[Finite element analysis of the impact of bone mass and volume of low-density area under tibial plateau on lower limb alignment].

Objective: To investigate the impact of the bone mass and volume of the low-density area under the tibial plateau on the lower limb force line by finite element analysis, offering mechanical evidence for preventing internal displacement of the lower limb force line in conjunction with knee varus in patients with knee osteoarthritis (KOA) and reducing bone mass under the tibial plateau. Methods: A healthy adult was selected as the study subject, and X-ray film and CT imaging data were acquired. Mimics 21.0 software was utilized to reconstruct the complete knee joint model and three models representing low-density areas under the tibial plateau with equal volume but varying shapes. These models were then imported into Solidworks 2023 software for assembly and verification. Five KOA finite element models with 22%, 33%, 44%, 55%, and 66% bone mass reduction in the low-density area under tibial plateau and 5 KOA finite element models with 81%, 90%, 100%, 110%, and 121% times of the low-density area model with 66% bone mass loss were constructed, respectively. Under physiological loading conditions of the human lower limb, the distal ends of the tibia and fibula were fully immobilized. An axial compressive load of 1 860 N, following the lower limb force line, was applied to the primary load-bearing area on the femoral head surface. The maximum stress within the tibial plateau, as well as the maximum displacements of the tibial cortical bone and tibial subchondral bone, were calculated and analyzed using the finite element analysis software Abaqus 2022. Subsequently, predictions regarding the alteration of the lower limb force line were made based on the analysis results. Results: The constructed KOA model accorded with the normal anatomical structure of lower limbs. Under the same boundary conditions and the same load, the maximum stress of the medial tibial plateau, the maximum displacement of the tibial cortical bone and the maximum displacement of the cancellous bone increased along with the gradual decrease of bone mass in the low-density area under the tibial plateau and the gradual increase in the volume of the low-density area under tibial plateau, with significant differences ( P<0.05). Conclusion: The existence of a low-density area under tibial plateau suggests a heightened likelihood of knee varus and inward movement of the lower limb force line. Both the volume and reduction in bone mass of the low-density area serve as critical initiating factors. This information can provide valuable guidance to clinicians in proactively preventing knee varus and averting its occurrence.

[Finite element analysis for predicting osteonecrosis of the femoral head collapse based on the preserved angles].

Objective: To establish finite element models of different preserved angles of osteonecrosis of the femoral head (ONFH) for the biomechanical analysis, and to provide mechanical evidence for predicting the risk of ONFH collapse with anterior preserved angle (APA) and lateral preserved angle (LPA). Methods: A healthy adult was selected as the study object, and the CT data of the left femoral head was acquired and imported into Mimics 21.0 software to reconstruct a complete proximal femur model and construct 3 models of necrotic area with equal volume and different morphology, all models were imported into Solidworks 2022 software to construct 21 finite element models of ONFH with LPA of 45°, 50°, 55°, 60°, 65°, 70°, and 75° when APA was 45°, respectively, and 21 finite element models of ONFH with APA of 45°, 50°, 55°, 60°, 65°, 70°, 75° when LPA was 45°, respectively. According to the physiological load condition of the femoral head, the distal femur was completely fixed, and a force with an angle of 25°, downward direction, and a magnitude of 3.5 times the subject's body mass was applied to the weight-bearing area of the femoral head surface. The maximum Von Mises stress of the surface of the femoral head and the necrotic area and the maximum displacement of the weight-bearing area of the femoral head were calculated and observed by Abaqus 2021 software. Results: The finite element models of ONFH were basically consistent with biomechanics of ONFH. Under the same loading condition, there was stress concentration around the necrotic area in the 42 ONFH models with different preserved angles composed of 3 necrotic areas with equal volume and different morphology. When APA was 60°, the maximum Von Mises stress of the surface of the femoral head and the necrotic area and the maximum displacement of the weight-bearing area of the femoral head of the ONFH models with LPA<60° were significantly higher than those of the models with LPA≥60° ( P<0.05); there was no significant difference in each index among the ONFH models with LPA≥60° ( P>0.05). When LPA was 60°, each index of the ONFH models with APA<60° were significantly higher than those of the models with APA≥60° ( P<0.05); there was no significant difference in each index among the ONFH models with APA≥60° ( P>0.05). Conclusion: From the perspective of biomechanics, when a preserved angle of ONFH is less than its critical value, the stress concentration phenomenon in the femoral head is more pronounced, suggesting that the necrotic femoral head may have a higher risk of collapse in this state.

Migration and distribution of cadmium in aquatic environment: The important role of natural biofilms.

For a better understanding of the migration process of trace metals in aquatic environment with multiple phases, dynamic processes of Cd reaching quasi-equilibrium among different phases, including water, natural biofilms and surficial sediments, were investigated, using microcosmic simulating systems. The processes of the re-equilibrium of Cd after a supplement of Cd and after an adjustment of solution pH were also investigated. The results showed both the migration of Cd from water to the solid materials, and the accumulation of Cd in the solid materials. (Modified) pseudo-second-order kinetic model can be used to simulate such processes. However, Cd content in biofilms and sediments varied in different ways: Cd in biofilms increased rapidly at first, then decreased, and finally approached constancy, while Cd in sediments increased slowly and continuously. The more the Cd was added in the water, the higher the Cd contents in solid phases, and the quicker the Cd accumulation and decrease process would be. The decrease of solution pH promoted the release of adsorbed Cd from the solid phases, especially from biofilms, while the increase of pH stimulated the migration of Cd to the solids. Therefore, as an indicator and temporary reservoir of trace metals in water, which respond rapidly to the variation of trace metal concentration in water, biofilms play a role in indicating and buffering the variation of trace metals in water. Although the response of sediments to the variation of metal concentration in water is very slow, most trace metals migrate to sediments eventually, thus sediments play a role as a more stable and massive reservoir for trace metals in water.