Based on the CT data and the structure characteristics of the femoral fractures during different healing stages, medical FE models of fractured femur treated with locking compression plate (LCP)were built.Under the physiological load of a standard body weight (70 kg) and the constraint condition,the stress distributions of LCP and fractured femur during healing were calculated by means of three-dimensional finite element analysis (3D-FEA).The results showed that the stress distribution in the LCP and the fractured femur was similar,during the initial stage which there was no newly formed bone or soft tissue in fracture site.The maximum von Mises stress (371.23,272.76 MPa) in the fractured femur was much higher than that in natural femur,and the intensive stress was concentrated mainly in the proximal area of the fractured femur.With the growth of bony callus bone in fracture site,the intensity of stress in proximal femur decreased.Contrasted to the two cases mentioned above,the value of the maximum von Mises stress (68.17 MPa) in bony callus bone stage decreased significantly,and was lower than the safe strength of natural bone.Therefore,appropriate training which is benefitial for the growth to new bone could be arranged for the better rehabilitation.
A three-dimensional finite element model of premaxillary bone and anterior teeth was established with ANSYS 13.0. The anterior teeth were fixed with strong stainless labial archwire and lingual frame. In the horizontal loading experiments, a horizontal retraction force of 1.5 N was applied bilaterally to the segment through hooks at the same height between 7 and 21 mm from the incisal edge of central incisor; in vertical loading experiments, a vertical intrusion force of 1.5 N was applied at the midline of lingual frame with distance between 4 and 16 mm from the incisal edge of central incisor. After loading, solution was done and displacement and maximum principle stress were calculated. After horizontal loading, lingual displacement and stress in periodontal membrane (PDM) was most homogeneous when the traction force was 14 mm from the edge of central incisor; after vertical loading, intrusive displacement and stress in PDM were most homogeneous when the traction force was 12 mm from the incisal edge of central incisor. The results of this study suggested that the location of center of resistance (CRe) of six maxillary anterior teeth is about 14 mm gingivally and 12 mm lingually to incisal edge of central incisor. The location can provide evidence for theoretical and clinical study in orthodontics.
This study was aimed to compare the mechanical characteristics under different physiological load conditions with three-dimensional finite element model of rigid fixation and elastic fixation in the lumbar. We observed the stress distribution characteristics of a sample of healthy male volunteer modeling under vertical, flexion and extension torque situation. The outcomes showed that there existed 4-6 times pressure on the connecting rod of rigid fixation compared with the elastic fixations under different loads, and the stress peak and area of force on elastic fixation were much higher than that of the rigid fixations. The elastic fixation has more biomechanical advantages than rigid fixation in promoting interbody lumbar fusion after surgery.
We developed a three-dimensional finite element model of the pelvis. According to Letournel methods, we established a pelvis model of T-shaped fracture with its three different fixation systems, i.e. double column reconstruction plates, anterior column plate combined with posterior column screws and anterior column plate combined with quadrilateral area screws. It was found that the pelvic model was effective and could be used to simulate the mechanical behavior of the pelvis. Three fixation systems had great therapeutic effect on the T-shaped fracture. All fixation systems could increase the stiffness of the model, decrease the stress concentration level and decrease the displacement difference along the fracture line. The quadrilateral area screws, which were drilled into cortical bone, could generate beneficial effect on the T-type fracture. Therefore, the third fixation system mentioned above (i.e. the anterior column plate combined with quadrilateral area screws) has the best biomechanical stability to the T-type fracture.
Objective To establish a three-dimensional finite element analysis model of the knee joint in fresh frozen cadavers, to verify the validity of the model and to simulate the stress distribution characteristics of the patellofemoral joint after combined proximal and distal knee extension rearrangement surgery for recurrent patellar dislocation. Methods One male and one female fresh frozen cadavers (4 knees in total), using voluntary body donations, were used to measure the maximum pressure on the patellofemoral articular surface at each passive flexion angle (0°, 30°, 60°, 90°, 120°) of the normal knee joint and the model after combined proximal and distal knee extension rearrangement surgery for recurrent patellar dislocation with tibial tuberosity-trochlear groove distance (TT-TG) value >2.00 cm using pressure-sensitive paper, respectively. Then, the 2 freshly frozen cadavers were used to construct three-dimensional finite element models of normal knee joints and postoperative knee joints, and the maximum pressure on the patellofemoral articular surface was measured at various passive flexion angles. The maximum pressure was compared with the measurement results of the pressure-sensitive paper to verify the validity of the three-dimensional finite element model. In addition, the maximum pressure on the patellofemoral joint surface measured by three-dimensional finite element was compared between the normal knee joint and the postoperative knee joint at various passive flexion angles, so as to obtain an effective three-dimensional finite element model for the simulation study of the stress distribution characteristics of the patellofemoral joint after combined proximal and distal knee extension rearrangement surgery for recurrent patellar dislocation. ResultsThe maximum pressure on the patellofemoral joint surface measured by pressure-sensitive paper and three-dimensional finite element measurements were similar at all passive flexion angles in the normal knee joint, with a difference of −0.08-0.06 MPa; the maximum pressure on the patellofemoral joint surface measured by pressure-sensitive paper and three-dimensional finite element measurements were also similar at all passive flexion angles in the knee after combined proximal and distal knee extension rearrangement surgery, with a difference of −0.04-0.09 MPa. The maximum pressure on the patellofemoral joint surface measured by three-dimensional finite elements were also similar between the normal knee joint and the knee joint after combined proximal and distal knee extension rearrangement surgery at all passive flexion angles, with a difference of −0.50-−0.03 MPa. ConclusionThe three-dimensional finite element model of the normal knee joint and the knee joint after combined proximal and distal knee extension rearrangement surgery can accurately and effectively quantify the change in the maximum pressure on the patellofemoral joint surface; for recurrent patellar dislocations with TT-TG value>2.00 cm, the combined proximal and distal knee extension rearrangement surgery can achieve a maximum pressure of the patellofemoral joint surface similar to that of the normal knee joint.
