Treatment of A3 thoracolumbar vertebral burst fractures with posterior minimally invasive channels and short tail pedicle screw fixation: technical report and efficacy analysis

Background To evaluate the clinical efficacy of common pedicle screw placement combined with pedicle screw fixation for the treatment of thoracolumbar burst fractures using a posterior minimally invasive approach. Methods Between May 2015 and December 2016, a total of 33 cases of thoracolumbar burst fracture (AO/Magerl type A3) were treated using a posterior minimally invasive procedure with ordinary pedicle screws under the channel in combination with injured vertebra transpedicular fixations. The patient cohort included 20 males and 13 females with an average age of 43.5 yr (range: 2661 yr). 16 cases were due to traffic accidents, whereas 11 cases were due to falls, and 6 cases of other injuries. All patients showed no nerve injury. Of the injured segments, 5 cases were T 11 , 14 were T 12 , 13 were L 1 , and one was L 2 .No patients presented with spinal nerve injury. The duration of the operations and intraoperative blood loss in each patient were recorded. The pain visual analogue scale (VAS) was used to estimate the degree of back -surgical incision pain. Measurements of the percentage of injured vertebral height loss and the sagittal Cobb angle, which was evaluated for correction of the kyphosis angle and height restoration using plain radiographs, Every patient were recorded preoperatively and at postoperative day 3, 6 month, 1 year, and final follow-up visits. Plain CT scans and reconstructions were used to assess fracture healing. Results No patients complications. The average operating time was 109.2 min 90130 and the average blood loss was 82.4 ml (range: 50150 ml). The VAS scores lumbar back 3rd postoperative follow-up were ± points and ± 0.68 points,

postoperatively (average 15.9 months). Compared to preoperative values, every patient in the percentage of vertebral height loss and the sagittal Cobb angle significantly improved over the follow-up period, with significant differences between day 3, 6 month, 1 year, and final follow-up visits (P<0.05). However, the difference was not significant between the groups at all postoperative time points (P>0.05). CT scans showed that the injured vertebrae healed well, with no subsidence, loosening, or fractures of the internal fixation.
Conclusion The minimally invasive posterior approach with common pedicle screw placements and combined pedicle screw fixation is similar to percutaneous minimally invasive screw fixation. The pedicle screw rests on a strong internal fixation to restore and maintain vertebral height. This procedure is safe and effective for the treatment of A3 thoracolumbar burst fractures, resulting in less trauma and bleeding as well as satisfactory deformity correction.

Background
The thoracic vertebrae and lumbar vertebrae are the intersections of physiological curvature. This area has experiences substantial stress and has a heavy load. Moreover, this area is easily fractured. Trauma is a common cause of thoracolumbar burst fractures [1] . Common causes of injury include traffic injuries, falls from height, and other injuries.
For patients with thoracolumbar burst fractures without nerve injury, short segmental transpedicular pedicle screw fixation is often used at home and abroad [2] . However, extensive open surgery and intraoperative traction may lead to ischemic necrosis and muscle fibrosis. Additionally, postoperative back pain is a common symptom [3] . Some patients may also have complications such as vertebral height loss and Cobb angle correction failure in the long term [4] , which are not conducive to the recovery of muscle function and the maintenance of spinal stability.
With continuous advancements and development of minimally invasive technology, percutaneous hollow pedicle screw reduction and fixation techniques are increasingly applied to the treatment of thoracolumbar fractures. Compared with traditional open surgery, this procedure reduces surgical trauma and postoperative pain, corrects kyphosis and reduces perioperative complications [5][6][7] . In view of this finding, in this study, we used a posterior percutaneous minimally invasive approach with common pedicle screw placement and fixation for the treatment of A3 thoracolumbar burst fractures. This approach achieved good clinical results. The report is as follows.

Clinical data and methods
The experimental protocol has been approved by the Ethics Committee of the Affiliated Hospital of Zunyi Medical University. The informed consent of the subjects was obtained before the operation. All the imaging data and experimental data were published as scientific research and articles.

