Percutaneous pedicle screw (PPS) fixation is a needle based procedure that requires fluoroscopic image guidance. Consequently, radiation exposure is inevitable for patients, surgeons, and operation room staff. We hypothesize that reducing the production of radiation emission will result in reduced radiation exposure for everyone in the operation room. Research was performed to evaluate reduction of radiation exposure by modifying imaging manner and mode of radiation source.
A total of 170 patients (680 screws) who underwent fusion surgery with PPS fixation from September 2019 to March 2020 were analyzed in this study. Personal dosimeters (Polimaster Ltd.) were worn at the collar outside a lead apron to measure radiation exposure. Patients were assigned to four groups based on imaging manner of fluoroscopy and radiation modification (pulse mode with reduced dose) : continuous use without radiation modification (group 1, n=34), intermittent use without radiation modification (group 2, n=54), continuous use with radiation modification (group 3, n=26), and intermittent use with radiation modification (group 4, n=56).
The average radiation exposure/screw was 71.45±45.75 μSv/screw for group 1, 18.77±11.51 μSv/screw for group 2, 19.58±7.00 μSv/screw for group 3, and 4.26±2.89 μSv/screw for group 4. By changing imaging manner from continuous multiple shot to intermittent single shot, 73.7% radiation reduction was achieved in the no radiation modification groups (groups 1, 2), and 78.2% radiation reduction was achieved in the radiation modification groups (groups 3, 4). Radiation source modification from continuous mode with standard dose to pulse mode with reduced dose resulted in 72.6% radiation reduction in continuous imaging groups (groups 1, 3) and 77.3% radiation reduction in intermittent imaging groups (groups 2, 4). The average radiation exposure/screw was reduced 94.1% by changing imaging manner and modifying radiation source from continuous imaging with standard fluoroscopy setting (group 1) to intermittent imaging with modified fluoroscopy setting (group 4). A total of 680 screws were reviewed postoperatively, and 99.3% (675) were evaluated as pedicle breach grade 0 (<2 mm).
The average radiation exposure/screw for a spinal surgeon can be reduced 94.1% by changing imaging manner and modifying radiation source from real-time imaging with standard dose to intermittent imaging with modified dose. These modifications can be instantly applied to any procedure using fluoroscopic guidance and may reduce the overall radiation exposure of spine surgeons.
Short segment fixation with transpedicular screw is a widely used technique to stabilize degenerative spondylolisthesis or traumatic spinal fractures. Percutaneous pedicle screw (PPS) fixation is a widely used technique to overcome the disadvantages of open pedicle screw fixation, such as higher infection rate, greater blood loss, more damage to paraspinal musculature, prolonged operation time, and longer hospital stay [
Gamma rays and X-rays are the most frequently used ionizing radiation in the medical field and have been classified as carcinogens by the World Health Organization [
Even routine image studies prior to fusion surgery, such as computed tomography (CT) scan of 5–6 vertebral levels and simple chest X-ray, involve 6–7 mSv and 0.1 mSv of radiation exposure, respectively [
This retrospective clinical study was performed in a single hospital. The study was approved by the Institutional Review Board of Wooridul Spine Hospital (IRB# 2020-04-WSH-008), and all patients gave informed consent before enrollment. The study was conducted in 246 patients who underwent fusion surgery with PPS fixation from May 2019 to March 2020. PPS was performed with either the Sextant system (Medtronic Inc., Memphis, TN, USA) or the Viper system (Johnson & Johnson Medical, Edison, NJ, USA). Procedures were performed using fluoroscopic image guidance in either continuous mode with standard dose or pulse mode with reduced dose.
Fusion surgery was indicated in patients with 1) higher than grade 1 spondylolisthesis with dynamic instability, 2) concomitant central and extra-foraminal intervertebral disc herniation who required total facetectomy, or 3) bilateral foraminal stenosis with isthmic defect. To unify the surgical techniques, only patients who underwent a single level lumbar interbody fusion fixed by sextant screw system were included in this study.
A spine surgeon in fellowship training performed all fixation procedures using the same C-arm fluoroscopy unit (Simens Arcadis Orbic; Simens AG, Muenchen, Germany). To minimize experience-based bias, the first 40 cases (176 screws) were excluded in this study. Nineteen additional multi-level fixation cases (118 screws) and 17 cases (68 screws) performed by the Viper system were excluded. Consequently, 170 cases (680 screws) were included in the final analysis. Patients were assigned to four groups based on fluoroscopy imaging manner and radiation modification (pulse mode with reduced dose) : real-time use without radiation modification (group 1), intermittent use without radiation modification (group 2), real-time use with radiation modification (group 3), and intermittent use with radiation modification (group 4) (
Demographic data was collected from patient medical charts. Sex, age, height, weight, body mass index (BMI), past medical history, operation level, and fusion type were recorded as demographic data. Anterior lumbar interbody fusion was classified as the anterior group, pre-psoas oblique and trans-psoas direct lateral lumbar interbody fusion were classified as the lateral group, and trans-foraminal and posterior lumbar interbody fusion were classified as the posterior group. Underlying radio-sensitive diseases were reviewed, including malignancy, thyroid disease (hyper- or hypothyroidism), and cataract.
