Abstract: Percutaneous vertebroplasty (PVP) is currently the main surgical treatment for osteoporosis vertebral compression fractures (OVCFs), and its main complication is leakage. Factors associated with leakage include case selection, operative technique, surgical instrumentation, cement material, and imaging equipment. In this article, we will describe the progress of research on the prevention and treatment of bone cement leakage from several major aspects Ling Qinjie, Department of Spine Surgery, The First Hospital of Guangzhou Medical University
Keywords: vertebroplasty, osteoporotic vertebral compression fracture, leakage, bone cement, navigation
Introduction
As the population ages, the number of patients suffering from osteoporosis is increasing, and OVCFs have become a common disease in the elderly. Traditional treatment methods include drugs, physiotherapy, bed rest and other conservative treatments, which can partially relieve the symptoms, but long-term bed rest can accelerate the loss of bone mass and muscle atrophy, which is not conducive to the recovery of the disease, and also cause great psychological and economic pressure on the patient and poor quality of life. PVP is the main surgical treatment for OVCFs, which can rapidly relieve patients’ pain, shorten their hospital stay, resume daily activities as soon as possible, and improve their quality of life.
In 1984, Dr. Dermand and Dr. Galibert of the French Department of Radiology first used PVP for C2 vertebral hemangioma with good pain relief [ 1]. 1988, Duquesnal et al. first applied PVP for OVCFs and this technique started to develop in Europe [ 2]. 1989, Kaemmeden used the bone cement infusion technique for spinal metastases [ 3]. 3]. the first case of PVP in the United States was done by Jensen in 1994 [4], which was subsequently approved by the FDA and then popularized throughout the United States, and since then PVP has been widely used to treat OVCFs.
Conventional vertebroplasty has many advantages: few operating devices, simple procedures and techniques, short operative time, good diffusion of low-viscosity PMMA, rapid restoration of strength and stiffness of the vertebral body, and significant pain relief. At the same time, it has many problems: the operation time is difficult to control, it cannot correct the kyphosis, and the pressure injection of bone cement can easily cause leakage. The literature reports that the leakage rate of PVP in OVCFs ranges from 29% to 42.6%, with an average of about 35% [5-8].
Sixty-seven percent of the complications of vertebroplasty are associated with leakage [9], and the factors affecting leakage are mainly ① case selection ② operative technique ③ surgical instrumentation ④ cement material ⑤ imaging equipment. Among them, ① and ② can be solved by the gate-keeping of surgical indications, standardized training and strict access system, while the operating instruments, cement materials and imaging equipment need further improvement and development.
1 Surgical instruments
1.1 PKP (Percutaneous kyphoplasty)
In 1994, Reiley et al. proposed the idea of an expandable bone tamp (IBT) based on PVP, i.e., PKP, to correct vertebral kyphoplasty by balloon expansion of the vertebral body followed by cement injection [10]. Lieberman et al. began to perform PKP surgery on patients, and the results of in vitro trials and preliminary clinical applications demonstrated that PKP surgery not only effectively reduced patients’ pain, but also restored some of the height of the compressed vertebral body, corrected the kyphosis, and improved the safety of intraoperative cement infusion [11]. Subsequently, Hadjipavlou et al. counted 1279 vertebrae undergoing PKP, and the overall leakage rate was 8.4% significantly lower than the 29% in the PVP group [6]. Hulme et al. concluded that the leakage rate in PKP was 9%, also lower than the 41% in the PVP group [7].
Advantages: partial height restoration of the vertebral body and some correction of the posterior convexity deformity; repeated use of the balloon in the same patient; injection of a more viscous bone cement under low pressure in a closed bone shell, resulting in a lower leakage rate, with a significant improvement in the leakage rate of 8%-9% compared to PVP.
Disadvantages: more complicated operation, hydraulic expansion of the vertebral body endplate or lateral wall re-fracture, difficult to control the direction, the risk of balloon rupture, unfixed shape after expansion, the phenomenon of “rebound”, prolonged operation time, expensive, difficult to popularize [12,13].
1.2 Sky bone expender system (Sky bone expender system)
In 2005, Tong et al. first implanted the Sky bone expander into the vertebral body to expand the diseased vertebrae under pressure, and then injected bone cement into the cavity to strengthen the vertebrae after retensioning, and treated 9 cases with 12 vertebrae with good results and no leakage [14]. all without leakage [14]. Unfortunately, in the same year, a federal court ruled that Disc-O-Tech’s Sky bone expander system infringed on Kyphon’s balloon expander patent and prohibited the import and sale of the product in the United States, so Sky was not popularized in the United States and articles on it are scarce. In 2006, Seel and Davies in the United Kingdom used a deer spine model to compare the biomechanics of PKP and Sky and found no difference in the stiffness and strength of the spine between the two [15]. out of the body and finally had to be left in the body, but all had no clinical manifestations and had good results after one year of follow-up [16]. However, there is still a lack of a large number of clinical cases reported.
