BACKGROUND: Current research lacks comprehensive investigation into the biomechanical changes in the spinal cord and nerve roots during scoliosis correction. This study employs finite element analysis to extensively explore these biomechanical variations across different Cobb angles, providing valuable insights for clinical treatment.
METHODS: A personalized finite element model, incorporating vertebrae, ligaments, spinal cord, and nerve roots, was constructed using engineering software. Forces and displacements were applied to achieve Cobb angle improvements, designating T1/2-T4/5 as the upper segment, T5/6-T8/9 as the middle segment, and T9/10-L1/2 as the lower segment. Simulations under traction, pushing, and traction + torsion conditions were conducted, and biomechanical changes in each spinal cord segment and nerve roots were analyzed.
RESULTS: Throughout the scoliosis correction process, the middle spinal cord segment consistently exhibited a risk of injury under various conditions and displacements. The lower spinal cord segment showed no significant injury changes under traction + torsion conditions. In the early correction phase, the upper spinal cord segment demonstrated a risk of injury under all conditions, and the lower spinal cord segment presented a risk of injury under pushing conditions. Traction conditions posed a risk of nerve injury on both sides in the middle and lower segments. Under pushing conditions, there was a risk of nerve injury on both sides in all segments. Traction + torsion conditions implicated a risk of injury to the right nerves in the upper segment, both sides in the middle segment, and the left side in the lower segment. In the later correction stage, there was a risk of injury to the upper spinal cord segment under traction + torsion conditions, the left nerves in the middle segment under traction conditions, and the right nerves in the upper segment under pushing conditions.
CONCLUSIONS: When the correction rate reaches 61-68%, particular attention should be given to the upper-mid spinal cord. Pushing conditions also warrant attention to the lower spinal cord and the nerve roots on both sides of the main thoracic curve. Traction conditions require attention to nerve roots bilaterally in the middle and lower segments, while traction combined with torsion conditions necessitate focus on the right-side nerve roots in the upper segment, both sides in the middle segment, and the left-side nerve roots in the lower segment.

OBJECTIVE: The purpose of this finite element analysis (FEA) study was to analyze the stress distribution on prosthetic components of splinted and nonsplinted prostheses, bone, and implants with different crown height space (CHS).
METHODS: Mandibular posterior segment was modeled with no resorption at the second premolar site and various amounts of resorption (0, 3, 6, and 9 mm) at the first molar site. Two adjacent implants (Straumann bone level implants, 4.1 mm×8 mm) were placed; at the second premolar site, the crown height was 8 mm and at the first molar site, the crown height varied (8, 11, 14, and 17 mm), depending on the amount of resorption. Both splinted and nonsplinted crowns were designed. Vertical and oblique loads of 400 N were applied to the crowns. von Mises stress was used to evaluate the stress distribution in the implant complex and maximum principal stress was used to evaluate the stress in the bone.
RESULTS: When oblique forces were applied, the highest von Mises stresses were observed for nonsplinted crowns in the 17 mm CHS group. The maximum principal and minimum principal stresses observed in bone under oblique loading increased with increased CHS for nonsplinted restorations.
CONCLUSIONS: Crown height affected the amount of stress in bone and implant components. When the crown height difference between two adjacent implants increases, splinting may be crucial.

BACKGROUND: Although the specific relationship between the stress changes in the external fixator during tibial fracture treatment and the bone healing process remains unclear, it is believed that stress variations in the external fixator scaffold can, to a certain extent, reflect the progress of tibial healing.
OBJECTIVE: This study aims to propose a non-invasive method for assessing the degree of fracture healing by monitoring the changes in stress transmission, the locations of stress-sensitive points, and displacement in the external fixator-tibia system during the healing process of tibial fractures.
METHODS: In this study, finite element models of tibial fractures at various healing stages were developed. Physiological conditions, including axial, torsional, and bending loads on the tibia, were simulated to evaluate stress and strain within the external scaffold-tibia system under normal physiological loading conditions.
RESULTS: The results indicate variations in the stress distribution between the external fixator and the tibia during different stages of healing. In the early phase of fracture healing, the external fixator plays a crucial role as the primary load-bearing unit under all three loading conditions. As the fracture healing progresses, the stress on the tibia gradually increases, concentrating on the medial part of the tibia under axial and torsional loading, and at the upper and lower ends, as well as the central part of the anterior and posterior tibia during bending loading. The stress at the callus gradually increases, while micro-movements decrease. The stress within the external bracket gradually decreases, with a tendency for the connecting rod to transfer stress towards the screws. Throughout the fracture healing process, the location of maximum stress in the external fixator remains unchanged. Under axial and torsional loading, the maximum stress is located at the intersection of the lowest screw and the bone cortex, while under bending loading, it is at the intersection of the second screw and the connecting rod.
CONCLUSIONS: During the bone healing process, stress is transferred between the external fixation frame and the bone. As bone healing advances, the stress on the connecting rods and screws of the external fixation frame decreases, and the amplitude of stress changes diminishes. When complete and robust fusion is achieved, stress variations stabilize, and the location of maximum stress on the external fixation frame remains unchanged. The intersections of the lowest screw and the bone cortex, as well as the second screw and the connecting rod, can serve as sensitive points for monitoring the degree of bone healing.

