Study design
Ethical approval for this retrospective study was provided by the Ethics Committee of the authors' institute. We routinely obtain written informed consent for accumulation of clinical data for future retrospective analyses from each patient who receives PMCP or PSFV at our hospital, including all patients in this study. The medical records of consecutive patients sustained OVBF without neurologic deficit and underwent PMCP or PSFV from May 2015 to April 2018 were reviewed (Fig. 1).
First, we selected 253 patients who received PMCP or PSFV. Inclusion criteria were as follows: 1) elderly (≥60 years), 2) thoracolumbar(T10 to L2) single fresh complete burst fracture (type A3 or A4 according to AOSpine thoracolumbar spine injury classification system)[11], 3) without neurological deficit, 4) being diagnosed with osteoporosis according to T value of dual-energy x-ray absorptiometry (DXA) less than -2.5. We then excluded poly-traumatized and other OVF types patients, and patients with symptoms of neurological deficits, preexisting spinal deformity or previous spinal operation, metastatic bone tumor or multiple myeloma, systemic or local infections and severe bleeding disorders. Finally, we analyzed 227 patients who were divided into two groups according to surgical techniques—PMCP (n=109) and PSFV (n=118) groups.
Preoperatively, standard clinical examination and evaluation including of the medical history, physical examination of percussion pain, assessment of the pain intensity [visual pain analogue scale (VAS)] , and the activity level [Oswestry Disability Index (ODI)] [12] were evaluated. X-rays of the relevant spinal region in two planes, Computed Tomography (CT) scan and magnetic resonance imaging (MRI) (T1-weighted and T2-weighted sequences including short tau inversion recovery sequences) and DXA were performed. All patients received a calcium supplementation (1000 mg of elemental calcium daily), and vitamin D (400~600 UI of vitamin D). Twenty patients in group PMCP and 27 patients in group PSFV received hormonal replacement therapy (estrogens and progestin). Bisphosphonates were given to 89 patients (zoledronate, n = 25; alendronate, n = 64) in group PMCP and 91 patients in group PSFV (zoledronate, n = 33; alendronate, n = 58).
Surgical technique
In PSFV group, all surgical procedures were performed under general anesthesia with endotracheal intubation. Patients were placed in a prone position on four bolsters placed on a radiolucent operating table with the abdomen freely suspended. Patients were installed with surgical bolsters placed under the thorax and the iliac crests in order to induce spinal lordosis and facilitate the reduction of the fracture. The manual lordotic manoeuvre was first performed to correct kyphosis. Percutaneous pedicle screw fixation was performed using Zina™ device (Sanyou Medical Co., Ltd, Shanghai, China) under frontal and lateral scopic control. A targeting cannulated needle (Sanyou Medical Co., Ltd, Shanghai, China) for each pedicle of the instrumented adjacent vertebrae is used to locate the pedicle. K-wires of 2mm are then passed through the needle.After removal of the targeting needle, cannulated pedicle screws were placed with extender sleeves in down into the pedicles of the non fractured vertebrae above and below the fractured vertebra and subsequently removal of all 4 K-wires. Lordotic manoeuvre was performed to restore vertebral body height and correct kyphosis. Following a 6-mm diameter trocar (Dragon Crown Medicial Co., Ltd., Jinan City, Shandong Province, China) in a cannula was inserted into opposite pedicle at the fractured vertebra. The position was controlled by an image intensifier, which was then enlarged with the use of an access cannula with a trocar. Once the cannula reached the optimal position, after removing the trocar, Polymethylmethacrylate (PMMA) cement was injected into the defect of the fractured body through the cannula under continuous fluoroscopic monitoring (Figure 1). The PMMA insertion was considered complete when it reached the posterior third of the vertebral body.
In PMCP group, all surgical procedures were performed under local anesthesia. Patients were positioned in a prone position on four bolsters placed on a radiolucent operating table with the abdomen freely suspended. A 1 cm skin incision was made lateral to the desired entry point of the pedicle to percutaneously. A trocar (Dragon Crown Medicial Co., Ltd., Jinan City, Shandong Province, China) in a cannula was inserted into pedicle at the fractured vertebra through pedicular approach as a working channel. After removing the trocar, a balloon was placed into the working channel and slowly inflated to create a low-pressure cavity for cement injection. Inflation continued until the balloon pressure up to 300 psi. Antero-posterior radiograph shows the balloon exceed the midline of the vertebra. Then the balloon was deflated and removed. If the balloon does not exceed the midline of the vertebra, a bilateral puncture is required. Then the balloon was deflated and removed. a mesh container (Dragon Crown Medicial Co., Ltd., Jinan City, Shandong Province, China) was advanced into the cavity. The mesh container is made of polyethylene terephthalate (PET). Then PMMA cement was manually injected into the mesh container within the treated vertebral body by applying a cement perfusion apparatus under fluoroscopic guidance. With the continuous injection of PMMA, the mesh container was inflated and the height of the fractured vertebral was restored. At a certain injection amount, PMMA cement leaked outside the mesh container from the meshes and entered bone trabeculae.The PMMA insertion was considered complete when it reached the posterior third of the vertebral body or had a potential tendency of cortical, epidural, and anterior venous cement leakage(Figure 2).
Operation time, estimated blood loss and PMMA volume were recorded. All patients were postoperatively followed clinically and radiographically the day after surgery, three months, six months and at every one-year interval thereafter. Patients were assessed for any neurologic complications. As for CT scan, all patients had it after surgery, one year and two years later. Segmental kyphosis, anterior and middle vertebral body height ratio (AVBHr and MVBHr), and canal compromise were measured using lateral radiograph and CT images. Cement leakage was determined using CT images of all section of fractured vertebra. Back pain intensity was recorded on VAS. Functional outcome was measured using the ODI. Three independent blinded spine surgeons finished the clinical evaluation of patients. Additionally, two other independent blinded spine surgeons assessed the radiographs.
Statistical analysis
SPSS 18 was used for statistical analysis. Continuous variables are expressed as mean±standard deviation. Statistical analysis was performed with for changes of each radiographic and functional parameter. Independent data, including age, body mass index(BMI), T-score, injury time, operation time, blood loss, hospital day, cost, and injected cement volume, were compared between groups PMCP and PSFV using the student t test. Differences in gender, distribution of fractured vertebral, BMI and cement leakages between two groups were compared using the chi-square test. Repeated measure ANOVA was used to compare VAS, ODI, AVBHr, MVBHr, canal compromise and Cobb angle between two groups. Statistically significant differences were defined at a 95% confidence level.