Objective To investigate the biomechanical characteristics of the CT-based lateral classification of Japanese Investigation Committee (JIC) type C1 osteonecrosis of the femoral head (ONFH) under different necrotic extents using finite element analysis, and to evaluate the validity of the CT-based lateral classification for assessing the risk of femoral head collapse. MethodsA finite element model of the hip joint was established based on CT data from a healthy 35-year-old male volunteer. According to the JIC C1 classification criteria, three necrotic extents were defined in the coronal plane: M1 (30%), M2 (50%), and M3 (70%). According to the sagittal location of the necrotic lesion, the femoral head was equally divided into anterior, middle, and posterior regions, and five types of the CT-based lateral classification were defined: type 1, involvement of the anterior region only; type 2, involvement of the anterior and middle regions; type 3, involvement of the anterior, middle, and posterior regions; type 4, involvement of the middle and posterior regions; and type 5, involvement of the posterior region only. A total of 15 finite element models were constructed by combining the three necrotic extents with the five CT-based lateral classification types. Bilateral standing loading was simulated, and the maximum von Mises stress and maximum displacement of the femoral head surface and necrotic region were recorded. Results Stress concentration was mainly located in the superolateral region of the femoral head directly above the necrotic lesion, consistent with previous studies. Within the same CT-based lateral classification type, increases in necrotic extent from M1 to M3 were associated with significant increases in the maximum von Mises stress and maximum displacement of the femoral head surface, as well as the maximum displacement of the necrotic region. No significant difference was found in the maximum von Mises stress in the necrotic region among M1, M2, and M3 groups (P>0.05). Except for the differences in the maximum von Mises stress on the femoral head surface between groups M2 and M3, and the differences in the maximum displacement in the necrosis region between groups M1 and M2 (P>0.05), there were significant differences in the maximum von Mises stress on the femoral head surface, the maximum displacement on the femoral head surface, and the maximum displacement in the necrosis region between other groups (P<0.05). At the same necrotic extent, the maximum von Mises stress and maximum displacement on the femoral head surface and in the necrosis region were significantly higher in type 3 than in other types; followed by type 2>type 1>type 4>type 5. Among them, there was no significant difference in the maximum von Mises stress on the femoral head surface between types 1 and 4, types 2 and 3, and the maximum displacement on the femoral head surface between types 1 and 2, types 2 and 3, types 4 and 5, as well as the maximum von Mises stress in the necrosis region between types 4 and 5, and the maximum displacement in the necrosis region between types 1 and 2, types 4 and 5, types 2 and 3, and types 4 and 5 (P>0.05); all other comparisons between different types showed significant differences (P<0.05). ConclusionBoth the location and extent of osteonecrosis affect the biomechanical stability of the femoral head, with lesion location, particularly involvement of the anterior weight-bearing region, exerting a greater influence on stress distribution. The CT-based lateral classification can effectively distinguish biomechanical differences associated with different necrotic locations and may provide a useful reference for evaluating the risk of femoral head collapse and guiding individualized treatment in patients with JIC type C1 ONFH.
Objective To investigate the impact of bone mass and volume of low-density zones beneath the tibial plateau on the maximum von Mises stresses experienced by the cartilage and meniscus in the knee joint. Methods The study included one healthy adult volunteer, from whom CT scans were obtained, and one patient diagnosed with knee osteoarthrisis (KOA), for whom X-ray films were acquired. A static model of the knee joint featuring a low-density zone was established based on a normal knee model. In the finite element analysis, axial loads of 1 000 N and 1 800 N were applied to the weight-bearing region of the upper surface of the femoral head for model validation and subsequent finite element studies, respectively. The maximum von Mises stresses in the femoral cartilage, as well as the medial and lateral tibial cartilage and menisci, were observed, and the stress percentage of the medial and lateral components were concurrently analyzed. Additionally, HE staining, as well as alkaline magenta staining, were performed on the pathological specimens of patients with KOA in various low-density regions. ResultsThe results of model validation indicated that the model was consistent with normal anatomical structures and correlated with previous calculations documented in the literature. Static analysis revealed that the maximum von Mises stress in the medial component of the normal knee was the lowest and increased with the advancement of the hypointensity zone. In contrast, the lateral component exhibited an opposing trend, with the maximum von Mises stress in the lateral component being the highest and decreasing as the hypointensity zone progressed. Additionally, the medial component experienced an increasing proportion of stress within the overall knee joint. HE staining demonstrated that the chondrocyte layer progressively deteriorated and may even disappear as the hypointensity zone expanded. Furthermore, alkaline magenta staining indicated that the severity of microfractures in the trabecular bone increased concurrently with the expansion of the hypointensity zone. Conclusion The presence of subtalar plateau low-density zone may aggravate joint degeneration. In clinical practice, it is necessary to pay attention to the changes in the subtalar plateau low-density zone and actively take effective measures to strengthen the bone status of the subtalar plateau low-density zone and restore the complete biomechanical function of the knee joint, in order to slow down or reverse the progression of osteoarthritis.
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). ConclusionThe 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.