The traditional posterior surgery for treatment of the thoracolumbar burst fractures is a relatively a straightforward surgical technique but can only give indirect reduction of the fractured vertebral body, and the means of supporting the anterior column are limited [13, 14]. Several studies has reported the loss of reduction caused by insufficient anterior column support with or without hardware failure was not uncommon [15, 16]. Posterior spinal fixation approach can be divided into long-segment fixation (fixation more than two upper and lower vertebral fracture), and short-segment fixation (involving one level above and one below the fractured level).
It has proved that long segment fixation is strong enough to stabilize the fractured spine. However, the fused spine becomes less flexible and more susceptible to low back pain. Meanwhile, short-segment posterior fixation is thought to stabilize the fractured vertebra efficiently while saving motion segments in compared to long segment fixation. However, previous studies reported the earlier implant failure and correction loss as the most important disadvantages of this method [3, 17]. McLain et al.  reported 52.5% of implant failure in their study on short-segment fixation in treatment of thoracolumbar burst fracture. Thus, several techniques with anterior column intervention have been suggested as alternative methods to overcome this limitation. The kyphotic deformity was corrected to a considerable extent with posterior fixation and indirect reduction. With the help of intact anterior longitudinal ligament and annulus of interverebral disc, it is easy to correct the kyphoctic deformity of the fracture spine by posterior pedicle screw devices. How to deal with a large amount of bone defect inside the fractured vertebral body which is a main problem. The large bone defect created inside the fractured vertebra after height restoration of injuried vertebral body had been speculated to be the most essential cause of that correction loss. Moreover, the restoration of the intervertebral disc height may also contribute to the loss of kyphotic correction . Beside that an usual laminectomy for the management of thoracolumbar burst fractures might lead to further spinal instability . It was hypothesized that the TIF might solve those problems by minimizing the correction loss. TIF technique removes a part of articular process at one side, and almost all spinal structures can be preserved. By impact bone graft into the intervertebral space and even into the vertebral body through the fractured endplate after disc excision, it is possible to reconstruct the anterior and middle columns of the fracture spine and stabilize of the instablility of fracured vertebral body. Therefore, it may provide additional stability with short pedicle screw fixation. Wang et al.  recorded the favorable outcomes without significant correction loss and hardware failure when combined short-segment pedicle screw fixation with TIF using granulated bone graft and cage for treatment of thoracolumbar unstable burst fracture. However, the efficacy of TIF using bone chip graft has not been reported.
Here, we reported the radiculogical outcomes of short posterior fixation with TIF using bone chip graft in the treatment of thoracolumbar unstable burst fracture, Denis type IIB, and with the mean follow-up was 53 months. The correction of kyphotic deformity which was evaluated by %AVB, VA and RA, was gradually lost and the average of correction loss was 10.2%, 2.9o, and 5.6o, respectively. Hardware failure occurred in 6 patients (16.7%) during the follow-up period, of which, 3 cases of screw breakage above fracture level, 2 cases of screw breakage below fracture level, and one case with rod pull-out of screw head (Fig. 3). These outcomes showed that the TIF with bone chip graft did not completely prevent the correction loss and hardware failure of short segment pedicle screw fixation for the treatment of thoracolumbar burst fracture. But, 4 out of 6 cases with hardware failures had good interbody fusion with Bridwell grade I or II, and all of such cases did not need to perform the revision surgery (Fig. 4). In order to prevent the hardware failure and correction loss of short-segment fixation in treatment of thoracolumbar unstable burst fracture, several additional procedures have been introducing but no ideal techniques have proved . Vu et al.  reported the radiological outcomes of the short posterior fixation and fusion for 31 patients with thoracolumbar burst fracture. They recorded 29% of the implant failure while the mean correction loss of RA and VA were 2.3o and 7o, respectively. Liao et al.  reported the outcomes of 27 patients with thoracolumbar burst fracture who were treated a six pedicle screw construct (group 1), and twenty-nine patients underwent a four screw construct and fractured vertebra augmentation by injectable calcium sulfate/phosphate cement (group 2). The authors found the rate of hardware failure and the mean correction loss of %AVB, RA were 11.1%, 8.9o, 4.2o in group 1 and were 27.6%, 13.3o, 6.3o in group 2, respectively.
The role of posterior/posterolateral fusion in minimization of late complications of short-segment fixation in treatment of thoracolumnbar burst fracture has been unclear and several authors suggested that posterior/posterolateral fusion would not be necessary when treating thoracolumbar burst fractures with a posterior pedicle screw fixation [22–24]. Futhermore, we also wanted to accurately evaluate the outcomes of TIF with bone chip graft in prevention of poor radiological outcomes of short posterior instrumentation so the posterior/posterolateral fusion was not added in these case series. However, we suppose that the posterior/posterolateral fusion in combination with TIF may provide the better prevention of the disadvantages of the short posterior fixation. Nevertheless, based on this study, we think that removal of implant after achievement of solid interbody fusion might be better than supplementation of the posterior/posterolateral fusion in term of reducing the hardware failure of short – segment posterior instrumentation, particularly in related to the implant failure of distal unfused spine level because it also restores simultaneously the motion of unfused spine by the removal of instrumentation. But, we need to do futher studies to confirm these issues. There have been reports that the posterior short-segment pedicle screw fixation combined with intermediate screw at the fractured vertebrae can help improve biomechanical stablility and achieve better reduction; cause less correction loss, and fewer hardware failures . However, Liao et al.  reported 3 cases of the implant failure after using six-screw construct in treatment of 27 patients with thoracolumbar unstable burst fracture. Thus, we suppose that this technique combined with TIF using bone chip graft may get better outcomes. However futher research is needed on this issue.
A limitation of this study was patients who involved in the research were all classified as Denis type IIB of a thoracolumbar burst fracture. It is robust result of the study, on the one hand, by the Denis type IIB classified as one of the most common type of fractures. And on another hand, there was lack of comparation of the hardware failure and progressive kyphosis between the two groups of LSC because of small sample size. In addition, this study did not present a ideal method in prevention of late complication of short-segment pedicle screw fixation in treatment of thoracolumbar burst fracture. Nevetheless, this is the first report of these complications of short posterior fixation with TIF using bone chip graft for treatment of thoracolumbar unstable burst fracture in Vietnam.