Introduction

Osteoporosis is a systemic metabolic disease caused by the loss of calcium ions in the body, resulting in a decrease in bone density and quality [1]. Osteoporotic vertebral compression fracture (OVCF) is a prevalent secondary condition of osteoporosis, marked by intense pain, spinal deformities, and potential complications, including venous thrombosis, spinal cord injury, and infection. It seriously affects the quality of life of patients and increases the mortality rate of the elderly [2, 3]. Current treatment methods for OVCF include conservative treatment and surgical treatment, and surgical treatment is divided into open surgery and minimally invasive surgery [4]. Due to the patient’s age, degree of osteoporosis, and anesthesia risk factors, open surgery usually cannot achieve the expected therapeutic effect, such as internal fixation loosening and repeated fractures. Therefore, minimally invasive surgery is usually used to treat OVCF clinically [5]. Vertebral augmentation (VA) is the primary method of minimally invasive treatment, including percutaneous kyphoplasty (PKP) and percutaneous vertebroplasty (PVP). Many surgeons use the pedicle puncture approach, the classic VA approach [6]. However, recent studies have shown that the width of the vertebral body pedicles and the coronal inclination to the vertebral body vary greatly between individuals [7]. In addition, the range of motion (ROM) of the T10-L2 vertebral body in various physiological movements of flexion and extension is more extensive in middle-aged and older women than in men, and the kyphosis angle is significantly smaller than that of men. However, after the age of 70–79, the kyphosis angle of women will increase [8]. Furthermore, Wang et al. [9] discovered that during VA on the vertebral body ranging from L1 to L5, the distance from the needle entry point to the vertebral body midline, puncture inclination, and puncture success rate were higher for the male vertebral body compared to the female vertebral body. These differences may cause the balloon and bone cement to fail to reach the anterior midline of the vertebral body during surgery, resulting in poor bone cement diffusion and unsatisfactory vertebral body reduction [10, 11]. Additionally, patients may have anatomical differences and vascular variations, so consistent use of the transpedicular approach may result in the inability of bone cement to achieve good distribution within the vertebral body, resulting in poor surgical results, or complications such as bone cement leakage, spinal cord injury, or vascular injury [12, 13]. Therefore, choosing the appropriate puncture path to repair the fractured vertebral body, reduce the stress on the vertebral body structure, and avoid intraoperative complications has become the main problem faced by clinicians [14,15,16]. Melton et al. [17] classified the morphological forms of vertebral fractures into wedge deformity, biconcave deformity, and collapse deformity. This classification method can cover the main compression forms of OVCF. Consequently, we propose to use precise puncture vertebral augmentation (PPVA) to treat these three types of OVCF.

The finite element analysis method is an effective discrete numerical calculation method that can perform mechanical analysis on a variety of structures and display the internal stress and deformation process when the model is stressed [18, 19]. It has been widely used in medicine and other fields, especially in bone diseases. Zhang et al. [20] used the finite element method to establish a three-dimensional model of osteoporotic adolescent scoliosis and elaborated on the stress changes of the entire lumbar segment. Zhao et al. [21] established finite element models of OVCFs vertebral bodies of different heights, analyzed their stress conditions before and after VA, and elaborated on the biomechanical effects of different types of vertebral bodies. Therefore, in order to understand the biomechanical effects of PPVA on different types of OVCFs, we used finite element modeling methods and analyzed the results, hoping to provide ideas for the clinical treatment of OVCF.

Methods

In this study, three osteoporotic thoracolumbar OVCF patients with wedge deformity, biconcave deformity, and collapse deformity fractures were selected. CT data of three patients before and after PPVA were extracted, vertebral body models before and after PPVA were established, and finite element analysis was performed. Under six physiological movements of the vertebrae, namely forward flexion, posterior extension, left bending, right bending, left rotation, and right rotation, the vertebral body stress changes of PPVA on different types of thoracolumbar OVCF were studied and used Mimics 21.0 (Belgian Materialize Company), Geomagic 2021 (scan data processing and 3D model data conversion application tool, Geomagic Company), SolidWorks 2021 (3D modeling processing software, Dassault Company), Ansys 2021R1 (finite element simulation calculation software, United States Ansys Corporation) to process the data. A CT scanner (Siemens, GER) collected raw data in DICOM format with a scan slice of 0.625 mm.

