Under the approval of the University Ethics Committee, a retrospective review was performed on patients who underwent PKP for OVCF at the Spine Department of second affiliated Hospital of Nanjing medical University between January 2016 and January 2020. Subjects was selected who met the inclusion criteria as follow: (1) Age >65 years old; (2) Fresh vertebral compression fracture was identified in thoracic and lumbar spine by MRI and visual analogue scale (VAS) score was more than 6; (3) The diagnosis of osteoporosis was confirmed by Dual-emission X-ray Absorptiometry（DXA）and t-value was less than -2.5; (4) PKP was performed unilaterally for OVCF under local anesthesia;(5) The whole clinical and radiographic records were completed. Patients with other pathologic fractures or the broken posterior wall of vertebral body were excluded from this study.
1.2 Surgical Procedures
All surgeries were performed by the same senior spinal surgeon team under local anesthesia, and each procedure was monitored by C arm fluoroscopy (GE company from USA, oec 9800series). Patient was placed in prone position, and his or her abdomen was kept suspended with the help of bolsters. The projection of target pedicle was marked on the skin, and a gentle force was exerted at the marked area to make target vertebrae overextend and indirectly reduced. Trocar and cannula systems (KMC; KINETIC MEDICAL Co. LTD, Shanghai, China) were used in this study. Trocar was punctured at the lateral margin of pedicle and then was stuck through pedicle into vertebral body with 20° or so extraversion angle and the sagittal direction paralleled to the upper endplate. The trocar was replaced by cannula with the guidance of pin. The kyphoplasty balloon was inserted into the anterior part of the vertebral body through the cannula. Contrast agent was propelled meticulously into balloon to restore vertebral height gradually. Then patient’s position was switched carefully to lateral decubitus position, which can make injected side superior. Polymethyl-methacrylate was injected steadily into the vertebrae after the balloon withdrawal. The injection would be terminated if the cement area was no longer enlarged, or cement leaked from vertebral body. In control groups, cement was injected unilaterally in prone position, and other procedures were as same as the above.
1.3 Symptom and Radiographic Evaluation
All symptoms and radiographic evaluations were gathered from each patient at the initial presentation and at every follow-up. The radiographic parameters, consisting of vertebral kyphotic angle and vertebral height, were evaluated on anteroposterior and lateral X-ray.
Vertebral kyphotic angle was measured using Cobb’s method from the upper endplate of fractured vertebrae to its lower endplate. Positive values were used to denote kyphosis, whereas negative values were used to indicate lordosis. The vertebral height was measured at bilateral pedicles. And cement distribution was classified into 3 grades: grade I, in which cement only distributed in the injected side of vertebrae. Grade II, in which cement crossed the vertebral midline but did not reach inner margin of contralateral pedicle. Grade III, in which cement crossed inner margin of contralateral pedicle. VAS scores and Oswestry disability index (ODI) scores were used to assess the symptom severity.
1.4 Data Analysis
All data were analyzed by SPSS (IBM SPSS 26.0, IBM Corp., Armonk, NY). Descriptive statistics, independent-sample t test, pair-sample t test and chi-square test were performed accordingly. Independent-sample t test and pair-sample t test were used to evaluate the surgical outcome in different position, whereas chi-square test was conducted to determine the influence of lateral decubitus position on the cement distribution in unilateral PKP. For all analyses, statistical significance was set at P<0.05.