(1) History Vertebroplasty (VP) is a new type of minimally invasive surgical intervention in the spine, which essentially involves the injection of a coagulating material into the vertebral body for the purpose of reducing pain and increasing stability of the vertebral body. In 1987, the authors reported seven cases of a similar operation and named it vertebroplasty, which is also known as percuteneous vertebroplasty (PVP) because of the percutaneous puncture operation. Some scholars later expanded the indications for this treatment to include other tumors (myeloma, metastatic tumors of the vertebral body) and vertebral compression fractures caused by osteoporosis. However, in the early 1990s, European scholars mainly focused on the application of VP in vertebral tumor lesions such as vertebral hemangioma, myeloma, and tumor metastatic lesions, and not much research was done on VP for osteoporotic vertebral compression fractures. 1993 Dion and Jensen performed the first vertebroplasty in the United States on a patient with vertebral metastases from breast cancer at the University of Virginia. Since then, vertebroplasty has gradually become popular in the United States and is widely used in the treatment of osteoporotic vertebral compression fractures for which conservative treatment has failed. This procedure was performed in China in the late 20th and early 21st centuries. In recent years, the development of VP as a promising treatment method has been very rapid, and the volume of surgery has been increasing year by year, and osteoporotic compression fractures for which conservative treatment is ineffective have become the main indications. (2) Indications and contraindications Since the introduction of vertebroplasty, its indications have broadened from vertebral hemangioma in the early stage to myeloma, bone metastases and osteoporotic vertebral compression fractures later. Currently, vertebroplasty is also used as a prophylactic treatment for patients at high risk for compression fractures and as an adjunct to stabilize the vertebral body before and after internal fixation surgery in spine surgery, among others. In recent years, scholars have summarized some experiences from a large number of clinical practices, and the indications and contraindications of VP have been discussed in depth. Indications include: ① primary or secondary vertebral compression fractures with painful symptoms. ② Extensive lysis or invasion of the vertebral body secondary to benign or malignant tumors (e.g., hemangioma, multiple myeloma, and metastatic lesions) with painful symptoms. ③ Vertebral fractures associated with osteonecrosis (Kummell’s disease) with painful symptoms. ④ Unstable compression fractures with confirmed movement of the wedge deformity. Absolute contraindications include: ① osteomyelitis of the vertebral body being treated. ② Acute traumatic fractures of non-osteoporotic vertebrae. (iii) Uncorrectable coagulation disorders and bleeding tendencies. ④ Allergic reaction to the drugs and instruments used in the operation. ⑤ Incomplete posterior wall of the vertebral body. Relative contraindications include: ① neurogenic pain or pain with lesions beyond the vertebral body, caused by compression unrelated to vertebral body collapse. ② Posterior displacement of the fracture mass resulting in spinal canal occupancy. (iii) Tumor protrusion into the epidural space with significant spinal canal occupancy. ④ Severe vertebral body collapse with vertebral body height compression of more than 70%. ⑤ More than 3 vertebrae are treated at one time. (3) The value of physical examination and imaging examination Patients with multiple vertebral compression fractures are difficult to specify painful vertebrae based on physical examination and plain films alone. Compression pain often does not accurately identify the affected vertebrae. Plain films, on the other hand, are more difficult to differentiate from healed old compression fractures. Do et al. concluded that MRI is useful in identifying the location and extent of spinal tumor invasion and in determining the course of vertebral compression fractures. The characteristic changes in bone marrow signal vary depending on the period of fracture. acute and subacute fractures within 30 days have low signal on T1-weighted and high signal on T2-weighted and STIR sequences. 