Advantages: mechanical expansion of the vertebral body, controlled expansion direction of the expander, fixed morphology after expansion, the ability to restore the height of the vertebral body to correct the posterior convexity deformity, and the advantages of easy operation and low price [17], with a leakage rate of 7.5%.
Disadvantages: forced expansion is prone to new fracture, increased risk of leakage and difficulty in pulling out the instrumentation, still some height loss, higher technical requirements for operation, cheaper but the dilator cannot be used repeatedly in the same patient.
1.3 Vessel-X Bone Material Filler
PKP and Sky bone expander is improved compared with PVP, but there are still some problems, balloon expansion in the intraoperative rupture occurred, Sky bone expander intraoperative fracture and withdrawal difficulties also exist, expander withdrawal after the vertebral body has the possibility of recollapse and spinal force line change.
In February 2002, Jerry Lin of Taiwan developed the first generation of bone material filler to address these problems, which was initially called Treadplasty because of its thread-like shape. This technique was presented at the triennial Asia Pacific Spine Alliance (APOA) meeting in Malaysia in September 2004 [18]. After continuous improvement, the Vessel-X Bone Material Filler was finally developed by Jerry Lin’s company A-Spine in Taiwan, which consists of a dense polymer mesh structure that encapsulates most of the bone cement and allows some of the cement to leak outside the mesh to anchor the surrounding bone tissue. In 2007, Flors et al. in Spain reported that Vessel-X was used to treat 37 OVCFs in 7 cases. In 2007, Flors et al. in Spain reported that only 1 of 37 OVCFs treated with Vessel-X leaked, with a leakage rate of 2.7% [21].
Advantages: it can be left in the body to maintain sufficient strength of the vertebral body, eliminating the “rebound” phenomenon and controlling the leakage of bone cement, with a leakage rate of 2.7%.
Disadvantages: a large number of clinical cases are still not reported.
1.4 Others
New device inventions are still being reported, such as the Vertebral BodyStenting (VBS) system used by Robert et al. in 2010 and the Jack Dilator-Kyphoplasty (DKP) in China [22,23], both of which have not yet been proven in a large number of trials and clinical cases. The results have not been proven in a large number of trials and clinical cases. Preoperative vertebral venography and pre-emptive gel sponges have also been attempted to reduce leakage rates, but have been abandoned due to cumbersome procedures and poor results [24,25,26].
2 Confidence high-viscosity bone cement system (CV, Confidence system)
The traditional filler material used in OVCFs is low-viscosity PMMA, which has several advantages: high compressive strength, good dispersion, and rapid restoration of strength and stiffness of the vertebral body. However, the disadvantages are also obvious: it is a non-biologically active material with high monomer toxicity, polymerization can generate high heat of 100-120°C, cannot be degraded, cannot restore the height of diseased vertebrae, cannot change the kyphosis deformity, difficult to grasp the operation time, easy to leak under low viscosity injection, and can cause related complications, such as high heat burns surrounding tissues, toxic absorption causes transient hypotension, nerve root spinal cord Compression, etc. After curing, the difference in elastic modulus with bone is large, and its tensile strength is only 1/4 of that of normal bone, and the mechanical and mechanical stability of bone cement is weakened by prolonged loading, and fatigue fracture may occur [27,28].
In 2003, Bohner M et al. proposed for the first time that the most effective way to reduce the leakage of PVP bone cement was to increase the viscosity of the bone cement [29]. 2005, D. Giannitsios et al. also showed that high-viscosity bone cement is a key factor in preventing the leakage of PVP, and pointed out that bone cement with a viscosity of 350 Pa-sec would not In May 2006, Disc-O-Tech, Inc. introduced the Confidence High Viscosity Bone Cement Vertebroplasty System, a new product developed in-house at the Meir Medical Center in Kasaba, Israel, which is an improvement on the conventional PMMA bone cement, to the world for the first time. In June of the same year, Baroud et al. also published a paper stating that the viscosity of the bone cement was the most important determinant of leakage and that injection at its high viscosity significantly reduced bone cement leakage [31]. A study by Anselmetti et al. in 2008 reached the same conclusions as Baroud [32]. An increasing number of in vitro trials and clinical applications have demonstrated that the leakage of high-viscosity bone cement in PVP is significantly lower than that of low-viscosity bone cement, and that there is no difference between the two in terms of volume injected, pain relief, and other new fractures caused [33,34,35]. In a prospective study in 2011, Folman et al. applied CV and Sky to 14 and 31 OVCFs, respectively, and concluded that Sky was superior in restoring vertebral height and correcting kyphosis, while CV was superior in price. Sky was superior in restoring the height of the vertebral body and correcting the kyphosis, while CV was superior in terms of price, but there was no difference between the two in terms of clinical outcomes in terms of pain reduction, and the safety profile was consistent, with no leakage occurring in either case [37].
