Objective To compare the biomechanical properties of personalized Y-shaped plates with horizontal plates, vertical plates, and traditional Y-shaped plates in the treatment of distal humeral intra-articular fractures through finite element analysis, and to evaluate their potential for clinical application. Methods The study selected a 38-year-old male volunteer and obtained a three-dimensional model of the humerus by scanning his upper limbs using a 64-slice spiral CT. Four types of fracture-internal fixation models were constructed using Mimics 19.0, Geomagic Wrap 2017, Creo 6.0, and other software: horizontal plates, vertical plates, traditional Y-shaped plate, and personalized Y-shaped plate. The models were then meshed using Hypermesh 14.0 software, and material properties and boundary conditions were defined in Abaqus 6.14 software. AnyBody 7.3 software was used to simulate elbow flexion and extension movements, calculate muscle strength, joint forces, and load torques, and compare the peak stress and maximum displacement of the four fixation methods at different motion angles (10°, 30°, 50°, 70°, 90°, 110°, 130°, 150°) during elbow flexion and extension. Results Under dynamic loading during elbow flexion and extension, the personalized Y-shaped plate exhibits significant biomechanical advantages. During elbow flexion, the peak internal fixation stress of the personalized Y-shaped plate was (28.8±0.9) MPa, which was significantly lower than that of the horizontal plates, vertical plates, and traditional Y-shaped plate (P<0.05). During elbow extension, the peak internal fixation stress of the personalized Y-shaped plate was (18.1±1.6) MPa, which was lower than those of the other three models, with significant differences when compared with horizontal plates and vertical plates (P<0.05). Regarding the peak humeral stress, the personalized Y-shaped plate model showed mean values of (10.9±0.8) and (13.1±1.4) MPa during elbow flexion and extension, respectively, which were significantly lower than those of the other three models (P<0.05). Displacement analysis showed that the maximum displacement of the humerus with the personalized Y-shaped plate during elbow flexion was (2.03±0.08) mm, slightly higher than that of the horizontal plates, but significantly lower than that of the vertical plates, showing significant differences (P<0.05). During elbow extension, the maximum displacement of the humerus with the personalized Y-shaped plate was (1.93±0.13) mm, which was lower than that of the other three models, with significant differences when compared with vertical plates and traditional Y-shaped plates (P<0.05). Stress contour analysis showed that the stress of the personalized Y-shaped plate was primarily concentrated at the bifurcation of the Y-shaped structure. Displacement contour analysis showed that the personalized Y-shaped plate effectively controlled the displacement of the distal humerus during both flexion and extension, demonstrating excellent stability. ConclusionThe personalized Y-shaped plate demonstrates excellent biomechanical performance in the treatment of distal humeral intra-articular fractures, with lower stress and displacement, providing more stable fixation effects.
Objective To compare the biomechanical differences among the three novel internal fixation modes in treatment of bicondylar four-quadrant fractures of the tibial plateau through finite-element technique, and find an internal fixation modes which was the most consistent with mechanical principles. Methods Based on the CT image data of the tibial plateau of a healthy male volunteer, a bicondylar four-quadrant fracture model of the tibial plateau and three experimental internal fixation modes were established by using finite element analysis software. The anterolateral tibial plateaus of groups A, B, and C were fixed with inverted L-shaped anatomic locking plates. In group A, the anteromedial and posteromedial plateaus were longitudinally fixed with reconstruction plates, and the posterolateral plateau was obliquely fixed with reconstruction plate. In groups B and C, the medial proximal tibia was fixed with T-shaped plate, and the posteromedial plateau was longitudinally fixed with the reconstruction plate or posterolateral plateau was obliquely fixed with the reconstruction plate, respectively. An axial load of 1 200 N was applied to the tibial plateau (a simulation of a 60 kg adult walking with physiological gait), and the maximum displacement of fracture and maximum Von-Mises stress of the tibia, implants, and fracture line were calculated in 3 groups. Results Finite element analysis showed that the stress concentration area of tibia in each group was distributed at the intersection between the fracture line and screw thread, and the stress concentration area of the implant was distributed at the joint of screws and the fracture fragments. When axial load of 1 200 N was applied, the maximum displacement of fracture fragments in the 3 groups was similar, and group A had the largest displacement (0.74 mm) and group B had the smallest displacement (0.65 mm). The maximum Von-Mises stress of implant in group C was the smallest (95.49 MPa), while that in group B was the largest (177.96 MPa). The maximum Von-Mises stress of tibia in group C was the smallest (43.35 MPa), and that in group B was the largest (120.50 MPa). The maximum Von-Mises stress of fracture line in group A was the smallest (42.60 MPa), and that in group B was the largest (120.50 MPa). Conclusion For the bicondylar four-quadrant fracture of the tibial plateau, a T-shaped plate fixed in medial tibial plateau has a stronger supporting effect than the use of two reconstruction plates fixed in the anteromedial and posteromedial plateaus, which should be served as the main plate. The reconstruction plate, which plays an auxiliary role, is easier to achieve anti-glide effect when it is longitudinally fixed in posteromedial plateau than obliquely fixed in posterolateral plateau, which contributes to the establishment of a more stable biomechanical structure.