42% of patients were found to have a high signal band under the fracture endplate on T2-weighted images by Cuenod et al. In addition subacute blood accumulation under the endplate can be found. It is possible that the signal may become isosignal after the use of gadolinium control agents. At nearly 1 month of fracture, the majority of compressed vertebral bodies have T1- and T2-weighted signals equivalent to normal bone marrow. The marrow signal of fully healed vertebrae recovers and sometimes becomes hyposignal in T1- and T2-weighted because of significant sclerosis. Do et al. concluded that MRI of Kummell disease showed fluid accumulation in the superior endplate with low signal in T1-weighting and significant high signal in T2-weighting. This MRI image lacks the signal of inflammatory changes around the vertebral body common to osteomyelitis or abscesses. Bone scans may also be useful in determining problematic vertebral compression fractures and may also help determine the site of acute fracture and fracture healing, especially in patients with multiple vertebral fractures.Maynard et al. concluded that increased tracer uptake at the fracture site was highly predictive of good outcomes in VP. In their study 26 out of 28 patients had pain relief. Bone scans are very sensitive for the diagnosis of vertebral compression fractures, and negative results are as likely to suggest a low likelihood of pain relief after surgery for this vertebra as negative MRI images. However, when a vertebral compression fracture is effectively treated, the bone scan remains positive for a long time, and Mathis et al. advocated that MRI be chosen whenever possible and that bone scan be considered only when MRI cannot be performed. This is because MRI provides a detailed anatomy in addition to reflecting both spinal stenosis and other abnormalities that affect the screening of patients for vertebroplasty. CT is mainly used to clarify the damage to the posterior wall of the vertebral body and the vertebral arch, as well as the anatomy of the vertebral body and the vertebral arch to guide the operation. (4) Operation technique (1) Infusion route The cervical spine lesion is usually punctured with a small puncture needle through the lateral or anterolateral approach into the vertebral body and infused with bone cement; C1 to C3 cervical spine can be done through the oropharyngeal approach, while C3 to C7 cervical spine is usually done through the anterolateral approach; T5 or T6 thoracic spine is difficult to operate due to its anatomical structure and location, so a small puncture needle of 13G or 16G can generally be used, and a trans-arch root or paracentral approach can be used. CT or combined use of X-ray fluoroscopy can reduce complications and facilitate operation. In the thoracolumbar spine, the transforaminal approach has been widely used instead of the postero-lateral approach because it significantly reduces the risk of cement leakage from the needle tract and pneumothorax. The postero-lateral approach next to the pedicle often passes through the intervertebral foramen and is prone to nerve root injury, especially when the cement leaks along the needle tract. However, the postero-lateral paravertebral approach can be considered for instillation in cases of lower lumbar spine or destruction of the pedicle. At the S1 and S2 levels, a transperineal approach is used in most cases, and sometimes a transsacral wing approach is also used. 2) Bone cement Polymethylmethacrylate (PMMA) is a widely used adhesive material in clinical practice and is the most commonly used bone cement for vertebroplasty, with the following advantages: familiar to orthopaedic surgeons; low viscosity, easy to handle, and easy to instill; contrast agent can be added; provides the necessary strength and stiffness quickly; not expensive, etc. . Disadvantages: no osteoconductivity and induction properties; poor histocompatibility; non-resorbability, cannot be replaced by normal bone tissue, and will also inhibit osteogenic reaction; high heat production during polymerization may bring irreversible damage to surrounding tissues when the cement leaks; monomer toxicity may cause systemic toxic reactions when leaking into the blood; poor X-ray opacity itself does not have radio-opaque, need to add additional contrast agent, etc. The dose of cement is too large. (3) The choice of dose The dose of bone cement infusion was the first concern of scholars. From the clinical point of view, there is no systematic study on how much bone cement dose can achieve good efficacy. In the early days, people were keen on maximizing the infusion dose, and the injection was usually stopped when cement leakage was observed under fluoroscopy or when it reached the outer wall of the vertebral body in clinical practice. The amount of cement injected in this way was relatively large, usually 8 to 10 ml or even more. As with other orthopedic devices used to aid in fracture healing, the purpose of vertebroplasty is to provide stability to the vertebral body during the fracture healing process. In this sense, vertebroplasty should be viewed as a fracture repair technique rather than a simple infusion filling. Studies have shown that pain relief is not related to the amount of cement infused, but rather to the distribution of cement within the vertebral body, particularly at the fracture plane. kallmes et al. compared the clinical results of VP with large doses of more than 3 ml and small doses of less than 3 ml, and the results were not significantly different. The authors concluded that complete filling should not be pursued, as the latter would increase the probability of leakage significantly. murphy et al. found that the risk of cement leakage increased with higher doses. in the study by belkoff et al. the leakage rate