Advantages: easy operation, instantaneous high viscosity, long injectable time (10-12 min), controllable injection direction and pressure, uniform distribution, low polymerization temperature, leakage rate comparable to PKP and Sky but cheaper than both.
Disadvantages: high pressure injection into the vertebral body may increase the chance of fat embolism, poor dispersibility, non-degradable, non-biologically active, more bone cement needs to be injected to correct the posterior convexity deformity (8~10ml for one vertebral body, while traditional PVP only needs to inject 3~5ml), increasing the chance of fracture of adjacent vertebral body.
3 Imaging equipment
The key to PVP leakage prevention and control lies in the percutaneous pedicle puncture access technique. The special anatomy of the pedicle and individual differences make the operation more difficult, and a slight deviation in direction can cause catastrophic injury. Previously, the puncture access technique relied on the aid of C-arm X-ray and CT machines and the operator’s experience. The operator’s empirical sense varies greatly among individuals, and repeated filming is required to confirm the technique with either a C-arm X-ray machine or a CT machine, which is tedious and increases not only the operation time but also the radiation injury to patients and medical workers. The design of accurate positioning and easy operation of imaging equipment has become an important task in the development of minimally invasive spine surgery. The most researched computer-aided surgery navigation system (CASNS) is used at home and abroad to optimize the infrared optical or electromagnetic positioning navigation system to understand the three-dimensional structure of the spine in real time, so as to complete the surgery more safely and finely.
The first surgical navigation system in 1986 was the combination of CT images and surgical microscope by Roberts et al. in the United States, using ultrasound localization to guide neurosurgery [38]. 1993 Steinann et al. applied computer navigation technology to fix the lumbar spine via the pedicle approach, and the accuracy of the approach was significantly improved compared with the traditional method, which was considered a milestone in the development of navigation technology in spine surgery [39]. This is considered a milestone in the development of navigation technology in spine surgery [39], and subsequently this technology has been continuously developed.
Navigation systems are mainly divided into ① passive ② active ③ semi-active, the most widely used are mainly ① passive, which can control the spatial trajectory of surgical instruments, but the surgery still needs to be completed by the surgeon, including CT, C-arm X-ray, MRI electromagnetic navigation system; ② active, which is a robot-assisted navigation system, the surgery is completely operated by robot hands, without the manual intervention of the surgeon. ③ semi-active, which belongs to the second generation of medical robotic surgery system, the operator can move the surgical tools within the safe range of robotic control, with both the precision of robot and the flexibility of human hands.
3.1 Passive navigation
3.1.1 CT navigation system
Image data is derived from preoperative scans, and data is exchanged between the imaging data and the navigation system through DICOM (Digital Imaging and Communications in Medicine) and PACS (Picture Archive and Communication Systems) technologies, and in the intraoperative Using matching techniques, CT images are combined with the actual anatomy of the patient.
Advantages: good image quality, ability to show complex anatomical structures such as the cervical spine and upper thoracic spine, feasible preoperative planning to develop surgical plans, and effective reduction of intraoperative x-ray exposure [40]. The penetration rate of 4.6% for lumbar implantation screws with CT navigation via the pedicle approach was reported abroad to be significantly lower than that of 13.4% with the conventional technique [41]. Subsequently, a penetration rate of 6.3% in the thoracic spine with CT navigation has also been reported [42].
Disadvantages: preoperative photographs increase the financial burden on the patient, intraoperative manual registration for calibration matching is required, the procedure is cumbersome, the operative time is longer, and the accuracy is poor [43].
3.1.2 C-arm X-ray machine navigation system
(1) C-arm X-ray machine two-dimensional navigation system
The acquired images are transmitted to the navigator by using a normal C-arm X-ray machine to obtain image information and completing the registration process through calibration. The accuracy of its matching directly affects the success or failure of the procedure.
Advantages: automatic registration, eliminating the need for manual alignment, simple operation, fluoroscopic images can be saved, real-time navigation, reduced staff radiation exposure, and a 3.73% arch root penetration rate [44], which is superior to CT navigation.