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.
In the study of oral orthodontics, the dental tissue models play an important role in finite element analysis results. Currently, the commonly used alveolar bone models mainly have two kinds: the uniform and the non-uniform models. The material of the uniform model was defined with the whole alveolar bone, and each mesh element has a uniform mechanical property. While the material of the elements in non-uniform model was differently determined by the Hounsfield unit (HU) value of computed tomography (CT) images where the element was located. To investigate the effects of different alveolar bone models on the biomechanical responses of periodontal ligament (PDL), a clinical patient was chosen as the research object, his mandibular canine, PDL and two kinds of alveolar bone models were constructed, and intrusive force of 1 N and moment of 2 Nmm were exerted on the canine along its root direction, respectively, which were used to analyze the hydrostatic stress and the maximal logarithmic principal strain of PDL under different loads. Research results indicated that the mechanical responses of PDL had been affected by alveolar bone models, no matter the canine translation or rotation. Compared to the uniform model, if the alveolar bone was defined as the non-uniform model, the maximal stress and strain of PDL were decreased by 13.13% and 35.57%, respectively, when the canine translation along its root direction; while the maximal stress and strain of PDL were decreased by 19.55% and 35.64%, respectively, when the canine rotation along its root direction. The uniform alveolar bone model will induce orthodontists to choose a smaller orthodontic force. The non-uniform alveolar bone model can better reflect the differences of bone characteristics in the real alveolar bone, and more conducive to obtain accurate analysis results.
Modified electroconvulsive therapy (MECT) and magnetic seizure therapy (MST) are effective treatments for severe major depression. MECT has better efficacy in the treatment than MST, but it has cognitive and memorial side effects while MST does not. To study the causes of these different outcomes, this study contrasted the electric filed strength and spatial distribution induced by MECT and MST in a realistic human head model. Electric field strength induced by MECT and MST are simulated by the finite element method, which was based on a realistic human head model obtained by magnetic resonance imaging. The electrode configuration of MECT is standard bifrontal stimulation configuration, and the coil configuration of MST is circular. Maps of the ratio of the electric field strength to neural activation threshold are obtained to evaluate the stimulation strength and stimulation focality in brain regions. The stimulation strength induced by MECT is stronger than MST, and the activated region is wider. MECT stimulation strength in gray matter is 17.817 times of that by MST, and MECT stimulation strength in white matter is 23.312 times of that by MST. As well, MECT stimulation strength in hippocampi is 35.162 times of that by MST. More than 99.999% of the brain volume is stimulated at suprathreshold by MECT. However, MST activated only 0.700% of the brain volume. The stimulation strength induced by MECT is stronger than MST, and the activated region is wider may be the reason that MECT has better effectiveness. Nevertheless, the stronger stimulation strength in hippocampi induced by MECT may be the reason that MECT is more likely to give rise to side effects. Based on the results of this study, it is expected that a more accurate clinical quantitative treatment scheme should be studied in the future.
Spinal cord stimulation (SCS) for pain is usually implanted as an open loop system using unchanged parameters. To avoid the under and over stimulation caused by lead migration, evoked compound action potentials (ECAP) is used as feedback signal to change the stimulating parameters. This study established a simulation model of ECAP recording to investigate the relationship between ECAP component and dorsal column (DC) fiber recruitment. Finite element model of SCS and multi-compartment model of sensory fiber were coupled to calculate the single fiber action potential (SFAP) caused by single fiber in different spinal cord regions. The synthetized ECAP, superimposition of SFAP, could be considered as an index of DC fiber excitation degree, because the position of crests and amplitude of ECAP corresponds to different fiber diameters. When 10% or less DC fibers were excited, the crests corresponded to fibers with large diameters. When 20% or more DC fibers were excited, ECAP showed a slow conduction crest, which corresponded to fibers with small diameters. The amplitude of this slow conduction crest increased as the stimulating intensity increased while the amplitude of the fast conduction crest almost remained unchanged. Therefore, the simulated ECAP signal in this paper could be used to evaluate the degree of excitation of DC fibers. This SCS-ECAP model may provide theoretical basis for future clinical application of close loop SCS base on ECAP.
The decrease of corneal stiffness is the key factor leading to keratoconus, and the corneal collagen fiber stiffness and fiber dispersion are closely related to the corneal biomechanical properties. In this paper, a finite element model of human cornea based on corneal microstructure, namely collagen fiber, was established before and after laser assisted in situ keratomileusis (LASIK). By simulating the Corvis ST process and comparing with the actual clinical results, the hyperelastic constitutive parameters and corneal collagen fiber stiffness modulus of the corneal material were determined before and after refractive surgery. After LASIK, the corneal collagen fiber stiffness modulus increased significantly, and was highly correlated with central corneal thickness (CCT). The predictive relationship between the corneal collagen fiber stiffness modulus and the corresponding CCT before and after surgery was: k1 before = exp(9.14 ? 0.009CCTbefore), k1 after = exp(8.82 ? 0.008CCTafter). According to the results of this study, the central corneal thickness of the patient can be used to estimate the preoperative and postoperative collagen fiber stiffness modulus, and then a personalized corneal model that is more consistent with the actual situation of the patient can be established, providing a theoretical reference for more accurately predicting the safe surgical cutting amount of the cornea.