OBJECTIVE: Femoral head necrosis is a challenging condition in orthopaedics, and the occurrence of collapse is an important factor affecting the prognosis of femoral head necrosis. Sclerosis bands are known to influence the collapse of the femoral head, yet there is a lack of research on the biomechanical role of sclerosis bands in non-vascularized fibular grafting surgery. This study aims to evaluate the biomechanical impact of sclerosis bands in femoral head necrosis and their role in non-vascularized fibular grafting surgery (NVFG) using finite element analysis.
METHODS: We constructed 11 finite element models based on CT scan data of a normal hip joint, simulating different sclerosis band thicknesses and defect scenarios. The models were analyzed for changes in femoral head displacement and von Mises stress. We constructed a hip joint model based on CT data from a normal hip joint, and after reconstruction, assembly, and optimization using 3-matic. We created five groups consisting of 11 finite element analysis models of the hip joint. Mesh partitioning and mechanical parameter settings were performed in ANSYS. The changes and differences in femoral head displacement and von Mises stress of these models were analyzed.
RESULTS: Increasing sclerosis band thickness led to reduced peak displacement of the femoral head by 28.6%, 42.9%, and 47.6%, and increased surface von Mises stress by 28.3%, 13.8%, and 13.0%, respectively. Post-surgery, peak displacement decreased in all groups compared to pre-surgery levels. Increasing sclerosis band thickness post-surgery resulted in decreased maximum von Mises stress of the femoral head by 13.9%, 3.0%, and 8.1%. Defect volume in the defect groups correlated with increased peak displacement of the femoral head by 10.0%, 30.0%, and 100.0%, and increased surface maximum von Mises stress of the femoral head by 9.3%, 14.0%, and 15.1%.
CONCLUSIONS: Sclerosis band formation exacerbates von Mises stress concentration on the femoral head surface. However, thicker sclerosis bands improve post-NVFG stability and mechanical performance. Larger anterior lateral sclerosis band defects significantly compromise postoperative stability, increasing the risk of collapse. Protecting the anterior lateral sclerosis band during NVFG surgery is crucial.

Aiming at the requirements of strong mobility and high flexibility of rescue and relief mobile pump trucks, this paper designs a new type of mobile pump truck frame based on existing mobile vehicle frame models. The materials used for the frame are 40Cr and Q235, and the finite element method is utilized to carry out static mechanical analysis and dynamic characteristic analysis. Simultaneously utilizing topology optimization and multi-objective genetic algorithm to optimize the design of the frame structure. The results show that the optimized pump truck frame can meet the strength design requirements of four typical working conditions: full load bending, full load torsion, emergency turning and emergency braking, while avoiding resonance phenomena caused by road surface and diesel engine vibration. Compared with the original frame model, the weight of the optimized frame is reduced by 87.88 kg, with a weight reduction rate of 10.89%, realizing the lightweight design requirements.

