and compared between the two groups.Results1.All the 35 patients were followed up for 12 to 48 months[(24.3±8.4)months].The operation time[(227.5± 49.6)min]and intraoperative bleeding loss[(1026.7±572.5)ml]in SD group were significantly less than those in FD group[(284.1±61.3)min]and[(1540.0±714.8)ml](P<0.05).2.There were no significant differences in hospitalization time,fracture healing time,Matta radiological standard score,modified Merle d’Aubignre-Postel score at the last follow-up between the two groups(P>0.05).There were 2 cases of traumatic arthritis in SD group(1 case underwent total hip replacement),and 3 cases of traumatic arthritis in FD group.None of the patients in two groups experienced complications such as screws entering into articular cavity,loosening or rupture of the internal fixation,and incision infection.ConclusionsBoth generations DAPSQ could achieve satisfactory short and medium-term results in the fixation of acetabular double-column fractures,and the quality of surgical reduction and functional recovery are similar.The application of the second generation DAPSQ can significantly reduce the operation time and intraoperative bleeding,which is an optimal choice in the treatment of acetabular double-column fractures.Part twoFinite element analysis of mechanical properties of second-generation DAPSQ fixed acetabular double-column fracturesObjectiveTo study the distribution characteristics of the second-generation DAPSQ quadrilateral screws and compare the biomechanical stability with traditional anterior reconstruction titanium plate plus 1/3 tube buttress plate fixed acetabular double-column fracture through three-dimensional finite element analysis.Methods1.Finite element analysis of the second generation DAPSQ in the fixation of acetabular double-column fractures with different placement methods of quadrilateral screws.The pelvis CT images of a 28-year-old healthy male adult volunteer were selected to establish the normal pelvis finite element model using the software of Mimics 19.0,Geomagic studio 12.0,Unigraphics NX 9.0 and ANSYS 17.0.With reference to the acetabular fractures classification of Letournel-Judet and AO,a left upper acetabular double-column fracture model was established,and fixed with the second generation DAPSQ.According to the number of quadrilateral screws,DAPSQ combined with one quadrilateral screw(OS group),double quadrilateral screws(DS group),three quadrilateral screws(TS group)and four quadrilateral screws(FS group)were respectively constructed.After setting the load and boundary conditions(vertical load:600N,torque:8 N·m),the average displacement of the fracture line and the stress distribution of internal fixation in the quadrilateral area were compared respectively under the simulated pelvic standing,sitting,standing plus healthy side rotation,and standing plus affected side rotation.2.Finite element comparison of mechanical properties of the second generation DAPSQ with the anterior reconstruction titanium plate plus 1/3 tube buttress-plate in the fixation of acetabular double-column fractures.The same method was used to establish the left upper acetabular double-column fractures model.The model was fixed by DAPSQ with titanium plate plus three quadrilateral screws including four types of nail arrangement(TS1 group,TS group,TS2 group and TS3 group),DAPSQ with titanium plate plus four quadrilateral screws(FS group)and anterior reconstruction titanium plate plus 1/3 tube buttress-plate(FT group).The average displacement of the fracture line and the stress distribution of the internal fixation were also analyzed and compared under the stimulated situation of pelvic standing,sitting,standing plus healthy side rotation,and standing plus affected side rotation.Results1.Under the four working conditions,the average displacement on the fracture path of quadrilateral plate was as follows:OS group>DS group>TS group>FS group.The displacement of FS group was significantly lower than that of OS group and DS group(P<0.05).There was no significant difference between TS group and FS group(P>0.05).The second-generation DAPSQ stress of the FS group in the sitting position was mainly concentrated on the titanium plate-screw junction near the large notch of the ischium.Among the 4 quadrilateral screws,the first quadrilateral screw at the proximal end beared the largest stress,and the maximum stress value was 150.83 mPa,which was far less than the yield strength of titanium materials.The quadrilateral screws also had stress concentration across the fracture line.The inner side was mainly subjected to pressure and the outer side was mainly subjected to tension.Quadrilateral screws tend to bend into the pelvis.2.Under the four working conditions,the average and the maximum displacement of fracture line in quadrilateral area were FT group>TS1 group>TS group>TS2 group>TS3 group>FS group,and the difference between FT group and the other five groups was statistically significant(P<0.05).Compared with the subgroups of second generation DAPSQ,the maximum stress of FT group was highest under the positions of standing or rotation,and the lowest when sitting.After the internal fixation models of each group continued to rotate toward the healthy side,they showed a decrease in stress,and continued rotation to the affected side showed an increase in stress.Conclusions1.The second generation DAPSQ fixed acetabular high double-column fractures has reliable biomechanical properties.The internal fixation stress is mainly concentrated arcross the titanium plate-screw junction near the large notch of the ischium.The maximum stress values are far less than the yield strength of titanium materials.Sitting,standing and rotating movements do not affect the stability of the internal fixation.At least 3 screws should be placed in the quadrilateral area for fixation.Where possible,screws in the quadrilateral area near the large ischial notch should be placed routinely to enhance the effective fixation of the posterior column fracture block.2.The preliminary mechanical test results show that the second generation DAPSQ fixed acetabular high double-column fractures shows better biomechanical stability compared with traditional anterior reconstruction titanium plate plus 1/3 tube buttress-plate when simulating human sitting and standing.In particular,it is more advantageous to restore the mechanical conduction of the sitting sacral arch.At the same time,the second-generation DAPSQ fixation of acetabular double-column fractures has significantly better anti-rotational performance than traditional anterior reconstruction titanium plate plus 1/3 tube buttress-plate fixation,but patients should pay attention to minimize turning to the affected side.Part threeBiomechanical comparison of second-generation DAPSQ with anterior reconstruction titanium plate