Objective To establish the finite element model of varus-type ankle arthritis and to implement the finite element mechanical analysis of different correction models for tibial anterior surface angle (TAS) in supramalleolar osteotomy. Methods A female patient with left varus-type ankle arthritis (Takakura stage Ⅱ, TAS 78°) was taken as the study object. Based on the CT data, the three-dimensional model of varus-type ankle arthritis (TAS 78°) and different TAS correction models [normal (TAS 89°), 5° valgus (TAS 94°), and 10° valgus (TAS 99°)] were created by software Mimics 21.0, Geomagic Wrap 2021, Solidworks 2017, and Workbench 17.0. The 290 N vertical downward force was applied to the upper surface of the tibia and 60 N vertical downward force to the upper surface of the fibula. Von Mises stress distribution and stress peak were calculated. Results The finite element model of normal TAS was basically consistent with biomechanics of the foot. According to biomechanical analysis, the maximum stress of the varus model appeared in the medial tibiotalar joint surface and the medial part of the top tibiotalar joint surface. The stress distribution of talofibular joint surface and the lateral part of the top tibiotalar joint surface were uniform. In the normal model, the stress distributions of the talofibular joint surface and the tibiotalar joint surface were uniform, and no obvious stress concentration was observed. The maximum stress in the 5° valgus model appeared at the posterior part of the talofibular joint surface and the lateral part of the top tibiotalar joint surface. The stress distribution of medial tibiotalar joint surface was uniform. The maximum stress of the 10° valgus model appeared at the posterior part of the talofibular joint surface and the lateral part of the top tibiotalar joint surface. The stress on the medial tibiotalar joint surface increased. Conclusion With the increase of valgus, the stress of ankle joint gradually shift outwards, and the stress concentration tends to appear. There was no obvious obstruction of fibula with 10° TAS correction. However, when TAS correction exceeds 10° and continues to increase, the obstruction effect of fibula becomes increasingly significant.
ObjectiveTo discuss the influence of artificial ankle elastic improved inserts (hereinafter referred to as “improved inserts”) in reducing prosthesis micromotion and improving joint surface contact mechanics by finite element analysis. Methods Based on the original insert of INBONE Ⅱ implant system (model A), four kinds of improved inserts were constructed by adding arc or platform type flexible layer with thickness of 1.3 or 2.6 mm, respectively. They were Flying goose type_1.3 elastic improved insert (model B), Flying goose type_2.6 elastic improved insert (model C), Platform type_1.3 elastic improved insert (model D), Platform type_2.6 elastic improved insert (model E). Then, the CT data of right ankle at neutral position of a healthy adult male volunteer was collected, and finite element models of total ankle replacement (TAR) was constructed based on model A-E prostheses by software of Mimics 19.0, Geomagic wrap 2017, Creo 6.0, Hypermesh 14.0, and Abaqus 6.14. Finally, the differences of bone-metal prosthesis interface micromotion and articular surface contact behavior between different models were investigated under ISO gait load. Results The tibia/talus-metal prosthesis interfaces micromotion of the five TAR models gradually increased during the support phase, then gradually fell back after entering the swing phase. The improved models (models B-E) showed lower bone-metal prosthesis interface micromotion when compared with the original model (model A), but there was no significant difference among models A-E (P>0.05). The maximum micromotion of tibia appeared at the dome of the tibial bone groove, and the ??micromotion area was the largest in model A and the smallest in model E. The maximum micromotion of talus appeared at the posterior surface of the central bone groove, and there was no difference in the micromotion area among models A-E. The contact area of the articular surface of the insert/talus prosthesis in each group increased in the support phase and decreased in the swing phase during the gait cycle. Compared with model A, the articular surface contact area of models B-E increased, but there was no significant difference among models A-E (P>0.05). The change trend of the maximum stress on the articular surface of the inserts/talus prosthesis was similar to that of the contact area. Only the maximum contact stress of the insert joint surface of models D and E was lower than that of model A, while the maximum contact stress of the talar prosthesis joint surface of models B-E was lower than that of model A, but there was no significant difference among models A-E (P>0.05). The high stress area of the lateral articular surface of the improved inserts significantly reduced, and the articular surface stress distribution of the talus prosthesis was more uniform. Conclusion Adding a flexible layer in the insert can improve the elasticity of the overall component, which is beneficial to absorb the impact force of the artificial ankle joint, thereby reducing interface micromotion and improving contact behavior. The mechanical properties of the inserts designed with the platform type and thicker flexible layer are better.
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.