Supramalleolar osteotomy (SMO) is a representative procedure to restore a malalignment in the varus ankle deformity by shifting the concentrated pressure on the medial ankle joint to the lateral area. Additionally, fibula osteotomy (FO) is selectively selected and performed according to the surgeon\'s preference. However, it is controversial whether FO is effective in shifting the abnormal pressure from the medial to the lateral area on the ankle joint. Some cadaveric studies have been performed to prove this. However, it is difficult to consistently reconstruct amount of the varus ankle deformities angle in cadavers and to guarantee reliable contact pressure between the ankle joint. Thus, the aim of this study was predicted and quantitatively compared a peak pressure between single SMO and SMO with FO procedure by using a finite element analysis as a powerful biomechanical tool to those limitations of cadaveric study. This study reconstructed total 4 3D foot and ankle models including a normal and pre-op model and 2 post-op models. The pre-op model was modified by assigning 10° varus tilting corresponding to stage 3b in the classification of varus ankle osteoarthritis based on the validated normal model. Also, the post-op models were reconstructed by applying single SMO and SMO with FO, respectively. All of the models were assumed as one-leg standing position and to mimic smooth ankle joint motion. Peak contact pressure change was predicted at the medial ankle joint by using computational simulation. As a result, 2 post-op models showed a remarkably peak pressure reduction by up to 5.5 times on the medial tibiotalar joint. However, a comparison between single SMO and SMO with FO model showed no appreciable differences. In conclusion, this study predicted that single SMO may be as effective as SMO with FO in reducing peak contact pressure on the medial tibiotalar joint in varus ankle osteoarthritis.

To investigate the biomechanical effects of direct ventricular assistance and explore the optimal loading mode, this study established a left ventricular model of heart failure patients based on the finite element method. It proposed a loading mode that maintains peak pressure compression, and compared it with the traditional sinusoidal loading mode from both hemodynamic and biomechanical perspectives. The results showed that both modes significantly improved hemodynamic parameters, with ejection fraction increased from a baseline of 29.33% to 37.32% and 37.77%, respectively, while peak pressure, stroke volume, and stroke work parameters also increased. Additionally, both modes showed improvements in stress concentration and excessive fiber strain. Moreover, considering the phase error of the assist device\'s working cycle, the proposed assist mode in this study was less affected. Therefore, this research may provide theoretical support for the design and optimization of direct ventricular assist devices.
为了研究直接心室辅助的生物力学影响以及探究最优的加载模式，本文基于有限元方法建立了心衰患者的左心室模型，并提出了一种维持压迫力峰值的加载模式，从血流动力学和生物力学两个方面与传统的正弦加载模式进行了对比。结果表明，两种模式都能显著提升血流动力学参数，射血分数分别从基线29.33%增加到37.32%与37.77%，峰值压力、每搏量和每搏功等参数都有所增加；且两种模式的应力集中、过度纤维应变等现象均有所改善。然而，当考虑到辅助装置工作周期的相位误差时，本文所提出的辅助模式受到的影响更小，故本文研究或可为直接心室辅助装置的设计和优化提供理论支持。.

The use of a filling block can improve the initial stability of the fixation plate in the open wedge high tibial osteotomy (OWHTO), and promote bone healing. However, the biomechanical effects of filling block structures and materials on OWHTO remain unclear. OWHTO anatomical filling block model was designed and built. The finite element analysis method was adopted to study the influence of six filling block structure designs and four different materials on the stress of the fixed plate, tibia, screw, and filling block, and the micro-displacement at the wedge gap of the OWHTO fixation system. After the filling block was introduced in the OWHTO, the maximum von Mises stress of the fixation plate was reduced by more than 30%, the maximum von Mises stress of the tibia decreased by more than 15%, and the lateral hinge decreased by 81%. When the filling block was designed to be filled in the posterior position of the wedge gap, the maximum von Mises stress of the fixation system was 97.8 MPa, which was smaller than other filling methods. The minimum micro-displacement of osteotomy space was -2.9 μm, which was larger than that of other filling methods. Compared with titanium alloy and tantalum metal materials, porous hydroxyapatite material could obtain larger micro-displacement in the osteotomy cavity, which is conducive to stimulating bone healing. The results demonstrate that OWHTO with a filling block can better balance the stress distribution of the fixation system, and a better fixation effect can be obtained by using a filling block filled in the posterior position. Porous HA used as the material of the filling block can obtain a better bone healing effect.
使用填充块可以改善开放式胫骨高位截骨术（OWHTO）初始稳定性，促进骨愈合。然而，填充块结构及材料对OWHTO的生物力学影响依然不清楚。本文通过对OWHTO解剖型填充块进行设计建模，采用有限元方法，研究了填充块结构及材料对OWHTO固定系统固定板、胫骨、螺钉、填充块的应力和楔形间隙处的微位移影响。在OWHTO引入填充块后固定板最大应力降低了30%以上，胫骨最大应力下降了15%以上，外侧铰链区域最大应力下降了81%。填充块采用楔形间隙后侧位置填充设计时，固定系统最大应力为97.8 MPa，明显小于其他填充方式，且截骨间隙微位移最小为–2.9 μm，大于其他填充方式。与钛合金和钽金属相比，填充块采用多孔羟基磷灰石（HA）时可获得较大的截骨开口间隙微位移以刺激骨愈合。本研究结果表明OWHTO固定系统引入填充块更好地平衡了整体的应力分布，填充块结构采用楔形间隙后侧位置填充设计可以获得更优的固定效果，填充块材料采用多孔HA时骨愈合效果会更好。.