ObjectiveTo explore the biomechanical stability of the medial column reconstructed with the exo-cortical placement of humeral calcar screw by three-dimensional finite element analysis. MethodsA 70-year-old female volunteer was selected for CT scan of the proximal humerus, and a wedge osteotomy was performed 5 mm medially inferior to the humeral head to form a three-dimensional finite element model of a 5 mm defect in the medial cortex. Then, the proximal humeral locking plate (PHILOS) was placed. According to distribution of 2 calcar screws, the study were divided into 3 groups: group A, in which 2 calcar screws were inserted into the lower quadrant of the humeral head in the normal direction for supporting the humeral head; group B, in which 1 calcar screw was inserted outside the cortex below the humeral head, and the other was inserted into the humeral head in the normal direction; group C, in which 2 calcar screws were inserted outside the cortex below the humeral head. The models were loaded with axial, shear, and rotational loadings, and the biomechanical stability of the 3 groups was compared by evaluating the peak von mises stress (PVMS) of the proximal humerus and the internal fixator, proximal humeral displacement, neck-shaft angle changes, and the rotational stability of the proximal humerus. Seven cases of proximal humeral fractures with comminuted medial cortex were retrospectively analyzed between January 2017 and December 2020. Locking proximal humeral plate surgery was performed, and one (5 cases) or two (2 cases) calcar screws were inserted into the inferior cortex of the humeral head during the operation, and the effectiveness was observed. Results Under axial and shear force, the PVMS of the proximal humerus in group B and group C was greater than that in group A, the PVMS of the internal fixator in group B and group C was less than that in group A, while the PVMS of the proximal humerus and internal fixator between group B and group C were similar. The displacement of the proximal humerus and the neck-shaft angle change among the 3 groups were similar under axial and shear force, respectively. Under the rotational torque, compared with group A, the rotation angle of humerus in group B and group C increased slightly, and the rotation stability decreased slightly. All the 7 patients were followed up 6-12 months. All the fractures healed, and the healing time was 8-14 weeks, with an average of 10.9 weeks; the neck-shaft angle changes (the difference between the last follow-up and the immediate postoperative neck-shaft angle) was (1.30±0.42)°, and the Constant score of shoulder joint function was 87.4±4.2; there was no complication such as humeral head varus collapse and screw penetrating the articular surface. ConclusionFor proximal humeral fractures with comminuted medial cortex, exo-cortical placement of 1 or 2 humeral calcar screw of the locking plate outside the inferior cortex of the humeral head can also effectively reconstruct medial column stability, providing an alternative approach for clinical practice.
Objective To analyze the biomechanical changes of hallux valus after Swanson prosthesis-arthroplasty of the 1st metatarsophalangeal joint combined with osteotomy and bone grafting of the 1st metatarsal bone by three-dimensional finite element analysis, so as to provide data basis for studying the changes of foot morphology and physiological function after hallux valus correction surgery. Methods A 65-year-old female patient with severe hallux valus admitted in January 2013 was selected as the research object. The CT data of the right foot was obtained, and the three-dimensional finite element models before and after Swanson prosthesis-arthroplasty of the 1st metatarsophalangeal joint combined with osteotomy and bone grafting of the 1st metatarsal bone were established by Mimics10.01, Geomagic Studio, and ANSYS12.0 software. ANSYS 12.0 software was used for nonlinear static stress analysis, and the hallux valgus angle (HVA), the intermetatarsal angle (IMA), and the von Mises stress distributions of the forefoot plantar surface and the 1st to 5th metatarsal bones were observed before and after operation. ResultsThe HVA and IMA were 56.3° and 16.3° before operation and 9.2° and 9.8° after operation, respectively. Before operation, the stress on the forefoot was the largest in the 4th metatarsal head zone and the smallest in the 1st metatarsal head zone; the stress on the medial side of the forefoot was significantly smaller than that on the lateral side, and the center of forefoot pressure was located on the lateral side. After operation, the stress on the forefoot was the largest in the 1st metatarsal head zone and the smallest in the 5th metatarsal head zone; the stress on the lateral side of the forefoot was significantly smaller than that on the medial side, and the center of forefoot pressure was located on the medial side. Before operation, the stress of the 5th metatarsal bone was the largest, and the 1st metatarsal bone was the smallest. After operation, the stress of the 1st metatarsal bone was the largest, and the 4th metatarsal bone was the smallest. Conclusion Swanson prosthesis-arthroplasty of the 1st metatarsophalangeal joint combined with osteotomy and bone grafting of the 1st metatarsal bone can effectively correct hallux valgus and make HVA, IMA, and plantar pressure distribution close to normal. However, postoperative stresses of the 1st to 5th metatarsal bones elevate, which may lead to associated complications.