Robot-assisted versus fluoroscopy-guided pedicle screw fixation of thoracolumbar compression fractures

Abstract

The aim of this study is to compare the clinical outcomes and accuracy of robot-assisted (RA) versus fluoroscopy-guided (FG) pedicle screw fixation of thoracolumbar compression fractures. We retrospectively enrolled 85 patients with surgically treated thoracolumbar compression fractures in our study (RA group, 45 patients; FG group, 40 patients). We analyzed the accuracy of pedicle screw placement by using the Gertzbein-Robbins classification, and calculated the one-time success rate (i.e., the rate of screws successfully inserted in the first attempt). We also evaluated volume of blood loss, operative time, visual analogue scale scores for pain, Cobb angle, and postoperative complications. The rates of grade A screw placement (96% vs 68.5%; P < .005), clinically acceptable screw placement (98.2% vs 86%; P < .005), and the one-time success rate (97.3% vs 82.5%; P < .005) were all significantly higher in the RA group than in the FG group. No differences were observed in sex, age, body mass index, volume of blood loss, operative time, visual analogue scale scores, Cobb angle, and postoperative complications between the 2 groups. Compared to FG surgery, RA surgery yielded greater accuracy and one-time success rates of pedicle screw fixation of thoracolumbar compression fractures, with comparable clinical outcomes.

1. Introduction

Thoracolumbar compression fractures are a common cause of backache among people.^[1] If the conservative treatment of such fractures fails, surgical intervention should be considered. A common surgical treatment for thoracolumbar compression fractures is pedicle screw fixation, which stabilizes the spine very well. However, the procedure is often complicated by screw malposition because of the complexity of the spinal anatomy and the interindividual variations in the morphology of the vertebral pedicles. Moreover, accurate screw placement is imperative to prevent injury to the adjacent vessels and nerves.^[2,3]

The rate of screw misplacement during fluoroscopy-guided (FG) pedicle screw fixation reportedly ranges from 8.3% to 50.3%.^[4,5] furthermore, the FG procedure is associated with drawbacks such as a limited surgical field and variable accuracy. Recently, robotic spinal surgery has been used to overcome the above shortcomings of FG surgery. We aimed to comparatively analyze robot-assisted (RA) versus FG pedicle screw placement among patients with thoracolumbar compression in terms of the accuracy of screw placement and the clinical outcomes of the patients.

2. Materials and methods

2.1. Patients

We retrospectively enrolled 85 patients with thoracolumbar compression fractures who were treated by the same team of orthopedists using posterior spinal surgery in our hospital between July 2021 and June 2022. The inclusion criteria were (1) adult patients (aged ≥18 years); (2) patients with a 1-level thoracolumbar compression fracture that required surgery; and (3) complete radiographic examination consisting of X-ray imaging performed preoperatively and 1 week, 3 months, and 6 months postoperatively, and pre- and postoperative computed tomography. The exclusion criteria were (1) incomplete data; (2) tumor, cervical trauma, infection, degenerative scoliosis, or developmental spinal deformity; and (3) a history of spinal surgery. Both groups of patients underwent minimally invasive surgery with percutaneous staples. In the RA group, the guide needle was placed with the assistance of the casting robot, while in the FG group, it was placed manually under c-arm fluoroscopic guidance. In both groups of patients, the operation was successfully completed without any cases of failed procedures leading to open surgery. The study was approved by the ethics committee of Peking University Aerospace School of Clinical Medicine before data collection and analysis. The need for informed consent forms from patients was waived because this is a retrospective study.

2.2. Main outcome measures

Using postoperative computed tomography scans, we graded the accuracy of pedicle screw placement according to the Gertzbein and Robbins scale^[6] as follows: screw completely within pedicle, grade A; pedicle cortical breach of <2 mm, grade B; pedicle cortical breach of 2 to <4 mm, grade C; and pedicle cortical breach of 4 to <6 mm, grade D. We calculated the ratio of the number of screws that were successfully placed in a single attempt to the total number of screws, which was termed the one-time success rate.^[7]

Other outcome measures included operative time, volume of blood loss, Cobb angle (i.e., angle between the upper edge of the upper injured vertebra and the lower edge of the lower injured vertebra), visual analogue scale (VAS) score, and postoperative complications. The VAS scores and Cobb angle were recorded before the surgery as well as 1 week and 6 months after the surgery.

