| BackgroundSacroiliac complex consists of the sacroiliac joint and the surrounding ligaments. It forms a drawbridge structure to stabilize the pelvic ring. It is the major stable structure of the pelvis, carrying the main stress load. About one out of six pelvic fractures implicate the sacroiliac complex. It would result in sacroiliac joint injury and peripheral ligaments damage. It further impairs the instability of pelvic ring. Therefore, the reconstruction of the stability of sacroiliac joint complex is of great importance in the treatment of the pelvic fractures.Since Avila first reported the anterior surgical approach in1941, it has become popular to perform the open reduction and internal fixation through the anterior approach in the treatment of sacroiliac joint injury. It is the main treatment strategy, especially in the old pelvic fracture. Nowadays, the reconstruction plate is the main internal instrumentation used in surgery through the anterior approach. It uses two reconstruction plates with three or four holes. The two plates are fixed across the sacroiliac joint with a60degree angle. Biomechanical studies have shown that it had great stability to fix the joint.However, the traditional reconstruction plate has some drawbacks. It might cause serious bleeding and injury of the lumbosacral trunk and the lateral femoral cutaneous nerve. At the beginning, two traditional reconstruction plates were placed in parallel. It is unstable, due to the instability of quadrilateral. Some studies reported that it was more biomechanically stabile to place the two reconstruction plates with60degree angle. But it is difficult to make sure the60degree angle in the small surgery field and the narrow space. Besides, due to the small safety region in the sacral side of sacroiliac joint, the complications occurs commonly, such as lumbosacral nerve injury and imprecise placement of plate.In order to solve the disadvantages of the conventional reconstruction plates mentioned above, we design a new internal fixation:the sacroiliac anterior papilionaceous plate (SAPP). It’s applicable for the treatment of anterior sacroiliac joint injury. To investigate the design parameters, anatomy safety, biomechanical stability and reliability for clinical application, we carry out a series of study, including anatomy studies of the sacroiliac joint, finite element analysis, biomechanical studies and retrospective clinical study.Part I:The Design and Validation of the Sacroiliac Anterior Papilionaceous Plate1. The basis of design1.1Screw Secure Area The sacralis ala is44.1±2.0mm high,22.3±1.8mm wide and49,4±1.4mm long. The auricular surface is L shaped. Its short axis is29.8±3.2mm wide, parallel to the sacralis ala platform. The long axis is54.1±4.9mm long, parallel to the ventral margin of sacrum. The width of the sacral wing platform is44mm, while the width of the articular surface is approximately30mm. The front three-quarters of the platform is the suitable area to place screw. According to the pelvic terrain map, the iliac bone is less than5mm thick in a round area near the sacroiliac joint. The diameter of the round area is about5cm. There are two ridges forming a90degree angle beyond and beneath the round area. The wings of SAPP should place on the ridges, thus the wings is designed with90degree angle. The length of the body is25mm.1.2Nerve Safety RegionOn the sacral ala platform, the distance between the sacroiliac joint line and the anterior branches of L4nerve root is closer than L5nerve root and the lumbosacral nerve trunk. It is22.2±2.6mm9.1±1.6mm from the dorsal to ventral. The narrowest distance is less than the width of the common plate, it is not appropriate to place internal fixation. The width of SAPP is designed as10mm, which is less than the distance from the anterior branches of L4nerve root to the sacroiliac joint line on the platform. Thus, the SAPP can be placed safely.2. Design Specifications and MaterialsThe sacroiliac anterior papilionaceous plate (SAPP) is designed as semi-butterfly shape, consists of the upper and lower wings and the body portion. The wings connect with the body respectively, forming135degree angle and the two wings are90degree angle across each other. The width of the plate is10mm. The length of the body portion and the wings are25mm. There’re6screw holes whose diameter is3.5mm. There is a temporary fixing hole on the body portion. At the two sides of the plate, there are3pairs of semi-circular aperture with a diameter of2. Omm. The material is Ti-6A1-4V alloy.3. Validation of the Design Feasibility4cadaver pelvis specimens of adult male (8sides) were included. Incite the abdominal wall, cut off the iliac muscle, remove the major psoas muscle, and fully reveal the sacroiliac joint. Carefully not damage the nerves and ensure the nerves in their original location. Then place the SAPP. Point A (the most forward point), point B (midpoint) and point C (the last point) were labeled on the medial edge of the body. The distance between A, B, C and anterior branches of L4, L5nerve root were measured.Results:SAPP had no touching with nerves. The distance between the medial edge of the plate and L4nerve root is shorter than L5. Point C (the most ventral point of the medial edge of the plate) is nearest to the L4nerve root (about2.5±1.2mm). Thus, it’s safe to place the plate. The depth of two sacral-side screws was about6mm and the depth of four iliac-side screws was about3mm. Screws could be placed avoiding the weak area of the ilium. It makes sure the well screw purchase. They can provide good biomechanical stability.Part II:The Finite Element Analysis and BiomechanicalStudy of Sacroiliac Anterior Papilionaceous PlateChapter I:Finite Element AnalysisMethods:One healthy volunteer (adult male,23-year-old, height172cm, weight70kg) was recruited. It gained permission from the ethical approval of the hospital ethics committee. Images of the pelvis were obtained by three-dimensional CT scans. Import the images into Mimics software to make three-dimensional model of the pelvis and meshing. Use Solidworks software to draw SAPP models (SAPP90and SAPP60), traditional reconstruction plate models (three holes) and two screws (long screw:50mm long; short screw:30mm long; both with a diameter of3.5mm). The three-dimensional pelvis model, plate models and screw models were imported into Abaqus