Patients
This is a prospective study with 266 patients with osteoporotic vertebral compression fractures (309 vertebrae) treated at our hospital during March 2015 to February 2018. The inclusion criteria were: 1) osteoporotic vertebral compression fracture confirmed by imaging examination; 2) back pain evaluated by visual analog scale above 4 points; 3) bone edema in the fractured vertebra on magnetic resonance imaging (MRI): high signal in T2-weighted images and short tau inversion recovery sequences, and low signal in T1-weighted images; 4) age over 50 years; 4) decreased bone mineral density (T scores < −1).
The exclusion criteria included: 1) spinal malignancy, infection or angioma; 2) spinal cord compression or vertebral canal stenosis more than 30%; 3) neurologic deficits; 4) uncorrectable bleeding disorders; 5) severe comorbidities of the heart, liver, kidney, or lung. This study was approved by the ethics committee of our hospital.
The patients were divided into three groups: group A (n = 99, 107 vertebrae) with high-viscosity OSTEOPAL V cement (Heraeus Medical GmbH, Germany), group B (n = 79, 100 vertebrae) with low-viscosity OSTEOPAL V cement, and group C (n = 88, 102 vertebrae) with low-viscosity Eurofix VTP cement (Synimed, France).
Surgical procedure
The patients were in the prone position. Parecoxib sodium 40 mg and dezocine 5 mg were intravenously administered 30 minutes before the surgery. Infiltration anesthesia was performed using 0.8–1% lidocaine along the puncture pathway. All surgeries were performed under fluoroscopy by two senior surgeons, Xaojun Zeng and Wei Wang. The destination of the vertebroplasty needle point was the vertebral edema shown by MRI. During the procedure, the needle was stopped and readjusted if severe pain or nerve root irritation occurred. The needle point was advanced to the position medial to the pedicle and near to the base of the spinous process (anteroposterior view), and the anterior one-third borderline of the vertebra (lateral view).
Cement preparation and implantation
The cement was prepared by mixing the polymer powder and the monomer liquid of PMMA in a dry, clean stainless-steel bowl at an ambient temperature of 22 °C. The high-viscosity OSTEOPAL V cement and the low-viscosity Eurofix VTP cement were prepared exactly according to the manufacturer's instruction. The low-viscosity OSTEOPAL V cement was prepared by reducing the amount of the polymer powder by 1–2 g. The cement paste was loaded into the injection gun immediately after the preparation process. At around 2 minutes 5 seconds after the mixing, the cement was injected into the fractured vertebra under fluoroscopy. The volume of injected cement was recorded.
Assessment of outcomes
Antiosteoporotic therapy was continued postoperatively. No analgesics were used postoperatively. The patients were encouraged to ambulate with a wide wrist belt at postoperative 24 hours. Cement leakage and filling were evaluated using X-ray and computed tomography (CT) within postoperative 3 days before the patients were discharged at postoperative 2–3 days. All patients were followed up for at least 6 months with radiography. Pain severity was evaluated preoperatively, intraoperatively, and at postoperative 2 days using the visual analog scale.
In the axial CT images, the cement border and the vertebral border were manually outlined using the PASC software (Fig. 1). Then the cement diffusion volume and the vertebral volume were automatically calculated by the software by combining the image layers. Cement filling percentage and cement diffusion rate were calculated using the following formulas.
cement filling percentage = cement diffusion volume / vertebral volume ×100%
cement diffusion rate = cement diffusion volume / cement injection volume
The anterior vertebral body height was measured in the lateral X-ray images. The percentage of further height loss at 6 months was calculated using the following formulas.
percentage of further height loss at 6 months = percentage of height loss at 6 months - percentage of height loss immediately after the surgery
percentage of height loss = (estimated original height – measured height) / estimated original height × 100%
estimated original height = (height of the superior vertebral body + height of the inferior vertebral body) / 2
Statistical analysis
Continuous data are presented as means and standard deviations and compared using the one-way analysis of variance followed by the Tukey’s post hoc test. Categorical data are presented as percentages and compared using the chi-square test. All statistical analyses were performed using the SPSS 25.0 (IBM, US).