Establishment of three-dimensional geometric model

Import the DICOM files of CT scans into Mimics 21.0 for 3D model reconstruction, initial identification and separation of muscles, soft tissues, and bones. Separate each vertebral body and bone cement required into separate individuals. Due to the influence of the quality of the CT image, software, and grayscale value, repair must be performed based on the CT DICOM images of each layer. The initially established vertebral body model was solidified, imported into an STL file and saved, and then imported into Geomagic 2021 software. All models were smoothed, spikes deleted, noise removed, and holes filled to preserve the vertebral body’s characteristics. Then, the contours were drawn, the surfaces and meshes were built, the surfaces were fitted to the initially optimized model, and finally, the model was saved as a STEP entity format. To achieve the effect of the CT model, import the saved model into SolidWorks 2021 software, perform origin matching, and assemble the vertebral body. Separate the cortical bone from the cancellous bone and set the thickness of the cortical bone to 1.5 mm [22]. Save the complete three-segment vertebral body model as a part format and reconstruct the intervertebral disc(nucleus pulposus, annulus fibrosus), endplates, and articular cartilage in the model. The above software extracts reconstructs and optimizes bone cement. The generated bone cement model is saved in SLDPRT format, and the bone cement model is assembled into a vertebral body model. Assemble the separated cortical bone and cancellous bone with other vertebral structures. Finally, we obtained complete three-dimensional models before and after PPVA for wedge deformity, biconcave deformity, and collapse deformity, a total of six models (Fig. 1).

Fig. 1
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Three-dimensional model of osteoporotic vertebral compression fracture. A wedge deformity; B biconcave deformity; C collapse deformity

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Establishment of finite element analysis model

Import the complete three-dimensional model into Ansys 2021 software to supplement the anterior longitudinal ligament, posterior longitudinal ligament, intertransverse ligament, interspinous ligament, supraspinal ligament, and ligamentum flavum. All supplementary element types support tensile deformation without compressive behavior. Based on the material properties used in previous OVCF studies (Table 1), material properties were assigned to cortical bone, cancellous bone, bone cement, endplates, cartilage, intervertebral discs (nucleus pulposus and annulus fibrosus), and various ligaments [23, 24]. The element types of cortical bone, cancellous bone, endplates, cartilage, and nucleus pulposus are defined as solid elements represented by materials with linear isotropic elasticity. The endplate, bone cement, and intervertebral disc (nucleus pulposus and annulus fibrosus) were divided into 2 mm meshes, and the articular cartilage was divided into 0.5 mm meshes [25]. According to previous literature studies, it is more reasonable when the volume unit mesh size is 0.6–1.0 mm, taking into account calculation accuracy and time. Therefore, the average unit thickness of cortical bone in this article is 1 mm [26, 27]. Then set the contact type of the model components, set the articular cartilage to frictionless contact, set the cortical bone and cancellous bone, intervertebral disc and endplate, facet joint cartilage and cortical bone directly as common nodes to avoid setting contact attributes. The model was meshed using the SOLID187 ten-node tetrahedral mesh. The preoperative wedge deformity model had 151,895 elements and 253,024 nodes, and the postoperative wedge deformity model had 167,201 elements and 280,680 nodes. The preoperative biconcave deformity model had 184,439 elements and 302,582 nodes, and the postoperative biconcave deformity model had 192,011 elements and 319,370 nodes. The preoperative collapse deformity model had 233,381 elements and 379,677 nodes, and the postoperative collapse deformity model had 241,345 elements and 394,631 nodes nodes. Save the meshed model to obtain a complete finite element model (Fig. 2).