software. Set properties and Young’s modulus of various materials. Set the number, location and stiffness of the pelvic ligaments. Set the boundary conditions in the bilateral acetabulum, bear600N load on the Sl upper endplate. Then get the stress distribution and displacement distribution of each modal. Compare the maximum displacement and rotational displacement angle between the models.Results:After the application of600N stress on the Sl endplate, the maximum displacement of SAPP90model was0.618mm, the rotational displacement was0.404degrees and the Von Mises stress was186N. For SAPP60, it was0.730mm,0.561degrees and275N respectively. For TP90model, it was0.886mm,0.769degrees and251N respectively. For TP60mode, it was0.778mm,0.748degrees and523N, respectively. For TP30model, it0.979mm,0.895degrees and241N. For TP00model is1.101mm,0.936degrees and232N. The maximum displacement of the whole pelvic model is0.478mm, the rotational displacement is0.298degrees, and Von mises stress is48.7N. The maximum displacement of the right sacroiliac joint injury model is1.992mm, the rotational displacement is3.146degrees; maximum of Von mises stress is221N, located on the ventral of left sacroiliac joint line.Conclusion:In all the testing models, SAPP90model had the minimal vertical displacement and the rotational displacement. It indicated that SAPP90had the best biomechanical stability. The stress distribution of SAPP90model focused on the plate, especially the lower screws. However, in the right sacroiliac joint dislocation model, stress focused on the left sacroiliac joint, due to no stable structure at the right side. The SAPP could reconstruct the stability of the posterior pelvic ring. It distributes the stress on both the sides. Among the traditional reconstruction plate models, TP60has the smallest vertical and rotation displacement and TP00has the biggest. It indicated traditional reconstruction plate with a60degree angle had better biomechanical stability than other TPs, but it is weaker than that SAPP.Chapter II:Biomechanical TestMethods:The right sacroiliac joint injury models were made by4pelvis specimens with ligaments (adult male) and16complete pelvis model (adult male, Sawbones1301-1). The models were connected to Instron biomechanical tester and precision non-contact magnetic grid displacement measurement system. The right sacroiliac joint was fixed with SAPP and TP separately. Then applied load on the S1endplate with speed of2mm/s, and the maximum load was set as600N. Measure the maximum stress and displacement when the SAPP and TP (wood-make) broke. Measure vertical displacement and rotational displacement of Ti-alloy-made SAPP and traditional reconstruction plate and calculate the stress-displacement curve. Compare and analyze the biomechanical stability of the sacroiliac anterior papilionaceous plate and the traditional reconstruction plate.Results:All wood made SAPP and traditional reconstruction plate ruptured when the load was less than600N. The stress value at the time of break was109.4±22.2N for SAPP90;87.8±17.6N for SAPP60,64.2±15.2N for TP90,64.9±10.2N for TP60,50.9±15.0N for TP00. Difference between the groups was statistically significant (p=0.047). When the load was600N, for SAPP90Ti, the vertical displacement was0.43±0.12mm, the rotational displacement was0.518±0.145degrees, the displacement-stress curve was:y=134.32x+45.474, R2=0.61. For TP60Ti, the vertical displacement was0.51±0.13mm, the rotational displacement was0.742±0.214mm, the displacement stress curve was:y=10.509x+62.808, R2=0.46. The difference of maximum displacement and rotation between two groups was statistically significant (p=0.049,0.032, respectively).Conclusion:According to the biomechanical comparison between wood-made SAPP and TP, SAPP90was able to beat the maximum stress load. Its displacement maximum stress curve slope is the greatest. It is indicated to be the optimal design. TP60bore the maximum stress load among the TPs. According to the biomechanical testing of Ti-alloy made SAPP90Ti and TP60Ti, SAPP90Ti had smaller vertical displacement and rotation displacement than TP60Ti. It indicated SAPP90Ti had better biomechanical stability than TP60Ti.Part III:The Clinical Application of SacroiliacAnterior Papilionaceous PlateObjective:to evaluate clinical application and short term outcome of Sacroiliac Anterior Papilionaceous Plate (SAPP) in treatment of sacroiliac joint disruption.Method:16consecutive patients with sacroiliac joint disruption associated with pelvic fracture enrolled in our hospital between2012.01. and2013.06. Detailed physical examination, X-rays, CT and FAST were performed before surgery. Operation was carried out after the patients’condition permitted usually7to14days after accident. All the16patients underwent SAPP fixation.13patients enrolled in last year as control group underwent reconstruction plate. Operation time, blood loss, placing time of SAPP were recorded. X ray films were performed after surgery to evaluate reduction condition by Matta criteria. X ray films and Majeed outcome were performed in follow up.Results:29patients were included in this study,16patients with16sacroiliac disruptions were treated by SAPP and13patients with14sacroiliac disruptions were treated by reconstruction plate. According to the Tile classification, there were17Type B and12Type C. For SAPP group, operation time was101.1±31.9min, blood loss1091.8±302.9ml, Placing time of SAPP was6.3±3.1min. For control group, operation time was110.8±29.6min, blood loss was1154.1±281.2ml, placing time of reconstruction plate was14.9±1.6min. According to Matta criteria, there were9excellent,14good,5fair,1poor. There were1lumbosacral nerve injury,7lateral femoral cutaneous nerve injury,2massive blood loss occurred, while none posterior infection occurred. Compared with control group, SAPP group experienced shorter placing time of SAPP, and less blood loss in type B pelvic fracture.Conclusion:As a new instrument, Sacroiliac Anterior Papilionaceous Plate (SAPP) could be well applied in treatment of sacroiliac disruption. Compared with reconstructed plate, SAPP obviously shorten placing time and facilitated placing procedure, while did not increase blood loss, neurological risk and infection rate and did not need different incision and reduction method. |
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