Comparison of the clinical efficacy of the Wiltse paraspinal approach and O-arm navigation for the treatment of thoracolumbar fractures

Background: To evaluate the clinical efficacy of the Wiltse paraspinal approach and percutaneous pedicle screw Methods: We enrolled a total of 54 patients with neurologically intact thoracolumbar fracture who received minimally invasive treatment. Among these, 28 patients were treated with pedicle screw fixation through the Wiltse paraspinal approach (WPSF), and another 26 were received percutaneous pedicle screw fixation under O-arm navigation (OPSF). Statistical methods were used to perform a detailed comparison of clinical outcomes, radiologic findings and complications between the two groups obtained preoperatively, postoperatively and at last follow-up. Results: There were no significant differences between the two groups in terms of the intraoperative bleeding, length of incision, postoperative hospitalization durations or accuracy rate of pedicle screw placement ( p >0.05). Visual analog scale (VAS) scores, Oswestry disability in dex (ODI) scores, local Cobb angle (LCA), vertebral wedge angle (VWA) and R value were notably improved after surgery, though no clear discrepancy between the groups at each time point ( p >0.05). However, the OPSF group had a longer operation time and greater surgical expenditure than the WPSF group ( p <0.05). Conclusions: Both WPSF and OPSF were safe and effective for the treatment of thoracolumbar fracture. Although the two groups showed favorable clinical and radiologic outcomes through the final follow-up, we recommended the minimally invasive WPSF given its lower duration of surgery and medical costs. A randomized controlled study of high-quality and with a larger sample size is required to comfirm our findings in the future.

Conclusions: Both WPSF and OPSF were safe and effective for the treatment of thoracolumbar fracture. Although the two groups showed favorable clinical and radiologic outcomes through the final follow-up, we recommended the minimally invasive WPSF given its lower duration of surgery and medical costs. A randomized controlled study of high-quality and with a larger sample size is required to comfirm our findings in the future.

Background
Traumatic spinal fractures occur frequently in the weakest biomechanical location of the thoracolumbar junction (T10-L2), which accounts for 90% of all spine fractures [1,2]. The traditional surgical treatment for thoracolumbar fracture is open posterior pedicle screw instrumentation.
However, the operative approach involves detaching the paravertebral muscles from the bone portion of the spine, which can lead to several problems such as increased intraoperative bleeding, soft tissue ischemia, muscle denervation and atrophy, and chronic back pain [3][4][5].
With the tremendous development of minimally invasive techniques, such as the paraspinal muscular approach through Wiltse space, percutaneous pedicle screw placement under fluoroscopy, and O-arm-based navigation systems for the implantation of pedicle screws, the incidence of the aforementioned approach-related complications can evidently be reduced. As a result, the patient can experience a smaller incision, rapidly reduced pain, shorter hospitalization stay, and a rapid return to life and work [3,[5][6][7][8][9][10]. These techniques fully abided by the concept of Enhancing Recovery After Surgery (ERAS) in orthopedics [11].
Nevertheless, for many minimally invasive techniques, we required a better understanding of the

Patient population
Patients with traumatic single-segment thoracolumbar fractures (T10-L2), treated in our hospital  Table 1.

WPSF group
The patient was placed in a prone position after the administration of general anesthesia. The injured vertebral body was located and labeled under fluoroscopic guidance of C-arm (Ziehm Imaging, Nuremberg, Germany). The surgeon made a midline inci sion of approximately 8cm at the operative region following routine sterilization and draping. The skin, subcutaneous tissue and lumbodorsal fascia were cut successively and the gap between the longissimus and multifidus muscles was separated bluntly to expose the entry point of the nail path. After the appropriate drilling and probing, six pedicle screws were installed sequentially by hand with the aid of C-Arm fluoroscopy, used to determine optimal locations for the pedicle screws. After the two connecting rods were implanted, the screws were tightened to reposition the anterior column of the vertebral body. The position of the internal fixation and restoration of the fracture centrum were again examined by radiology.

OPSF group
After satisfactory tracheal intubation and general anesthesia, the patient was placed in a prone position on a Jackson radiolucent table, and the surgical site was sterilized and draped. A reference frame was installed on the spinous process following the removal of the peripheral soft tissue. The Oarm (Medtronic, CO, USA) performed a first scan to acquire an intraoperative 3D image and the radiological data was transferred to a StealthStation navigation system (Medtronic, CO, USA). The surgeon moved the passive planar probe to confirm the entry point of the stab incision, guided by the 3D image navigation system. A hole for the guide wire was drilled, the guide wire was inserted, and the pedicle screws were tapped and implanted without any manual regulation. The screws were adjusted for the direction and length through the images provided by the navigation equipment, to construct the optimal trajectory. The connecting rods were prebent properly and then inserted percutaneously. The tailcaps of the distal vertebral screws and those in the injured vertebra were tightened along the connecting rods, and then the height of the fracture vertebra was restored by stretching. Finally, the tailcaps of the proximal screws were tightened. The O-arm performed another scan to confirm the correct position of the internal fixation.
The incision was rinsed and closed with interrupted suturing. No drainage tube was inserted for either groups. All patients underwent routine prophylactic antibiotics for 2 days and were instructed to stand while wearing a brace on the third day after surgery.