After anterior or lateral approach interbody cage insertion, patients were placed in the prone position on a radiolucent Wilson’s table under general anesthesia for PPS insertion. The procedure was performed in the same position for patients who underwent posterior approach interbody cage insertion. During the procedure, a single plane C-arm fluoroscopy unit was used for intraoperative imaging. After confirmation of the surgical level in anteroposterior (AP) and lateral fluoroscopic images, the midline, lateral border of pedicles, and Jamshidi needle insertion points were marked on the skin.
Radiation exposure measurement began with confirmation of the skin incision point by Jamshidi needle. Personal dosimeters (PM1621 personal dosimeter; Polimaster Ltd., Minsk, Republic of Belarus) were worn at the collar outside of lead aprons. After a 1.5–2.0 cm skin incision was made, the Jamshidi needle was placed on the outer margin of the superior articular process and transverse process junction. Proper needle placement was evaluated by AP fluoroscopic image. Then, the needle was advanced until it was close to the medial margin of the pedicle. The C-arm was then moved to the lateral angle and the needle was further advanced for more than half of the vertebral body depth. A linear guide wire was then placed through the inside hole of the Jamshidi needle. After wire placement, tapping and placement of the real screw, rod connection, and final capping were performed with lateral fluoroscopic inspection.
Procedures of groups 1 and 2 were performed under continuous mode with standard dose using an automatic setting of the C-arm machine. The continuous mode had a frequency of 30 fractions/second, and dose was 70 to 90 kV with 4 to 6 mA at the AP position and 95 to 110 kV with 5 to 6 mA at the lateral position. For groups 3 and 4, frequency was changed to pulse mode (8 fractions/second) and dose was reduced by 2–5 kV while maintaining original mA value. Dose was reduced until the cortical bone margin of the pedicle and the vertebral body were visible with proper clearance to perform the procedure. Fluoroscopic images of standard and reduced radiation dose were demonstrated on
Bone mineral density (BMD) was assessed in every patient before fusion surgery to evaluate bone quality. Preoperative radiologic evaluation was performed on preoperative CT, and the existence of sclerosis, small pedicle, and facet joint hypertrophy was evaluated. These radiologic features are considered obstacles for PPS insertion because they obstruct passage of the bone needle and cover the needle insertion point. Patients with these features require more frequent fluoroscopic imaging to confirm correct instrument insertion. Sclerosis was defined as cancellous bone with similar density to cortical bone (
Operation time was assessed from the beginning of Jamshidi needle insertion to removal of all sextant screw systems. Cement augmentation was performed for osteoporotic bone or whenever screw loosening was detected after reduction procedure. Operation time and number of cases of cement augmentation were counted as intraoperative information. Radiation was measured by personal dosimeter in units of µSv. Fluoroscopic time was recorded by the C-arm machine. These values were divided by the number of screws. Therefore the radiation exposure per screw (µSv/screw) can be calculated from the result of this study. As 20 mSv is recommended radiation exposure limit per year for radiation workers by ICRP, the number of screws to reach the annual limit of 20 mSv can be calculated by dividing 20 mSv by µSv/screw.
Postoperative radiologic evaluation was performed on postoperative magnetic resonance image (MRI), and the distance and direction of pedicle breach were evaluated. Breach was divided to 3 grade categories defined as follows : grade 0 (within 2.0 mm), grade 1 (2.0–4.0 mm), and grade 2 (4.0–6.0 mm) [
Demographics, preoperative radiologic evaluation, intraoperative information, radiation exposure, and radiologic outcome were compared among groups 1, 2, 3, and 4. For prior homogeneity tests across groups, one-way analysis of variance was used for variables with average values, and chi-square test was used for categorical values.
The results of demographic analysis are summarized in
The results are summarized in
Mean operation time was significantly longer in groups 1 and 3 (50.03 and 42.08 minutes, respectively). Cement augmentation was performed in 16.5% (28/170) of the whole patient population, and the majority of these cases were in groups 1 and 2. Eleven of them were in group 1, and nine of them were in group 2, which was significantly different.