plus 1/3 tube buttress-plate fixed acetabular double-column fracturesObjectiveTo compare the mechanical differences of non-anatomical second-generation DAPSQ with that of anatomical traditional anterior reconstruction titanium plate plus 1/3 tube buttress-plate fixed acetabular double column fracture using cadaver model biomechanical methods.MethodsSix adult formalin-preserved corpses were selected to make a complete pelvic specimen.The upper end of the model was retained to the upper edge of the lumbar 4-vertebral body and the lower end was retained to the upper 1/3 of the bilateral femoral shaft.Strain gauge and strain rosette were affixed on the anterior column,posterior column and the quadrilateral area of the left pelvis,respectively.The loading and measuring instruments included German’s Zwick Z100 material machine,domestic RNJ-500 microcomputer controlled torsion machine,domestic XL2118A static resistance strain indicator,Japan’s Mitutoyo multifunctional digital dial indicator(provided by mechanics experiment center of Wuhan University of Technology).Firstly the complete pelvis(group A)biomechanical data of the axial compression test of standing,sitting and torsion test of supine position were measured,and then the same data of the second-generation DAPSQ(group B)and anterior reconstruction titanium plate plus 1/3 tube buttress-plate(group C)randomly fixed the models were detected after the left high double-column fracture model were made on the cadaver.The total axial displacement of pelvis,the displacement of fracture line and the strain value of strain gauge were recorded in the three groups at 200N to 800N vertical load.The torque values and strain values in the quadrilateral area corresponding to the torsion angles of 2°,4°,6° and 8° were also recorded.Results1.General situation.In group B and group C,the anterior and posterior columns of the acetabulum were well fixed and confirmed as anatomical reduction by X-ray and CT three-dimensional reconstruction.During the whole test,none of the titanium plate or screws showed looseness,pullout or rupture in both groups.The lateral displacement of the inner wall and the longitudinal displacement of the acetabular dome were less than 2 mm,and neither reached the failure criterion of internal fixation.2.Axial compression test in sitting position.As the vertical load increased from 200N to 800N,the axial compression displacement of the three groups showed a linear increase trend.The axial displacement in group C was significantly larger than those in group A and group B(P<0.05),while the difference between group A and group B was not significant(P>0.05).Under 600N physiological load,the pelvic axial stiffness of group B was 84.1%of group A,and there was no significant difference between groups(P>0.05).While the axial stiffness of group C was only 61.5%of group A,which was significantly lower than those of group A and group B(P<0.05).Under 600N load,the strain value of posterior column showed group C>group A>group B,and the strain value of group C was significantly higher than that of group A and group B(P<0.05),and there was no significant difference between group A and group B(P>0.05).The strain value of anterior column was group C>group A>group B,and there was no significant difference between them(P>0.05).In group B and group C,the lateral displacement of the inner wall and the longitudinal displacement of the acetabular dome were all within 1mm.The axial stiffness of 6 specimens in group B was stable,while 1 specimen in group C was axially unstable.3.Axial compression test in standing position.As the vertical load increased from 200N to 800N,the axial compression displacement in three groups increased linearly.The axial displacement in group C was significantly greater than that in group A and group B at all levels of vertical load(P<0.05),while the displacement in group B was significantly greater than that in group A(P<0.05).Under 600N physiological load,the axial stiffness of group B was 75.3%of group A,while group C was only 54.5%of group A.The difference between the three groups was statistically significant(P<0.05).In group B,the lateral displacement of the inner wall and the longitudinal displacement of the acetabular dome were all within 1mm.While in group C,there were 2 cases of central dislocation of the femoral head and 1 case of upward dislocation.4.Torsion test in supine position.As the torsional angle increased from 2° to 4°,the torsion value increased linearly.The torsion stiffness of group B was 95.3%of group A,and there was no significant difference between the two groups(P>0.05).While the torsion stiffness of group C was only 65.1%of group A,which was significantly lower than that of group A and group B(P<0.05).The maximum tensile strain in the quadrilateral area was greater than the compressive strain.The maximum tensile and compressive strain in the quadrilateral area of group C were significantly higher than in group A and B(P<0.05),while group B were lower than that in group A(P<0.05).In group B,the direction of the maximum tensile strain in the quadrilateral area was-39.10°,which was basically the same as the direction of quadrilateral screws.Conclusions1.In sitting position,compared with anterior reconstruction titanium plate plus 1/3 tube buttress-plate,the axial stiffness of acetabular double-column fracture fixed by the second generation DAPSQ is stronger,and has no significant difference with the complete pelvis.In the group of second generation DAPSQ,the stress changes in the anterior and posterior columns of the acetabulum are more similar to the complete pelvis.Therefore,it is safe and reliable for patients to take the sitting position early after operation.2.In standing position,the axial stiffness of the pelvis fixed by the second generation DAPSQ is smaller than the complete pelvis,but it is still significantly stronger than the traditional anterior reconstruction titanium plate plus 1/3 tube buttress-plate.And the hip joint instability or internal fixation failure do not occur after the second generation DAPSQ fixation.Therefore,the stability of the early standing position fixed by the second generation DAPSQ is better than anterior reconstruction titanium plate plus 1/3 tube buttress-plate,but the time of standing should be carefully selected.3.In the rotating position,the torsion stiffness of the pelvis fixed by the second generation DAPSQ is equivalent to the complete pelvis,and significantly better than the anterior reconstruction titanium plate plus 1/3 tube buttress-plate.After the fixation of the second generation DAPSQ,the direction of the maximum tensile strain is consistent with the direction of quadrilateral screws.The stability of internal fixation is not affected by turning over to the affected side. |
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