Role of the proximal tibiofibular joint on the biomechanics of the knee joint: A three-dimensional finite element analysis.

PURPOSE: The proximal tibiofibular joint (PTFJ) is easily ignored, although many diseases of the knee are caused by PTFJ injuries. Therefore, studying PTFJ biomechanics is very important. The effects of PTFJ injury on ankle function have been reported. However, few studies have assessed the effects of PTFJ injury on the knee joint. This study was performed to describe the biomechanical effects of PTFJ on the knee joint according to a three-dimensional finite element model. METHODS: The knee joint of a healthy volunteer was scanned by CT and MRI. CT and MRI scanning data in DICOM format were imported into Mimics software. Subsequently, 3D models of the normal and PTFJ injured knee, including the bone, cartilage, meniscus and ligament structures were established, and their validity was verified on the basis of available studies in literature. The biomechanical changes in the two knee models under different conditions were compared. RESULTS: The validity of the intact model was verified. No significant difference was observed in tibial mobility in the two models under the conditions of 134 N forward, 10 N·m internal rotation and 10 N·m valgus load. After application of 134 N backward, 10 N·m varus and external rotation load with respect to the tibia, the posterior movement of the tibia and the varus and external rotation angles of the tibia were 3.583±0.892 mm, 4.799±0.092° and 18.963±0.027° in the normal knee model, and 5.127±1.224 mm, 5.277±0.104° and 21.399±0.031° in the PTFJ injury model, respectively, and a significant statistical difference was observed. CONCLUSIONS: PTFJ played an important role in maintaining the posterolateral stability of the knee joint and thus deserves more attention in clinical operations.

Three-dimensional digital anatomical measurement of modified sacroiliac screws.

PURPOSE: To rebuild a model of the pelvis and effectively simulate the trajectory of modified sacroiliac screws, we measured the parameters of each screw and screw channel and assessed the safety and feasibility of the parameters in adults. METHOD AND MATERIALS: One hundred (50 males and 50 females) normal adult pelvic computed tomography (CT) images were randomly selected and imported into Mimics software to rebuild the three-dimensional pelvis model. In these models, each ideal channel of modified screws was simulated, and then we obtained the precise parameters of screws and channels using Mimics and Three-matic software. RESULTS: The results of the comparison (right vs. left) showed that there were no significant differences in any of the angles, radius or M1SI parameters (the first modified sacroiliac). However, one parameter (BS) of M2SI (the second modified sacroiliac), two parameters (AP and BS) of M3SI (the third modified sacroiliac), and three parameters (AP, BS, L) of M4SI (the fourth modified sacroiliac) were statistically significant (P < 0.05). The result of comparison (between genders) showed that there were no significant differences in M1SI and M2SI; in contrast, the radius, length and the α angle of M3SI and M4SI were significantly different between genders (P < 0.05), and the radius of M4SI required special attention. If the radius of the limiting screw channel was > 3.50 mm, 52 cases (52%, 24 males and 28 females) could not complete the M4SI screw placement among 100 samples. If the radius of the limiting screw channel was > 3.0 mm, a total of 10 cases (10%, 2 males and 8 females) could not complete the M4SI screw placement. CONCLUSION: Through the measurement of 100 healthy adult real three-dimensional pelvic models, we obtained the parameters of each modified sacroiliac screw and measured the three angles of each screw based on international coordinates for the first time, which can instruct clinical application.

Finite element analysis of infra-acetabular screw fixation for the treatment of acetabular posterior column fracture.

BACKGROUND: Infra-acetabular screws have been described to increase the fixation strength of acetabular fractures with separation of the columns. Previous studies were based on the simulation of the anterior column fractures without modelling the biomechanical effect of the screw in the posterior column fractures. The purpose of this study was to compare the stability of different internal fixation models of posterior column fracture and to provide a theoretical basis for the clinical application of infra-acetabular screws. METHODS: Five internal fixation models of acetabular posterior column fracture were simulated using five implants, including one reconstruction plate (PCP model), one posterior column screw (PCS model), one infra-acetabular screw (PIS model), one infra-acetabular screw and one reconstruction plate (PIS + PCP model), and one infra-acetabular screw and one posterior column screw (PIS + PCS model). After meshing, material parameter, and boundary condition settings, a vertical downward load of 500 N was applied on the surface of the sacrum. To evaluate the biomechanical properties, the stress distribution and von Mises peak stress were recorded and analyzed, and the displacement distributions of the upper and lower fracture surfaces were compared. RESULTS: In model PCP, the maximum stress of the plate is 71.952 MPa; in model PCS, the maximum stress of the screw is 52.740 MPa; in model PIS, the maximum stress of the screw is 68.985 MPa; in model PIS + PCP, the maximum stress of the plate is 64.695 MPa and the maximum stress of the screw is 39.679 MPa; and in model PIS + PCS, the maximum stress of the posterior column screw is 48.197 MPa and the maximum stress of the infra-acetabular screw is 65.201 MPa. The maximum stresses of implants are all located on the fracture surfaces. The average displacement differences of the upper and lower fracture surfaces are compared as follows: model PIS + PCS (0.03503 mm) < model PIS + PCP (0.08205 mm) < model PCP (0.10096 mm) < model PCS (0.19007 mm) < model PIS (0.23546 mm). CONCLUSION: With sufficient biomechanical stability, infra-acetabular screws can be used as a supplementary fixation for the treatment of acetabular posterior column fractures. It is recommended to fix the fracture by the combined application of the infra-acetabular screw and posterior column screw.