Table 1 Finite element model component material properties
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Fig. 2
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Finite element analysis model for osteoporotic vertebral compression fracture. A wedge deformity; B biconcave deformity; C collapse deformity

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Finite element analysis

A total of six models before and after PPVA of wedge deformity, biconcave deformity, and collapse deformity were used for finite element analysis. In order to simulate the motion of the patient’s thoracolumbar spine in different motion states, it is necessary to set boundary conditions and loads on the model. Constrain the mobility of all nodes on the inferior surface of the third vertebral body of the model and limit any rotation and displacement on the X, Y, and Z axes to fix the inferior surface of the third vertebral body [28]. The longitudinal axis of the spine applies a vertical pressure of 500N on the upper surface of the first vertebral body around the Z-axis. This load is evenly distributed across the entire surface to mimic the load experienced by the human thoracolumbar vertebrae in an upright position. In order to simulate the physiological movements of the human thoracolumbar vertebrae in daily activities, it is necessary to apply additional torque to the movements of the vertebrae. Apply a forward torque of 10N/m around the Y-axis to simulate the load under extension motion; Apply a reverse torque of -10N/m on the Y-axis to simulate the load under flexion motion; Apply a horizontal forward torque of 10N/m and a reverse torque of -10N/m around the X-axis to simulate the load under left and right bending, respectively; Apply a left rotation torque of 10N/m and a reverse right rotation torque of -10N/m around the Z-axis to simulate the load under left and right rotation, respectively [29,30,31,32,33]. According to the three-column concept of the spine, 85% of the applied pressure acts on the front and middle columns, 15% acts on the posterior columns, and the force is evenly distributed at each node [34]. Calculate the von Miese stress of three types of vertebral bodies and the von Mises stress of adjacent vertebral bodies, and evaluate the stress changes of the vertebral body after PPVA treatment.

Result

Wedge deformity

Stress changes in fractured vertebral body

In the wedge deformity model, the T11 vertebral body is fractured, and the adjacent vertebral bodies are the T10 and T12 vertebral bodies. The stress distribution cloud diagram of the T11, T10, and T12 vertebral bodies is shown below (Fig. 3). Under the six different physiological movements of the vertebral body, the maximum stress on the T11 vertebral body before PPVA was generated by forward flexion, which was 32.231Mpa, while the maximum stress generated was the smallest by posterior extension, which was 24.704Mpa (Table 2). The maximum stress on the T11 vertebral body after PPVA was generated by right bending, which was 21.79Mpa, while the maximum stress generated was the smallest by left bending, which was 16.967Mpa (Table 2). After PPVA, the maximum stress of the T11 wedge deformed vertebral body was significantly decreased, with forward flexion decreased by 44.22%, posterior extension decreased by 26.66%, left bending decreased by 32.69%, right bending decreased by 21.13%, left rotation decreased by 37.34%, and right rotation decreased by 35.45% (Fig. 4).

Fig. 3
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Stress distribution cloud diagram of wedge vertebral body and adjacent vertebral bodies before and after PPVA. Pre, Preoperative; Post, Postoperative

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Table 2 Wedge deformity vertebral body and adjacent vertebral bodies stress before and after PPVA
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Fig. 4
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Stress changes in wedge deformity vertebral body and adjacent vertebral bodies under six physiological movements after PPVA

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Stress changes in adjacent vertebral bodies

Under the six different physiological movements of the vertebral body, the maximum stress on the T10 vertebral body before PPVA was generated by right bending, which was 34.49Mpa, while the maximum stress was the smallest generated by left rotation, which was 27.767 (Table 2). The maximum stress on the T10 vertebral body after PPVA was generated by forward flexion, which was 33.037Mpa, while the maximum stress was the smallest generated by left bending, which was 25.128Mpa (Table 2). After PPVA, except for forward flexion, the maximum stress of adjacent vertebral body T10 decreased to varying degrees under other different physiological movements. Forward flexion increased by 8.59%, posterior extension decreased by 16.94%, left bending decreased by 10.1%, right bending decreased by 10.55%, left rotation decreased by 3.64%, and right rotation decreased by 8.93% (Fig. 4). Under the six different physiological movements of the vertebral body, the maximum stress on the T12 vertebral body before PPVA was generated by right bending, which was 31.967Mpa, while the maximum stress was the smallest generated by left bending, which was 24.414 (Table 2). The maximum stress on the T12 vertebral body after PPVA was generated by forward flexion, which was 28.271Mpa, while the maximum stress was the smallest generated by posterior extension, which was 18.657Mpa (Table 2). After PPVA, the maximum stress of adjacent vertebral body T12 was significantly decreased, with forward flexion decreased by 44.22%, posterior extension decreased by 26.66%, left bending decreased by 32.69%, right bending decreased by 21.13%, left rotation decreased by 37.34%, and right rotation decreased by 35.45% (Fig. 4).