All experimental methods complied with approved guidelines.^[8] We compared the data between the RA and FG groups. Two authors selected patients according to the selection criteria and collected all the patient data. Two different authors conducted the data analyses.

2.3. Statistical analysis

SPSS v21.0 (SPSS Inc., Chicago, IL) was used for all statistical analyses. Continuous data were expressed as mean ± SD when they satisfied the criteria for a normal distribution, as determined using the Kolmogorov–Smirnoff test. The chi-square test was used to evaluate categorical data. Differences with P values of <.05 were deemed statistically significant.

3. Results

This study involved 85 patients with thoracolumbar compression fractures, including 45 patients who underwent RA surgery and 40 patients who underwent FG surgery. We found no significant differences in type of fracture, age, gender, body mass index, fracture level, operative time, volume of blood loss, and complication rate between the RA and FG groups (Table 1).

Table 1.

Patient demographics.

	Robot-assisted surgery (n = 45)	Fluoroscopy-guided surgery (n = 40)	P value
Age (years)	42 (7.9)	43 (6.3)	.556
Gender (male/female)	22/23	19/21	.922
Body mass index (kg/m2)	24 (2.7)	24 (2.4)	.443
Number of screws used	225	200	–
Operative time (min)	58 (8.1)	71 (15.5)	.138
Blood loss (mL)	35 (7.5)	38 (9.6)	.745
Complications	1 (nerve injury)	1 (nerve injury) 2 (screw loosening)	.138
Fracture level (T10/T11/T12/L1/L2/L3)	3/4/12/15/8/3	2/3/11/13/9/2	.934

Values are shown as mean (standard deviation) or absolute numbers.

In the RA group, the accuracy of screw placement was as follows: grade A, 216 (96%) screws; grade B, 5 (2.2%) screws; grade C, 3 (1.3%) screws; and grade D, 1 (0.5%) screw. In the FG group, the corresponding accuracy rates were 137 (68.5%), 35 (17.5%), 10 (10.0%), and 8 (4%) screws, respectively. The rates of grade-A accuracy (P < .001) and clinically acceptable accuracy (grades A plus B; P = .036) as well as the one-time success rate (P = .035) were significantly greater in the RA group than in the FG group (Table 2). In addition, we found no significant differences in the indicators of clinical outcomes, that is, VAS scores and Cobb angle, between the 2 groups, either preoperatively or at 1 week or 6 months postoperatively (Table 3).

Table 2.

Summary of radiographic outcomes according to the Gertzbein-Robbins classification.

Grade	Robot-assisted surgery (n = 225 screws)	Fluoroscopy-guided surgery (n = 200 screws)	P value
A	216	137	.000
B	5	35
C	3	20
D	1	8
A + B	221 (98.2%)	172 (86%)	.036
One-time success rate	219 (97.3%)	165 (82.5%)	.035

Table 3.

Clinical outcomes.

	Robot-assisted surgery (n = 45)	Fluoroscopy-guided surgery (n = 40)	P value
VAS score
Preoperative	7.3 ± 0.8	7.2 ± 0.9	.857
1 week after surgery	2.0 ± 0.6	1.9 ± 0.5	.754
6 months after surgery	1.2 ± 0.3	1.1 ± 0.4	.661
Cobb angle (°)
Preoperative	10.8 ± 2.1	10.2 ± 2.3	.541
1 week after surgery	3.1 ± 0.7	3.0 ± 0.5	.689
6 months after surgery	2.8 ± 0.5	2.7 ± 0.5	.552

VAS = visual analogue scale.

4. Discussion

The present study revealed that compared to FG surgery, RA surgery resulted in a significantly higher accuracy of screw placement and a significantly higher one-time success rate, with comparable clinical outcomes, among adult patients with 1-level thoracolumbar compression fractures. Thoracolumbar compression fractures are commonly encountered in the orthopedic department. For patients younger than 60 years, pedicle screws are often used to restore the vertebral height and the spinal curvature. Although spinal surgeons are generally well versed with the technique of pedicle implantation, the accuracy of screw insertion remains a cause for concern. It has been reported that 3% to 55% of pedicle screws in the thoracic spine and 5% to 41% of pedicle screws in the lumbar spine are misplaced.^[9] In conventional surgery, which is manually performed, the accuracy of screw insertion can decrease as fatigue sets in prolonged operations, affecting the surgeon’s freehand motions. In RA surgery, a robot platform serves as a computerized mechanical positioning system that not only provides excellent 3-dimensional visualization but also holds tools over prolonged periods and performs repetitive motions. It also reduces intraoperative radiation exposure. Recently, many authors have reported that RA spinal surgery is associated with improved accuracy and good clinical outcomes.^[2,3]

