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, we research on one of the frequent thoracolumbar spine fractures (T12), one of the suitable stiffness bone cement volume (equivalent to 30% of T12 vertebral volume), and top two fracture type (wedge and biconcave) of OVCFs [30-32]. We demonstrated whether different fracture type (wedge and biconcave) has a potentially effect on height restoration after augmentation of OVCFs. To clarify the biomechanical comparison of wedge and biconcave deformity of different height restoration after augmentation of OVCFs, we performed finite element analysis of the von Mises stresses of vertebrae, intervertebral disc, facet joints, displacement, and range of motion (ROM) of wedge and biconcave deformity were compared at four different heights (Genant 3, 2, 1, 0) after T12 vertebral augmentation. Collectively, our data demonstrated that the vertebral height after vertebral augmentation restores to Genant 0 in wedge deformity, affecting the von Mises stress, displacement, and ROM, which may increase the risk of fracture; Whereas restoration height restored or not in biconcave deformity.
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 [3, 33-35]. 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 [36]. 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 stress of T12 in wedge deformity decreased as the vertebral height in neutral position, flexion, extension and left axial rotation, whereas increased sharply in bending at Genant 0; No significant changes in biconcave deformity. The displacement and ROM of the wedge fracture had ups and downs, while a decline in all positions excluding extension in biconcave fracture.
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 neutral position, 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 [37]. 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 [38]. 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 [39]. There was no significant difference between the maximum von Mises stresses of vertebral heights (Genant 3, 1, and 0) after T12 undifferentiated fracture typed OVCFs augmentation [22]. However, unlike the previous research, our study compared wedge and biconcave deformity. This difference in fracture type may account for the different result.