Biconcave deformity

Stress changes in fractured vertebral body

In the biconcave deformity model, the fracture is T11 vertebral body, and the adjacent vertebral bodies are the T10 and T12 vertebral bodies. The stress distribution cloud diagram of T10, T11, and T12 vertebral bodies is shown below (Fig. 5). Under six different physiological movements of the vertebral body, the maximum stress on the T11 vertebral body before PPVA was generated by right bending, which was 23.774Mpa, while the maximum stress was the smallest generated by forward flexion, which was 19.137Mpa (Table 3). The maximum stress of the T11 vertebral body after PPVA was generated by posterior extension, which was 25.134Mpa, while the maximum stress was the smallest generated by forward flexion, which was 18.708Mpa (Table 3). After PPVA, the maximum stress of the T11 vertebral body with biconcave deformity increases except for forward flexion and left bending. Forward flexion decreased by 2.22%, posterior extension increased by 27.29%, left bending decreased by 7.47%, right bending increased by 2.41%, left rotation increased by 16.6%, and right rotation increased by 10.47% (Fig. 6).

Fig. 5
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Stress distribution cloud diagram of biconcave deformity vertebral body and adjacent vertebral bodies before and after PPVA. Pre, Preoperative; Post, Postoperative

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Table 3 Biconcave deformity vertebral body and adjacent vertebral bodies stress before and after PPVA
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Fig. 6
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Stress changes in biconcave deformity vertebral body and adjacent vertebral bodies under six physiological movements after PPVA

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Stress changes in adjacent vertebral bodies

Under six different physiological movements of the vertebral body, the maximum stress on the T10 vertebral body before PPVA was generated by posterior extension, which was 37.406Mpa, while the maximum stress was the smallest generated by left bending, which was 31.73Mpa (Table 3). The maximum stress of the T10 vertebral body after PPVA was also generated by posterior extension, which was 33.341Mpa, while the maximum stress was the smallest generated by forward flexion, which was 26.197Mpa (Table 3). After PPVA, the maximum stress of adjacent vertebral body T10 decreased, especially during forward flexion, which decreased by 27.95%, posterior extension decreased by 10.87%, left bending decreased by 7.29%, right bending decreased by 13.71%, left rotation decreased by 11.92%, and right rotation decreased by 13.12% (Fig. 6). Under six different physiological movements of the vertebral body, the maximum stress on the T12 vertebral body before PPVA was generated by posterior extension, which was 26.623Mpa, while the maximum stress was the smallest generated by forward flexion, which was 21.474Mpa (Table 3). The maximum stress of the T11 vertebral body after PPVA was generated by left bending, which was 27.58Mpa, while the maximum stress was the smallest generated by forward flexion, which was 23.629Mpa (Table 3). After PPVA, the maximum stress of adjacent vertebral body T12 was decreased by 4.5% in posterior extension, while forward flexion increased by 10.04%, posterior extension decreased by 4.5%, left bending increased by 12.82%, right bending increased by 1.75%, left rotation increased by 0.97%, and right rotation increased by 2.62% (Fig. 6).

Collapse deformity

Stress changes in collapse deformity vertebral body

In the collapse deformity model, the fracture is in the T12 vertebral body, and the adjacent vertebral bodies are the T11 and L1 vertebral bodies. The stress distribution cloud diagram of the T12, T11, and L1 vertebral bodies is shown below (Fig. 7). Under six different physiological movements of the vertebral body, the maximum stress on the T12 vertebral body before PPVA was generated by forward flexion, which was 19.274Mpa, while the maximum stress was the smallest generated by left bending, which was 15.804Mpa (Table 4). The maximum stress of the T12 vertebral body after PPVA was also generated by forward flexion, which was 17.848Mpa, while the maximum stress was the smallest generated by right bending, which was 14.409Mpa (Table 4). After PPVA, the stress of the collapsed deformed vertebral body T12 decreased under six physiological movements, with forward flexion decreased by 7.4%, posterior extension decreased by 17.39%, left bending decreased by 3.52%, right bending decreased by 23.07%, left rotation decreased by 7.01%, and right rotation decreased by 3.71% (Fig. 8).

