## 1 Introduction  
Pedic instrumentation is considered a safe and effective technique for treating osteoporortic burst fractures because of the stability offered to the spine in the initial postoperative period [1; 2; 3]. Instrumented fixation is often used to limit the movement of one or two segments in an effort to preserve spinal motion following a thoracolumbar burst fracture.  
A number of studies comparing long segment fixation (stabilization of two levels above and below the fracture level) and short segment pedicle instrumentation reported a higher number of hardware-related failures with short segment fixation, such as screw bending, screw pull-out at upper segments, and screw fracture at long term follow-up [4; 5; 6].  
Methods for treating thoracolumbar burst fractures aim to decompress the spinal canal and stabilize the spine to prevent progressive kyphotic spinal deformity. A hybrid fixation method using verteboplasty and cement-augmented screws has been demonstrated as a practical technique for treating such burst fractures [7; 8]. [PERSON] et al. [9] reported that patients treated with cement-augmented short segment fixation, with or without posterolateral bone fusion, better maintained the vertebral height, and were less susceptible to screw loosening than patients treated with non-cement-augmented short segment fixation with posterolateral bone fusion.  
Increasing the bending strength and pull-out strength of cement-augmented screws has been proposed as a method for improving long-term fixation [10], but the biomechanical effect of secondary fractures and adjacent vertebral bodies filled with bone cement on the adjacent segments is not clear. Secondary fractures at adjacent vertebral bodies after percutaneous verteboplasty remains a serious complication, and may place the segment at greater risk of developing osteoporosis [11; 12]. [PERSON] et al. [13] reported that high stiffness-augmented bone cement increases the stress on the inferior endplate and cortical bone at the adjacent vertebral body. However, no studies to date have examined how a hybrid fixation method using verteboplasty and cement-augmented screws may affect the adjacent vertebral bodies following treatment of an osteopororotic burst fracture.  
Post-traumatic kyphotic deformity or non-union/secondary vertebral fractures can be detrimental to a patient's lifestyle and often cause persistent back pain and spinal instability [14]. Biomechanical studies have shown that long-segment fixation is superior to four-screw constructs for unstable thoracolumbar burst fractures, because it increases the stiffness of the implant and reduces the collapse rate of the fractured body [15]. However, short-segment fixation can preserve the mobility of motion segments, and hence, is becoming a popular alternative for unstable burst fractures. But, the downside of using short-segment fixation alone, is that it has been reported with a high incidence of implant failure and secondary kyphotic deformity [4; 5; 6]. Theoretically, cement augmentation can provide anterior support for vertebral burst fractures, allowing for short-segment posterior fixation with cement-augmented pedicle screws which can enhance the anchoring strength and bending stiffness of the segment. This hybrid fixation method combines verteboplasty with short-segment cement-augmented fixation. However, few studies to date have evaluated the effect of augmentation on the adjacent vertebral endplate [13]. The aim of this study was to evaluate the effect of cement augmentation on adjacent vertebrae after osteopororotic verteboplasty supplemented with cement-augmented screws for the treatment of thoracolumbar burst fractures. In addition, biomechanical data from pedicle screws with and without bone cement augmentation in a short-segment fixation model was evaluated.