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. ResultsThe 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.
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.