In the present study, we did not find any significant between-group differences in age, gender, body mass index, operative time, volume of blood loss, Cobb angle, VAS score, and postoperative complications. Furthermore, the VAS score and Cobb angle did not differ between the study groups, either preoperatively or at 1 week or 6 months postoperatively. However, both screw-placement accuracy and one-time success rate were higher in the RA group than in the FG group.

Although RA surgery has many advantages, it remains controversial. A randomized controlled trial^[10] found significantly poorer screw placement using RA surgery than using freehand surgery (85% vs 93%); intraoperative revision was required for 10 screws in the RA group and only 1 screw in the freehand group. Additionally, a meta-analysis^[11] found no difference in accuracy between these 2 techniques. Although Fan et al^[6] reported that RA surgery yielded significantly higher screw-insertion accuracy than freehand surgery (acceptable accuracy: 97.3%, 95% confidence interval: 1.38–2.07, P < .01; clinically acceptable accuracy: 90.8%, 95% confidence interval: 1.17–2.08, P < .01), statistically significant heterogeneity may have affected their results. Our findings revealed that compared with FG surgery, RA surgery resulted in more accurate pedicle screw placement and a higher rate of clinically acceptable screw placement (grades A plus B). These findings may be attributable to the following: First, the FG surgical procedure could easily result in physical and mental fatigue, which may have reduced its accuracy, whereas the RA surgery could help to minimize fatigue.^[10,12] Second, the robot platform provided the optimal point, direction, and depth of screw insertion, which helped surgeons visualize the surgical path and avoid injuring important adjacent structures.

The higher one-time success rate of RA surgery is likely attributable to the more accurate placement tracks provided by the RA system, which also ensured that the preoperatively planned screw paths and directions could be reliably and repeatedly reproduced during the actual surgery, regardless of the patient’s intraoperative position.^[13] Successful screw placement in a single attempt is desirable, as multiple attempts at screw insertion into the injured vertebrae can injure the facet joints and the surrounding soft tissues, and may lead to postoperative loosening of the pedicle screws or even failure of fixation in patients with thoracolumbar compression fractures. In our study, 2 screws were found to be loose at the 6-month follow-up in the FG group.

Hyun et al^[14] found similar operative times for RA and FG surgeries. Our results were consistent with those of Hyun et al. As surgeons become more familiar with the still-new RA technique, they will become more skilled, and the operative time may become shorter. We also found no difference in the volume of blood loss between the 2 study groups. Moreover, the clinical outcomes at the final 6-month follow-up were identical in both groups, implying that both surgical procedures were a good choice for patients with thoracolumbar compression fractures.

Some limitations of the present study should be acknowledged. First, this was a single-center study; we have planned a prospective multicenter study in the near future. Second, the sample size was small, especially at the final follow-up, which may have induced potential biases. We will enroll a larger number of patients in our prospective study. Third, we did not collect data such as duration and dose of radiation exposure of the patients due to incomplete information. Finally, we did not randomly assign patients to the RA and FG groups, and the type of treatment was selected by the patients themselves.

In conclusion, compared to the FG technique, the RA technique of pedicle screw fixation provided comparably good clinical outcomes, more accurate pedicle screw placement, and a higher one-time success rate of screw placement among patients with thoracolumbar compression fractures. Thus, the RA technique is a safe and effective option for patients with 1-level thoracolumbar compression fractures because it not only provides an optimal screw-placement track and excellent 3-dimensional visualization but also helps reduce intraoperative radiation exposure. We hope our findings will help guide the selection of treatments for thoracolumbar compression fracture and provide a reference for future studies on RA surgery.

Author contributions

Conceptualization: Yongjun Li, Xing Wei, Yonghui Liang.

Data curation: Yongjun Li, Yonghui Liang, Guangze Song.

Formal analysis: Yongjun Li, Xing Wei.

Writing – original draft: Yongjun Li, Xing Wei.

Writing – review & editing: Xing Wei, Guangze Song.