Osteoporotic fracture of the vertebral body is very common in the elderly, and traditional treatment requires long-term bed rest, fixation and drug treatment. Due to reduced activity, osteoporosis is further aggravated in patients, and fractures occur repeatedly. Meanwhile, spending a long time in bed leads to bedsore, deep venous thrombosis and other complications . Osteoporotic fractures of vertebral bodies can seriously affect the quality of life of patients and threaten their physical and mental health . Therefore, pain relief, early activity and spinal stabilization are the key points in the treatment of thoracolumbar osteoporotic compression fractures . PKP can reconstruct the vertebral body height, increase the stiffness of vertebral bodies, immediately stabilize the vertebral body, quickly relieve back pain, reduce the complications in bed, improve cardiopulmonary function, improve the quality of life of elderly patients and is currently the preferred treatment of OVCF [10, 11].In recent years many scholars have proposed the use of a unilateral pedicle puncture in PKP [5, 6, 12, 13]. Compared with bilateral PKP, unilateral PKP produced advantages such as a shorter surgery time, smaller dosage of cement, lower risk of cement leakage, and relieved a higher degree of intractable pain at short-term follow-up after surgery . Indeed, unilateral puncture PKP can reduce both the operation time and complications of bilateral punctures . However, it may cause an uneven distribution of bone cement on both sides of the vertebral body, thus resulting in wedge formation of the non-punctured vertebral body, although this is still controversial [15,16,17,18]. Therefore, in recent years, increasing attention has been paid to comparative studies on the filling effect of single versus double puncturing cement [4, 19,20,21].
The unilateral approach has obvious advantages in terms of the operation time, radiation exposure and device cost , but it is often necessary to increase the angle of the puncture, thus leading to the penetration of the inner wall of the vertebral pedicle and an increased risk of spinal cord and nerve root injuries. The bilateral approach, on the other hand, has a higher operation time and puncture risk. Some studies [22, 23] have shown that unilateral percutaneous vertebroplasty for OVCF can achieve the same clinical effect as the traditional bilateral approach by grasping the intraoperative insertion angle and using the method of multiple pushing while backing.
The advantage of the unilateral bending vertebroplasty is that it does not need to overemphasize the inclination angle. One only needs to master the basic technique of transpedicle puncture to achieve a symmetrical distribution of bone cement, ensure the continuity of bone cement distribution in the midline area, and provide stronger sagittal plane stress to support spinal injuries . Compared with the traditional direct unilateral approach, which uses “single point and single time” perfusion, the angle type of bone cement injection can not only ensure the uniform distribution of bone cement, but also reduce the injection pressure, thus helping to reduce the leakage rate of bone cement. Performing PKP with a unilateral puncture and a bending angle can lead to a uniform distribution of bone cement on both sides, achieving a similar effect to that of performing a bilateral puncture. Meanwhile, in terms of operation time, puncture risk and X-ray exposure, PCKP also has the same advantages of the unilateral approach.
At present, the results from comparative studies of single and double punctures are not uniform. Tohmeh et al.  and Steinmann et al. , through in vitro mechanical experiments, found that unilateral PKP was effective in reconstructing the stiffness and strength of injured vertebrae and there was no significant difference compared with bilateral puncture. Kim et al.  suggested that unilateral puncture PKP was not as effective as a bilateral puncture in restoring vertebral stability. Authors argue that there is an unbalance of the piercing cement filling and a possible mechanical deflection. It has been reported  that when unilateral pedicle puncture PKP was performed, bone cement filling was limited to the semi-vertebral body and could restore the axial compression strength of the vertebral body. But under a lateral pressure load, the stiffness of the non-punctured side was significantly lower than that of the punctured side. When the bone cement filling crossed the midline, the stiffness of both sides of the vertebral body can be more evenly enhanced, so as to achieve a balanced enhancement of the vertebral physicochemical performance and reduce the risk of postoperative vertebral physicochemical deflection and wedge fractures on the non-punctured side . In this study, unilateral angle puncture was used for PCKP. When the puncture needle reached the ideal position in the vertebral body, the balloon expanded, and bone cement was dispersed in the front and middle of the vertebral body, which was significantly different from that of PKP after bilateral balloon expansion, in which the bone cement was mainly distributed on the sides of the vertebral body. OVCF were mainly at the collapse of the anterior, middle and endplate of the vertebral body. The volume of bone cement inpoured into the PCKP group was lower than that of the traditional PKP group, but the bone cement in the anterior and middle of the vertebral body was more in line with the biomechanics of the fractured vertebral body.
Bone cement leakage is a serious complication of vertebroplasty. Previous studies [11, 26] have suggested that the fracture of the perivertebral wall or endplate, the pressure of bone cement perfusion and the volume of bone cement perfused are the main causes of bone cement leakage. Throughout this study, we suggest that the direction of injection is also an influencing factor of bone cement leakage. Conventional PKP is required to correct kyphotic deformities of an injured vertebra by injecting bone cement at the point where the puncture needle tip reaches 1/3 of the front of the vertebra. At this point, when the puncture needle is injected with bone cement toward the anterior edge of the vertebra, leakage in the front and side of the bone cement is likely to occur. However, in this study, when the elbow cannula entered the front 1/3 of the vertebral body, the distal end of the cannula was toward the rear side, so the bone cement injection space was large and the bone cement injection pressure was low, which prevented from causing leakage. Indeed, bone cement leakage occurred in only 3 of the 36 vertebral bodies of patients from the PCKP group (8.3%), far lower than that reported in previous literature (about 14.6%) . Intraoperative real-time X-ray fluoroscopy monitoring can reduce the amount of bone cement leakage, thus avoiding pulmonary embolism, spinal canal stenosis, spinal cord compression, nerve injury and other serious complications.There are several limitations to our study. The results of this study may be limited by the relatively short follow-up time (6 months), the relatively small number of participants, and the fact that this was a single-center study. Therefore, the conclusions drawn from this study remain to be validated by larger prospective randomized controlled clinical trials and longer follow-up.