was found to be three times higher with 8 ml of perfusion than with 6 ml. In addition, excessive bone cement may increase vertebral stiffness leading to fracture of adjacent vertebrae. The appropriate dose is not simply quantitative. Even if the dose is the same, differences in bone cement products, different solid-to-liquid ratios, the addition of contrast agents or antibiotics, and individual vertebral body size differences can affect perfusion results. Individualized selection of perfusion dose under established bone cement conditions is a good direction to investigate. Tack et al. found a strong correlation between PMMA cement volume and the area of trabecular space measured by CT, and the amount of cement infusion can be estimated in advance by CT scan and finite element analysis to achieve individualized treatment. 4) Analgesic hypothesis It is not known whether pain relief is secondary to mechanical stabilization, chemical toxicity, or thermal necrosis effects on neural tissue. The most intuitive explanations include simple mechanical stabilization of the fracture, i.e., the bone cement stabilizes the vertebral body, resulting in reduced loading of the small joints. However additional ideas include anesthetic effects produced by the local chemical, vascular and thermal effects of PMMA acting on the nerve endings of the surrounding tissue. There are currently three main hypotheses: (1) microfractures in the vertebral body are fixed after cement injection, reducing the relative motion between microfracture ends; (2) the cement takes some of the load, which reduces the load on the cancellous bone; and (3) sensory nerve endings in the cancellous bone are destroyed by the exothermic or cytotoxic nature of the monomer during polymerization of the bone cement. 5) Clinical efficacy The advent of vertebroplasty has led to a new treatment option for osteoporotic compression fractures. Vertebroplasty provides significant relief of back pain and also prevents re-fracture of the treated vertebrae. The technique is minimally invasive, with significant immediate results, and has been widely used. Osteoporotic compression fractures have also become the most used indication for vertebroplasty in clinical practice today. Many studies have shown clear short-term results with vertebroplasty, and in 1997 Jensen et al. reported that 26 out of 29 patients with 47 cases who had failed to respond to pain medication had improved symptoms after vertebroplasty, with a 90 percent relief rate. They performed 112 vertebroplasty in 75 individuals 97 times over a 19-month period, with fracture duration ranging from 6 weeks to 10 years, all of whom had failed to respond to conservative treatment. There were 91 of 97 complete or major remissions, 4 slight improvements, 2 no changes, and no aggravated patients. Medium- to long-term follow-up also showed continued or further improvement in the efficacy of vertebroplasty.Alvarez et al. followed 260 patients with 423 vertebroplasty procedures for 12 months, and the patients’ VAS scores decreased from 8.9 to 2.7.Winking et al. followed 38 patients with vertebroplasty for 12 months, and the VAS scores decreased from 7 to 2.6, and the Oswestry lower back pain function (Oswestry Low Back Pain Disorder) decreased from 7 to 2.6. Perez-Higueras et al. followed 13 vertebroplasty patients for an average of 65 months, and the VAS score decreased from 90.7 to 21.5 at 5 years, with positive results. 6) Complications Although vertebroplasty is widely used in clinical practice, its complications should not be ignored. Recently, the FDA has warned about side effects due to high extravasation rate of PMMA on its website. Nussbaum compiled reports of complications related to vertebroplasty published by the FDA from 1999 to June 27, 2003. A total of 19 adverse reactions were reported, 11 of which were clearly related to transforaminal vertebroplasty, 5 to posterior posterolateral access, and 3 to unknown access. A total of 3 deaths were reported via the transforaminal approach, but they were not related to cement leakage. There was one case of paralysis, two cases of cardiac arrest, two cases of hypersensitivity or decreased blood pressure, two cases of cement embolism, and five cases of instrumentation rupture, the latter three of which were all clinically asymptomatic. There were 4 deaths in the lateral approach, 1 due to patient allergy to cement, 1 due to cement leakage through the posterior wall of the vertebral body, and 2 due to a single multisegmental vertebroplasty (8 and 11 segments). There was also one case of instrumentation rupture. (1) Complications unrelated to cement leakage (i) Local pain The most common complication is localized pain at the skin puncture site, which may be an abrasion or hematoma. Local pain can worsen in the hours or days after surgery, but mostly resolves within 72h. The degree of pain may be related to the amount of bone cement infusion. Small abrasions can be relieved by applying medications or can be reduced by applying pressure to the incision after trocar removal. Postoperative