Clinical evaluation
The clinical indicators examined included operative time, intraoperative blood loss, total length of inci sion, postoperative hospitalization time and operation expenditure. We appraised the efficacy of the procedure by using the visual analog scale (VAS) scores, calculated on a scale of 0-10 preoperatively, postoperatively and at final follow-up. The Oswestry disability in dex (ODI) scores were also evaluated on a scale of 0%-100% preoperatively and at fi nal follow-up. All patients in both groups completed the survey independently, without receiving any suggestions during the investigation. All patients of the two groups were received a follow-up period for at least 12 months independently, and complications were recorded.

Radiologic assessment
The radiological outcomes were measured preoperatively and at 3 days and 12 months after the operation. The local Cobb angle (LCA), which reflected the changes in segmental kyphosis, was assessed between the superior endplate of the upper adjacent vertebra and the inferior endplate of the lower adjacent vertebra. The vertebral wedge angle (VWA) was measured between the superior endplate and the inferior endplate of the fractured centrum [12]. The ratio of the anterior margin height of the fractured vertebra (R value) was determined as described by Li et al [5].

Results
There were no significant differences in age, gender, injured segment, fracture type, blood loss, length of incision or postoperative hospitalization time between the two groups (p>0.05, Table 1). All patients underwent surgery successfully, and no serious complications, such as infection, blood vessel injury, or spinal cord or nerve root injury occurred. All patients experienced a mean follow-up duration of 16.1±2.6 months (12~20 months) in group A (Fig. 3) and 16.0±2.5 months (12~20 months) in group B (Fig. 4), with no significant difference between the groups (p=0.84  Table 2). However, these was no significant difference regarding ODI scores between the groups preoperatively and at the last followup (p>0.05).

Radiologic outcomes
The accuracy of pedicle screw placement was 97.6% (164/168) in group A and 96.8% (151/156) in group B, with no significant difference between the groups (p=0.63). The LCA in both groups was markedly decreased after surgery, and these were well maintained at the last follow-up (p<0.05, Table 3). There was no significant difference regarding LCA between the two groups at either time point (p>0.05). The correction and loss of LCA in group A were 6.9±6.2° and 1.8±2.9°, respectively, while those in group B were 6.8±5.6° and 1.5±2.7°, respectively, which showed no apparent differences between the groups (p>0.05).
The average preoperative VWA was reduced significantly after surgery in both groups, and these values were well preserved until the final follow-up (p<0.05,

Discussion
Posterior open surgery is one of the most common surgical methods for the treatment of thoracolumbar fractures [6]. There are several ineluctable drawbacks in conventional open posterior pedicle screw fixation. The muscles along the spine are stripped from the bone portion of the spine, exposing the facets and transverse processes to position the screws accurately. This could lead to complications associated with the surgical approach, including excessive intraoperative bleeding, intramuscular loss of innervation and ischemia, and even long-term muscle atrophy and scarring, which are related to intractable back muscle pain and dysfunction [3]. Anatomically, the posterior muscles and ligaments of the thoracolumbar spine play an important role in maintaining stability.
Therefore, these muscles and ligaments should be well preserved in operations of thoracolumbar vertebral fractures [5].
In recent years, minimally invasive surgery has developed rapidly, broadening the surgical indications bleeding, shorter operation and hospitalization times, and more accurate placement of pedicle screws [5][6][7]9,17,18]. However, comparisons of the clinical effects and radiological results between the two minimally invasive techniques have not been reported in the literature. In this study, there were no significant differences in intraoperative blood loss, length of incision, or postoperative hospital stay between the two groups. The VAS scores and ODI scores obtained after application of the two minimally invasive techniques were significantly lower than the corresponding preoperative scores, and no difference was found between the groups. Therefore, we believe that the two minimally invasive nailing methods can achieve the same therapeutic effect for thoracolumbar fractures.
Regarding operative time, the paravertebral approach group showed markedly shorter values than the O-arm navigation group, possibly because the placement and operation of the O-arm imaging system is more time consuming and the surgeon was unfamiliar with the relevant special instruments.
In addition, we also compared the surgical cost expenditures of the two groups and found expectedly There are also some limitations in the current research. First, the study was retrospective, and the treatment options for the recruited patients mainly depended on their preference, which implied a lack of randomization. However, there were no significant differences in the preoperative clinical and X-ray data between the two groups. Second, only 54 patients were ultimately included in this study; thus the conclusions drawn from the statistics lack sufficient power. Third, the follow-up duration in the study was relatively short. An extended observation period should be implemented to better evaluate clinical efficacy, aggravated kyphosis, and the failure of fixation. In the future, randomized controlled trials and additional assessment methods could confirm the results of our study.

Conclusion
The

Ethics approval and consent to participate
This study is a retrospective clinical study and has been approved by The First Affiliated Hospital of Soochow University Ethics Committee. All patients had signed the consent form.

Consent for publication
Not applicable.

Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests.

Funding
This work was supported by the National Natural Science Foundation of China (NSFC) under grant No.
Critical revision of article: XSZ, MFG.  Tables   Table 1 Demographic data of patients.  Table 2 Clinical data of VAS and ODI score. Table 3 Radiological data of LCA, VWA, R value, and accuracy of pedicle screw placement.