The average total radiation exposure, fluoroscopic time, radiation exposure/screw, and fluoroscopic time/screw showed significant differences across groups (
The results are summarized in
According to the results of this study, average radiation exposure/screw can be reduced 94.1% by changing the imaging manner and modifying radiation source from real-time multiple shot imaging with standard fluoroscopy setting (group 1, 71.45 µSv/screw) to intermittent single shot imaging with modified fluoroscopy setting (group 4, 4.26 µSv/screw). Available number of screws per year can be calculated from this result by dividing this value from annual recommended radiation exposure. This indicates that the surgeon of group 1 would insert about 280 screws (70 vertebral levels) while the surgeon of group 4 would insert about 4695 screws (1174 vertebral levels) to reach the 20 mSv average annual limit of radiation exposure for radiation workers. The number of screws that surgeons can insert to maintain the average annual radiation exposure limit is about 1062 (265 vertebral levels) for group 2 and 1021 (255 vertebral levels) for group 3. This study demonstrated that reduction of intraoperative radiation can be simply achieved by changing the imaging manner and fluoroscopy settings from continuous mode to pulse mode with minor kV reduction. In addition, only five pedicle screws were breached greater than 2 mm, and they did not cause any radiculopathy symptoms. There was no significant difference in pedicle breach rate among the groups. Therefore, the overall effective breach rate was 0%. The results also indicate that the procedure can be performed safely even in groups with modified radiation.
Image quality should be appropriately maintained for surgeons to perform PPS procedures and avoid any complications caused by mal-positioning of the bone needle or wire during the procedure or pedicle breach. The kV is the energy of photons, and mA is the quantity of photons [
Since PPS insertion mostly relies on fluoroscopic images, it is more difficult to perform the procedure for patients with factors that lower image quality or who have abnormal anatomic features around the screw insertion point. This leads to more frequent fluoroscopic imaging during the procedure, which is also related to more radiation exposure for surgeons and patients. In this study, preoperative anatomic features such as sclerosis, pedicle size, and facet joint hypertrophy were measured on preoperative CT. These features were more frequently observed in groups 1 and 3 with statistical significance (
There are also other recommendations for reducing radiation exposure. Yoshihara and Paulino [
Many other spinal procedures require fluoroscopic guidance. Ahn et al. [
To the author’s knowledge this is the first study demonstrated the radiation exposure reduction effect of radiation source modification with pulse mode during the PPS procedure. However this study involves some limitations. First, selection and recall bias were possible due to the retrospective nature of this study. Analyzing risk factors for changing imaging manner and the mode of radiation source are also significant aspects. However, it couldn’t be achieved because patients were designated to each group retrospectively without documenting the prior imaging manner and fluoroscopy setting. Although some preoperative radiologic features were indicated as candidate risk factors, prospective study design is needed for the identification of the risk factors in near future. Despite the exclusion of the first 40 cases, data interpretation is still susceptible to the surgeon’s learning curve bias. Third, measurements of radiation dose were limited to the anterior chest area of the surgeon. Radiation exposure for other body parts was not measured. Radiation exposure was also not measured on other medical personnel or patients. Fourth, pedicle breach was evaluated on postoperative MRI, which contains artifacts that may compromise accurate evaluation. Finally, clinical outcomes such as postoperative pain, disability, and satisfaction were not assessed. Despite these limitations, this study proves decreased radiation exposure with modification of imaging manner, mode, and dose of fluoroscopy.
The average radiation exposure/screw of a spine surgeon can be reduced 94.1% by modifying the imaging manner and radiation source from real-time multiple shot imaging with continuous mode to intermittent single shot imaging with pulse mode and reducing the kV setting. The radiation exposure of spine surgeons, operative staff, and patients should be as low as reasonably achievable to avoid the stochastic effect of radiation exposure. These modifications can be instantly applied to any procedure using fluoroscopic guidance and will contribute to reduced overall radiation exposure of spine surgeons.
No potential conflict of interest relevant to this article was reported.
Informed consent was obtained from all individual participants included in this study.
Conceptualization : HJK, ESP
Data curation : HJK
Formal analysis : HJK
Funding acquisition : CHP, SHL
Methodology : HJK, SWC
Project administration : CHP, SHL
Visualization : HJK
Writing - original draft : HJK
Writing - review & editing : HJK, ESP, SWC
Flow-chart of classification criteria for groups 1, 2, 3, and 4. Patients were grouped based on radiation modification and imaging manner.
Anteroposterior (A) and lateral (B) images were obtained after K-wire placement followed by rod insertion (C) using continuous mode with standard dose fluoroscopy. After modifying radiation source to pulse mode with reduced dose, image quality decreased slightly (D-F).
