The vertebral morphology of OVCFs varies in shape and height. Melton et al. divided the spine fracture into three types: wedge deformity, biconcave deformity, and crush deformities [11]. The Genant visual semi-quantitative method is based on the reduction in the anterior, middle, and posterior vertebral heights by lateral X-rays. It has been widely used in clinical and epidemiological studies [11]. Percutaneous vertebral augmentation enhances the strength of the fractured vertebral and restores the height of the vertebrae [16]. After the cement is injected into the fractured vertebral, the restoration of the height of the anterior vertebral can improve the kyphosis in the wedge fracture and improve the stress of the upper and lower endplates and adjacent intervertebral discs in biconcave fractures. The height of the vertebral may be complete, partial, or unable to restore after vertebral augmentation. Some vertebral collapse again after vertebral augmentation. Completely recovery of the fractured vertebral height determining whether to increase the risk of fractured is controversial. OVCFs patients with wedge fractures after PVA recovery of anterior vertebral can moderately improve kyphosis and center of gravity forward for restoration in sagittal imbalance, reduce the stress on the paraspinal muscles of patients with OVCFs to maintain balance [33]. Although the biconcave deformities after PVA do not affect the kyphosis and the center of gravity, it can improve the biomechanical changes of the endplates of the fractured vertebral and adjacent intervertebral discs, and influence the mechanical distribution of adjacent vertebral. In this study, the von Mises stress during flexion, extension, and lateral flexion are significantly higher than that of neutral position, and the position should be avoided as much as possible, especially during the fracture healing period.
Three-dimensional finite element analysis can be simulated physiological load, and different loads are applied to the model to calculate the dynamic mechanical range of the vertebral under different heights of vertebral after PVA. The simulation study on the mechanical change state of intervertebral disc, facet joint, and adjacent vertebrae was carried out [34]. In this study, elderly osteoporosis patient was selected, and CT data were obtained. The FEM of osteoporosis T11-L2 was successfully established and validated. Based on the above, different fracture types (wedge and biconcave) were constructed on OVCFs. The FEM of T12 OVCFs was compared with four different vertebral height after PVA, the von Mises stress of vertebrae, intervertebral disc and facet joint, and the displacement and ROM of T11-L2.
Some researchers have analyzed the biomechanical of the L2 fractured vertebral of OVCFs after PVA by finite element analysis, which can enhance the strength of the fractured vertebral and increase the vertebral load. In the study of patients with OVCFs, bone cements (3, 5, and 10 ml) with different elastic moduli (1800, 500, and 150 MPa) were injected into the L2 fractured vertebrae. In the neutral position, flexion and extension, lateral bending and axial rotation position, the vertebral showed similar maximum von Mises stress, and the maximum stress of the cortical bone and the lower endplate adjacent to the vertebral body L1 increased significantly; In the upright, flexion, extension, and lateral bending (left and right) positions, the maximum von Mises stress of the vertebral increases with the increase of the elastic modulus of the cement. The finite element analysis of patients with OVCFs after PVA of T12 fractured vertebral suggests that insufficient bone cement and asymmetric distribution may lead to a maximum displacement of the vertebral body, and a significant increase in maximum von Mises stress of cancellous and cortical bone, which may lead to re-fracture of the T12 vertebral and fracture of the adjacent vertebral [36]. This finite element analysis did not study the different heights of OVCFs after PVA. Based on the FEM of T12 wedge deformity in patients with non-osteoporosis, the maximum von Mises stress of the lower endplate of T11 vertebral and the upper endplate of L1 vertebrae, and the compression of T12 anterior vertebral (compressed to 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, and 10%) are positively correlated [37]. There was no significant difference between the maximum von Mises stresses of vertebral heights (grade 3, 1, and 0) after T12 undifferentiated typed OVCFs augmentation [22]. In our study, the biomechanical effect of wedge and biconcave deformity were compared in four different height restoration (Genant 3, 2, 1, and 0). after augmentation of OVCFs through finite element analysis. We suggested that the vertebral height restores to Genant 0 can affect the von Mises stress (vertebral body, intervertebral disc, facet joint), displacement and ROM, which may lead to an increased risk of re-fracture; Whereas restoration height required or not in biconcave deformity due to no significant biomechanical change.