Fig. 7
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Stress distribution cloud diagram of collapse deformity vertebral body and adjacent vertebral bodies before and after PPVA. Pre, Preoperative; Post, Postoperative

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Table 4 Collapse deformity vertebral body and adjacent vertebral bodies stress before and after PPVA
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Fig. 8
figure 8

Stress changes in biconcave deformity vertebral body and adjacent vertebral bodies under six physiological movements after PPVA

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Stress changes in adjacent vertebral bodies

Under six different physiological movements of the vertebral body, the maximum stress on the T11 vertebral body before PPVA was generated by forward flexion, which was 35.524Mpa, while the maximum stress was the smallest generated by posterior extension, which was 25.348Mpa (Table 4). The maximum stress of the T11 vertebral body after PPVA was generated by left bending, which was 28.802Mpa, while the maximum stress was the smallest generated by right rotation, which was 14.409Mpa (Table 4). After PPVA, the stress of adjacent vertebral body T11 decreased significantly during six physiological movements, with the most notable reduction observed during right rotation movements. Forward flexion decreased by 27.87%, posterior extension decreased by 4.37%, left bending decreased by 14.75%, right bending decreased by 20.58%, left rotation decreased by 17.01%, and right rotation decreased by 22.66% (Fig. 8). Under six different physiological movements of the vertebral body, the maximum stress on the L1 vertebral body before PPVA was generated by posterior extension, which was 16.911Mpa, while the maximum stress was the smallest generated by forward flexion, which was 13.643Mpa (Table 4). The maximum stress of L1 vertebral body after PPVA was generated by forward flexion, which was 20.673Mpa, while the maximum stress was the smallest generated by right bending, which was 15.939Mpa (Table 4). After PPVA, only the stress of posterior extension and right bending of adjacent vertebral body L1 decreased under six physiological movements, and the stress of right bending decreased very slightly. In addition, the stress of forward flexion increased significantly, reaching 51.53%. In other movements, posterior extension decreased by 7.68%, left bending increased by 7.72%, right bending decreased by 8.1%, left rotation increased by 22.18%, and right rotation increased by 19.82% (Fig. 8).

Discussion

The thoracolumbar vertebral body is the stage of transition from thoracic physiologic kyphosis to lumbar vertebral body physiologic lordosis. Its anatomical structure is relatively unique, making it particularly vulnerable to damage from external forces [35]. Moreover, the vertebral body undergoes degenerative changes with age, leading to vertebral body fibrosis and uneven stress distribution, resulting in high-stress concentration in certain parts of the vertebral body. More importantly, due to the decrease in bone density and quality, osteoporosis can cause changes in the shape and height of the vertebral body. As a consequence, the incidence of OVCF is often higher in the thoracolumbar spine compared to other segments of the spine [36]. VA is currently the main method for treating OVCF. Inject bone cement into the fractured vertebral body through the pedicle to alleviate pain and strengthen the vertebral body [37]. Due to differences in pedicle diameter, pedicle axis asymmetry, and potential variability or malformation of the pedicles, blood vessels, and nerves, as well as the influence of factors such as vertebral body size, mobility, and kyphosis angle. A single-pedicle approach may not achieve the expected clinical results [7,8,9,10,11,12,13, 38]. In addition, the abduction angle and puncture trajectory of the puncture needle mainly depend on the experience of the surgeon. However, due to the different muscle thickness of the patient’s lower back and the width of the vertebral pedicle, once the puncture position or puncture angle deviates, the puncture success rate will be affected. Therefore, we propose PPVA to treat thoracolumbar OVCF. In order to explain the surgical effect of PPVA in treating OVCF, we established a three-dimensional model using quantitative CT images of patients before and after PPVA. Six models allow us to observe better the stress conditions of the three types of OVCF. In addition, unlike previous studies that simulated bone cement into a cylindrical or spherical shape, the model used accurate intraoperative bone cement shapes, which further ensured the accuracy of the finite element model and stress data.

