The Biomechanical Simulation And Finite Element Analysis Of Internal Fixations For Acetabular Fracture

High-energy violence may cause acetabular fractures, which are often combined with organs, blood vessels, nerve damage and so on, with serious damage to the anatomy of the hip. In addition, acetabular fracture belong intra-articular fracture, surgical treatment require anatomic reduction and stable fixation. If the treatment was poor, the serious complications, such as traumatic arthritis, femoral head necrosis, would often occur. So acetabular fractures have high morbidity and mortality. Therefore, the treatment of acetabular fractures is particularly important. From the clinical point of view, based on the acetabular inverted Y-shaped structure, Judet and Letournel made proposed two columns thoery. The anterior column was also known as the iliopubic column, which include the iliac crest front, acetabular lip, the front wall, the top part of the mortar, all pubic, iliac wing underneath the front of the pelvis and a small entrance leading edge. The posterior column composed by part of the ilium and the ischial was also known as the iliac sit column, which include the sciatic notch, after acetabular lip, the posterior wall, part of the acetabular roof and all ischial.Acetabular fractures may simply involve the posterior column or anterior column, while also involving the double column. During the past several years, the researches of treatment for acetabular fractures were mostly concentrated in the measurement of the anterior or the posterior column and the biomechanical study of double column fractures, and obtaining some progress. Technology base also developed from the entity pelvis cadavers, gradually extended to three-dimensional finite element based on CT. It was low cost, adequate sample size, accurate result, better adaptability to apply the finite element techniques to pelvic and acetabular fractures. In this study, we would use the finite element technology, according to the pelvis acetabulum CT to establish the anterior column, posterior column and T-shaped acetabular fracture fixation models, biomechanical research executed sequentially.Part 1:Construction and Validation normal pelvis acetabulum modelObjectiveTo establish an effective pelvis acetabulum model, and provide the basis for constructing acetabular fracture fixation model.MethodsAccording to pelvic CT of healthy volunteers, use Mimics, Geomagic, Solidworks software to build pelvic acetabular bone model and optimize the model, and then import the model into Ansys software to assign material property, mesh, add related pelvic acetabular ligament, establishing a three-dimensional finite element model. Last examine its effectiveness.ResultsThe distances of the bony salient points for the pelvis had no significant difference (P> 0.05) between the before and after optimization. Finite element analysis results showed:in standing, the stress mainly conducted from the sacrum to both sides of the sacroiliac joint and ilium, then along with the arcuate line and greater sciatic notch, end to the hip joint and bilateral femur.ConclusionThe pelvic acetabular morphology and mechanical model, established by use of three-dimensional finite element technology was effective, and could be used for subsequent experiments.Part 2:Finite element analysis of internal fixation for acetabular anterior column fractureObjectiveTo evaluate the biomechanical stability of kinds of internal fixations in treatment of acetabular anterior column fracture.MethodsFinite element modeling software was used to establish internal fixation models for treating low acetabular anterior column fracture, including lag screws (A), anterior column reconstruction plates (B), not across the pubic symphysis subcutaneous plates(C) and across the pubic symphysis subcutaneous plates (D), and models for treating high acetabular anterior column fracture, including lag screws (E), anterior column reconstruction plates (F). The finite element analysis was carried out in standing and sitting by the same loading way.ResultsIn standing and sitting, the maximum displacement and the mean node displacement of fracture lines of low acetabular anterior column fracture of A (respectively 0.514mm,0.634mm and 0.432±0.085mm、0.473±0.108 mm) were larger. And these of D (respectively 0.507mm,0.629mm and 0.429±0.084mm、 0.464±0.109 mm) were minimal. And the difference among A, B, C and D were significant. No matter than in standing and sitting, the maximum displacement and the mean node displacement of fracture lines of high acetabular anterior column fracture of F were all minimal.ConclusionThe stability of across the pubic symphysis subcutaneous plate fixation treating for acetabular fractures of the lower anterior column was best. Reconstruction plating the anterior high column had better mechanical stability than lag screw.Part 3:Finite element analysis of three kinds of internal fixation for acetabular posterior column fractureObjectiveTo evaluate the biomechanical stability of long plates and retrograde percutaneous lag screws in internal fixation surgery for the treatment of acetabular posterior column fracture.MethodsFinite element modeling software was used to establish internal fixation models for treating a acetabular posterior column fracture, including a small sciatic notch lag screws (A), lag screws through the ischial tuberosity(B) and a long plate (C). The finite element analysis was carried out in standing and sitting by the same loading way.ResultsIn standing and sitting, the maximum displacement:A were 0.431mm,0.339mm; B were 0.447mm,0.339mm; C were 0.437mm,0.293mm, respectively). And the mean node displacement of fracture lines:A were 0.393±0.043 mm,0.321±0.018 mm; B were 0.408±0.045 mm,0.319±0.017 mm; C were 0.395±0.045 mm,0.275± 0.015 mm; respectively). In standing, A were minimal. In sitting, C were minimal. The difference among A, B and C were significant.ConclusionIn standing, lag screws through small sciatic notch had better stability. In sitting, column a long reconstruction plate fixing had better stability.Part 4:Finite element analysis of the stability of T-shaped acetabular fractures by different internal fixation methodsObjectiveTo evaluate the biomechanical stability of four internal fixations in treatment for the T-shaped acetabular fractures.MethodsFinite element modeling software was used to establish internal fixation models for treating the T-shaped acetabular fractures, including double column lag screws (A), anterior column plate combined with posterior column lag screw (B), posterior column plate combined with anterior column lag screw (C) and both anterior and posterior column plates (D). The finite element analysis was carried out in standing and sitting by the same loading way.ResultsIn standing and sitting, the maximum displacement and the mean node displacement of anterior and posterior column fracture lines of acetabular fracture of T type were both A＞B＞C＞D. A (maximum displacement in standing: anterior column 0.516mm, posterior column 0.504mm; maximum displacement in sitting:anterior column 0.631mm, posterior column 0.487mm; mean displacement in standing:anterior column 0.507±0.004mm, posterior column 0.469± 0.021mm; mean displacement in sitting:0.581±0.035 anterior column mm, posterior column 0.390±0.051mm) was maximum. D(maximum displacement in standing:anterior column 0.0.498mm, posterior column 0.0.486mm; maximum displacement in sitting:anterior column 0.523mm, posterior column 0.0.417mm; mean displacement in standing:anterior column 0.490±0.004mm, posterior column 0.453±0.020mm; mean displacement in sitting:anterior column 0.481 ±0.029mm, posterior column 0.329±0.047mm) was minimum. And the difference among A, B, C and D were significant.ConclusionThe stability of double column reconstruction plates fixation treating for acetabular fracture of T type was best, followed by posterior column reconstruction plate combined with anterior column lag screw. Both were preferred to traditional fixed manners.