Clinical data
A total of 33 patients with A3 thoracolumbar burst fractures who were admitted to our department from May 2015 to December 2016 were included in the present study.The patients included 20 males and 13 females, aged 26 61 years, with an average of 43.5 years. The causes of injury were as follows: 16 cases were due to traffic accidents, whereas 11 cases were due to falls, and 6 cases of other injuries. All patients showed no nerve injury. The following segments were injured: 5 cases of T 11 , 14 cases of T 12 , 13 cases of L 1 , and 1 case of L 2 . The inclusion criteria were as follows: ① single segment vertebral fracture; ② fracture classification: type A3 (according to AO-Magerl classification) [8] ; ③ surgery within 10 days after the injury; and ④ no nerve damage. The following exclusion criteria were used: ① neurological dysfunction requiring spinal decompression; ② fractures of two or more segments; ③ fixation of more than 3 segments; and ④ pathological fractures.

Surgical methods
Endotracheal intubation was performed, and general anesthesia was administered. In the prone position, the chest and hip were elevated, and the abdomen was suspended to obtain a preliminary reduction in the injured vertebrae. We used C-arm X-ray fluoroscopy to mark the projection of the vertebral body of the injured vertebrae and the upper and lower vertebral bodies. A conventional disinfection drape was used, and we inserted a Kirschner wire by percutaneous puncture at the surface marker. The position and direction of the Kirschner wire were well visualized by C-arm fluoroscopy. We introduced a cortical bone cannula for percutaneous vertebroplasty along the Kirschner wire. Then, we removed the Kirschner wire and inserted a long guide needle for a percutaneous minimally invasive pedicle screw in the expanded cortical sleeve. After adjusting the reverse and angle, we tapped the long guide needle into the middle of the vertebral body and removed the cortical bone cannula. Next, we made a 1.5 cm transverse incision in the skin centered on the long guide needle. The percutaneous minimally invasive pedicle screw working sleeve was inserted along the long guide needle to expand the soft tissue to establish the nailing channel. After the wire was removed, the long guide pin was removed, and a single plane common pedicle screw was built along the channel. Next, we inserted a prebent titanium rod along the soft tissue channel; we first locked the lower vertebral body titanium rod and then properly opened it between the lower vertebral body and injured vertebrae. The collapsed end plate was reset by the curvature of the prebent titanium rod and the pedicle screw of the injured vertebra. Then, the nail rod was locked. Saline was used to wash the incision. Next, the incision was sutured and wrapped. All procedures were performed by a physician who is experienced and skilled in minimally invasive pedicle screw placement techniques. (Fig. 1)

Postoperative treatment and rehabilitation
Antibiotics were used to prevent wound infection within 24 hours after surgery. At 2 to 3 days after surgery, patients were instructed to wear a thoracic and lumbar spine support brace and start exercises in bed.Did not advocate strenuous activity or exercise.At 3 to 4 weeks after surgery, we recommended resuming normal life and daily work but avoiding physical labor and weight-bearing at the waist. The thoracic and lumbar spine brace was removed 2 months after surgery, and functional back muscle exercise was started to avoid the disuse of the waist and back muscles.

Observation index
We recorded the operation time and the amount of intraoperative blood loss. A pain visual analogue scale (VAS) was used to assess the degree of postoperative low back pain. An Xray of the thoracolumbar vertebral body was examined before surgery and at, 3 day

Statistical methods
Analysis was performed using SPSS 18.0 statistical software, and the measurement data are expressed as the mean ± standard deviation (x±s). Repeated measures analysis of variance was used before and after surgery. P<0.05 was statistically significant.