skin pain is more common in malignant lesions but does not require special management; Kaufmann et al. suggested that cement deposition in the subcutaneous channel may be the cause of local pain and suggested that a slight advancement of the needle tip toward the upper endplate after instillation could disconnect the cement column and avoid cement residual in the subcutaneous channel. (ii) Rib fractures Rib fractures can occur in elderly patients with osteoporosis due to their posture. jensen et al. reported 2 rib fractures in 29 individuals after 47 vertebral VP. (iii) Other The possibility of pneumothorax during VP of the upper and middle thoracic spine has been reported but is rare. Infection is also relatively rare. chiras reported a case of secondary infection in an immunosuppressed patient after surgery. yu et al. reported a case of severe septic spondylitis found 1 month after VP for a T12 osteoporotic compression fracture. walker et al. reported 2 cases of postoperative infection with osteomyelitis after VP, which resolved after internal fixation with lesion removal. The authors concluded that VP surgery should be chosen with caution in patients with a history of infection. kallmes et al. found 1 case of Staphylococcus epidermidis infection in 250 patients who were on multiple immunosuppressive drugs. (2) Complications related to cement leakage Many complications are mainly caused by leakage of cement, and leakage to different sites can have different symptoms: (1) leakage to paravertebral tissue is the most common and often has no clinical manifestations. If the vertebral cortex is already broken or damaged by puncture, the cement may leak into the paravertebral soft tissues. Sometimes the tip of the needle may be outside the vertebral body despite the fact that it is still inside the vertebral body on the lateral view, but the tip may have been over-punctured. (2) Leakage into the intervertebral space is not uncommon. Intervertebral disc leakage is usually asymptomatic, but its prolonged presence may cause changes in the biomechanical properties of the adjacent vertebral body. Especially in patients with osteoporosis and severe compression fractures of the vertebral body, it is possible to increase the incidence of adjacent vertebral fractures. Postoperative cemented disc leakage has been reported in 35% of patients with severe compression fractures of the vertebral body. The authors found that the occurrence of leakage was not related to the shape of the fractured vertebral body. (3) Leakage into the paravertebral veins. This is rarely clinically symptomatic, but pulmonary embolism and cerebral embolism have been reported. The consequences of such complications, when they do occur, can be quite serious. (4) Leakage into the epidural or intervertebral foramen. When there is a defect in the posterior vertebral body bone, the incidence of this type of leakage is over 50%. However, few patients are symptomatic, and only rarely do they require surgical decompression due to spinal cord or nerve root compression. In addition to cortical disruption, cement leakage is mainly related to perfusion dose, perfusion pressure, and puncture site.Ryu et al. reviewed 159 individuals with 347 vertebral VP and found a 26.5% incidence of leakage into the epidural space on CT. It was also found in the study that leakage occurred significantly more frequently above T7 than below T7 vertebrae, and the higher the perfusion dose, the higher the leakage rate. The location of the puncture tip and venous return were not significantly associated with leakage. (3) Preventive measures The American Society of Interventional Radiology Practice Committee requires that the VP complication rate be controlled to less than 2% for osteoporotic patients and less than 10% for oncology patients. The key to controlling complications is to reduce the leakage of bone cement. Therefore, how to prevent the leakage of bone cement is the main problem facing VP. There are many clinical methods to reduce leakage, such as: careful estimation of the degree of bone destruction before surgery, good intraoperative monitoring equipment, venography before cement injection, using the thickest possible puncture needle and increasing the viscosity of the cement, and using a lateral injection puncture needle. Even so, the incidence of leakage is still high, and fortunately, the vast majority of leaks do not produce clinical symptoms. Laredo et al. advocate avoiding placement of the needle tip below the disrupted endplate or in the central vascularized area of the vertebral body. In severely compressed vertebrae, the needle tip should be placed as far forward as possible to allow anterior to posterior dispersion of the bone cement during infusion. In compression fractures with vacuums and fissures, the needle tip should enter or be as close as possible to the space in order to achieve good clinical results. The transforaminal approach in the thoracolumbar spine should avoid damaging the cortex within the pedicle, especially in the upper thoracic spine, which is prone