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.
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.
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.