BACKGROUND: Previous studies have reported that positive buttress is as effective as anatomical reduction in treating young femoral neck fractures, but whether this effect is related to the Pauwels classification remains unclear. The purpose of this study was to retrospectively analyze the clinical prognosis of positive buttress in young femoral neck fractures with different Pauwels classifications, as well as to assess its biomechanical properties.
METHODS: A total of 170 young patients with femoral neck fractures who were treated with three cannulated screws were included in this study. Patients were divided into three groups based on their preoperative Pauwels classification. Each group was divided into three subgroups based on the reduction quality: positive buttress, negative buttress and anatomical reduction. The femoral neck shortening, the incidence of necrosis of the femoral head (AVN) and the Harris hip scores at the last follow-up were compared across the three reduction quality within each Pauwels classification. Subsequently, a volunteer was recruited, CT data of the hip was obtained, and finite element models representing different reduction quality under varying Pauwels classifications were established. The biomechanical properties of each model were then evaluated following the application of strains.
RESULTS: In Pauwels type I, there were no significant differences in postoperative femoral neck shortening, incidence of AVN, or Harris score among the three types of reduction quality (P > 0.05). However, positive buttress provided superior biomechanical stability compared to negative buttress and anatomical reduction. In Pauwels type II, the incidence of AVN was similar between the positive buttress and the anatomical reduction groups, and both were significantly lower than that in the negative buttress (P < 0.05). The Harris score of the positive buttress was higher than that of the negative buttress, and there was no significant difference in the occurrence of femoral neck shortening between the three groups (P > 0.05). Finite element analysis showed that the biomechanical stability of positive buttress was equivalent to anatomical reduction, and both were better than negative buttress. In Pauwels type III, the incidence of AVN in the anatomical reduction group was lower than that in both the positive buttress and negative buttress (P < 0.05). There was no significant difference in the occurrence of AVN or femoral neck shortening between positive buttress and negative buttress (P > 0.05). There was also no difference in postoperative Harris scores between the three reduction qualities (P > 0.05). Both positive buttress and negative buttress exhibited identical biomechanical qualities and were inferior to anatomical reduction.
CONCLUSIONS: The biomechanical and clinical dominance of positive buttress correlates with Pauwels type. Specifically, Positive buttress is biomechanically stable in Pauwels types I and II. In Pauwels type III, positive buttress is not advantageous. As the Pauwels angle increases, the biomechanical benefit of the positive buttress is lost. Therefore, regardless of the Pauwels classification, negative buttress should be avoided after reduction of femoral neck fractures in young patients.

This study uses finite element analysis to investigate the potential application of shorter dental implants as a substitute for longer implants in the lower jaw (mandible). FEA allows the evaluation of the stress patterns around the implant-bone interface, a critical factor for successful osseointegration. Ten models were generated, encompassing five long (L1-L5) and five short implant models (S1-S5) with variations in diameter and length. Hypermesh software was utilized to meticulously prepare the FEA models, ensuring accurate mesh generation. The FEA simulations were conducted under four distinct loading scenarios (100 N occlusal load, 40 N lateral load, 100 N oblique at 30°, and 100 N oblique at 45°) to realistically mimic the forces exerted during biting, using an ABAQUS CAE solver. The results revealed that the von Mises stress generated within the short implant models was demonstrably lower compared to their long implants. Additionally, a significant drop in stress was observed with increasing the diameter of the short implants, to a certain diameter range. These findings suggest the potential for successful substitution of long implant model L4 with short implant model S4 due to the demonstrably lower stress values achieved. Furthermore, the data indicates the possibility of utilizing short implant models S3 and S5 as alternatives to long implant models L3 and L5, respectively. These observations hold significant promise for evaluating the feasibility of replacing long implants with shorter variants, potentially leading to a reduction in implant-related failures.