to extravasation once the PMMA is damaged. Jang et al. suggested that: the bone cement polymerized to a paste when perfused can reduce leakage compared to liquid form, especially when perfusing tumor-rich vertebrae; high-quality X-ray fluoroscopy and PMMA with added contrast can help prevent embolism; multisegmental perfusion is prone to pulmonary embolism and should be chosen with special care; if the tip of the needle is found to enter the vessel, it should be repositioned or blocked with gel sponge. et al. suggested that filling with gelatin sponge before perfusion or partially closing the vessel before perfusion by puncture could reduce leakage of bone cement. aebli et al. suggested that when perfusing bone cement via unilateral arch root approach, decompression via contralateral arch root drilling might reduce complications caused by leakage. In 22 ewes, vertebroplasty was performed with a 4-segment unilateral arch approach and 10 of them were drilled through the contralateral arch. The results showed a decrease in mean arterial pressure, partial pressure of oxygen and pHD and an increase in partial pressure of carbon dioxide, while the degree of change was reduced in the contralateral drilling group. The degree of pulmonary vascular fat embolism also decreased from 19% to 9%. 7) Kyphoplasty Kyphoplasty (KP) is the treatment of vertebral compression fractures with a balloon in addition to VP. In 1998, Kyphon’s expandable balloon was approved by the FDA for use in fracture reduction and/or creation of cavities in cancellous bone. Current IBP balloons are available in 15mm and 20mm diameters and are capable of operating in T5 to L5. The KP is often performed via a transforaminal approach, which can be used in the thoracic spine between the head of the rib and the pedicle, or in the lumbar spine via a posterior lateral approach. The general KP procedure consists of a small skin incision, fluoroscopic access to the fractured vertebral body with an 11G puncture needle through the arch or paravertebral roots, removal of the puncture needle, placement of an operating tube to establish a working channel to the posterior vertebral body, insertion of a 4.19 mm trocar needle into the tube or use of a hand drill to enlarge the intravertebral channel, and introduction of the IBP. The IBP is introduced and placed below the collapsed endplate in order to elevate the endplate while reducing compression on both sides and posteriorly; under fluoroscopic monitoring, the IBP is gradually expanded with contrast agent through a pressure syringe, and the pressure value is closely monitored; after satisfactory expansion, the IBP is recovered and withdrawn, and the perfusion agent is deployed and injected into the vertebral cavity under fluoroscopic monitoring, with a filling volume generally 1 to 2 ml more than the final volume of the IBP expansion, so that the perfusion agent is compatible with the surrounding loose volume. Carrino believes that the indicators for cessation of expansion include: proper repositioning of the compression fracture is complete; IBP pressure reading of 220 psi; X-ray fluoroscopy showing IBP contact with the vertebral cortex; and IBP expansion to a maximum volume of 4 ml for a 15-mm diameter balloon and 6 ml for a 20-mm diameter balloon. leakage. For most acute fractures, the balloon should be retained on one side of the vertebral body after bilateral ballooning to avoid loss of repositioning. It has also been suggested that a unilateral pedicle approach can also complete KP with satisfactory results. Restoration of vertebral height, correction of kyphosis and reduction of cement leakage are considered to be the most important aspects of KP over vertebroplasty (VP), and Belkoff et al. compared the results of KP and VP in ex vivo experiments, showing that KP restored 97% of the lost height, whereas VP restored only 30%. Both forming methods significantly increased the compressive strength of the vertebral body. In addition, only the KP group was able to restore the stiffness of the vertebral body. The authors concluded that compared with VP, KP creates a cavity in the affected vertebrae, restores vertebral body height, and corrects the kyphosis deformity. Belkoff et al. reported that KP significantly restored vertebral height compared to VP, which also restored height better, but not as well as KP. The aforementioned clinical reports of KP also suggest that KP has a significant ability to restore vertebral height, and Lieberman et al. concluded that the bone cement was thin and prone to leakage during VP infusion. Phillips et al. showed a lower incidence of transvascular and cortical cement leakage due to KP compared to VP in ex vivo experiments. The authors concluded that the higher pressure during VP infusion and the lower pressure during KP infusion due to the presence of a cavity reduced cement leakage. In addition, the formation of intravertebral cavities during KP is accompanied by compaction of cancellous bone, which to some extent blocks cement leakage into the vasculature or outside the vertebral body.