PPVA is modified based on the classical pedicle VA puncture. Preoperative preparation is the same as VA. The patient is kept in the prone position, the abdomen is suspended, and the C-arm X-ray locates the fractured vertebra. The design of the puncture approach was based on preoperative X-ray and CT scan images, the front and middle 1/3 of the vertebral body are used as the end point of the puncture needle and the injection point of bone cement. This area allows bone cement to diffuse from one side to the opposite side, allowing the bone cement to be well distributed within the fractured vertebral body [39]. The middle part of the vertebral body pedicle is used as a safe puncture point. Connect the puncture endpoint and the safe path point to make an extension line to the skin to serve as the skin needle entry point. Finally, the distance from the three points and the angle between the puncture path and the midline were measured. At the same time, measure the inclination angle of the puncture route and the vertebral body, the maximum inclination angle, and the minimum inclination angle to ensure that the spinal canal will not penetrate during the operation. The planned approach and inclination angle obtained were marked on the patient's body surface to facilitate intraoperative puncture. After routine disinfection and anesthesia, make a longitudinal incision of approximately 5 mm at the needle entry point in the skin puncture unilaterally into the anterior 1/3 of the vertebral body. Replace with the working cannula and push in bone cement. When the bone cement has spread to the posterior 1/3 of the vertebral body, withdraw the working casing. The above process can reduce the deflection of the bone puncture needle as much as possible during operation, and achieve maximum safety and accuracy. In addition, PPVA can to operate independently of the pedicle. During the operation, the direction and depth of the working channel can be flexibly adjusted to ensure that the bone cement is dispersed on both sides of the fractured vertebral body to the greatest extent. Avoid deviation of the needle insertion position, as the puncture needle cannot reach the target location and damage the internal wall of the pedicle, causing spinal cord or nerve damage. This approach can shorten the operation time, reduce the patient’s discomfort during the operation, and improve the stability of the fractured vertebral body.

Our study focused on the von Mises stress of three different types of thoracolumbar OVCF before and after PPVA, and the results showed that in the T11 vertebral body with wedge deformity, the forward flexion position exhibited the highest von Mises stress, possibly due to the decreased height of the anterior edge of the vertebral body. The stress reduction was most prominent in the forward flexion position following the injection of bone cement into the vertebral body. In addition, PPVA also significantly improved the stress of the adjacent vertebral bodies of the deformed vertebral body. Although the stress of the T10 vertebral body during forward flexion increased, the overall stress showed a downward trend. Through stress distribution cloud diagram analysis, before PPVA, the center of the wedge deformed and adjacent vertebral bodies showed low stress levels, while the periphery showed high stress levels. However, after PPVA treatment, the stress distribution within the vertebral body became more uniform. This even stress distribution helps prevent excessive cement migration within the vertebral body and reduces the risk of vertebral body collapse [40, 41].

There is a tendency for the stress on the T11 vertebral body to increase in biconcave deformity after PPVA, especially in the extension position and left rotation. This phenomenon may be attributed to three factors. Firstly, the lower height of the center of the vertebral body contrasts with the increased height of the anterior and posterior edges. Secondly, the rigidity of the vertebral body is enhanced by the filling of bone cement. Third, the ROM of the vertebral body is the smallest during posterior extension, and due to the unique structure of the biconcave deformity and the influence of bone cement, the stress is concentrated on the posterior edge of the vertebral body. In addition, due to the increased stiffness of the vertebral body filled with bone cement, the stress on the adjacent vertebral body T12 shows an increasing trend, increasing the possibility of fracture of the T12 vertebral body [42]. On the contrary, the stress situation of adjacent vertebral body T10 was significantly improved, especially the stress during forward flexion of the vertebral body is significantly decreased. Although PPVA causes increased stress in the biconcave deformed vertebral body, it improves the stress distribution in fractured vertebral body and adjacent vertebral bodies, preventing high stress from being concentrated on one side of the vertebral body. In addition, when the biconcave deformed vertebral body and adjacent vertebral bodies are in posterior extension, the stress on the intervertebral structure is relatively more significant than in other forms of motion but is smaller in forward flexion. Therefore, for the postoperative rehabilitation and daily life of patients with biconcave deformity, we recommend using the forward flexion position while avoiding excessive posterior extension to prevent refracture of the operative vertebral body and fracture of adjacent vertebral bodies.