Disadvantages: unclear imaging, because it is a two-dimensional image, it cannot be segmented and does not provide three-dimensional alignment; poor image quality for the cervical spine, upper thoracic spine, obese patients, patients with excessive osteoporosis, or complex anatomical structures.
(2) C-arm X-ray machine 3D navigation system
Also known as the intraoperative CT navigation system, manufactured by Siemens in 1999, is the world’s first mobile C-arm machine three-dimensional imaging equipment, named Siremobil ISO C (3-D). The navigation system is actually a “C” arm machine with optimized image processing combined with infrared machine tracking, which can add surgical tools and design surgical access at will, reconstruct axial, sagittal and coronal images of the vertebral body, clearly display the cortex and spinal canal around the pedicle, virtual three-dimensional spinal structure, and provide precise positioning of the approach through the pedicle. In 2003, Holly et al. reported that the accuracy of this technique was 100% in the lumbar spine and 92% in the thoracic spine when it was applied to the percutaneous thoracolumbar approach for screw placement [45]. 2006, they reapplied this technique to the percutaneous posterior cervical screw fixation and only one case was found to be in a poor position, with a misintervention rate of 2.4% [46]. 2008, Ito et al. reported a misintervention rate of 2.8% in the cervical spine [ 47]. Subsequent articles have reported a misplacement rate of 1.6% to 1.8% in the lumbar spine with 3D navigation, which is superior to both conventional unguided and 2D-guided percutaneous nailing [48,49].
Advantages: in addition to the advantages of a C-arm 2D image navigation system, it can obtain high-resolution 3D image images and can navigate multiple vertebral stages simultaneously; it can be applied to all vertebral levels, expanding the surgical indications.
Disadvantages: easy image drift, coarse images, and still not as good quality as CT images. The image quality remains low in cases of obesity, osteoporosis or spinal deformity; special equipment is expensive and difficult to popularize.
(3) MRI electromagnetic navigation system
A special two-dimensional navigation system that uses electromagnetic tracer technology rather than the classical optical tracer technology, but studies have demonstrated that both have similar accuracy [50,51,52].
Advantages: automatic registration, low X-ray radiation, ease of operation, ability to accurately navigate the 3 vertebral bodies around the transmitter, which can solve the biggest disadvantage of navigation one image drift.
Disadvantages: expensive, all instruments must be antimagnetic, special operating rooms are required, insufficient space for the operator to operate, and the display of bony structures is not ideal.
3.2 Active navigation
This is a robotic navigation system that allows the operator to perform minimally invasive surgery under the guidance of a remotely operated robot, thereby improving the precision and safety of the surgery.
The first medical robot was used in 1985 to guide the positioning of probes in brain tissue biopsies using the Puma 560 industrial robot [53], and was first reported by Shoham in 2003 for spine surgery [54]. Subsequently, after continuous development, a more mature one is the SpineAssist robot developed in Israel, which has been approved by the FDA for clinical applications.
3.2.1 SpineAssist system
Advantages: automatic alignment of preoperative and intraoperative images, low radiation exposure, and high accuracy. 2010 Devito et al. reported a retrospective analysis of 840 patients who underwent spine surgery with the SpineAssist robotic system over a four-year period, of whom 49% were minimally invasive percutaneous procedures, with a good postoperative CT review showing only a 1.7% misintervention rate [55]. A comparison of pedicle screw placement between conventional open surgery, open robotic-guided surgery, and percutaneous robotic-guided surgery showed no difference in operative time between robotic surgery and conventional open surgery, but the former was superior to the latter in terms of surgical nail placement accuracy, fluoroscopy time, length of hospital stay, and postoperative complications. There is no difference between percutaneous robotic surgery and open robotic surgery in all these aspects of comparison, and the former is less invasive [56].
Disadvantages: intraoperative images need to be aligned with the robot, requiring an additional minor procedure to mount the robot’s frame on the bone around the operative area; large errors in the implantation of S1 pedicle screws; inadequate arm type of the robot, which partially fails to reach the planned screw position; occasional computer crashes or system crashes, but recovery time is faster and all data and images are automatically recovered [55].
3.3 Semi-active navigation
Most of the semi-active navigation systems are still in the experimental research stage and have not yet seen clinical applications reported [57].
PVP, with the assistance of imaging devices, especially navigation systems, can improve the accuracy of puncture and reduce the leakage rate; monitor the procedure in real time to improve surgical safety; and reduce the radiation exposure of patients and medical personnel.
4 Summary
CASNS is an important direction for the future development of minimally invasive surgery.
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