Results
The

Discussion
The thoracolumbar junction is composed of a relatively stable thoracic vertebra and lumbar vertebra with greater mobility. Due to its special anatomical relationship, spinal injury often occurs in this region [9][10] . In the past 30 years, great advancements have occurred in the treatment of thoracolumbar fractures [11] . Conservative treatment of patients with thoracolumbar burst fractures without nerve injury can also achieve better clinical results than surgery in terms of low back pain and functional recovery [12] .
However, for unstable thoracolumbar fractures, surgical treatment should be preferred [13] . The goals of treating unstable thoracolumbar fractures include: restoring spinal stability, preventing or reducing deformities, spinal decompression, and enabling early functional exercise. In all surgical strategies, the posterior short-segment pedicle screw is widely used for the treatment of thoracolumbar fractures. In addition, this procedure is easy to use, lowers the number of pedicle screws used, reduces the amount of bleeding, and shortens the surgical incision, making it more popular in clinical practice [14] .
However, short-segment pedicle screw fixation may also cause problems such as longterm stress deficiency leading to internal fixation failure, loss of the correction rate and increased incision pain [15] . Multisegmented fixation of the injured vertebra can be used to maintain greater biomechanical stability of the anterior column and avoid these issues [16] . moreover, there is a risk of loosening and fracture of the internal fixation [17] . In addition, the percutaneous pedicle screw is more expensive than the traditional common one-way pedicle screw, and the vertebral body reduction effect on the burst fracture is not optimal.
Thus, clinical use of the percutaneous pedicle screw has relative indications.
Qiang Yuan et al. [18] performed structural mechanical analysis by computer simulation of the effect of a vertical stress screw on fractured vertebrae in thoracolumbar fractures.
Yuan and colleagues' findings suggested that the placement of the pedicle screw through the injured vertebra has the following advantages: ① it provides good three-dimensional fixation, reduces the hanging effect of the parallelogram internal fixation, increases stability, and reduces kyphosis; ② reducing the stretching of the fixed segmental disc is conducive to the recovery of the height of the fractured vertebral body; and ③ it can effectively share the stress of the pedicle screw and connecting rod. Norton et al. [19] also confirmed that the pedicle screw fixation is more conducive to restoring the height of the anterior column of injured vertebrae, which can better achieve bone reduction in injured vertebrae in the spinal canal, and maintain the lower disc of the injured vertebra.
Moreover, the wedge angle can be effectively corrected, and the stability is good. In tools.Intraoperative C-arm X-ray localization is as invasive as percutaneous minimally invasive pedicle screw placement. In the present study, minimally invasive cannula insertion was used to establish the pedicle screw placement channel. Because the screw was inserted in the common pedicle screw, there was no long guide. Needle guiding is necessary to smoothly insert the screw along the channel, the operating sleeve is fixed, and displacement is prevented before the long guiding needle is removed; ⑤ screws should be placed as close as possible to the same line. When the connecting rod is placed without the aid of minimally invasive tools, it is relatively difficult to install through the soft tissue channel. Thus, placement of the pedicle screw on the same side as the straight line is required to facilitate the placement of the connecting rod; ⑥ the placement of the titanium rod through the subcutaneous paraspinal muscle space can significantly reduce damage to the paravertebral muscle tissue [20] , and the titanium rod must be prebent to facilitate intraoperative reduction; and ⑦ when intraoperative expansion is performed, the lower vertebral body nut should be locked first. Then, the lower vertebral body and injured vertebra can be appropriately opened.

Conclusions
In summary, a posterior minimally invasive incision, common pedicle screw fixation, and pedicle screw fixation for thoracolumbar burst fractures demonstrates the advantages of minimally invasive treatment and stabilizes the anterior column through reconstruction.
This approach also prevents complications such as late correction loss and internal fixation failure. Thus, this technique can be used as a minimally invasive treatment for A3

Consent for Publication
Informed Consent (written) was obtained from all participants included in this study.

Availability of Data and Material
The datasets used during the current study are available from the corresponding author on reasonable request.

Competing Interests
Drs. Fujun Wu, Songli Ju, GenYi Hou, Jun Ao, NiJiao Huang, Sheng Ye and Xin Wang declare no competing interests in this study.

Funding
This study was financially supported by National Natural Science Foundation of China