Three anatomic features interfere with percutaneous pedicle screw insertion. Rigid sclerosis with high bone density on preoperative computed tomography is visible on left L4 pedicle and vertebral body (white arrow) (A). Pedicle with vertical diameter of 5.3 mm is visible on left L5 peidcle (white arrow) (B). Bilateral facet joint hypertrophy is visible on both L4–5 facet joints (white arrow) (C).
Results of post-hoc comparisons using Tukey Honest significant difference test. Surgeon radiation exposure per screw is expressed in microsieverts (A), and fluoroscopic time per screw is expressed in seconds (B).
Demographics
Group 1 (n=34) | Group 2 (n=54) | Group 3 (n=26) | Group 4 (n=56) | ||
---|---|---|---|---|---|
Sex | 0.784 | ||||
Female | 20 | 35 | 16 | 31 | |
Male | 14 | 19 | 10 | 25 | |
Age (years) | 66.00±10.62 | 64.06±10.55 | 63.46±7.49 | 65.43±9.29 | 0.671 |
Height (cm) | 158.53±9.54 | 158.76±9.35 | 159.38±8.21 | 157.32±8.79 | 0.756 |
Weight (kg) | 62.74±11.84 | 62.57±12.25 | 63.15±9.90 | 63.14±8.90 | 0.992 |
BMI (kg/m2) | 24.88±3.57 | 24.71±2.79 | 24.78±2.65 | 25.54±3.18 | 0.504 |
Past medical history | |||||
Malignancy | 4 | 1 | 4 | 1 | 0.022 |
Thyroid related disease | 2 | 4 | 0 | 2 | 0.488 |
Catalact | 6 | 13 | 4 | 4 | 0.112 |
Operated level | 0.300 | ||||
L3–4 | 2 | 5 | 2 | 5 | |
L4–5 | 20 | 38 | 13 | 40 | |
L5–S1 | 12 | 11 | 11 | 11 | |
Fusion type | 0.063 | ||||
Anterior | 16 | 22 | 14 | 13 | |
Lateral | 8 | 15 | 8 | 26 | |
Posterior | 10 | 17 | 4 | 17 |
Values are presented as mean±standard deviation or number. BMI : body mass index
Preoperative radiologic evaluation, intraoperative information, and radiation exposure
Group 1 (n=34) | Group 2 (n=54) | Group 3 (n=26) | Group 4 (n=56) | ||
---|---|---|---|---|---|
Preoperative radiologic evaluation | |||||
BMD (T-score) | -1.02±1.45 | -1.11±1.59 | -1.17±1.45 | -0.69±1.78 | 0.464 |
Sclerosis | 10 | 2 | 6 | 7 | 0.009 |
Small pedicle | 4 | 0 | 4 | 1 | <0.001 |
Facet hypertrophy | 12 | 2 | 11 | 3 | <0.001 |
Intraoperative information | |||||
Operation time (minutes) | 50.03±9.00 | 35.78±9.54 | 42.08±9.25 | 36.16±5.77 | <0.001 |
Cement augmentation | 11 | 9 | 3 | 5 | 0.029 |
Radiation exposure | |||||
Radiation exposure (μSv) | 285.81±183.01 | 75.09±46.05 | 78.33±27.99 | 17.05±11.55 | <0.001 |
Fluoroscopic time (seconds) | 248.65±59.64 | 62.67±39.36 | 222.46±30.64 | 86.04±50.95 | <0.001 |
Radiation exposure per screw (μSv/screw) | 71.45±45.75 | 18.77±11.51 | 19.58±7.00 | 4.26±2.89 | <0.001 |
Fluoroscopic time per screw (seconds/screw) | 62.16±14.91 | 15.67±9.84 | 55.62±7.66 | 17.51±12.74 | <0.001 |
Values are presented as mean±standard deviation or number. BMD : bone mineral density
Radiologic outcome and complication
Group 1 screws (n=136) | Group 2 screws (n=216) | Group 3 screws (n=104) | Group 4 screws (n=224) | Total (n=680) | ||
---|---|---|---|---|---|---|
Pedicle breach | ||||||
Grade 0 | 135 | 214 | 103 | 223 | 0.757 | 675 |
Grade 1 | 1 | 2 | 1 | 1 | 0.901 | 5 |
Grade 2 | 0 | 0 | 0 | 0 | - | 0 |
Deviation of breach | ||||||
Medial | ||||||
Grade 0 | 2 | 1 | 1 | 2 | 0.834 | 5 |
Grade 1 | 0 | 0 | 0 | 0 | - | 0 |
Lateral | ||||||
Grade 0 | 2 | 3 | 2 | 1 | 0.703 | 8 |
Grade 1 | 1 | 2 | 1 | 1 | 0.901 | 5 |
Complication | 0 | 0 | 0 | 0 | - | 0 |