PPVA significantly improved the overall stress of the collapsed deformed vertebral body T12 and adjacent superior vertebral body T11, especially the vertebral body extension and right bending movements. However, the stress on the lower vertebral body L1 exhibited a rising trend, with the most significant increase observed during forward flexion and left rotation movements, which was similar to the previous research results of Ah-Reum Cho [43]. This may be caused by the fact that the L1 vertebral body is the junction of the thoracic and lumbar vertebral bodies, and is the site of the highest concentration of stress in the whole body during activities.

In this study, we found that the stress difference between wedge deformity, biconcave deformity, and collapse deformity fractures before and after PPVA was huge. We combined relevant literature and clinical experience and found that this difference not only comes from the vertebral body morphology, but is also closely related to the patient’s gender, age, osteoporosis degree, and bone cement filling [44, 45]. We used finite element analysis to prove the effectiveness of PPVA for thoracolumbar OVCF. In both wedge deformed and collapsed deformed vertebral bodies, the stress after PPVA was significantly reduced. However, for vertebral body with biconcave deformity, the effect of PPVA treatment is unsatisfactory. In addition, PPVA affects the stress of adjacent vertebral bodies of the three types of OVCF. Although the stress of the inferior vertebral body with double concave deformity and collapse deformity is increased, the stress cloud map shows that the stress distribution of the vertebral body is relatively uniform compared with that before PPVA, which avoids partial stress concentration leading to refracture. Recent studies have shown that increased stress on the adjacent vertebral bodies is a risk factor for fracture. In particular, osteoporotic vertebral bodies are susceptible to the stiffness of bone cement, whereas normal vertebral bodies do not have this concern [46]. Therefore, we recommend that OVCF patients who undergo PPVA treatment, especially those with biconcave and collapsed vertebral bodies, receive a certain period of anti-osteoporosis treatment after surgery.

There are some limitations to the study. Firstly, this study mainly observed the overall stress of the vertebral body at the macro level, the same material properties were used to establish the models, without taking into account individual differences in patient gender, age, and osteoporosis degree. Secondly, the finite element model is established based on the patient’s own CT imaging data, which may limit the breadth and representativeness of the model. Therefore, it cannot represent that PPVA has the same surgical effect on different patients with the same fracture type. In the future, the sample size needs to be expanded. Thirdly, since the establishment of the model is directly based on the patient’s CT data, there is no comparison with the normal vertebral body model to verify the validity of the model. Fourthly, In this study, the stress changes of the vertebral body were mainly observed. In order to ensure data management, the model established was relatively simplified and the specific parameters of the intervertebral disc proposed by Niemeyer et al. [47] were not used for accurate modeling. Fifthly, the stress situation of the finite element model uses the normal physiological motion state of the vertebral body under ideal conditions, which cannot truly simulate the mechanical environment of the human body in daily life, and further biomechanical research is needed. In addition, the results of the finite element analysis can only explain the stress on the vertebral body in the short term after surgery, and cannot predict the long-term clinical effects. Therefore, in the future, we will focus on long-term follow-up of patients. Our purpose is to propose a new VA idea for treating OVCF in the thoracolumbar segment, and we will conduct more research in the future to further improve the efficacy of treating OVCF.

Conclusion

In summary, PPVA shows positive surgical results in the treatment of wedge-shaped and collapsed deformed vertebral bodies, although its effectiveness in the treatment of biconcave vertebral bodies is limited. However, this still provides a reference basis for the clinical use of PPVA to treat OVCF. According to each patient’s specific case and imaging data, an individualized puncture route can be developed to improve the puncture success rate and increase the quality of the operation.